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Acta Crystallographica Section C

Crystal Structure
Communications
ISSN 0108-2701

A head-to-head isomer of di--pivalamidato-4 N,O-bis[(1,10phenanthroline-2N,N )platinum(II)] dinitrate dihydrate0

Ken Sakai, Mai Kurashima, Norinobu Akiyama, Naoki Satoh, Takashi Kajiwara andTasuku Ito

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Acta Cryst. (2003). C59, m345–m349

Ken Sakai et al.  [Pt2 (C5 H10 NO)2 (C12 H8 N2 )2 ](NO3 )2 .2H2 O

metal-organic compounds
Acta Crystallographica Section C

Crystal Structure
Communications
ISSN 0108-2701

A head-to-head isomer of di-l-pivalamidato-j4N,O-bis[(1,10-phenanthroline-j2N,N0 )platinum(II)] dinitrate
dihydrateaaa

Ken Sakai, * Mai Kurashima, Norinobu Akiyama, Naoki
Satoh,a Takashi Kajiwarab and Tasuku Itoba

Department of Applied Chemistry, Faculty of Science, Tokyo University of Science,
Kagurazaka 1-3, Shinjuku-ku, Tokyo 162-8601, Japan, and bDepartment ofChemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
Correspondence e-mail: ksakai@rs.kagu.tus.ac.jp
Received 17 July 2003
Accepted 18 July 2003
Online 9 August 2003

In the title compound, [Pt2(C5H10NO)2(C12H8N2)2](NO3)22H2O, the intradimer PtÐPt distance is relatively shortÊ ], which must be due to the strong intramole[2.8489 (17) A
cular ±-stacking interactions between the phenanthroline
moieties. The dimers stack along the c axis, forming onedimensional columns in which very intriguing d±d, ± andd± interactions exist. Although the dimer±dimer Pt  PtÊ ], some shortdistances are very long [4.340 (2) and 4.231 (2) Ainterdimer Pt  C contacts leading to strong interdimerÊ ].
associations are found [3.325 (19) and 3.402 (19) A

Comment
Interest in recent years has concentrated on one-dimensional
platinum chain systems consisting of dinuclear entities doubly
bridged, in cis positions, by amidate or carboxylate ligands(Sakai, Takeshita et al., 1998; Sakai, Ishigami et al., 2002). Oneof the attractive features of such dimers lies in their structural¯exibility, which allows a change in the PtÐPt distance uponchange in Pt oxidation state. Such ¯exibility must be considered a unique characteristic of the `U-shaped' dimers
mentioned above as it is not exhibited by the quadruply
bridged dimers, which are known as `lantern dimers'. In thiscontext, we recently succeeded in developing quite unusual
Magnus-type one-dimensional double salts involving a pivalamidate-bridged Pt(bpy) dimer, namely [Pt2(bpy)2(-pivalamidato)2]2+ (bpy = 2,20 -bipyridine; Sakai, Akiyama et al.,2002). Note that two geometrical isomers, viz. head-to-head(HH) and head-to-tail (HT), are possible for this class of
doubly bridged dimer as a result of the asymmetric feature of
the amidate NÐCÐO units. As part of the project, we report
here the crystal structure of the 1,10-phenanthroline (phen)analog in a HH arrangement, viz. HH-[Pt2(phen)2(-pivalamidato)2](NO3)22H2O, (I). We also obtained crystals of the
HT isomer, details of which will be reported elsewhere.
Acta Cryst. (2003). C59, m345±m349

The asymmetric unit of (I) consists of a dimer cation, twonitrate anions, and two water molecules. The mean-plane
calculations performed for the four coordinated atoms revealthat the two Pt coordination environments are planar; theÊ for the N1/N2/N5/N6
four-atom r.m.s. deviation is 0.015 A
Êplane and 0.021 A for the O1/O2/N3/N4 plane. The dihedral
angle () between the two Pt coordination planes within the
dimer unit and their average torsional twist (!) about the PtÐ
Pt axis are estimated as 21.5 (4) and 13 (3) , respectively,
where ! = 0 indicates that the two Pt coordination planes
stack in an eclipsed fashion. On the other hand, the two phen
ligands are also found to be planar; the 14-atom r.m.s. deviaÊ for the plane de®ned by atoms N1/N2/C1±C12tion is 0.023 A
Êand 0.030 A for the plane de®ned by atoms N3/N4/C13±C24.
The dihedral angle between the phen planes [6.2 (3) ] issmaller by 15.3 (4) than that between the two Pt coordination
planes, indicating that a relatively strong -stacking interaction exists in the dimer unit (Figs. 2 and 3a), where theÊ . Atoms Pt1 and Pt2 areinterplanar spacing is 3.56 (11) A
shifted from the individual coordination planes by 0.016 (7)Ê , respectively. They are both shifted towards
and 0.028 (8) A
the outside of the dimer unit as if they were attempting tomove away to resist the attractive forces induced by the strong
intradimer phen±phen stacking interaction. The intradimerÊ ] is shorter than that observedPtÐPt distance [2.8489 (17) AÊfor the bpy analog {ca 2.87 A for HH-[Pt2(bpy)2(-pivalami-

Figure 1

The structure of (I), showing the atom-labeling scheme. Displacement
ellipsoids are shown at the 50% probability level and H atoms have been
omitted for clarity.

DOI: 10.1107/S0108270103015920

electronic reprint# 2003 International Union of Crystallographym345

metal-organic compounds
dato)2]2+; unpublished results}. This is consistent with ourinterpretation that aromatic ligands in equatorial positions
promote the attractive interaction between the two Pt coordination planes within the dimer unit.
As shown in Fig. 4, the dimer cations stack along the c axis,
giving beautiful cationic one-dimensional columns, viz. [HHPt2(phen)2(-pivalamidato)2]n2n . The Pt1ÐPt2 vector is tilted
by ca 22 with respect to the c axis, resulting in relatively longÊ;interdimer Pt  Pt distances [4.340 (2) and 4.231 (2) A
Table 1]. On the other hand, counter-ions and water molecules
are inserted into the channels beside the dimer chains to giveanionic one-dimensional chains [(NO3)22H2O]n2nÿ (Fig. 4a),where hydrogen bonds are formed between nitrate and water
atoms O9 and O10 (Table 2). This is the ®rst example of acrystal structure in which either a Pt(bpy) or a Pt(phen) dimer
doubly bridged with amidate ligands gives a `one-dimensional
column', in spite of the fact that several crystal structures havealready been reported for dimers of this type, viz. HH-[Pt2(bpy)2(-3,3-dimethylglutarimidato)2]2(NO3)4 (Matsumoto &Urata, 1993) and HT-[Pt2(bpy)2( -pyrrolidinonato)2](ClO4)2(Matsumoto, Harashima et al., 1992). All the reported
compounds were prepared as Pt(bpy) dimers bridged byexocyclic amidate ligands having sterically bulky amidaterings, leading to the partial blocking of dimer±dimer associations. Importantly, the blocking effect of exocyclic amidate

Figure 3
Figure 2

A view showing two crystallographically independent dimer±dimer
associations. H atoms have been omitted for clarity.

m346

Ken Sakai et al.  [Pt2(C5H10NO)2(C12H8N2)2](NO3)2.2H2O

Views showing three different stacking interactions within the onedimensional column: (a) an intradimer association, (b) an interdimer
association through a twofold axis and (c) an interdimer association
through an inversion center. H atoms have been omitted for clarity.
[Symmetry codes: (i) ÿx, y, 12 ÿ z; (ii) ÿx, 1 ÿ y, ÿz.]electronic reprint

Acta Cryst. (2003). C59, m345±m349

metal-organic compounds
ligands can be eliminated by employing chain amidate ligands,
such as acetamidate, as reported by the authors (Sakai &Matsumoto, 1989; Matsumoto, Sakai et al., 1992). Thus, theone-dimensional framework observed in (I) must be promotedby the use of pivalamidate, which belongs to the chain amidate
family.
Although Pt  Pt interactions are not extended in a onedimensional manner, the dark-red (almost black) nature of (I)implies that somewhat strong intermolecular interactions areenhanced within the columnar stack of dimers. As shown in
Fig. 2, two crystallographically independent dimer±dimer
interactions are found. The dimer±dimer association achieved
through an inversion center [see the Pt2  Pt2ii geometry in
Fig. 2; symmetry code: (ii) ÿx, 1 ÿ y, ÿz] is stabilized byseveral interactions discussed below. One is an edge-to-faceinteraction formed between the tert-butyl and phen moieties;
the other is a dipole±dipole interaction between the cisPtN2O2 coordination planes, as previously reported for many
tetranuclear platinum complexes made up of amidate-bridged
cis-Pt(NH3)2 dimers (Sakai, Tanaka et al., 1998). Two reports
also show that similar HH dimers stack to give a dimer ofdimers based on the stack of PtO2(bpy) units in which acrystallographic inversion center is located at the mid-point of
the interaction (TroÈtscher et al., 1990; Matsumoto & Urata,

1993). It is also quite reasonable to consider that cis-PtN2O2
units rather than PtN4 units tend to stack through an inversion
center in order to form a more stable dipole±dipole interaction, as a much larger dipole would result at the cis-PtN2O2
unit compared with the PtN4 unit. In addition to these interactions, a relatively strong d± interaction exists, Pt2  C13ii =Ê (Fig. 3c). Other short contacts in this structure
3.325 (19) A
are listed in Table 2.
Two adjacent dimers are also correlated with a twofold axis
[see the Pt1  Pt1i geometry in Figs. 2 and 3b; symmetry code:(i) ÿx, y, 12 ÿ z]. In this case, the dimer±dimer interaction is not
only stabilized by a ±-stacking interaction between theÊ ], but alsophen moieties [the interplanar spacing is 3.36 (7) A
by hydrophobic interactions between the tert-butyl moieties.
Although two relatively weak hydrogen bonds are involved inthis geometry (Table 3), they do not participate in the stabilization of the interdimer association. A considerable d±
Ê ]. Other
interaction is also observed [Pt1  C12i = 3.402 (19) A
short contacts are summarized in Table 2.
We think that the strong d±d, ± and d± interactions
observed in the present one-dimensional system may lead tounusual physical properties. Detailed studies on the luminescence and electrical-conduction properties of (I), together
with those of related compounds, are still in progress in ourlaboratory.

Experimental
A solution of PtCl2(phen) [0.5 mmol, 0.22 g; prepared in the samemanner as reported for PtCl2(bpy); Morgen & Burstall, 1963],
AgNO3 (1 mmol, 0.17 g) and pivalamide (1.5 mmol, 0.15 g) in water(30 ml) was re¯uxed in the dark for 2 d. The solution was then ®ltered
while hot to remove precipitated AgCl. The ®ltrate was left to standin air at room temperature overnight. The deposited dark-red crystals
were collected by ®ltration (yield 50%). The compound was dissolvedin water at 338 K (ca 0.1 g/2 ml H2O), followed by ®ltration of the hot
solution. Leaving the ®ltrate to stand in air at room temperature
overnight afforded the ®nal product, (I), as dark-red prisms (yield30%). Analysis calculated for C34H40N8O10Pt2: C 36.76, H 3.63, N
10.09%; found: C 36.58, H 3.46, N 10.02%.
Crystal data
[Pt2(C5H10NO)2(C12H8N2)2](NO3)22H2O
Mr = 1110.92
Monoclinic, C2/cÊa = 22.454 (10) AÊ
b = 13.341 (6) AÊc = 27.271 (13) A= 113.701 (14)
Ê3
V = 7480 (6) A
Z=8

Dx = 1.973 Mg mÿ3
Mo K radiation
Cell parameters from 867
re¯ections
 = 3.1±19.8
 = 7.54 mmÿ1
T = 296 (2) K
Prism, dark red
0.15  0.10  0.05 mm

Data collection

Crystal packing views showing one-dimensional columns consisting of
dimer units (a) along the c axis and (b) along the b axis. H atoms havebeen omitted for clarity.

Bruker SMART APEX CCDdetector diffractometer! scans
Absorption correction: multi-scan(SADABS; Sheldrick, 1996)
Tmin = 0.509, Tmax = 0.686
18 755 measured re¯ections
6557 independent re¯ections
3177 re¯ections with I > 2(I)Acta Cryst. (2003). C59, m345±m349

Ken Sakai et al.  [Pt2(C5H10NO)2(C12H8N2)2](NO3)2.2H2O

Figure 4

electronic reprint

Rint = 0.129
max = 25.0
h = ÿ26 ! 25
k = ÿ15 ! 13l = ÿ27 ! 32
57 standard re¯ections
frequency: 330 min
intensity variation: 0.2%m347

metal-organic compounds
Table 1

Ê ,  ).
Selected geometric parameters (APt1ÐPt2
Pt1  Pt1i
Pt2  Pt2ii
Pt1ÐN1
Pt1ÐN2Pt2ÐN32.8489 (17)4.340 (2)4.231 (2)2.027 (12)1.999 (11)2.008 (14)Pt2ÐN4
Pt1ÐN5
Pt1ÐN6Pt2ÐO1
Pt2ÐO21.980 (14)2.009 (14)1.985 (12)2.029 (12)2.033 (12)N6ÐPt1ÐN2
N6ÐPt1ÐN5
N2ÐPt1ÐN5
N6ÐPt1ÐN1
N2ÐPt1ÐN1
N5ÐPt1ÐN1

93.3 (5)87.6 (5)179.1 (5)175.2 (5)82.3 (5)96.9 (5)N4ÐPt2ÐN3
N4ÐPt2ÐO1
N3ÐPt2ÐO1
N4ÐPt2ÐO2
N3ÐPt2ÐO2
O1ÐPt2ÐO2

81.4 (6)174.9 (5)94.3 (5)98.5 (5)179.6 (7)85.8 (5)N2ÐPt1ÐPt2ÐN4
N1ÐPt1ÐPt2ÐN3

ÿ16.3 (5)
ÿ15.1 (6)N5ÐPt1ÐPt2ÐO1
N6ÐPt1ÐPt2ÐO2

ÿ12.5 (5)ÿ10.6 (4)Symmetry codes: (i) ÿx; y; 12 ÿ z; (ii) ÿx; 1 ÿ y; ÿz.

Table 2Ê ).
Contact distances (APt1  C12i
Pt2  C13ii
Pt2  N3ii
N1  C11i
N2  N2i
N6  N6i
C8  C8i
O1  C17ii

O3B  O9
O4A  O9
O7  O10A
O7  O10B
O9  O6i
O10A  O5Aii
O10B  O4Bii
O10B  O5Bii

3.402 (19)3.325 (19)3.426 (18)
3.23 (2)3.26 (3)3.63 (3)3.36 (4)3.53 (3)2.67 (4)3.30 (3)2.95 (4)3.03 (4)3.00 (2)2.76 (5)3.11 (5)3.27 (5)Symmetry codes: (i) ÿx; y; 12 ÿ z; (ii) ÿx; 1 ÿ y; ÿz.

Table 3Ê ,  ).
Hydrogen-bonding geometry (ADÐH  ADÐHH  AD  A

DÐH  A

N5ÐH5  O9

0.86

2.43

3.21 (2)151

Re®nementRe®nement on F 2
R[F 2 > 2(F 2)] = 0.067
wR(F 2) = 0.122
S = 0.80
6557 re¯ections
478 parameters

H-atom parameters constrained
w = 1/[ 2(Fo2) + (0.0126P)2]
where P = (Fo2 + 2Fc2)/3(/)max < 0.001
Ê ÿ3max = 2.16 e AÊ ÿ3min = ÿ1.25 e A

It is often possible to determine the binding direction of the O andNH moieties of the amidate group by comparing the results of leastsquares calculations performed for two possible directions (Sakai etal., 2003). On the other hand, it is not very likely that the HH and HT
isomers possess the same intradimer PtÐPt distance (Sakai, Tanaka
et al., 1998). We decided to abandon the possibility that the two
isomers co-exist in a disorder model, since the Pt atoms possess
Ê 2. Consemoderately small Ueq values of 0.0404 (2) and 0.0450 (2) A
quently, one of two possible directions of the OÐCÐN group was
adopted for each pivalamidate ligand. The locations of atoms O1 andN5 have been rationally determined from the comparison of two sets
Ê 2 and Ueq(N5) = 0.053 (4) AÊ 2,of Ueq values: Ueq(O1) = 0.065 (4) AÊ 2 and Ueq(O instead of N5) =and Ueq(N instead of O1) = 0.040 (4) AÊ 2. On the other hand, it was rather dif®cult to evaluate the0.080 (4) A
validity of our assignment of the locations of atoms O2 and N6 based
Ê 2 and Ueq(N6) =on the following values: Ueq(O2) = 0.063 (4) AÊ 2, and Ueq(N instead of O2) = 0.036 (4) AÊ 2 and Ueq(O0.041 (4) A

m348

Ken Sakai et al.  [Pt2(C5H10NO)2(C12H8N2)2](NO3)2.2H2O

Ê 2. Finally, we decided to select the former
instead of N6) = 0.067 (4) A
assignment, since it was quite reasonable to suppose this compound
to be a HH isomer from many viewpoints, as discussed in theComment. As a result of this selection, a relatively short contact is
Ê , N6Ð
observed at N6ÐH6  H6iÐN6i, where H6  H6i = 2.11 A
i
i
i

Ê
H6  H6 = 151 , N6  N6 = 3.63 (3) A and N6ÐH6  H6 ÐN6i =ÿ51 (Fig. 3b and Table 2). However, such an unusually short contact
has been observed in many systems; for instance, H(NH3)  H(NH3)Ê were observed in one casedistances in the range 2.31 (8)±2.40 (7) A(Hollis & Lippard, 1983), and H(en)  H(en) distances in the range
Ê were observed in HH-[PtIII
2.2±2.3 A
2 (en)2(- -pyridonato)2(NO2)(NO3)]2+ (en = ethylenediamine; O'Halloran et al., 1986). These
unusually short H  H contact distances are due to a strong PtÐPt
bond formed between the two cis-Pt(NH3)2 or Pt(en) moieties.
Although the H6  H6i contact in (I) still seems too short, it must be
taken into consideration that H6 was located geometrically. The
actual H6  H6i distance could be longer than that described above
to give a more reasonable/acceptable situation with only a slightmodi®cation of the H6 position.
One of the two tert-butyl groups shows orientational disorder inwhich two sets of positions (C32A/C33A/C34A and C32B/C33B/
C34B) are located around atom C31. The disordered C atoms were
presumed to have the same isotropic displacement parameter.
Furthermore, all six C(tertiary)ÐC(methyl) distances and threeC(methyl)ÐC(methyl) distances within each site were restrained tobe equal. The occupation factors of sites A and B converged at 58 (2)and 42 (2)%, respectively. In the other tert-butyl group, the anisotropic displacement parameter (ADP) values of atom C27 are
unusual. However, re®nement with a reasonable disorder model was
unsuccessful. One of the two nitrate ions was also regarded as being
disordered over two sets of positions (N7A/O3A/O4A/O5A and N7B/
O3B/O4B/O5B). All the disordered atoms within each site wereassumed to have the same isotropic displacement parameter. MoreÊ , threeover, the NÐO distances were restrained to be 1.22 (1) AO  O distances within each site were restrained to be equal, andeach nitrate ion was restrained to be planar. The occupation factors ofsites A and B converged at 59 (2) and 41 (2)%, respectively.
All H atoms were located at idealized positions [CÐH(aromatic) =Ê , CÐH(methyl) = 0.96 A
Ê and NÐH = 0.86 A
Ê ] and included in
0.93 Athe re®nement in riding-motion approximation, with Uiso(aromaticH) = 1.2Ueq(C), Uiso(methyl H) = 1.5Ueq(C) and Uiso(H) = 1.2Ueq(N).
Water H atoms were not located. In the ®nal difference FourierÊ ÿ3 weresynthesis, seven residual peaks in the range 1.00±2.16 e A
Ê of the Pt atoms. The deepest hole was locatedobserved within 1.35 AÊ from Pt1. The maximum and minimum principal-axis ADP
0.84 Aratios of atoms N3 and N4 were 3.5 and 7.2, respectively. Theseabnormal ADP values might be the result of a low ratio of observed/
unique re¯ections (48%).
Data collection: SMART (Bruker, 2001); cell re®nement: SAINT(Bruker, 2001); data reduction: SAINT; program(s) used to solve
structure: SHELXS97 (Sheldrick, 1997); program(s) used to re®ne
structure: SHELXL97 (Sheldrick, 1997); molecular graphics: KENX
(Sakai, 2002); software used to prepare material for publication:
SHELXL97, TEXSAN (Molecular Structure Corporation, 2001),
KENX and ORTEPII (Johnson, 1976).

This work was supported by Grants-in-Aid for Scienti®cResearch on Priority Areas (Nos. 10149248, 11136246, and12023247 `Metal-assembled Complexes') from the Ministry of
Education, Science, Sports, and Culture of Japan. This work
was partly supported by a Grant-in-Aid for Scienti®celectronic reprint

Acta Cryst. (2003). C59, m345±m349

metal-organic compounds
Research (No. 14340223) from the Ministry of Education,
Science, Sports, and Culture of Japan.

Bruker (2001). SAINT (Version 6.22) and SMART (Version 5.625). Bruker
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Acta Cryst. (2003). C59, m345±m349

Ken Sakai et al.  [Pt2(C5H10NO)2(C12H8N2)2](NO3)2.2H2O

Supplementary data for this paper are available from the IUCr electronicarchives (Reference: FG1705). Services for accessing these data aredescribed at the back of the journal.

References

electronic reprint

m349