Preparation and crystal structures of novel bis(maleodintriledithiolato) platinum(III) complexes

Inorganica Chimica Acta 335 (2002) 15
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Preparation and crystal structures of novel bis(maleodintriledithiolato) platinum(III) complexes Juliane Bremi, Erminio d’Agostino, Volker Gramlich, Walter Caseri *, Paul Smith Institut fu¨r Polymere, ETH Zentrum, NW E 88.2, Universita¨tsstrasse 41, CH-8092 Zu¨rich, Switzerland Received 17 September 2001

Abstract [Pt(NH2Oc)4][Pt(mnt)2]2 was prepared by oxidation of [Pt(NH2Oc)4][Pt(mnt)2] with iodine (mnt stands for maleodinitriledithiolate and Oc for octyl). UV and IR spectra confirmed that the [Pt(mnt)2]2 and not the [Pt(NH2Oc)4]2 unit was oxidized, yielding [Pt(mnt)2]  entities where platinum is present in the uncommon formal oxidation state III. [Pt(NH2Oc)4][Pt(mnt)2] crystallized from acetone or dimethyl sulfoxide with two solvent molecules per formula unit as revealed by X-ray diffraction studies of single crystals. ˚ as a consequence of intermolecular p-interactions The [Pt(mnt)2]  moieties formed parallel pairs in the crystals spaced by 3.57 A between mnt ligands. The electrostatic attractions between the oppositely charged [Pt(NH2Oc)4]2 and [Pt(mnt)2]22 units or the pinteractions between neighboring [Pt(mnt)2] units were obviously not sufficient to cause a stacking of the coordination units as in the case of [Pt(NH2Oc)4][Pt(mnt)2] or [Pt(CNCH3)4][Pt(mnt)2]2; it appears that the crystal structure of [Pt(NH2Oc)4][Pt(mnt)2]2 is markedly influenced by packing of the alkyl groups. # 2002 Elsevier Science B.V. All rights reserved. Keywords: X-ray diffraction; Bis(maleodintriledithiolato) platinum(III) complexes; p-interactions; IR spectroscopy

1. Introduction Coordination units of the type [M(mnt)2]z, where mnt denotes maleodinitriledithiolate, have attracted attention for their ability to undergo one-electron redox processes. A complex of the type [M(mnt)2]z can adopt different charge states, for example z/0, 1 and 2 for M /Co, Cu, Ni, Pd, or Pd [1
/3]. There has been some discussion if mnt should be regarded in such compounds as a dithiolate, S(CN)C
/C(CN)S , or as a dithioketone, S
/(CN)C /C(CN)
/S [3]. Since the bond lengths between the central carbon atoms in [M(mnt)2]z ˚ [2]) are much closer to typical complexes (1.31
/1.39 A ˚ [4]) than to those of C /C values of C
/C bonds (1.33 A ˚ [4]), coordinated mnt appears to be bonds (1.54 A described more accurately by the dianion structure. This view is supported by molecular orbital calculations, which indicate that the dithiolate structure indeed better represents the bond status, although the charge is delocalized over the entire coordination unit [3]. Hence,

* Corresponding author. Tel.: /41-1-632 2218; fax: /41-1-632 1178.

it has been concluded that e.g. the formal oxidation state of the platinum atoms in the complexes with z /0, 1 and 2 is adequately attributed to II, III, and IV, respectively [3,5] and rare formal oxidation states are ascribed to transition metals in various mnt complexes, such as PtIII, PdIII, NiIII, NiIV, or RhII [3,5,6]. Recently, Magnus’ salt derivatives with [Pt(mnt)2]2 have been synthesized and analyzed by, among other techniques, X-ray diffraction of single crystals [5,7]. and These substances, [Pt(CNCH3)4][Pt(mnt)2] [Pt(NH2Oc)4][Pt(mnt)2] where Oc denotes octyl, contain a linear backbone of platinum atoms. However, while [Pt(CNCH3)4][Pt(mnt)2] showed equidistant platinum atoms (typical characteristics of the Magnus’ salts analyzed so far by X-ray diffraction at single crystals) ˚ , [Pt(NH2Oc)4][Pt(mnt)2] surprisseparated by 3.33 A ingly contained two different and unusually long Pt/Pt ˚ ), which appeared in alternate distances (3.86 and 4.01 A sequence. It has been assumed that these uncommon spacings between the platinum atoms are a result of the optimization of the packing of the alkyl groups which competes with the attraction of the oppositely charged coordination units, the latter favoring a linear stacking of the coordination planes with a Pt /Pt distance as

0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 0 7 5 5 - 7

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short as possible [7]. Oxidation of [Pt(CNCH3)4][Pt(mnt)2] to [Pt(CNCH3)4][Pt(mnt)2]2 yielded crystal structures where the position of the coordination units relative to each other strongly depended on the solvent from which [Pt(CNCH3)4][Pt(mnt)2]2 was crystallized due to the inclusion of solvent molecules [5]. In this article, we report on the oxidation of [Pt(NH2Oc)4][Pt(mnt)2] and the structures of the reaction products [Pt(NH2Oc)4][Pt(mnt)2]2 crystallized from two different solvents.

2. Experimental 2.1. General The starting compounds and solvents were obtained from commercial sources (Fluka, Aldrich, Johnson Matthew) and used as received. For UV measurements in acetone and acetonitrile UV grade was used (Fluka). (NBu4)[Pt(mnt)2] was prepared according to the literature [8]. Elemental analyses of carbon, hydrogen, nitrogen and chlorine were performed by the microelemental service of the Laboratorium fu¨r Organische Chemie at ETH Zu¨rich. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) was performed with equipment from Netzsch (DSC 200 and TG 209, respectively) under nitrogen atmosphere at a standard heating rate of 10 8C min 1. IR spectra were recorded on a Bruker IFS 66v spectrometer using CsCl pellets of 1.3 cm diameter pressed under a load of 10 ton. For the X-ray data collection, PICKER-STOE (Cu Ka radiation) and Syntex P21 (Mo Ka radiation) diffractometers were used. Since only weakly scattering small crystals (average linear dimensions 0.07 mm) were available, the collected data were limited to 2u B/408 for Mo Ka and 2u B/1008 for Cu Ka The integration technique was used for the absorption correction.

black crystals of [Pt(NH2Oc)4][Pt(mnt)2]2 precipitated, which were collected by filtration on a Teflon† filter (pore diameter 1 mm), washed with 10 ml n-pentane and 10 ml diethyl ether, and dried (yield 61%). To prepare crystals suited for X-ray diffraction, [Pt(NH2Oc)4][Pt(mnt)2]2 ×/2(CH3)2CO (117.4 mg) was dissolved in boiling acetone (60.8 ml). After cooling to r.t., diethyl ether (6.1 ml) was added at ambient. The solution was cooled in an ice bath for several days during which crystals formed. Elemental analysis (in % w/w, calculated values in brackets) for C54H88N12S8O2Pt3: C 36.51 (36.44), H 4.91 (4.95), N 9.26 (9.45), S 13.87 (14.44).1H NMR in d6-acetone, chemical shifts in ppm, all signals were broad and couplings were not resolved: 0.89 (3H), 1.33 (10H), 1.88 (2H), 3.14 (2H), 5.08 (2H). 13C NMR in d6-acetone, chemical shifts in ppm (two carbon atoms of the octyl group were either not resolved or overlapped with the signal of the solvent, and the signals of the carbon atoms of mnt were not observed due to the extremely long relaxation times): 14.6, 23.6, 27.9, 32.5, 32.9, 49.1. 195Pt NMR spectra of sufficient quality were not obtained, either because of dynamic processes or extremely short relaxation times.

3. Results [Pt(NH2Oc)4][Pt(mnt)2]2 was prepared according to Scheme 1 by oxidation of dissolved [Pt(NH2Oc)4][Pt(mnt)2] with iodine. [Pt(NH2Oc)4][Pt(mnt)2]2 crystallized from acetone or dimethyl sulfoxide in triclinic ¯ with two solvent lattices of the space group P/1; molecules per unit cell (Fig. 1) while no evidence was found for the presence of the possible reduction products I  or I3. The unit cell dimensions in those two structures were in the same region, although they differed somewhat, as evident from Table 1. The [Pt(mnt)2]  units formed ecliptic and parallel pairs ˚ in both crystals. These with Pt /Pt distances of 3.57 A

2.2. [Pt(NH2Oc)4][Pt(mnt)2]2 ×/2CH3)2CO If not otherwise indicated, in the following synthesis, filtrations were performed with sintered-glass funnels, type N4, diameter 2, 4 or 6 cm, and the products were dried at 102 mbar for 24 h. [Pt(mnt)2][Pt(NH2Oc)4] (135.4 mg, 0.11 mmol), which had been prepared according to the literature [7], was dissolved in 15 ml of acetone at 60 8C. The resulting solution was cooled to room temperature (r.t.), and iodine (25.4 mg, 0.1 mmol) dissolved in acetone (5 ml) was added. The solution became slightly darker during mixing. After 1 min, the mixture was poured into 50 ml ethanol and subsequently cooled at /78 8C (CO2
/ isopropanol) and left for approximately 3 h. Shiny

Scheme 1. Reaction [Pt(NH2Oc)4][Pt(mnt)2]2.

scheme

for

the

preparation

of

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Fig. 1. Crystal structures of (a) [Pt(NH2Oc)4][Pt(mnt)2]2 ×/2(CH3)2CO and (b) [Pt(NH2Oc)4][Pt(mnt)2]2 ×/2(CH3)2SO.

pairs were well separated from the [Pt(NH2Oc)4]2 moieties. The coordination planes of the oppositely charged ions were not parallel to each other but crossed at an angle of 55.48 (acetone complex) or 53.88 (dimethyl sulfoxide complex), respectively and, in contrast to [Pt(NH2Oc)4][Pt(mnt)2] or [Pt(NCCH3)4][Pt(mnt)2]2 [5,7], parallel stacks of coordination planes were absent in [Pt(NH2Oc)4][Pt(mnt)2]2. Selected bond lengths and angles in the two [Pt(NH2Oc)4][Pt(mnt)2]2 complexes are given in Tables 2 and 3. The average Pt/S bond lengths ˚ , respectively, were in the typical of 2.266 and 2.263 A region of Pt-mnt complexes [5,7,9
/13] but significantly below the Pt /S distances in [Pt(NH2Oc)4][Pt(mnt)2] ˚ ) [7]. Similarly, the Pt /S bond lengths in the (2.282 A various [Pt(CNCH3)4][Pt(mnt)2]2 complexes (with or without solvent molecules in the crystal) were below ˚ [5]. the value in [Pt(CNCH3)4][Pt(mnt)2] by 0.04
/0.05 A It appears, therefore, that the oxidation of PtII /PtIII in bis(mnt) complexes is accompanied by a small but significant decrease in the Pt /S bond lengths, which

might be rationalized as a result of an increase in electrostatic attraction between the platinum center with higher formal charge and the negatively charged sulfur atoms of the mnt ligands. The Pt /N distances of 2.06
/ ˚ were in the range of values reported for other Pt/ 2.08 A ˚ ) or Pt/NH2Oc complexes (2.0
/2.1 A ˚ mnt (2.28
/2.30 A [7]), and the angles between the coordinated sulfur or nitrogen atoms, respectively, agreed with a square planar coordination geometry. The C
/C bond lengths ˚ in the acetone and 1.37 A ˚ in the dimethyl of 1.35 A sulfoxide complex, respectively, were in the range of alkene bonds indicating that mnt was present in the dithiolate form (cf. Section 1). The alkyl groups in the [Pt(NH2Oc)4]2 units were arranged in centrosymmetric pairs. They were present only in one of these pairs in alltrans conformation (cf. Fig. 1). The infrared frequencies of [Pt(NH2Oc)4][Pt(mnt)2]2 are listed in Table 4. Characteristic vibrations of mnt, NH2Oc and the Pt /S bond were clearly present. Basically, the positions of the C
/C and Pt/S stretching

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Table 1 Crystallographic data of [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2CO and [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2SO [Pt(NH2Oc)4][Pt(m- [Pt(NH2Oc)4][Ptm)2]2 × 2(CH3)2CO (mnt)2]2 × 2(CH3)2SO C54H88N12O2Pt3S8 1778.07 P/1¯/ Triclinic 10.814(3) 11.705(6) 14.087(4) 101.01(3) 95.67(2) 92.05(3) 1739.0(1) 1 1.740 6.744 879 293(2) 1.78, 20.04 Mo Ka 3261 Full-matrix leastsquares on F2 Data/restraints/parameters 3261/0/359 0.909 Goodness-of-fit on F2 Final R indices [I  2s (I )] R1  0.0330, wR2  0.0825 R indices (all data) R1  0.0397, wR2  0.0843 Largest difference peak 1.061 and 1.020 ˚ 3) and hole (e A

Formula M Space group Crystal system ˚) a (A ˚) b (A ˚) c (A a (8) b (8) g (8) ˚ 3) V (A Z (formula units) Dc (g cm3) m (mm 1) F (000) T (K) Umin, Umax Radiation Independent reflections Refinement method

C52H88N12O2Pt3S10 1818.1 P/1¯/ triclinic 10.588(13) 11.522(11) 15.031(13) 105.57(7) 95.04(9) 91.86(9) 1764.(3) 1 1.705 14.023 886 293(2) 3.06, 50.00 Cu Ka 3629 Full-matrix leastsquares on F2 3629/0/363 1.068 R1  0.0373, wR2  0.0963 R1  0.0405, wR2  0.0990 1.578 and 1.076

vibrations of MII / and MIII /mnt complexes are sensitive to the formal oxidation state of the metal atoms whereas the v(C /N), p (C/CN), and the v (C /S) are less suited to distinguish between MII and MIII complexes, as evident from Table 5. Obviously, the v (C
/C) shift to lower and the v(M /S) to higher frequencies in the higher oxidation state of the platinum atoms, and the corresponding frequencies of [Pt(NH2Oc)4][Pt(mnt)2]2 indicate, indeed the presence of [Pt(mnt)2], i.e. of a PtIII /mnt complex. Peaks stemming from the solvent molecules included in the [Pt(NH2Oc)4][Pt(mnt)2]2 crystals, were hardly visible; a weak signal at 1700 cm 1 in the acetone-containing complex might be due to the C
/ O stretching vibration of acetone. UV
/VIS/NIR absorption spectra were recorded in acetonitrile in the range of 200
/1500 nm. The spectrum of [Pt(NH2Oc)4][Pt(mnt)2]2 (Fig. 2) revealed absorption maxima (lmax) at 227 nm (extinction coefficient o / 82 000 M1 cm 1), 313 nm (o /25 000 M1 cm 1), 458 nm (o /8000 M1 cm 1), 521 nm (o /120 M 1 cm 1), 608 nm (o /2000 M1 cm 1), and 853 nm (o / 26 000 M1 cm 1). Since [Pt(NH2Oc)4]Cl2 shows only one lmax in the considered region at 237 nm (in

Table 2 ˚ ) in [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2CO and Selected bond lengths (A [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2SO Bond length

[Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2CO

[Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2SO

Pt(1) S(1) Pt(1) S(2) Pt(1) S(3) Pt(1) S(4) Pt(2) N(5) Pt(2) N(6) C(1)  C(2) C(5)  C(6) N(1) C(3) N(2) C(4) N(3) C(8) N(4) C(7)

2.260(3) 2.268(3) 2.270(3) 2.266(3) 2.059(7) 2.079(8) 1.352(14) 1.375(13) 1.111(12) 1.121((14) 1.144(13) 1.137(13)

2.262(4) 2.265(2) 2.258(3) 2.266(3) 2.076(6) 2.080(6) 1.371(12) 1.375(12) 1.141(12) 1.133(11) 1.149(11) 1.131(12)

In brackets: S.D. of the last digits. Table 3 Selected bond angles (8) in [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2CO and [Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2SO Bond angle

[Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2CO

S(1) Pt(1) S(2) 89.98(10) S(1) Pt(1) S(3) 89.30(10) S(2) Pt(1) S(4) 90.78(10) S(3) Pt(1) S(4) 89.96(10) Pt(1) S(1) C(1) 102.4(4) S(1) C(1) C(2) 123.5(9) S(2) C(2) C(1) 121.5(9) N(5) Pt(2) 89.8(3) N(6)

[Pt(NH2Oc)4][Pt(mnt)2]2 × 2(CH3)2SO 89.85(12) 89.40(11) 90.85(11) 89.92(11) 103.0(3) 121.3(7) 123.1(7) 89.8(3)

In brackets: S.D. of the last digits.

chloroform) [14], the lmax between 300 and 900 nm in the spectrum of [Pt(NH2Oc)4[Pt(mnt)2]2 are related to the [Pt(mnt)2] units. The band at 313 nm appears to be due to an L /L*, those at 521 and 608 nm to d
/d or L / M, and that at 853 nm to an L(p) /M transition [15]. Comparison with the data of (NBu4)[Pt(mnt)2], (NBu4)2[Pt(mnt)2], and [Pt(NH2Oc)4][Pt(mnt)2] in Table 6 implies that the strong absorptions of [Pt(NH2Oc)4][Pt(mnt)2]2 in the VIS/NIR region are characteristic for [Pt(mnt)2]  but not for [Pt(mnt)2]2, in particular since the lmax around 605 and 850 nm in the [Pt(mnt)2]  compounds are absent in the spectra of the [Pt(mnt)2]2 complexes. The investigations were supplemented with measurements of the thermal stability and electric conductivity of [Pt(NH2Oc)4][Pt(mnt)2]2 crystallized from acetone. The thermal stability was investigated with DSC. Two irreversible endothermal transitions at 137 and 160 8C appeared upon heating, which are attributed to decomposition processes. The electrical conductivity was below the detection limit of our equipment of 10 10 S cm 1, i.e. [Pt(NH2Oc)4][Pt(mnt)2]2 acted as an insula-

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Table 4 Infrared absorption frequencies of [Pt(NH2Oc)4][Pt(mnt)2]2 Assignment [19
/21]

[Pt(NH2Oc)4][Pt(mnt)2]2

n (N  H)

3253 3155 2951 2926 2855 2210 1602 1435 1466 1375 1162 1115 880 722 524 503 388 356 333

n (C  H)

n (CN) d (NH2) n (C
C) d (CH2) d (CH3) n (C  S), n (C C) p (C  CN) n (C  S) g(CH2) Attribution ambiguous

n (Pt  S) a

Fig. 2. UV
/VIS/NIR [Pt(NH2Oc)4][Pt(mnt)2]2.

a

a

Shoulder.

tor. Finally, the 1H NMR and 13C NMR spectra in perdeuterated acetone revealed little information; the spectra merely confirmed the presence of the 1-aminooctane ligand showing a single set of its characteristic resonances (see Section 2).

4. Discussion Oxidation of [Pt(NH2Oc)4][Pt(mnt)2] with iodine leads to the formation of [Pt(NH2Oc)4][Pt(mnt)2]2 with two solvent molecules (acetone or dimethyl sulfoxide, respectively) included in the crystal lattice. The chemical formula of [Pt(NH2Oc)4][Pt(mnt)2]2 is basically consistent with two different pairs of formal oxidation states of the platinum atoms, namely [PtIV(NH2Oc)4]4/

absorption

spectrum

of

2[PtII(mnt)2]2 or [PtII(NH2Oc)4]2/2[PtIII(mnt)2]. Since the coordination sphere of platinum in [PtIV(NH2Oc)4]4 is expected to be octahedral, the empty coordination sites could be occupied by the two solvent molecules per formula unit or the nitrile groups of the mnt ligands. However, X-ray crystal data showed that the solvent molecules and the nitrile groups were not in an appropriate position for coordination. Further, IR and UV data supported the view of the bis(maleodinitrile) platinum units being present as monoanions, i.e. the platinum atoms in [Pt(NH2Oc)4][Pt(mnt)2]2 are present in the formal oxidation states II and III, respectively and it appears from Xray analysis that this oxidation is accompanied by a small but significant decrease in the Pt /S bond lengths. Table 6 Most pronounced VIS/NIR absorption maxima (lmax in nm) and extinction coefficients (o in M 1 cm 1, in brackets) of various platinum mnt complexes (in acetonitrile except (NBu4)[Pt(mnt)2] which was dissolved in acetone) Compound

lmax (o ) III

[Pt(NH2Oc)4][Pt (mnt)2]2 (NBu4)[PtIII(mnt)2] [Pt(NH2Oc)4][PtII(mnt)2] (NBu4)2[PtII(mnt)2]

458 (8000) 454 (9700)

608 (2000) 853 (26 000) 604 (3000) 851 (32 000) 469 (6500) 477 (9000)

Table 5 Comparison of selected infrared absorption frequencies of [Pt(NH2Oc)4][Pt(mnt)2]2 with those of other complexes with mnt coordinated to MII or MIII, with M Pt or Ni Compound

n (C
C)

n (C N)

n (C  S), n (C  S)

p (C CN)

n (C S)

n (Pt S)

[PtII(NH2Oc)4][PtII(mnt)2]

1482

1153

1108

883

[PtII(NH2Oc)4][PtIII(mnt)2]

1435

2210 2205 2210

1162

1115

880

[NBu4]2[PtII(mnt)2]

1479

1151

1109

885

[NBu4][PtIII(mnt)2]

a

2197 2186 2208

1162

1109

881

330 322 356 333 332 318 357 330

[NEt4]2[NiII(mnt)2] [19] [NEt4][NiIII(mnt)2] [19] Na2[NiII(mnt)2] [19] Na[NiIII(mnt)2] [19]

1485 1435 1485 1435

2195 2194 2205 2190

1170 1160 1160 1160

1105 1105 1110 1105

865 885 865 880

a

Attribution uncertain due to overlap with d (CH2).

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The [Pt(mnt)2]  entities formed parallel ion pairs ˚ . This spacing lies between the with a spacing of 3.57 A van der Waals diameter of carbon and sulfur (3.4 and ˚ , respectively [4]), i.e. in a suited region for p3.7 A interactions between the mnt ligands of adjacent coordination units [10,16]. The distances between neighboring [Pt(mnt)2] moieties, therefore, exceeded those ˚ [14] and of typical Pt /Pt bond lengths of 2.6
/2.8 A significant Pt /Pt interactions are thus not expected to occur. The electrostatic attractions between the oppositely charged [Pt(NH2Oc)4]2 and [Pt(mnt)2]22 ions could result in a quasi-one-dimensional structure [14,17,18] with a backbone of linearly arranged platinum atoms as observed for Magnus’ green salt and its derivatives [1,14]. Columnar stacks of the [Pt(mnt)2]  ions might also be expected as a result of interactions between the p-orbitals of adjacent [Pt(mnt)2]  units, as ˚ ), Rb[Ptfound e.g. in Li3[Pt(mnt)2]4 ×/8H2O (3.64 A (mnt)2]×/2H2O, H3O[Pt(mnt)2]×/H2O and N(C2H5)4[Pt(mnt)2]2 with interplanar spacings between 3.36 and ˚ [10
/12,16]. A stacking of coordination units was, 3.90 A however, not observed in [Pt(NH2Oc)4][Pt(mnt)2]2. For comparison, in [Pt(CNCH3)4][Pt(mnt)2]2, which was crystallized in the neat form or with two molecules acetonitrile or nitromethane per formula unit stacked structures were established in all cases [5]. However, the composition of these columns markedly depended on the solvent. Designating the anion [Pt(mnt)2] as A  and the cation [Pt(CNCH3)4]2 as C2, the columns were composed of arrays of (AA C2C2)n in the acetonitrile complex, of (A C2)n in the nitromethane complex, and of (AA C2)n in the solvent-free complex. By contrast, corresponding differences in the structure of [Pt(NH2Oc)4][Pt(mnt)2]2 with included acetone or dimethyl sulfoxide were not observed. It appears that the packing of the octyl groups mainly determined the arrangement of the coordination units, and the included solvent molecules filled free volume arising from crystallization of the alkyl groups.

platinum /mnt complexes described in the literature [10
/12,16] was not found for [Pt(NH2Oc)4][Pt(mnt)2]. In addition, the pronounced influence of included solvent molecules on the crystal structure of [Pt(CNCH3)4][Pt(mnt)2]2 was not observed for [Pt(NH2Oc)4][Pt(mnt)2]2. It appears that the crystal structure is mainly determined by the packing of the alkyl groups and that the p-attractions between the [Pt(mnt)2]  entities or the electrostatic attractions between the oppositely charged [Pt(NH2Oc)4]2 and [Pt(mnt)2]22 units are not strong enough to cause a stacking of coordination units in [Pt(NH2Oc)4][Pt(mnt)2]2.

Acknowledgements We are indebted to A. Ha¨ne and Y. Sta¨dler for experimental assistance.

References [1] [2] [3] [4] [5]

[6] [7] [8] [9] [10] [11]

5. Conclusions We have demonstrated that the [Pt(mnt)2]2 moiety in [Pt(NH2Oc)4][Pt(mnt)2] can be oxidized with iodine to [Pt(mnt)2]  where platinum is present in the uncommon formal oxidation state III. The resulting [Pt(NH2Oc)4][Pt(mnt)2]2 crystals contained two molecules of acetone or dimethyl sulfoxide, respectively, per formula unit when crystallized from either of these solvents. The [Pt(mnt)2]  entities were arranged in both ˚ as a crystals in parallel pairs spaced by 3.57 A consequence of p-interactions between adjacent mnt ligands. A stacking of coordination units as in other

[12] [13] [14] [15] [16] [17] [18] [19] [20] [21]

J.S. Miller, A.J. Epstein, Prog. Inorg. Chem. 20 (1976) 1. J.A. McCleverty, Prog. Inorg. Chem. 10 (1968) 49. P.I. Clemenson, Coord. Chem. Rev. 106 (1990) 171. L. Pauling, Grundlagen der Chemie, Verlag Chemie, Weinheim, 1973. H. Bois, N.G. Connelly, J.G. Crossley, J.-C. Guillorit, G.R. Lewis, A.G. Orpen, P. Thornton, J. Chem. Soc., Dalton Trans. (1998) 2833. J.A. McCleverty, Prog. Inorg. Chem. 10 (1968) 49. J. Bremi, V. Gramlich, W. Caseri, P. Smith, Inorg. Chim. Acta 322 (2001) 23. A. Davison, R.H. Holm, R.E. Benson, W. Mahler, Inorg. Synth. 8 (1979) 16. W. Gu¨ntner, G. Gliemann, U. Klement, M. Zabel, Inorg. Chem. 165 (1989) 51. A. Kobayashi, Y. Sasaki, H. Kobayashi, A.E. Underbill, M.M. Ahmad, J. Chem. Soc., Chem. Commun. (1982) 391. M.M. Ahmad, D.J. Turner, A.E. Underbill, A. Kobayashi, Y. Sasaki, H. Kobayashi, J. Chem. Soc., Dalton Trans. (1984) 1759. P.I. Clemenson, A.E. Underbill, M.B. Hursthouse, R.L. Short, J. Chem. Soc., Dalton Trans. (1989) 61. M.E. Cradwick, D. Hall, R.K. Philips, Acta Crystallogr. 27 (1971) 480. J. Bremi, D. Brovelli, W. Caseri, G. Ha¨hner, P. Smith, T. Tervoort, Chem. Mater. 11 (1999) 977. S.I. Shupack, E. Billig, R.J.H. Clark, R. Williams, H.B. Gray, J. Am. Chem. Soc. 86 (1964) 4594. K.W. Browall, L.V. Interrante, J. Coord. Chem. 3 (1973) 27. L.V. Interrante, R.P. Messmer, Inorg. Chem. 10 (1971) 1175. W.B. Connick, R.E. Marsh, W.P. Schaefer, H.B. Gray, Inorg. Chem. 36 (1997) 913. C.W. Schla¨pfer, K. Nakamoto, Inorg. Chem. 14 (1975) 1338. D.M. Adams, J.B. Cornell, J. Chem. Soc. A (1968) 1299. S. Kuzumizu, N. Kojima, T. Ban, I. Tsujikawa, Bull. Chem. Soc. Jpn. 60 (1987) 2547.