Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 169-172, 2005

Multidentate Dipyridyl Derivatives as Chelates for Rhenium(V)Thomas I. A. Gerber,*, a Abubak’r Abrahams,a and P. MayerbaDepartment of Chemistry, P.O. Box 77000, Nelson Mandela Metropolitan University, Port Elizabeth 6031,
South AfricabDepartment of Chemistry, Ludwig-Maximilians University, D-81377 München, Germany
Received: July 31, 2005; In Final Form: September 30, 2005
Rhenium(V) complexes with the following multidentate dipyridyl ligands were prepared: 2,2’-dipyridylamine(DPA), 1,2-bis(2-pyridyl)ethylene (DPE) and di-(2-picolyl)amine (HDIPA). Reactions of a twofold molar excessof the potentially NN donor ligand DPA with trans-[ReO(OEt)Cl2 (PPh3)2] in ethanol led to isolation of a monomer[ReOCl2 (OEt)(DPA)] (1). Treatments of trans-[ReOCl3(PPh3)2] with a tenfold molar excess of DPA in ethanol at
reflux yielded [ReO2 (dpa) 2]Cl (2), but with a twofold molar excess a dimer ( µ-O)[{ReOCl 2 (dpa)}2] (3a) was
isolated. The latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature led to adark green product, also with the formulation ( µ-O)[{ReOCl2 (dpa)}2] (3b). Reacting equimolar quantities of (nBu4N)[ReOCl4] and HDIPA in acetone led to [ReOCl(OH2)(DIPA)]Cl (4) in which HDIPA acted as a monoanionicterdentate chelate. The reaction of trans-[ReOCl3 (PPh3)2] with DPE, in which DPE undergoes a metal-promoted
nucleophilic attack by a water molecule, produces a complex with a general formula [ReO(DPE.OH)Cl2] (5).

1. Introduction
Oxorhenium(V) complexes with terdentate dianionic ONX(X = O, S) donor Schiff base ligands have been well studied.1, 2, 3 It was found that the three donor atoms are bonded tothe metal on the cis equatorial plane with respect to the Re = O
linkage in complexes of the type [ReOCl(ONX)(MeOH)]. A
study of oxorhenium(V) complexes with terdentate Schiff baseligands having the ONN donor-atom set has shown that it is theimino nitrogen that is bonded trans to the oxo oxygen in complexes of the type [ReOCl 2 (ONN)].4 We have previously
reported the products [ReOCl2 (ONN)] obtained from the reaction of trans-[ReOCl 3 (PPh 3) 2 ] with terdentate ONN-donor
ligands of the pyridylaminophenol type, which are similar to theterdentate Schiff base ligands, except that they contain an amino
nitrogen in place of the imino nitrogen.5
We report here the synthesis of rhenium(V) complexes withthe following multidentate dipyridyl ligands: 2,2’-dipyridylamine (DPA), di-(2-picolyl)amine (HDIPA) and 1,2-bis(2pyridyl)ethylene (DPE).
2. Experimental
Materials. Trans-[ReOCl3(PPh3)2],6 (n-Bu4N)[ReOCl4]7 andtrans-[ReOI2(OEt)(PPh3)2]8 were synthesized by literature methods. 2,2’-Dipyridylamine (DPA), 1,2-bis(2-pyridyl)ethylene(DPE) and di-(2-picolyl)amine (HDIPA) were obtained commercially (Aldrich). Solvents were refluxed over appropriate
drying agents, and distilled and degassed before use. Infrared
spectra were obtained using KBr disks. The instrumentation
used is the same as reported earlier.5
Synthesis of [ReOCl2 (OEt)(DPA)] (1). DPA (137 mg, 800µmol) was added to a stirred suspension of trans-[ReOCl3(PPh3)2](300 mg, 360 µmol) in 10 cm 3 ethanol, and the mixture washeated under reflux for 30 min. After about 10 min of heating
the lime-green colour of the starting material changed to purple,
and after heating was stopped and the solution cooled to room
temperature, a purple solid was filtered off. Recrystallization*Corresponding author. E-mail: thomas.gerber@nmmu.ac.za.
FAX: +27(41)5044236.

from dichloromethane/ethanol afforded dark blue crystals. Yield= 58%, mp 299−301 ˚C. IR (cm−1): ν(Re = O) 954 s, ν(C = C)
1587 s, ν(C = N) 1630 s, ν(N-H) 3216 w, δ(OCH2) 916 vs, ν(ReN) 524 m, ν(Re-Cl) 318 m.
Synthesis of trans-[ReO2 (DPA)2]Cl (2). DPA (626 mg, 3.65mmol) in ethanol (5 cm3) was added to a stirred suspension oftrans-[ReOCl3(PPh3)2] (331 mg, 400 µmol) in the same solvent(10 cm3), and the resulting solution was heated under reflux for
30 min. During this time the solution changed colour from yellow-green to brown, and after 20 min a bright orange precipitate
was formed. After cooling the mixture to room temperature thesolid was filtered off, washed with ethanol (2 × 2 cm3) and dried
under vacuum. Crystals of the 3H2O solvate, suitable for X-ray
diffraction, were obtained by slow evaporation of the motherliquor from the synthetic solution. Yield = 72%, mp 229 ˚C. IR(cm−1): ν(O = Re = O) 814 vs, ν(C = C) 1582 s, ν(C = N) 1637 s,
ν(N-H) 3232 w, ν(Re-N) 540 m.
Synthesis of ( µ-O)[{ReOCl2 (DPA)} 2] (3a). To an ethanol(10 cm 3) suspension of trans-[ReOCl3 (PPh3) 2] (300 mg, 400µmol) was added DPA (137 mg, 800 µmol). The mixture washeated under reflux for 30 min, generating a brown solution
from which a green solid precipitated. The mixture was cooled
to room temperature and the green product was filtered off after
standing overnight. It was then washed with cold ethanol anddiethyl ether, and vacuum dried. Recrystallization was fromacetonitrile. Yield = 76%, mp 274 ˚C. IR (cm−1): ν(Re = O) 913
m, ν(Re-O-Re) 697 vs, ν(C = C) 1585 s, ν(C = N) 1632 s, ν(NH) 3297 w, ν(Re-N) 529 m, ν(Re-Cl) 317 m, 322 m.
Synthesis of ( µ-O)[{ReOCl2 (DPA)} 2] (3b). A solution of
DPA (190 mg, 1110 µmol) in ethanol (10 cm3) was added dropwise to a stirred suspension of 324 mg (552 µmol) of (nBu4N)[ReOCl4] in 10 cm3 of ethanol. An intense purple solution
was obtained in a few minutes, and after stirring for 30 min a darkgreen crystalline precipitate was filtered off, washed rapidly withwater, acetone and diethyl ether, and dried under vacuum.
Recrystallization was from DMSO/ n-hexane. Yield = 74%, mp
246 ˚C. IR (cm−1): ν(Re = O) 923 m, ν(Re-O-Re) 697 vs, ν(C =C) 1585 s, ν(C = N) 1628 s, ν(N-H) 3301 m, ν(Re-N) 534 m,
ν(Re-Cl) 319 m.
Synthesis of [ReOCl(OH2)(DIPA)] (4). HDIPA (0.0244 g,
123 µmol) dissolved in 6 cm 3 acetone was added to a light© 2005 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 12/28/2005

170 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

Gerbergreen, stirred solution of (n-Bu4N)[ReOCl4] (0.07191 g, 123µmol) in the same solvent (6 cm3). A dark green solid immediately formed, and the suspension was stirred for further 4 h
at room temperature. The solid was removed by filtration,
washed with acetone (2 × 3 cm 3), and dried under vacuum.
Recrystallization from acetonitrile produced avocado-green
crystals, suitable for X-ray diffraction studies. Yield = 65%,
mp > 300 ˚C. IR (cm−1): ν(Re = O) 957 vs, ν(C = N) 1613 s,
ν(C = C) 1562 w, ν(Re-Npy) 590 m, ν(Re-N) 664 w, ν(Re-Cl)
309 m.
Synthesis of [ReOCl2 (DPE.OH)] (5). A solution of 43 mg(235 µmol) of DPE in 10 cm 3 ethanol was added to a suspension of trans-[ReOCl3(PPh3)2](in 5 cm3) ethanol. The mixture
was heated under reflux for 24 h. The colour of the solution
gradually turned from green to blue, with the continuous precipitation of a blue compound. After cooling to room temperature, the blue precipitate was collected by filtration, washedwith ethanol (2 × 2 cm3) and dried under vacuum. Yield = 90%(51 mg); mp 223 ˚C. IR (cm−1): ν(Re = O) 940; ν(Re-N) 523,
511; ν(Re-O) 441; ν(Re-Cl) 322.
X-ray Structure Determination. Data collection was performed at 200 K on a Nonius Kappa CCD using Mo Kα radiation. Nonhydrogen atoms were refined with anisotropic
displacement parameters; hydrogen atoms bound to carbon
were idealized and fixed. Due to twinned crystals in 4 only theRe, Cl(1), Cl(2), O(1) and O(2) were refined anisotropically.
Structural refinements were carried out by the full-matrix
least-squares method on F 2 using the program SHELXL-97.9
The crystal data and details of the structure determinations are
given in Table 1.
3. Results and Discussion
Structure of [ReOCl 2 (OEt)(DPA)]. The rhenium atom
(Figure 1) is at the centre of a distorted octahedral environment.
The basal plane is defined by a N2Cl2 donor set. The ethoxide
ion and the oxo group are in trans axial positions. Distortion
form an ideal rhenium centred octahedron mainly result in anonlinear O(1) = Re-O(2) axis of 169.6(2)˚, accomplished byN(1) -Re-Cl(2) and N(3) -Re-Cl(1) angles of 175.6(2)˚ and
179.0(2)˚ respectively. The rhenium atom is lifted out of themean equatorial plane by 0.0488(1) Å towards O(1), which is
the result of the nonorthogonal angles O(1)-Re-N(1) = 87.9(3)˚,O(1)-Re-N(3) = 85.7(2)˚, O(1)-Re-Cl(1) = 95.1(2)˚ and O(1)-ReCl(2) = 96.0(2)˚. The pyridine rings of DPA are “flapped”

N2

C4

C7

C5

C8

C3

C6

O1

N3
C9
N1

C2

Re

C 10

C1
Cl1

Cl2
O2
C11
C12

Figure 1. An ORTEP view of the structure of 1, showing the atomlabelling scheme and thermal ellipsoids drawn at the 40% probability
level (Re-O(1) = 1.690(5), Re-O(2) = 1.866(5), Re-N(1) = 2.131(4),Re-N(3)=2.156(7), Re-Cl(1) = 2.384(2), Re-Cl(2) = 2.408(2), O(2)C(11) = 1.430(9); O(1)-Re-O(2) = 169.6(2), N(1)-Re-N(3) = 86.1(3),Cl(1)-Re-Cl(2) = 88.3(1), C(5)-N(2)-C(6) = 129.4(6)).

around N(2) away from O(1) towards O(2). The two rings
make dihedral angles of 32.24˚ and 31.79˚ with the mean equatorial plane, and 30.25˚ with each other.
Structure of trans-[ReO2 (DPA) 2]Cl·3H 2O. The rhenium
atom is at the centre of an octahedron with the equatorial plane
formed by a N4 pyridinic donor set (Figure 2). The two oxogroups are in trans positions relative to each other with theO(1)-Re-O(2) bond angle close to linearity at 179.2(1)˚. The
Re = O distances (1.762(3) Å average) and the Re-N distances(from 2.137(4) to 2.150(4) ) lie in the range usually found inother trans-dioxo [ReO2L4] + cations (where L = py10 or imidazole11). The rhenium atom is coplanar with the four nitrogen
donor atoms (it is 0.0086 out of the mean equatorial N4 plane
towards O(1)), with the result that the four O(1)-Re-N angles
are all orthogonal (from 90.08(13)˚ to 90.45(13)˚). The average
bite angle of the two DPA ligands equals 83.80(15)˚ [N(1)-ReN(3) = 83.95(15)˚; N(4)-Re-N(6) = 83.64(15)˚], which is larger
than that of 2,2’-bipyridine (BIPY) in rhenium(V) complexes(~75˚).12
Structures of ( µ-O)[{ReOCl 2 (DPA)} 2 ] (3a) and ( µ-O)[{ReOCl 2 (DPA)} 2 ]·2DMSO (3b·2DMSO). Complexes 3a

TABLE 1: Crystal Data and Structure Refinement Details for 1, 2, 3a, 3b, 4 and 5
1

2·3H2O

3a3b·2DMSO

4 · Cl5

Empirical FormulaC12H14N3O2Cl2Re

C20H24ClN6O5Re

C20H18Cl4N6O3Re2

C24H30Cl4N6O5S2Re2

C12H14N3Cl2O2Re

C12H11N2O2Cl2Re

Formula Weight489.37

650.1

904.6

1060.9489.37472.34Temperature (K)

200

200

200

200

200

200

Crystal System

Orthorhombic

Triclinic

Tetragonal

Triclinic

Monoclinic

Orthorhombic

Space group

Pna21

P�

I41/a

P�

P21/n

Pbca

a (Å)

14.8212(4)7.3141(3)13.8640(6)9.0089(11)8.2765(4)11.3582(9)b (Å)

7.6036(2)11.2706(4)13.8640(6)9.2570(11)12.1139(9)14.9274(12)c (Å)

13.1638(4)13.8906(6)25.5319(17)10.9635(14)14.6718(8)16.1135(13)Volume (Å )1483.5(1)1112.7(1)4907.5(4)800.6(2)1467.90(15)2732.0(4)

Z

4

2

8

1

4

8

Density (calcd., Mg/m−3)

2.191

1.940

2.449

2.200

2.214

2.297

Absorption coefficient (mm−1) 8.555

5.626

10.330

8.063

8.645

9.284

F(000)

928

636

3376

506

928

1776

Crystal Size (mm)0.18 × 0.03 × 0.02

0.07 × 0.10 × 0.12 0.07 × 0.13 × 0.20

0.05 × 0.10 × 0.14

0.03 × 0.05 × 0.12 0.03 × 0.18 × 0.26

Theta min-max

3.15–25.01

3.2–27.4

2.6 –28.0

2.0 –28.1

2.2–24.0

2.5–24.0

R, wR20.0251, 0.0509

0.0367, 0.0756

0.0181, 0.0403

0.0272, 0.0591

0.0475, 0.1107

0.0285,0.05

Unit cell dimensions

3

J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 171

Multidentate Dipyridyl Derivatives as Chelates for Rhenium(V)
C19

C2

C18

C3

C5

C20
C1

C4
N1

C1

O2
Cl1

C6

Cl2

Re

N3

C1 0

C7

C14

C13

C 10

N3

Cl1

N2

O2

C11

C9

Re

Cl2

O1

N4

O1

N1

Re

C15

C6

C5

C16

N5

N2

C2

C17
N6

C8

C7

C4

C3

C10

N3

N1

C1

O1
C9

C9

C2
C6

C8

C12

Figure 2. Molecular structure of 2 (Re-O(1) = 1.764(3), Re-O(2) =1.760(3), Re-N(1) = 2.140(4), Re-N(3) = 2.150(4), Re-N(4) = 2.137(4),Re-N(6) = 2.137(4); O(1)-Re-O(2) = 179.2(1), O(1)-Re-N(1) = 90.1(1),O(1)-Re-N(6) = 90.5(1), C(5)-N(2)-C(6) = 126(1)).

C8

C5

N2

C7

C3

C4

Figure 4. ORTEP plot of 3b (Re-O(1) = 1.695(5), Re-O(2) = 1.9258(4)Re-N(1) = 2.127(4), Re-N(3) = 2.132(5), Re-Cl(1) = 2.380(2), Re-Cl(2)= 2.405(2); O(1)-Re-O(2) = 171.1(1), Re-O(2)-Re = 180.00, N(1)-ReN(3) = 86.7(2)).
O2

C3
C4

Cl1

C1

C2

N1

Re

N3

N2

C5

C7

C6

C12

C8

C11

C10
C9

O1

Figure 5. X-ray structure of 4 (Re-O(1) = 2.21(1), Re-O(2) = 1.663(9),Re-N(1) = 2.08(1), Re-N(2) = 1.89(1), Re-N(3) = 2.08(1), Re-Cl(1) =2.462(3); O(1)-Re-O(2) = 167.2(4), N(1)-Re-N(3) = 153.9(4), O(2)-ReN(1) = 99.0(5), C(6)-N(2)-Re = 118.3(9)).

Figure 3. ORTEP view of the crystal structure of 3a (Re-O(2) =1.692(3), Re-O(1) = 1.9151(3), Re-Cl(1) = 2.398(1), Re-Cl(2) =2.375(1), Re-N(1) = 2.127(3), Re-N(3) = 2.147(3); Re-O(1)-Re =172.3(2), O(1)-Re-O(2) = 169.5(1), N(1)-Re-N(3) = 87.6(1)).

(Figure 3) and 3b(Figure 4) each consists of two independent[ReOCl2 (DPA)] units bridged by an oxygen atom. In 3a, the O= Re-O-Re = O backbone shows considerable deviation fromlinearity [O(2)-Re-O(1) = 169.5(1)˚; Re-O(1)-Re = 172.3(2)˚],with bending of the Re2O3 axis towards the two π-stacked pyridine rings coordinated via N(3). In 3b, the bridging O(2) lies
on a crystallographic inversion centre, making the Re-O-Re
angle exactly 180˚. The two O(1) = Re-O(2) angles are also
equal at 171.1(1)˚.
Each rhenium is centred in a distorted octahedron with theequatorial plane formed by a N2Cl2 donor set. The 3a molecule
adopts a conformation in which the ReN2Cl2 planes are mutually rotated by 61.42˚ about the Re2O3 axis, which, together
with the bond along the Re-O-Re axis, allows the symmetryrelated pyridine rings coordinated through N(3) on opposite
sides of the molecule to interact at an average contact distanceof 3.27 Å. The dihedral angle between the least-squares planes
through these two stacked pyridine rings is 6.24˚. In 3b the
ReN2Cl2 planes are mutually rotated by 180.0˚, so that the chlorines of one ReON2Cl2 unit almost eclipse the nitrogen atomsof the other part of the molecule. The distances of the chlorine

atoms of one unit to the pyridine planes in the other unit are on
average 3.080 Å, that is, about equal to the sum of the van der
Waals radii.
In 3a, the pyridine rings of each DPA ligand are “flapped”
towards the bridging oxygen O(1). In contrast, the pyridine
rings in 3b are “flapped” towards the terminal oxo groups.
Structure of [ReOCl(OH2)(DIPA)](4). The rhenium atom
is at the centre of a distorted octahedron (Figure 5). The basal
plane is defined by the two pyridyl nitrogen atoms N(1) andN(3), the deprotonated secondary amine nitrogen N(2) and thechloride Cl(1). The oxo group O(2) and the O(1) of the coordinated water molecule are in trans axial positions. Distortion
from an ideal rhenium-centred octahedron mainly results in anonlinear O(1)-Re-O(2) axis of 167.2(4)˚, accomplished by N(1)Re-N(3) and Cl(1)-Re-N(2) angles of 153.9(4)˚ and 162.9(4)˚
respectively. The rhenium atom is lifted out of the mean equatorial N3Cl plane by 0.34 Å towards O(2), which is the result of
the nonorthogonal angles O(2)-Re-N(1) = 99.0(5)˚, O(2)-ReN(2) = 106.4(5)˚, O(2)-Re-N(3) = 102.5(5)˚ and O(2)-Re-Cl(1)= 90.6(4)˚. The Re-O(1) distance of 2.21(1) Å is within of thevalue of 2.23(2) Å found for water molecules bound trans to theoxo atom in [ReOCl2 (tu)(H2O)]Cl and [ReOCl3 (tu)(H2O)].13, 14
The short Re-N(2) bond length of 1.89(1) Å is considerably
shorter than the average Re-NH lengths of 2.21(2) Å found incomplexes containing ligands of the pyridylaminophenol type,5and illustrates a significant multiple bond character.
Structure of [ReO(DPE.OH)Cl 2](5). The structure contains discrete, monomeric, neutral monooxorhenium(V) com-172 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005

GerberBond lengths and angles in the complex show no unusual
features, being within the range expected from the comparisonof other six-coordinate monooxo complexes of Re(V).2, 3, 8−12

O2
Cl1

Cl2
C12
C11

Re

C1
C2

N2

N1

Supplementary Material. Full lists of crystallographic
data are available from the authors upon request.

O1
C10
C8

C5
C6

C3
C4

Acknowledgements. The authors are grateful to the National
Research Foundation (Grant #TTK2004081100014) and
NMMU for financial assistance.

C9
C7

Figure 6. Molecular structure of 5 (Re-O(1) = 1.916(5), Re-O(2) =1.694(5), Re-Cl(1) = 2.363(2), Re-Cl(2) = 2.351(2), Re-N(1) =2.147(7), Re-N(2) = 2.168(6), O(1)-C(6) = 1.454(9); O(1)-Re-O(2) =160.1(2), O(2)-Re-Cl(1) = 98.7(2), N(1)-Re-Cl(1) = 90.5(2), N(1)-ReN(2) = 88.5(2), Cl(1)-Re-Cl(2) = 89.88(8), Re-O(1)-C(6) = 117.1(4)).

plex units, and the crystal packing is governed by van der
Waals contacts. No intermolecular hydrogen bonds exist, andweak intramolecular hydrogen bonds are observed between
C(1)H(1)···O(2) (2.947(9)Å) and C(12)H(12)···O(2) (2.85(1)Å).
The DPE.OH moiety acts as a uninegative, terdentate NON
donor ligand. Severe distortions from the ideal Re-centeredoctahedral configuration are as follows; (i) the Re atom lies outof the equatorial mean plane by 0.15 Å toward the oxo ligand;(ii) the nonlinear O(1)-Re-O(2) axis of 160.1(2)˚ is accomplished by Cl(1)-Re-N(2) and Cl(2)-Re-N(1) angles of 174.4(2)˚and 170.0(2)˚, respectively; (iii) the edge distances are observedin a rather narrow range (from 3.01 Å for N(1)···N(2) to 3.33 Å
for Cl(1)···Cl(2), and the interligand angles in the equatorial
plane depart from the ideal 90˚ (from 86.5 to 93.4˚); (iv) in the
X2N2O2 coordination polyhedron the Re atom is +1.02 Å awayfrom the Cl (1) Cl (2) O (2) plane, and −1.35 Å from theN(1)N(2)O(1) one, the angle between the two triangles being
12.1˚.

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