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Acta Crystallographica Section C

Crystal Structure
Communications
ISSN 0108-2701

Editor: George Ferguson

Di--pivalamidato-4 N:O;O:N-bis[(2,2 -bipyridine-2N,N )(sulfatoO)platinum(III)] tetrahydrate in a head-to-tail isomerism
00Kazuo Yokokawa and Ken Sakai

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Acta Cryst. (2004). C60, m244–m247

Yokokawa and Sakai  [Pt2 (C5 H10 NO)2 (SO4 )2 (C10 H8 N2 )2 ]4H2 O

metal-organic compounds
the formation of the PtIIIÐPtIII single bond in the Pt(bpy)dimers is hindered by repulsive interaction between the two
bpy units. We have now found, for the ®rst time, that an`amidate-bridged PtIII(bpy) dimer' can be isolated in a stable
crystalline form, and we report here the synthesis and crystal
structure of HT-[Pt2III(bpy)2(-pivalamidato)2(SO4)2]4H2O,(I).

Acta Crystallographica Section C

Crystal Structure
Communications
ISSN 0108-2701

Di-l-pivalamidato-j4N:O;O:Nbis[(2,20 -bipyridine-j2N,N0 )(sulfatojO)platinum(III)] tetrahydrate in ahead-to-tail isomerism
Kazuo Yokokawa and Ken Sakai*
Department of Applied Chemistry, Faculty of Science, Tokyo University of Science,
Kagurazaka 1-3, Shinjuku-ku, Tokyo 162-8601, Japan
Correspondence e-mail: ksakai@rs.kagu.tus.ac.jp
Received 23 March 2004
Accepted 2 April 2004
Online 11 May 2004

The title compound, [Pt2III(C5H10NO)2(SO4)2(C10H8N2)2]4H2O, is the ®rst reported example of a complex in which anamidate-bridged Pt(bpy) dimer is stabilized in the oxidationlevel of PtIII (bpy is 2,20 -bipyridine). The asymmetric unit
consists of one half of the formula unit with a twofold axis
passing through the center of the dimer. The intradimer PtIIIÐ
Ê ] is comparable to those
PtIII bond distance [2.5664 (6) A
reported for -pyridonate-bridged cis-diammineplatinum(III)Ê ; Hollis & Lippard (1983).
dimers [2.5401 (5)±2.5468 (8) A
Inorg. Chem. 22, 2605±2614], in spite of the close contact
between the bpy planes within the dimeric unit. The axial PtÐÊ.
Osulfate distance is 2.144 (7) A

The asymmetric unit of (I) consists of one-half of theformula unit (Fig. 1). A twofold axis passes through the centerof the dimeric unit. There is, therefore, a crystallographic
requirement that this is a head-to-tail isomer. Analysis of theisotropic atomic displacement parameters of the O- andN-donors of pivalamidate revealed no evidence for any
disorder of the O and NH moieties (see Experimental). The
hydrogen-bonding geometry given in Table 3 also supports thevalidity of our treatment with regard to the binding directionof pivalamidate. To the best of our knowledge, this is the ®rst
structural characterization of a diplatinum(III) complex
capped by two sulfate ions, even though stepwise axial sulfateligation equilibria were previously investigated for an -pyr-Comment
Amidate-bridged cis-diammineplatinum dimers, [Pt2II(NH3)4(-amidato)2]2+ (amidate is -pyridonate, -pyrrolidinonate,acetamidate, etc.), have been reported to undergo one-step
two-electron oxidation to give the corresponding Pt2III dimers,
with a simultaneous uptake of two axial donors at both ends ofthe unit, as well as bond formation between the PtIII centers,
resulting in the formation of [Pt2III(NH3)4(-amidato)2X2]n+ions (X is an axial donor ligand and n depends on the charge of
X). Reversible redox waves corresponding to the Pt2II/Pt2III
couple have been observed at 0.4±0.6 V versus SCE (Hollis& Lippard, 1983; Matsumoto & Matoba, 1986; Sakai et al.,1998). On the basis of the binding directions of the two
amidate bridges, two geometric isomers, viz. head-to-head(HH) and head-to-tail (HT) isomers, are possible for this classof dimers. On the other hand, the dimers containing Pt(bpy)units instead of cis-Pt(NH3)2 units have been shown to exhibit
irreversible redox waves corresponding to the Pt2II/Pt2III couple;
irreversible oxidation±reduction waves were observed at
1 V versus SCE for HT-[Pt2II(bpy)2(- -pyrrolidinonato)2](ClO4)2 (Matsumoto et al., 1992). These results suggest that

m244

# 2004 International Union of Crystallography

Figure 1

The structure of (I), showing the atom-labeling scheme. Displacement
ellipsoids are shown at the 50% probability level. H atoms have been
omitted for clarity and only one orientation is shown for the disordered
tert-butyl groups. Dashed lines denote hydrogen bonds.

DOI: 10.1107/S010827010400811X

electronic reprint

Acta Cryst. (2004). C60, m244±m247

metal-organic compounds
rolidinonate-bridged cis-diammineplatinum(III) dimer bymeans of spectrophotometric titration (Sakai, Tsubomura &Matsumoto, 1993).
The intradimer PtIIIÐPtIII distance in (I) [Pt1ÐPt1i =Ê ; symmetry code: (i) ÿx, y, 3 ÿ z] is unexpectedly
2.5664 (6) A
2short, in spite of the steric hindrance promoted between thebpy planes within the dimeric unit, and is comparable tothose reported for -pyridonate-bridged cis-diammineplatiÊ for HH-[Pt2III(NH3)4num(III) dimers {PtIII±PtIII = 2.5401 (5) A(-C5H4NO)2(H2O)(NO3)](NO3)32H2O and PtIIIÐPtIII =Ê
2.5468 (8) A
for
HT-[Pt2III(NH3)4(-C5H4NO)2(NO3)2](NO3)20.5H2O (Hollis & Lippard, 1983)}. On the other hand,Ê shorter than those
the PtIIIÐPtIII distance in (I) is 0.1 A
reported for -pyrrolidinonate-bridged cis-diammineplaÊ for HHtinum(III) dimers {PtIIIÐPtIII = 2.644 (1) A
III[Pt2 (NH3)4(-C4H6NO)2(NO2)(NO3)](NO3)2H2O (Abe etFigure 2

The structure of (I), viewed along the Pt1ÐPt1i vector. H atoms and watermolecules have been omitted for clarity; only one orientation is shownfor the disordered tert-butyl groups. [Symmetry code: (i) ÿx, y, 32 ÿ z.]Ê for HH-[Pt2III(NH3)4(al., 1991), PtIIIÐPtIII = 2.6366 (7) A
C4H6NO)2(Cl)2](NO3)2 (Sakai et al., 1998) and PtIIIÐPtIII =Ê for HH-[Pt2III(NH3)4(-C4H6NO)2(Cl)(NO3)]2.6239 (9) A(NO3)2H2O (Sakai et al., 1998); see also Sakai, Sakamoto et al.
(2003) and Sakai et al. (2004)}. Thus, a relatively short andstrong PtIIIÐPtIII bond is achieved in (I). As shown in Fig. 2
and Table 2, there are some short intramolecular bpy±bpy
contacts, namely N3  N2i, N3  C6i and C15  C6i.
The mean-plane calculations performed for the four-coordinated atoms (N1, N2, N3 and O1i) reveal that the Pt coordination plane is slightly deformed but is roughly planar, theÊ . Atom Pt1 is
four-atom r.m.s. deviation being 0.029 A
displaced from the mean plane de®ned by atoms N1, N2, N3
Ê towards atom Pt1i within the unit. The
and O1i by 0.024 (3) Adihedral angle () between the two Pt coordination planes
within the dimeric unit and their mean torsional twist (!)
about the PtÐPt axis are 17.1 (3) and 16.8 (4) , respectively(see Fig. 2; see also torsion angles in Table 1). The dihedral
angle between the two bpy planes within the dimeric unit is16.3 (2) . Thus, the bpy plane is nearly coplanar with the Pt
coordination plane [they are inclined by 2.7 (3) to one
another].
Ê ] is comparable
The axial PtIIIÐOsulfate distance [2.144 (7) A
to those reported for -pyridonate-bridged cis-diammineplaÊ andtinum(III) dimers {PtIIIÐO(axial H2O) = 2.122 (6) A
III
ÿ
III
Ê
Pt ÐO(axial NO3 ) = 2.193 (7) A for HH-[Pt2 (NH3)4(-C5H4NO)2(H2O)(NO3)](NO3)32H2O, and PtIII±O(axial
Ê for HT-[Pt2III(NH3)4(-C5H4NO)2NO3ÿ) = 2.17 (1) A(NO3)2](NO3)20.5H2O (Hollis & Lippard, 1983)}.
As shown in Fig. 3, the crystal packing is partly stabilized byrelatively weak hydrophobic interactions between the tertiary
butyl moieties and the bpy units, where the shortest interÊ . The dimer±
molecular bpy  bpy separation is 3.69 (1) A
dimer interactions along the c axis are also stabilized by
Osulfate  Owater  Owater  Osulfate hydrogen bonds [i.e.
Ê,O5  O7  O6ii  O3ii, where O5  O7 = 2.750 (12) A
ii
ii
ii
Ê
Ê
O7  O6 = 2.784 (14) A and O6   O3 = 2.864 (13) A;symmetry code: (ii) x, 2 ÿ y, z ÿ 12; see also Table 2]. The dimeris also connected to a neighboring dimer via an inversion
center by forming Osulfate  Owater  Osulfate hydrogen bonds[i.e. O5  O7  O4( 12 ÿ x, 52 ÿ y, 2 ÿ z); O7  O4( 12 ÿ x, 52 ÿ y,
Ê ; see also Table 2].
2 ÿ z) = 2.828 (12) A

Experimental

Figure 3

A stereoview of the crystal packing of (I). Non-H atoms have been drawn
as ideal spheres, and H atoms and hydrogen bonds have been omitted;
only one orientation is shown for the disordered tert-butyl groups.
Acta Cryst. (2004). C60, m244±m247

For the synthesis of (II), a suspension of PtCl2(bpy) (1 mmol, 0.42 g;
Morgen & Burstall, 1934), AgNO3 (2 mmol, 0.34 g) and pivalamide(1.5 mmol, 0.15 g) in water (7 ml) was re¯uxed for 3 h in the dark,
during which time the color of the solution turned deep red. The
solution was then ®ltered while it was hot in order to remove theprecipitated AgCl. Leaving the ®ltrate at room temperature overnight afforded (II) as deep-red block-like crystals, which werecollected by ®ltration and air-dried (yield 65%). Complex (II) was
puri®ed by recrystallization from hot water [compound (II) (0.1 g)
was dissolved in 1 ml of water; 80% of the product was recollected]. Analysis calculated for C30H46N8O13Pt2: C 32.26, H 4.15, N
10.03%; found: C 32.30, H 3.91, N 9.99%. IR (KBr, cmÿ1): 3421 (w,br), 2360 (m), 2341 (w), 1607 (w), 1560 (m), 1489 (w), 1454 (w), 1384(s), 1188 (w), 1029 (w, br), 769 (m), 722 (m), 650 (m, br), 419 (w). UV±Yokokawa and Sakai  [Pt2(C5H10NO)2(SO4)2(C10H8N2)2]4H2O

electronic reprintm245

metal-organic compounds
Vis (in H2O, 293 K): max = 306 nm (" = 20400 Mÿ1 cmÿ1), max =361 nm (" = 2080 Mÿ1 cmÿ1), max = 475 nm (" = 2110 Mÿ1 cmÿ1).
195
Pt NMR (D2O, 296 K, referenced to ÿ1624 p.p.m. of K2PtCl4):
ÿ2064 p.p.m. (singlet characteristic of HT). Complex (II) wascon®rmed to be a head-to-tail isomer, part of which was reported by
Sakai, Takeshita & Tsubomura (1993). For the synthesis of (I), a
solution of (II) (0.25 mmol, 0.28 g) and K2S2O8 (0.3 mmol, 0.08 g) inwater (15 ml) was stirred at room temperature for 15 min. The
solution was ®ltered to remove impurities and then evaporated todryness. The yellow powder deposited was redissolved in a minimum
amount of water (3 ml). Leaving the solution to stand in air at room
temperature for a few days afforded (I) as yellow prisms, which werecollected by ®ltration and air-dried by suction (yield 68%). Analysis
calculated for C30H44N6O14Pt2S2: C 30.88, H 3.80, N 7.20%; found: C
30.82, H 3.10, N 7.09%. IR (KBr, cmÿ1): 3440 (m, br), 3077 (w, br),
2962 (w), 1606 (m), 1581 (m), 1503 (w), 1454 (m), 1426 (w), 1370 (w),1313 (w), 1253 (w), 1182 (s), 1117 (vs), 1076 (w), 1051 (w), 1012 (vs),917 (m), 873 (s), 777 (m), 614 (m), 587 (w). The crystals were stable inair at room temperature. A diffraction-quality single crystal was
mounted on a glass ®ber and used in the data collection.

Table 2Ê ).
Short intramolecular contacts (A2.864 (13)2.750 (12)2.828 (12)2.784 (14)3.125 (10)3.221 (12)3.515 (18)
3.411 (12)3.595 (13)3.636 (16)3.605 (14)C15  C6i
N2  C5Biv
C6  C5Biv
C7  C5Biv
C8  C5Biv
C9  C5Biv
C10  C5Biv
C7  C3Aiv
C8  C3Aiv
C14  C12v

3.228 (13)3.59 (3)3.60 (4)3.64 (4)3.64 (4)3.58 (3)3.549 (18)
3.62 (2)3.66 (2)3.741 (15)Symmetry codes: (i) ÿx; y; 32 ÿ z; (ii)x; 2 ÿ y; 12  z; (v) 12 ÿ x; 32 ÿ y; 2 ÿ z.

1
5
2 ÿ x; 2 ÿ y; 2 ÿ z;(iii) x; 2 ÿ y; z ÿ 12; (iv)O3  O6
O5  O7
O7  O4ii
O7  O6iii
N3  N2i
N3  C6i
C10  C10i
C11  N2i
C11  C10i
C13  C7i
C14  C6i

Table 3Ê ,  ).
Hydrogen-bonding geometry (ADÐH  A
N1ÐH1  O4

DÐH
0.86

H  A
2.01

D  A
2.757 (10)DÐH  A
144

Crystal data
Dx = 2.085 Mg mÿ3
Mo K radiation
Cell parameters from 7382
re¯ections
 = 2.5±27.5
 = 7.70 mmÿ1
T = 296 (2) K
Prism, yellow
0.18  0.11  0.08 mm[Pt2(C5H10NO)2(SO4)2(C10H8N2)2]4H2O
Mr = 1167.01
Monoclinic, C2=cÊ
a = 22.535 (2) AÊ
b = 11.9796 (12) AÊc = 16.4774 (17) A= 123.285 (2)Ê3
V = 3718.5 (6) A
Z=4

Data collection
Bruker SMART APEX CCDdetector diffractometer! scans
Absorption correction: Gaussian(XPREP in SAINT; Bruker,
2001)
Tmin = 0.147, Tmax = 0.623
20 489 measured re¯ections

4288 independent re¯ections
3218 re¯ections with I > 2(I )Rint = 0.145
max = 27.5
h = ÿ29 ! 29
k = ÿ15 ! 15
l = ÿ21 ! 21Re®nementRe®nement on F 2
R[F 2 > 2(F 2)] = 0.044
wR(F 2) = 0.128
S = 1.104288 re¯ections
238 parameters
H-atom parameters constrained

w = 1/[ 2(F 2o ) + (0.0564P)2]
where P = (F 2o + 2F 2c )/3(/)max = 0.001
Ê ÿ3max = 2.78 e AÊ ÿ3min = ÿ1.61 e A
Extinction correction: SHELXL97
Extinction coef®cient: 0.00183 (14)Table 1

Ê ,  ).
Selected geometric parameters (APt1ÐO1i
Pt1ÐO2
Pt1ÐN1
Pt1ÐN2
Pt1ÐN32.004 (6)2.144 (7)1.993 (7)2.027 (7)2.015 (7)Pt1ÐPt1i
O1ÐC1
N1ÐC1
C1ÐC2

2.5664 (6)1.282 (10)1.302 (11)1.492 (12)N1ÐPt1ÐN3
N1ÐPt1ÐN2
N3ÐPt1ÐN2
N1ÐPt1ÐO2
N3ÐPt1ÐO2
N2ÐPt1ÐO2
N1ÐPt1ÐO1i

96.1 (3)176.8 (3)80.7 (3)94.8 (3)90.0 (3)85.7 (3)86.9 (3)O1iÐPt1ÐN3
O1iÐPt1ÐN2
O1iÐPt1ÐO2
O1ÐC1ÐN1
O1ÐC1ÐC2
N1ÐC1ÐC2

175.7 (2)96.3 (3)86.7 (2)121.9 (8)116.6 (8)121.5 (8)N1ÐPt1ÐPt1iÐO1

16.5 (3)N3ÐPt1ÐPt1iÐN2i

17.0 (3)Symmetry code: (i) ÿx; y; 32 ÿ z.

m246

Yokokawa and Sakai  [Pt2(C5H10NO)2(SO4)2(C10H8N2)2]4H2O

As recently reported for several different dimers doubly bridged
by chain amidate ligands (Sakai, Kurashima et al., 2003; Sakai, Ikuta
et al., 2003; Sakai, Shiomi et al., 2003), it is often possible to determine
the binding direction of the O- and N-donors of each amidate on thebasis of the results of least-squares calculations performed for two
possible directions. Moreover, when the Ueq values of Pt atoms arereasonably small, a disorder model based on the mixing of HH and
HT isomers is not favored, since the intradimer PtÐPt distances ofthe HH and HT isomers are, in general, markedly different from one
another (Sakai et al., 1998). In (I), atom Pt1 has a reasonably small
Ê 2], indicating that the mixing of the HH and
Ueq value [0.02294 (15) A
HT isomers is not likely to be promoted in this system. The locationsof atoms O1 and N1 have been determined rationally from theÊ2comparison of two sets of Ueq values, viz. Ueq(O1) = 0.0277 (12) A
2
Êand Ueq(N1) = 0.0273 (15) A , and Ueq(N instead of O1) =Ê 2 and Ueq(O instead of N1) = 0.0448 (18) AÊ 2. The
0.0152 (12) A
former set, corresponding to the reported combination, clearly showsa good balance and was therefore adopted as a reasonable set. As aresult, the H atom on atom N1 was located at an idealized position asa riding atom, as mentioned below. The tertiary butyl group showsorientational disorder in which two sets of positions (C3A/C4A/C5A
and C3B/C4B/C5B) are located around atom C2. The disordered C
atoms were assumed to have the same isotropic displacement parameter. Furthermore, all six CtertiaryÐCmethyl distances within each sitewere restrained to be equal, as were the three CmethylÐCmethyl
distances. The occupation factors of sites A and B converged at70.7 (15) and 29.3 (15)%, respectively. All H atoms, except for thoseof water molecules, were located at their idealized positions as ridingÊ (for aromatic H atoms), CÐH = 0.96 A
Ê (foratoms [CÐH = 0.93 AÊmethyl H atoms) and NÐH = 0.86 A] and included in the re®nementin the riding-motion approximation [with Uiso(H) = 1.2Ueq(carrieratom)]. Water H atoms were not located. In the ®nal differenceÊ ÿ3 were
Fourier synthesis, 32 residual peaks in the range 1.02±2.78 e AÊobserved, not only within 1.4 A of atom Pt1 but also near atoms O2,
O3, O4, O5, O6, O7, C2, C11 and C13. The deepest hole was locatedÊ from atom Pt1.
0.54 A
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®neelectronic reprint

Acta Cryst. (2004). C60, m244±m247

metal-organic compounds
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 partly supported by a Grant-in-Aid for
Scienti®c Research (B) (No. 14340223) from the Ministry of
Education, Culture, Sports, Science and Technology of Japan.
Supplementary data for this paper are available from the IUCr electronicarchives (Reference: GD1315). Services for accessing these data aredescribed at the back of the journal.

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Johnson, C. K. (1976). ORTEPII. Report ORNL-5138. Oak Ridge National
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Yokokawa and Sakai  [Pt2(C5H10NO)2(SO4)2(C10H8N2)2]4H2O

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