<PAGE>

                                                                     EXHIBIT 4.2

                              PURCHASE AGREEMENT

                             DATED MARCH 30, 2000

                                    BETWEEN

                          DIVINE INTERVENTURES, INC.

                                      AND

                                AON CORPORATION
<PAGE>

                               TABLE OF CONTENTS

<TABLE>
<S>                                                                      <C>
Section 1. Authorization, Purchase and Sale............................   1

     1A.     Authorization of the Class C Common Stock.................   1
     1B.     Purchase and Sale of the Class C Common Stock.............   1

Section 2. The Closing.................................................   1

Section 3. Representations and Warranties of the Company.                 2

     3A.     Organization and Corporate Power..........................   2
     3B.     Authorization; No Breach..................................   2
     3C.     Title to Shares...........................................   3
     3D.     Governmental Consent, etc.................................   3
     3E.     Disclosure................................................   3
     3F.     Exchange Listing..........................................   3

Section 4. Representations, Warranties and Covenants of Purchaser......   3

     4A.     Organization and Corporate Power..........................   4
     4B.     Authorization; No Breach..................................   4
     4C.     Governmental Consent, etc.................................   4
     4D.     Investment Representations................................   5
     4E.     Purchaser's Principal Place of Business...................   6
     4F.     Solicitation of Proxies...................................   6
     4G.     Notice....................................................   6
     4H.     No Group..................................................   7

Section 5. HSR Filings.................................................   7

Section 6. Conditions of the Purchaser's Obligations at the Closing....   7

     6A.     Representations and Warranties............................   7
     6B.     Performance...............................................   7
     6C.     Officer's Certificate.....................................   7
     6D.     Opinion of Company Counsel................................   8
     6E.     Commercial Agreement......................................   8
     6F.     Amended Certificate of Incorporation......................   8

Section 7. Conditions of the Company's Obligations at the Closing......   8

     7A.     Representations and Warranties............................   8
     7B.     Performance...............................................   8
</TABLE>
<PAGE>

<TABLE>
<S>                                                                      <C>
     7C.     Officer's Certificate.....................................   8
     7D.     Commercial Agreement......................................   8

Section 8. Termination.................................................   9

Section 9. Indemnification.............................................   9

     9A.     Company Indemnification...................................   9
     9B.     Purchaser Indemnification.................................   9
     9C.     Survival of Representations and Warranties................  10

Section 10. Definitions................................................  10

Section 11. Miscellaneous..............................................  11

     11A.    Expenses..................................................  11
     11B.    Remedies..................................................  11
     11C.    Legends...................................................  11
     11D.    Lock-up Agreements........................................  12
     11E.    Rule 144..................................................  12
     11F.    Successors and Assigns....................................  12
     11G.    Severability..............................................  13
     11H.    Counterparts..............................................  13
     11I.    Descriptive Headings; Interpretation......................  13
     11J.    Governing Law.............................................  13
     11K.    Notices...................................................  13
     11L.    No Strict Construction....................................  14
</TABLE>

Exhibit A -  Form of Opinion of Katten Muchin Zavis
Exhibit B -  Form of Memorandum of Understanding
<PAGE>

                          DIVINE INTERVENTURES, INC.

                              PURCHASE AGREEMENT


          THIS PURCHASE AGREEMENT (this "Agreement") is made as of March 30,
                                         ---------
2000 between divine interVentures, inc., a Delaware corporation (the "Company"),
                                                                      -------
and Aon Corporation, a Delaware corporation (the "Purchaser").  Except as
                                                  ---------
otherwise indicated herein, capitalized terms used herein are defined in Section
                                                                         -------
10 hereof.
--

     WHEREAS, the parties desire to enter into a long-term strategic
relationship as further described herein.

     WHEREAS, as part of such strategic relationship, Purchaser desires to make
an investment in the Company, on the terms and conditions described herein.

     WHEREAS, such strategic relationship and the agreement entered into by the
Company and the Purchaser in connection therewith, is a condition to the
execution and delivery of this Agreement and the issuance to the Purchaser of
the Company's equity securities.

     NOW THEREFORE, in consideration of the mutual promises contained in this
Agreement and other good and valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties to this Agreement hereby agree as
follows:

          Section 1.  Authorization, Purchase and Sale.
                      --------------------------------

          1A.  Authorization of the Class C Common Stock.  The Company shall
               -----------------------------------------
authorize the issuance and sale to the Purchaser of an aggregate number of
shares of its Class C Non-voting Common Stock, par value $0.001 per share (the
"Class C Common Stock") to meet the calculation set forth in Section 1B below.
 --------------------                                        ----------
The Class C Common Stock is convertible into shares of the Company's Class A
Common Stock on a one-for-one basis (adjusted appropriately in the event the
shares of Class A Common Stock are subdivided into a greater number, whether by
stock split, stock dividend or otherwise, or combined into a lesser number,
whether by reverse stock split or otherwise) at the option of Purchaser at any
time; provided that the Purchaser complies with the requirements of Section 5
                                                                    ---------
hereof.

          1B.  Purchase and Sale of the Class C Common Stock.  The Company shall
               ---------------------------------------------
sell to the Purchaser, and subject to the terms and conditions set forth herein,
the Purchaser shall purchase from the Company, upon the consummation of a
Qualified IPO, that number of shares of Class C Common Stock equal to the result
of $25,000,000 divided by the purchase price stated on the face of the final
prospectus in connection with the Qualified IPO as the price per share to the
public of the Company's Class A Common Stock in the Qualified IPO, which
purchase price shall be paid in immediately available funds.

          Section 2.  The Closing.  The closing of the purchase and sale of the
                      -----------
Class C Common Stock to the Purchaser (the "Closing") shall take place at the
                                            -------
offices of Katten Muchin
<PAGE>

Zavis, 525 West Monroe Street, Chicago, IL 60661, immediately following the
consummation of the Qualified IPO. At the Closing, the Company shall deliver a
stock certificate or stock certificates evidencing all of the shares of the
Class C Common Stock to be purchased by Purchaser hereunder, registered in
Purchaser's name, upon the payment of the aggregate purchase price therefor, by
wire transfer of immediately available funds to an account designated by the
Company in writing to Purchaser at least three business days prior to the
Closing.

          Section 3.  Representations and Warranties of the Company.  As a
                      ---------------------------------------------
material inducement to the Purchaser to enter into this Agreement and purchase
the Class C Common Stock, the Company hereby represents and warrants that:

          3A.  Organization and Corporate Power.  The Company is a corporation
               --------------------------------
duly organized, validly existing and in good standing under the laws of the
State of Delaware and is qualified to do business in every jurisdiction in which
the failure to so qualify would reasonably be expected to have a material
adverse effect on the financial condition, operating results or assets of the
Company. The Company possesses all requisite corporate power and authority
necessary to carry out the transactions contemplated by this Agreement and each
of the Transaction Documents to which the Company is a party.

          3B.  Authorization; No Breach.
               ------------------------

               (i)  The execution, delivery and performance of this Agreement
     and each of the Transaction Documents to which the Company is a party will
     have been duly authorized by the Company as of the Closing upon the
     approval hereof by the Company, its Board of Directors and its
     stockholders. This Agreement and the Transaction Documents to which the
     Company is a party will each constitute a valid and binding obligation of
     the Company, enforceable in accordance with its terms as of the Closing,
     subject, as to enforceability, to the laws of bankruptcy, insolvency,
     reorganization and other laws of general applicability relating to or
     affecting creditor's rights and to general principles of equity.

               (ii) The execution and delivery by the Company of this Agreement
     and all Transaction Documents to which the Company is a party, the sale and
     issuance of the Class C Common Stock hereunder, the issuance of the Class A
     Common Stock upon conversion of Class C Common Stock (except, with respect
     thereto, any filings required under the HSR Act and the termination or
     expiration of any applicable waiting period under the HSR Act), and the
     fulfillment of and compliance with the respective terms hereof and thereof
     by the Company, do not and will not as of the Closing (i) conflict with or
     result in a breach of the terms, conditions or provisions of, (ii)
     constitute a default under, (iii) result in the creation of any lien,
     security interest, charge or encumbrance upon the Company's or any
     subsidiary's capital stock or assets pursuant to, (iv) give any third party
     the right to modify, terminate or accelerate any obligation under, (v)
     result in a violation of, or (vi) require any authorization, consent,
     approval, exemption or other action by or notice or declaration to, or
     filing with, any court or administrative or governmental body or agency
     pursuant to, the Certificate of Incorporation of the Company or the amended
     and restated bylaws of the Company, or any material law,

                                       2
<PAGE>

     statute, rule or regulation to which the Company or any subsidiary is
     subject, or any agreement, instrument, order, judgment or decree to which
     the Company or any subsidiary or any of any of their respective assets are
     subject, except for the filing of the Amended Certificate and any filings
     required after the date hereof under federal or state securities laws.

          3C.  Title to Shares.  Upon issuance in accordance with the terms
               ---------------
hereof,  the Class C Common Stock to be purchased hereunder, and the Class A
Common Stock issuable upon conversion of such shares of Class C Common Stock,
will be duly and validly issued, fully paid, nonassessable, the Purchaser will
have good and marketable title to such shares, free and clear of all liens,
claims and encumbrances of any kind (including, without limitation, pre-emptive
rights), other than (a) transfer restrictions hereunder (including Sections 11C
                                                                   ------------
and 11D below) and under the other agreements contemplated hereby, (b) transfer
    ---
restrictions under federal and state securities laws and (c) liens, claims or
encumbrances imposed due to the actions of the Purchaser, and the shares of
Class A Common Stock issuable upon conversion of such shares of Class C Common
Stock will have been fully reserved for issuance upon such conversion.

          3D.  Governmental Consent, etc.  Except for any filings required under
               -------------------------
the HSR Act with respect to the conversion of the Class C Common Stock into
Class A Common Stock and the termination or expiration of any applicable waiting
period under the HSR Act, no permit, consent, approval or authorization of, or
declaration to or filing with, any governmental authority is required in
connection with the execution, delivery and performance by the Company of this
Agreement or any of the Transaction Documents to which the Company is a party,
or the consummation by the Company of any other transactions contemplated hereby
or thereby.

          3E.  Disclosure.  (a) The Company has provided the Purchaser with a
               ----------
copy of Amendment No. 2 to the Company's Registration Statement on Form S-1
(Registration No. 333-92851) as filed with the Securities and Exchange
Commission on March 16, 2000 (the "Registration Statement"), and will provide
the Purchaser with a copy of any and all amendments to the Registration
Statement filed, by the Company with the Securities and Exchange Commission
prior to the Closing.  (b) As of the date hereof, neither this Agreement, any
Transaction Document to which the Company is a party nor the Registration
Statement (nor, as of the effective date of the Registration Statement, any
amendment to the Registration Statement made after the date hereof), taken as a
whole, contains (or will contain) any untrue statement of a material fact or
omits (or will omit) to state a material fact necessary to make the statements
herein or therein not misleading.

          3F.  Exchange Listing.  As of the Closing, the shares of the Class A
               ----------------
Common Stock issuable upon conversion of the Class C Common Stock being
purchased hereunder will be listed on The Nasdaq Stock Market's National Market.

          Section 4.  Representations, Warranties and Covenants of Purchaser.
                      ------------------------------------------------------
As a material inducement to the Company to enter into this Agreement and issue
and sell Class C

                                       3
<PAGE>

Common Stock to the Purchaser, the Purchaser hereby represents, warrants and
covenants to the Company (which representations, warranties and covenants shall
survive the Closing) that:

          4A.  Organization and Corporate Power.  The Purchaser is a corporation
               --------------------------------
duly organized, validly existing and in good standing under the laws of Delaware
and is qualified to do business in every jurisdiction in which the failure to so
qualify would reasonably be expected to have a material adverse effect in the
financial condition, operating results or assets of the company.  The Purchaser
possesses all requisite corporate power and authority necessary to carry out the
transactions contemplated by this Agreement.

          4B.  Authorization; No Breach.
               ------------------------

               (ii) The execution, delivery and performance of this Agreement
     and each of the Transaction Documents to which Purchaser is a party have
     been duly authorized by Purchaser. This Agreement and each of the
     Transaction Documents hereby to which Purchaser is a party each constitute
     a valid and binding obligation of Purchaser, enforceable against Purchaser
     in accordance with its terms as of the Closing subject, as to
     enforceability, to the laws of bankruptcy, insolvency, reorganization and
     other laws of general applicability relating to or affecting creditor's
     rights and to general principles of equity.

               (ii) The execution and delivery by Purchaser of this Agreement
     and Transaction Documents to which Purchaser is a party and the fulfillment
     of and compliance with the respective terms hereof and thereof by
     Purchaser, do not and shall not as of the Closing (i) conflict with or
     result in a breach of the terms, conditions or provisions of, (ii)
     constitute a default under, (iii) result in the creation of any lien,
     security interest, charge or encumbrance upon the Purchaser's or any
     Subsidiary's capital stock or assets pursuant to, (iv) give any third party
     the right to modify, terminate or accelerate any obligation under, (v)
     result in a violation of, or (vi) require any authorization, consent,
     approval, exemption or other action by or notice or declaration to, or
     filing with, any court or administrative or governmental body or agency
     pursuant to, the charter or bylaws of Purchaser, or any law, statute, rule
     or regulation to which Purchaser is subject, or any agreement, instrument,
     order, judgment or decree to which Purchaser is subject, other than filings
     under the HSR Act in connection with the conversion of the Class C Common
     Stock into Class A Common Stock and the termination or expiration of any
     applicable waiting period under the HSR Act.

          4C.  Governmental Consent, etc.  Except for any filings required under
               --------------------------
the HSR Act with respect to the conversion of Class C Common Stock into Class A
Common Stock and the termination or expiration of any applicable waiting period
under the HSR Act, no permit, consent, approval or authorization of, or
declaration to or filing with, any governmental authority is required in
connection with the execution, delivery and performance by Purchaser of this
Agreement or any of the other agreements contemplated hereunder, to which
Purchaser is a party, or the consummation by Purchaser of any other transactions
contemplated hereby or thereby.

                                       4
<PAGE>

     4D.  Investment Representations.

               (i)    Investment Purpose.  Purchaser is acquiring the Class C
                      ------------------
     Common Stock and the Class A Common Stock issuable upon conversion of the
     Class C Common Stock (collectively, the "Securities") for its own account,
                                              ----------
     not as a nominee or agent, for investment only and not with a view towards,
     or for resale in connection with, the public sale or distribution thereof.

               (ii)   Accredited Investor Status.  Purchaser is an "accredited
                      --------------------------
     investor" as that term is defined in Rule 501(a)(3) of Regulation D.

               (iii)  Qualified Institutional Buyer.  Purchaser is a "qualified
                      -----------------------------
     institutional buyer", as such term is defined in Rule 144A promulgated
     under the Securities Act.

               (iv)   Reliance on Exemptions. Purchaser understands that the
                      ----------------------
     Securities are being offered and sold to it in reliance on specific
     exemptions from the registration requirements of United States federal and
     state securities laws and that the Company is relying in part upon the
     truth and accuracy of, and Purchaser's compliance with, the
     representations, warranties and agreements of Purchaser set forth herein in
     order to determine the availability of such exemptions and the eligibility
     of Purchaser to acquire such securities.

               (v)    No General Solicitation. The Purchaser initiated
                      -----------------------
     discussions with the Company relating to the purchase and sale of the
     Securities contemplated by this Agreement on an unsolicited basis prior to
     the date of this Agreement. The Purchaser did not initiate such
     discussions, nor did Purchaser decide to enter into this Agreement, as a
     result of any general solicitation or general advertising within the
     meaning of Rule 502(c) under the Securities Act, including the filing of
     the Registration Statement.

               (vi)   Information.  Purchaser has been furnished with all
                      -----------
     materials relating to the business, finances and operations of the Company
     and materials relating to the offer and sale of the Securities which have
     been requested by Purchaser.  Purchaser has been afforded the opportunity
     to ask questions of the Company.  Purchaser understands that its investment
     in the Securities involves a high degree of risk.  Purchaser has sought
     such accounting, legal and tax advice as it has considered necessary to
     make an informed investment decision with respect to its acquisition of the
     Securities.  The Purchaser has received and reviewed a copy of the
     Registration Statement, including without limitation, the language therein
     under the caption "Risk Factors".

               (vii)  No Governmental Review.  Purchaser understands that no
                      ----------------------
     United States federal or state agency or any other government or
     governmental agency has passed on or made any recommendation or endorsement
     of the Securities or the fairness or suitability of the investment in the
     Securities nor have such authorities passed upon or endorsed the merits of
     the offering of the Securities.

                                       5
<PAGE>

               (viii) Transfer or Resale.  Purchaser understands that: (a) the
                      ------------------
     Securities have not been and are not being registered under the Securities
     Act or any state securities laws, and may not be offered for sale, sold,
     assigned or transferred unless (A) subsequently registered thereunder or
     (B) sold in reliance on an exemption therefrom; and (b) neither the Company
     nor any other person is under any obligation to register such securities
     under the Securities Act or any state securities laws or to comply with the
     terms and conditions of any exemption thereunder.  In this regard,
     Purchaser represents that it is familiar with SEC Rule 144, and understands
     the resale limitations imposed thereby and by the Securities Act.
     Purchaser is able to bear the economic risk of its investment in the
     Securities for an indefinite period of time.

               (ix)   Sophistication.  Purchaser is an investor in securities of
                      --------------
     companies in the development stage and acknowledges that it is able to fend
     for itself, has knowledge and experience in financial and business matters,
     knows of the high degree of risk associated with investments generally and
     particularly investments in the securities of companies in the development
     stage, is capable of evaluating the merits and risks of an investment in
     the Securities and is able to bear the economic risk of an investment in
     the Securities in the amount contemplated. Purchaser has adequate means of
     providing for its current financial needs and contingencies and will have
     no current or anticipated future needs for liquidity which would be
     jeopardized by the investment in the Securities. Purchaser can afford a
     complete loss of its investment in the Securities.

               (x)    Further Limitations of Disposition.  Without in any way
                      ----------------------------------
     limiting the representations set forth above, the Purchaser agrees not to
     make any disposition of all or any portion of the Securities unless and
     until:

                      (1)    There is then in effect a registration statement
          under the Securities Act covering such proposed disposition and such
          disposition is made in accordance with such registration statement; or

                      (2)(i) The Purchaser shall have notified the Company of
          the proposed disposition and shall have furnished the Company with a
          statement of the circumstances surrounding the proposed disposition,
          and (ii) if reasonably requested by the Company, the Purchaser shall
          have furnished the Company with an opinion of counsel, reasonably
          satisfactory to the Company, that such disposition will not require
          registration of such shares under the Securities Act.

          4E.  Purchaser's Principal Place of Business.  The Purchaser
               ---------------------------------------
represents that its principal place of business is Chicago, Illinois.

          4F.  Solicitation of Proxies.  Purchaser will not participate in any
               -----------------------
solicitation of proxies by anyone other than the Company with respect to the
voting of the Securities.

          4G.  Notice.  Purchaser shall notify the Company no later than 15 days
               ------
prior to Purchaser's acquisition of an additional number of securities of the
Company in an amount equal to greater than 1% of the Company's outstanding
Capital Stock, and all such acquisitions shall

                                       6

<PAGE>

comply with federal and state securities laws.

          4H.  No Group.  Purchaser shall not form or participate in a "group"
               --------
(as defined in Rule 13d-5 of the Exchange Act) with respect to any securities of
the Company.

          Section 5.  HSR Filings.  As promptly as practicable after the date of
                      -----------
this Agreement, each of the parties hereto will make any filings required by the
HSR Act to be made by it in order to consummate the transactions contemplated
hereby and required in connection with the conversion of Class C Common Stock to
Class A Common Stock, and each party hereto will cooperate with the other party
hereto in connection with any such filings required by the HSR Act.
Notwithstanding anything to the contrary contained herein, nothing in this
Agreement will require any Person, whether pursuant to an order of the Federal
Trade Commission or the United States Department of Justice or otherwise, to
hold separate or dispose of any assets, lines of business or equity interests,
or otherwise take any action that would affect its business or the business of
any subsidiary, in order to obtain the consent of the Federal Trade Commission
or the United States Department of Justice to the transactions contemplated by
this Agreement. Each of the parties hereto shall promptly provide the other
party (or its counsel) copies of all filings made and any materials submitted in
connection with the HSR Act. The Class C Common Stock issued to Purchaser (i)
may be converted by Purchaser into Class A Common Stock only if all consents,
approvals or authorizations of, or declarations to or filings with, any
governmental authority, including, without limitation, filings required under
the HSR Act and the termination or expiration of any applicable waiting period
under the HSR Act, as may be required for such conversion have been obtained or
made, as the case may be, to the reasonable satisfaction of the Company and (ii)
shall be converted at such time.

          Section 6.  Conditions of the Purchaser's Obligations at the Closing.
                      --------------------------------------------------------
The obligation of the Purchaser to purchase and pay for the Class C Common Stock
is subject to the fulfillment, at or before the Closing, of each of the
following conditions:

          6A.  Representations and Warranties.  The representations and
               ------------------------------
warranties of the Company contained in Section 3, except for those stated to be
                                       ---------
made as of the date hereof, shall be true and correct in all material respects
at and as of the Closing as though then made, except to the extent of changes
caused by the transactions expressly contemplated herein or in the Transaction
Documents.

          6B.  Performance.  The Company shall have performed and complied with
               -----------
all agreements, obligations and conditions contained in this Agreement that are
required to be performed or complied with by it on or before the Closing.

                                       7
<PAGE>

          6C.  Officer's Certificate.  The Company shall deliver to the
               ---------------------
Purchaser an Officer's Certificate, stating that (i) the conditions described in
Sections 6A, 6B, 6D 6E and 6F have been satisfied; (ii) the Company has made all
-----------  --  -- --     --
filings under all applicable federal and state securities laws necessary to
consummate the transactions contemplated by this Agreement in compliance with
such laws; and (iii) all corporate and other proceedings required to be taken by
such party in connection with the transactions contemplated hereby to be
consummated at or prior to the Closing have been taken.

          6D.  Opinion of Company Counsel.  Purchaser shall have received from
               --------------------------
Katten Muchin Zavis, counsel for the Company, an opinion, dated as of the
Closing, in the form of Exhibit A attached hereto.
                        ---------

          6E.  Commercial Agreement.  The Company, or an Affiliate, shall have
               --------------------
executed and delivered a Memorandum of Understanding in the form attached as
Exhibit B hereto.
---------

          6F.  Amended Certificate of Incorporation.  The Company shall deliver
               ------------------------------------
evidence that its Certificate of Incorporation, as amended to reflect the terms
of the Class C Common Stock (the "Amended Certificate"), has been filed with the
Secretary of State of Delaware and is in full force and effect under the laws of
the State of Delaware as of the Closing.

          Section 7.  Conditions of the Company's Obligations at the Closing.
                      ------------------------------------------------------
The obligations of the Company to Purchaser under this Agreement are subject to
the fulfillment on or before the Closing of each of the following conditions:

          7A.  Representations and Warranties.  The representations and
               ------------------------------
warranties of Purchaser contained in Section 4 shall be true at and as of the
                                     ---------
Closing as though then made.

          7B.  Performance.  Purchaser shall have performed and complied with
               -----------
all agreements, obligations and conditions contained in this Agreement that are
required to be performed or complied with by it on or before the Closing.

          7C.  Officer's Certificate.  The Purchaser shall deliver to the
               ---------------------
Company an Officer's Certificate, stating that (i) the conditions described in
Sections 7A, 7B, 7D and 7E have been satisfied; (ii) the Purchaser has made all
------------ --  --     --
filings under all applicable federal and state securities laws necessary to
consummate the transactions contemplated by this Agreement in compliance with
such laws; and (iii) all corporate and other proceedings required to be taken by
such party in connection with the transactions contemplated hereby to be
consummated at or prior to the Closing have been taken.

          7D.  Commercial Agreement.  The Purchaser shall have executed and
               --------------------
delivered the Memorandum of Understanding in the form attached as Exhibit B.
                                                                  ---------

          7E.  Corporate Consents.  The Company shall have obtained the consent
               ------------------
of its Board of Directors and its stockholders authorizing the execution,
delivery and performance of this Agreement and the Transaction Documents to
which the Company is a party, the filing of

                                       8
<PAGE>

the Amended Certificate and the issuance and sale of the Class C Common Stock
hereunder.

          Section 8.  Termination.  This Agreement may or will be terminated at
                      -----------
any time prior to the consummation of the Closing under the following described
circumstances:

               (i)    automatically upon the mutual written consent of the
                      Company and the Purchaser;

               (ii)   by either of the Company or the Purchaser by delivery of
                      written notice thereof, if the Qualified IPO shall not
                      have been consummated prior to the four-month anniversary
                      of the date of this Agreement;

               (iii)  automatically upon the consummation of the Qualified IPO,
                      if the Closing is not occurring immediately after the
                      Qualified IPO; or

               (iv)   this Agreement may be terminated at any time by Purchaser
                      if the Company shall not have delivered to Purchaser by
                      April 10, 2000, an Officer's Certificate stating that the
                      conditions described in Section 7E have been satisfied and
                      including evidence that the Amended Certificate has been
                      filed with the Secretary of the State of Delaware and is
                      in full force and effect.

          Section 9.  Indemnification.
                      ---------------

          9A.  Company Indemnification.  In consideration of Purchaser's
               -----------------------
execution and delivery of this Agreement and acquiring the Securities hereunder
and in addition to all of the Company's other obligations under this Agreement,
the Company shall defend, protect, indemnify and hold harmless Purchaser and all
of its officers, directors, employees and agents (including, without limitation,
those retained in connection with the transactions contemplated by this
Agreement) (collectively, the "Indemnitees") from and against any and all
                               -----------
actions, causes of action, suits, claims, losses, costs, penalties, fees,
liabilities and damages, and expenses in connection therewith (irrespective of
whether any such Indemnitee is a party to the action for which indemnification
hereunder is sought), and including reasonable attorneys' fees and disbursements
(the "Indemnified Liabilities"), incurred by the Indemnitees or any of them as a
      -----------------------
result of, or arising out of, or relating to any misrepresentation in or breach
of any of the representations and warranties or any nonfulfillment or breach of
any covenant or agreement on the part of the Company under this Agreement,
provided that the Company shall not be liable to an Indemnitee under this
Section 9A for any liability if such liability is caused solely by such
----------
Indemnitee's fraud, willful misconduct or gross negligence or default or breach
under this Agreement.  To the extent that the foregoing undertaking by the
Company may be unenforceable for any reason, the Company shall make the maximum
contribution to the payment and satisfaction of each of the Indemnified
Liabilities which is permissible under applicable law.

          9B.  Purchaser Indemnification.  In consideration of the Company's
               -------------------------
execution and delivery of this Agreement and all of Purchaser's obligations
under this Agreement,

                                       9
<PAGE>

Purchaser shall defend, protect, indemnify and hold harmless the Company and all
of its officers, directors, employees and agents (including, without limitation,
those retained in connection with the transactions contemplated by this
Agreement) (collectively, the "Company Indemnitees") from and against any and
                               -------------------
all actions, causes of action, suits, claims, losses, costs, penalties, fees,
liabilities and damages, and expenses in connection therewith (irrespective of
whether any such Company Indemnitee is a party to the action for which
indemnification hereunder is sought), and including reasonable attorneys' fees
and disbursements (the "Company Indemnified Liabilities"), incurred by the
                        -------------------------------
Company Indemnitees or any of them as a result of, or arising out of, or
relating to any misrepresentation in or breach of any of the representations and
warranties or any nonfulfillment or breach of any covenant or agreement on the
part of the Purchaser under this Agreement, provided that the Purchaser shall
not be liable to an Company Indemnitee under this Section 9B for any liability
                                                  ----------
if such liability is caused solely by such Company Indemnitee's fraud, willful
misconduct or gross negligence or default or breach under this Agreement. To the
extent that the foregoing undertaking by the Purchaser may be unenforceable for
any reason, the Purchaser shall make the maximum contribution to the payment and
satisfaction of each of the Company Indemnified Liabilities which is permissible
under applicable law.

          9C.  Survival of Representations and Warranties.  All of the
               ------------------------------------------
representations and warranties contained herein shall survive the Closing for a
period of six (6) months.

          Section 10.  Definitions.  For the purposes of this Agreement, the
                       -----------
following terms have the meanings set forth:

          "Affiliate" of any particular Person means any other Person
           ---------
controlling, controlled by or under common control with such particular Person,
where "control" means the possession, directly or indirectly, of the power to
direct the management and policies of a Person whether through the ownership of
voting securities, contract or otherwise.

          "Class A Common Stock" means the Company's Class A Common Stock, par
           --------------------
value $.001 per share.

          "HSR Act" means the Hart-Scott-Rodino Antitrust Improvements Act of
           -------
1976, as amended, and the Premerger Notification Rules promulgated thereunder.

          "Person" means any individual, partnership, corporation, limited
           ------
liability company, association, joint stock company, trust, joint venture,
unincorporated organization or governmental entity or any department, agency or
political subdivision thereof.

          "Qualified IPO" shall mean an underwritten public offering of Class A
           -------------
Common Stock with gross proceeds of not less than $120,000,000.

          "Securities Act" means the Securities Act of 1933, as amended, or any
           --------------
similar federal law then in force.

          "Securities and Exchange Commission" includes any governmental body or
           ----------------------------------
agency succeeding to the functions thereof.

                                      10

<PAGE>

          "Securities Exchange Act" means the Securities Exchange Act of 1934,
           -----------------------
as amended, or any similar federal law then in force.

          "Transaction Documents" means all documents, instruments, certificates
           ---------------------
or other agreements being delivered in connection with or pursuant to this
Agreement.

          Section 11.  Miscellaneous.
                       -------------

          11A. Expenses.  The Company shall pay, and hold the Purchaser and all
               --------
holders of Securities harmless against liability for the payment of the fees and
expenses incurred with respect to the enforcement of the rights (in connection
with a breach or threatened breach by the Company) granted under this Agreement,
the other agreements contemplated hereby to which the Company is a party or the
Amended Certificate.

          11B. Remedies.  Each holder of Securities shall have all rights and
               --------
remedies set forth in this Agreement and all rights and remedies which such
holders have been granted at any time under any other agreement or contract and
all of the rights which such holders have under any law.  Any Person having any
rights under any provision of this Agreement shall be entitled to enforce such
rights specifically (without posting a bond or other security), to recover
damages by reason of any breach of any provision of this Agreement and to
exercise all other rights granted by law.

          11C. Legends.
               -------

               (i)  The certificates evidencing the Securities will include the
     legend set forth below, which the Purchaser has read and understands:


          THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
          SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAW, AND
          MAY NOT BE OFFERED, SOLD, TRANSFERRED OR OTHERWISE DISPOSED OF UNLESS
          REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND ANY
          APPLICABLE STATE SECURITIES LAWS OR AN EXEMPTION FROM SUCH
          REGISTRATION IS AVAILABLE.  THESE SECURITIES ARE ALSO SUBJECT TO
          INVESTMENT REPRESENTATIONS AND A LOCKUP AGREEMENT WITH THE CORPORATION
          PURSUANT TO A PURCHASE AGREEMENT DATED MARCH 30, 2000 WHICH RESTRICTS
          THE TRANSFER THEREOF UNTIL [insert one year anniversary of closing], A
          COPY OF WHICH CAN BE OBTAINED FROM THE CORPORATION AT ITS EXECUTIVE
          OFFICES.

               (ii) By accepting the certificates bearing the aforesaid legend,
     Purchaser agrees, prior to any transfer of the Securities represented by
     the certificates and subject to the restrictions in Section 11D, to give
                                                         ------------
     written notice to the Company expressing its desire to effect such transfer
     and describing briefly the proposed transfer.

                                      11
<PAGE>

     Upon receiving such notice, the Company shall present copies thereof to its
     counsel and the following provisions shall apply:

                      (a)  subject to Section 11D, if, in the reasonable opinion
                                      -----------
     of counsel to the Company, the proposed transfer of such Securities may be
     effected without registration under the Securities Act and applicable state
     securities acts, the Company shall promptly thereafter notify Purchaser,
     whereupon Purchaser shall be entitled to transfer such Securities, all in
     accordance with the terms of the notice delivered by Purchaser and upon
     such further terms and conditions as shall be required to ensure compliance
     with the Securities Act and the applicable state securities acts, and, upon
     surrender of the certificate evidencing such Securities, in exchange
     therefor, a new certificate not bearing a legend of the character set forth
     above if such counsel reasonably believes that such legend is no longer
     required under the Securities Act and the applicable state securities acts;
     and

                      (b)  subject to Section 11D, if, in the reasonable opinion
                                      -----------
     of counsel to the Company, the proposed transfer of such Securities may not
     be effected without registration under the Securities Act or the applicable
     state securities acts, a copy of such opinion shall be promptly delivered
     to Purchaser, and such proposed transfer shall not be made unless such
     registration is then in effect.

               (iii)  The Company may, from time to time, make stop transfer
     notations in its records and deliver stop transfer instructions to its
     transfer agent to the extent its counsel considers it necessary to ensure
     compliance with the Securities Act and the applicable state securities
     acts.

          11D. Lock-up Agreements.  In order to induce the Company to enter into
               ------------------
this Agreement, until the 12-month anniversary of the Closing, Purchaser shall
not, directly or indirectly, sell, offer to sell, contract to sell, assign,
transfer or otherwise dispose of, or engage in any other transaction (including,
without limitation, any pledge, put, call, collar, hedge or short sale) which
reduces the risk of ownership of, any of the Securities.  Purchaser agrees and
consents to the entry of stop transfer instructions with the Company's transfer
agent against the transfer of the Securities held by the Purchaser except in
compliance with the foregoing restrictions.

          11E. Compliance with Rule 144.   At any time after the Qualified IPO
               ------------------------
and subject to Section 11D above, if the Purchaser proposes to sell any of the
               -----------
Securities in compliance with Rule 144 (including Rule 144(k)) of the Securities
and Exchange Commission under the Securities Act, the Company  will (i)
forthwith furnish to such holder, upon request, a written statement of
compliance with the filing requirements of the Securities Exchange Commission as
set forth in such Rule 144, as such rule may be amended from time to time, and
(ii) use its reasonable best efforts to make available to the public and
Purchaser such information as will enable the Purchaser to make sales pursuant
to such Rule 144.

          11F. Successors and Assigns.  Except as otherwise expressly provided
               ----------------------
herein, all covenants and agreements contained in this Agreement by or on behalf
of any of the parties

                                      12

<PAGE>

hereto shall bind and inure to the benefit of the respective successors and
assigns of the parties hereto whether so expressed or not. Notwithstanding the
foregoing or anything to the contrary herein, the parties may not assign this
Agreement.

          11G. Severability.  Whenever possible, each provision of this
               ------------
Agreement shall be interpreted in such manner as to be effective and valid under
applicable law, but if any provision of this Agreement is held to be prohibited
by or invalid under applicable law, such provision shall be ineffective only to
the extent of such prohibition or invalidity, without invalidating the remainder
of this Agreement.

          11H. Counterparts.  This Agreement may be executed simultaneously in
               ------------
two or more counterparts, any one of which need not contain the signatures of
more than one party, but all such counterparts taken together shall constitute
one and the same Agreement.

          11I. Descriptive Headings; Interpretation.  The descriptive headings
               ------------------------------------
of this Agreement are inserted for convenience only and do not constitute a
substantive part of this Agreement.  The use of the word "including" in this
Agreement shall be by way of example rather than by limitation.

          11J. Governing Law.  The general corporation law of the State of
               -------------
Delaware shall govern all issues and questions concerning the relative rights
and obligations of the Company and its stockholders. All other issues and
questions concerning the construction, validity, enforcement and interpretation
of this Agreement and the schedules and exhibits hereto shall be governed by,
and construed in accordance with, the laws of the State of Illinois, without
giving effect to any choice of law or conflict of law rules or provisions
(whether of the State of Illinois or any other jurisdiction) that would cause
the application of the laws of any jurisdiction other than the State of
Illinois. In furtherance of the foregoing, the internal law of the State of
Illinois shall control the interpretation and construction of this Agreement
(and all schedules and exhibits hereto), even though under that jurisdiction's
choice of law or conflict of law analysis, the substantive law of some other
jurisdiction would ordinarily apply.

          11K. Notices.  All notices, demands or other communications to be
               -------
given or delivered under or by reason of the provisions of this Agreement shall
be in writing and shall be deemed to have been given when delivered personally
to the recipient, sent to the recipient by reputable overnight courier service
(charges prepaid) or mailed to the recipient by certified or registered mail,
return receipt requested and postage prepaid.  Such notices, demands and other
communications shall be sent to Purchaser at the address indicated for Purchaser
at the address set forth below or as otherwise indicated on the stock records of
the Company, and to the Company at the address indicated below:

     If to the Company:

                              divine interVentures, inc.
                              4225 Naperville Road, Suite 400
                              Lisle, Illinois 60532
                              Attention: General Counsel

                                      13

<PAGE>

     With a copy to:          Katten Muchin Zavis
                              525 W. Monroe Street
                              Suite 1600
                              Chicago, Illinois 60661-3693
                              Attention: Matthew S. Brown, Esq.


     If to the Purchaser:     Aon Corporation
                              123 Wacker Drive
                              Chicago, Illinois 60606
                              Attention: Raymond I. Skilling

     With a copy to:          Sidley & Austin
                              One First National Plaza
                              Chicago, Illinois 60603
                              Attention: Thomas A Cole, Esq.

or to such other address or to the attention of such other person as the
recipient party has specified by prior written notice to the sending party.

          11L. No Strict Construction.  The parties hereto have participated
               ----------------------
jointly in the negotiation and drafting of this Agreement.  In the event an
ambiguity or question of intent or interpretation arises, this Agreement shall
be construed as if drafted jointly by the parties hereto, and no presumption or
burden of proof shall arise favoring or disfavoring any party by virtue of the
authorship of any of the provisions of this Agreement.


                 [Remainder of page intentionally left blank.
                           Signature page follows.]

                                      14
<PAGE>

          IN WITNESS WHEREOF, the parties hereto have executed this Purchase
Agreement on the date first written above.



                                    DIVINE INTERVENTURES, INC.


                                    By: /s/ Michael P. Cullinane
                                       -----------------------------------
                                          Michael P. Cullinane
                                          Executive Vice President



                                    AON CORPORATION


                                    By: /s/ Patrick G. Ryan
                                       -----------------------------------
                                    Its: Chairman and CEO
                                        ----------------------------------




                    (SIGNATURE PAGE TO PURCHASE AGREEMENT)