DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1998, 3901–3903 3901 Preparation and structures of the mixed-metal clusters Pt2M2Se2Cl2(PPh3)4 (M 5 Cu, Ag) and Pd2Au2Se2(SeH)2(PPh3)4. An entry to ternary clusters Pierre D. Harvey,*† Andreas Eichhöfer and Dieter Fenske * Institut für Anorganische Chemie, Universität Karlsruhe, Engesserstrasse, Gebäude – Nr. 30.45, 76128 Karlsruhe, Germany Received 23rd September 1998, Accepted 19th October 1998 Both cis- and trans-Pt(PPh3)2Cl2 react with Se(SiMe3)2 and CuCl or AgO2CR (R 5 Me, Ph) in THF to form the mixedmetal clusters Pt2M2Se2Cl2(PPh3)4 (M 5 Cu or Ag, respectively), and likewise Au(PPh3)Cl reacts with Pd(acac)2, to form Pd2Au2Se2(SeH)2(PPh3)4. The preparation of copper chalcogenide clusters is of great interest for the synthesis of nanoparticles.1 The preparation of the largest crystallographically characterized copper cluster, Cu146Se73(PPh3)30, was recently reported, along with a number of other clusters with diVerent nuclearities.1 The synthesis of such materials follows this general reaction scheme: 2CuCl 1 Se(SiMe3)2 1 xPR3 æÆ “Cu2Se(PR3)x” 1 2ClSiMe3 (1) where PR3 is either an alkyl, aryl or mixed alkyl/aryl phosphine.This chemistry has also been extended to silver, and similar results have been obtained.1 Binary systems of the type Pt/Se, Pt/Te and Au/Se have been explored by various groups, and the preparations of binuclear and trinuclear species such as (PPh3)2- Pt(m-Se)2Pt(PPh3)2,2 L2Pt(m-Te)2PtL2 (L = PPh3, PEt3; L2 = dppm),3 Pt3Se2(dppe)3,3 [Se(AuPPh3)3]PF6 and Au2Se(PPh3)2,4 have also been reported.In this work we wish to take advantage of the capacity of the Se atom to coordinate an extra M group in order to promote M–M9 bonding, and mixed-metal cluster formation. The synthesis and crystal structures of three novel ternary clusters, Pt2M2Se2Cl2(PPh3)4 (M = Cu 1, Ag 2), and Pd2Au2Se2(SeH)2(PPh3)4 3 which are the first examples of cluster compounds containing Pt/Cu/Se, Pt/Ag/Se,‡ and Pd/Au/ Se are now presented.These compounds represent potential precursors as an entry to larger mixed-metal clusters via the presence of displaceable Cl atoms, and phosphine groups. In relation with this study, we find that examples of Pt–Cu bondcontaining clusters are rather rare, where only six have been characterized from X-ray crystallography.5 For the Pt–Ag analogues, many more examples are known.6 The clusters 1 and 2 can easily be prepared from the following general reactions:§ 2Pt(PPh3)2Cl2 1 2CuCl 1 2Se(SiMe3)2 THF 1 1 4ClSiMe3 (2) 2Pt(PPh3)2Cl2 1 2Ag(O2CR) 1 2Se(SiMe3)2 THF 2 1 4RCO2SiMe3 (3) where R = Me, or Ph, and the Pt(PPh3)2 Cl2 species can be either the cis- or trans-isomers.When the chalcogenide reagent Se(SiMe3)2 is slowly added dropwise into solutions containing Pt(PPh3)2Cl2 and CuCl or AgO2CR (R = Me, Ph) in stoichiometric amount (1:1:1) in the presence of 2 equivalents of PPh3, and at 240 8C, the solutions pass from a deep yellow to a dark brown coloration.Upon slowly warming the solutions to room temperature over several hours, and letting them sit for several days, large orange crystals were readily obtained, and were identified from X-ray crystallography as Pt2M2Se2Cl2(PPh3)4 (M = Cu, Ag). The X-ray structure analysis¶ reveal the isostructural behavior of these two isocentric clusters, where two M–Cl units sit above and under the planar P2Pt(m-Se)2PtP2 fragment, and the Pt2M2Se2 core forms a strongly distorted octahedral structure (C2h symmetry, see Fig. 1). The coordination of the M–Cl units occurs via only one formal Se–M single bond with distances [d(Se–Cu) 2.274(1), d(Se–Ag) 2.548(2) Å] that are normal in comparison with the related binary “M2Se(PR3)x” clusters (M = Cu, Ag).1 Thus the Se atoms adopt a m3-binding mode with Pt–Se bond distances of 2.474(1) and 2.485(1) Å for M = Cu, and 2.509(2) and 2.478(1) Å for M = Ag.The Pt–Se–Pt and Pt–Se–M angles are 97.96(3), and 79.70(4) and 74.44(4)8 for M = Cu, and 98.58(5), and 74.32(5) and 73.56(6)8, for M = Ag. The smaller Pt–Se–M angles are associated with the presence of Pt ? ? ? M interactions. Indeed no formal Pt–M bonding occurs where the Pt–M distances range from ª2.92 to 3.05 Å. This result contrasts greatly with all Pt–Cu bondcontaining clusters for which the Pt–Cu bonds are reported to be ª2.53 < d(Pt–Cu) < ª2.74 Å.5 Despite the long Pt–Cu distance, significant Pt ? ? ? Cu interactions are readily anticipated,7 as these values are located well inside the sum of the van der Waals radii.On the other hand for the Pt2Ag2 analogue, such distances are not uncommon in the literature.6 Such interactions are also felt in the Se–M–Cl angles which deviate slightly from linearity generally encountered in pure sp hybridation. The “(PPh3)2Pt(m-Se)2Pt(PPh3)2” frame is not greatly aVected Fig. 1 Molecular structure for clusters 1 and 2.The H-atoms are omitted for clarity. Selected bond distances (Å) and angles (8) are as follows; 1: Pt–Se 2.474(1), 2.485(1), Pt–P 2.279(2), 2.291(2), Pt–Cu 2.916(1), 3.047(1), Cu–Cl 2.129(3), Cu–Se 2.274(1), Se ? ? ? Se 3.254(2), Pt ? ? ? Pt 3.753(2); Se–Pt–Se 82.04(3), P–Pt–P 100.30(7), Pt–Se–Pt 97.96(3), Se–Cu–Cl 176.90(11)8. 2: Pt–Se 2.509(2), 2.478(1), Pt–P 2.293(4), 2.318(3), Pt–Ag 3.028(2), 3.037(1), Ag–Cl 2.361(5), Ag–Se 2.548(2), Se ? ? ? Se 3.253(3), Pt ? ? ? Pt 3.781(3); Se–Pt–Se 81.42(5), P–Pt–P 96.63(12), Pt–Se–Pt 98.58(5), Se–Ag–Cl 171.59(15)8.3902 J.Chem. Soc., Dalton Trans., 1998, 3901–3903 upon complexation with the M–Cl groups. However, by comparison with the literature data reported for the “free” (PPh3)2Pt(m-Se)2Pt(PPh3)2 dimer,2 some bond distances have increased. Indeed the average Pt–Se and Pt–P bond lengths are 2.449 and 2.277Å for Pt2Se2(Ph3)4,2 2.480 and 2.285 Å for 1, and 2.494 and 2.306 Å for 2, respectively.This eVect is clearly steric on one side, but also some electronic factors such as electronic density change at the Pt atoms promoting Pt ? ? ? M interactions, could also contribute to the bond length variations. Cluster 3 can be prepared in a similar fashion in the dark in reasonable yield according to: 2Au(PPh3)Cl 1 2Pd(acac)2 1 4Se(SiMe3)2 1 2PPh3 1 2H2O THF 3 1 “XSiMe3” (X = Cl, acac, OH) (4) 3 crystallizes as red-orange crystals. This time the excess of PPh3 is not used as a stabilizing/solubilizing agent, but as a reactant.X-Ray crystallographic analysis indicates that 3 is also a centrosymmetric cluster (point group Ci), again showing a strongly distorted Pd2Au2Se2 octahedral (Fig. 2). As for 1 and 2, the d10 electronic configuration metal is bonded to the d8–d8 dimer (PPh3)(SeH)Pd(m-Se)2Pd(PPh3)(SeH) (C2h point group) via a formal Se–Au single bond [2.412(2) Å] leading to weak PdII ? ? ? AuI contacts [3.067(2) and 3.300(2) Å].7 Both Pd and Au carry a single PPh3 ligand which diVers from 1 and 2 where both PPh3’s are bonded to the Pt only.One other diVerence is the presence of SeH groups [1H NMR d(ppm) 0.123] instead of Cl. The fact that clusters 1 and 2 have extra Cl atoms and 3 exhibits SeH centers opens the door to further extension of this chemistry towards larger clusters or the incorporation or another type of metal. Further research in this area is in progress. Acknowledgements We are grateful to the Deutsche Forschungsgemeinschaft (SFB195), to the Fonds der Chemischen Industrie and the EU through the HCM program for financial support.Pierre D. Harvey also thanks the University of Karlsruhe for financial support (guest Professor). Notes and references † Work performed while on sabbatical leave from the Université de Sherbrooke, Canada. Present address: Département de Chimie, Université de Sherbrooke, Sherbrooke, P.Q., Canada, J1K 2R1. E-mail: pharvey@courrier.usherb.ca ‡ According to the Cambridge Data Bank a compound formulated as Fig. 2 Molecular structure for 3. The H-atoms are omitted for clarity. Selected bond distances (Å) and angles (8) are as follows: Au–Se 2.412(2), Au–P 2.261(6), Au–Pd 3.067(2), 3.300(2), Pd–Se(H) 2.446(3) Pd–Se 2.486(3); Se–Au–P 176.4(1), Se–Pd–P 175.5(2), Se–Pd–Se 84.8(1), P–Pd–Se(H) 93.2(2), Pd–Se–Pd 95.2(1)8. [(PPh3)2PtAg2SeCo{(PPh2CH2CH2)3CMe}]BF4 has been described in G. Baldi, M. di Vaira, L.Niccolai, M. Peruzzini and P. Stoppioni, Eur. Cryst. Meeting, 1985, 9, 164, but no formal report of this cluster exits. § Preparation of 1 : 0.35g (0.50 mmol) of either cis- or trans-Pt(PPh3)Cl2 was mixed with 0.050 g (0.50 mmol) of dry CuCl and 0.26 g (1.0 mmol) of PPh3 in 20 ml of dry THF under N2(g) at room temperature. Then the unstirred solution was cooled to ª240 8C using an acetone bath and N2(l), prior to slow addition of ª0.10 ml (1.1 mmol) of Se(SiMe3)2. The solution turned yellow, pale orange, and deep brown during these additions. The solution was then allowed to warm up over several hours until room temperature was reached.After several days in the dark, large orange crystals readily appeared and were collected for X-ray analysis. Yield ª50%. 31P NMR (C6D6) d 28.23 [1J(PaPt) = 3057, 1J(PbPt) = 2964; 3J(PaPt) = 1564, 3J(PbPt) = 1442; 2J(PP) = 88Hz]. Preparation of 2: this cluster was prepared in the same way as described for 1 except that both AgO2CR starting materials (R = Me, Ph) were used (0.085 g, 0.50 mmol, R = Me; 0.11 g, 0.50 mmol, R = Ph), instead of CuCl and the solution was kept in the dark at all times.Orange crystals were obtained in all cases over a period of several weeks. For the crystal reported in this work, an addition of a wet acetone (unpurified)– benzene mixture to the THF solutions was made. Crystallisation appeared more rapidly (ª1 day). Yield ~80%. 31P NMR(C6D6) d 27.94 [1J(PaPt) = 2984, 1J(PbPt) = 2882; 3J(PaPt) = 1615, 3J(PbPt) = 1426; 2J(PP) = 92 Hz].Preparation of 3: 0.30 g (1 mmol) of Pd(acac)2, 0.49 g (1 mmol) of Au(PPh3)Cl and 0.52 g (2 mmol) of PPh3 (excess) were dissolved in 25 ml of THF at room temperature. Then the solution was cooled to ª240 8C and kept in the dark prior to adding 0.50 ml (ª3 mmol) of Se(SiMe3)2. The solution was allowed to warm to room temperature over several hours. After several days in the dark, water was introduced very slowly into the solution over a period of several days and orange-red crystals appeared over this addition period.The crystals are light stable. Yield ª50%. 1H NMR(C6D6) d 0.123 and 0.300 [SeH, 1J(SeH) = 3.3 Hz] for compounds a and b (chemical exchange in solution), 6.8–7.5 (C6H5P, br bands). 31P NMR (C6D6) d 6.6 (free PPh3 in chemical exchange, very br), 16–30 (PdP and AuP, complex, both isomers). ¶ Crystal data. For 1?THF: C80H60Cl2Cu2O2P4Pt2Se2, orange plate, M = 961.62, monoclinic, space group P21/n, a = 14.828(3), b = 14.221(3), c = 18.032(4) Å, b = 102.62(3)8, V = 3710.5(13) Å3, at 200(2) K, Z = 2, Dc = 1.721 g cm23, m = 5.509 mm21, 2qmax = 52.028, 7117 independent reflections measured (Rint = 0.1104) on a STOE IPDS diVractometer.All Pt, Cu, Se, Cl and C atoms were refined anisotropically, to yield R = 0.0632, wR2 = 0.1696, S = 1.013 for 6365 data [Fo > 4sFo]. For 2?C6H6?2H2O: C78H60Ag2Cl2O2P4Pt2Se2, small orange hexagonal plate, M = 1987.88, triclinic, space group P1� , a = 11.386(2), b = 13.499(3), c = 14.169(3) Å, a = 64.73(3), b = 80.95(3), g = 70.48(3)8, V = 1854.7(6) Å3, at 200(2) K, Z = 1, Dc = 1.780 g cm23, m = 5.464 mm21, 2qmax = 52.088, 5205 independent reflections measured (Rint = 0.0529) on a STOE IPDS diVractometer.All C, Ag, Cl, O, P, Pt and Se atoms were refined anisotropically to yield R = 0.0651, wR2 = 0.1850, S = 1.117 for 4434 [Fo > 4sFo]. For 3?2THF: C80H76Au2O2P4Pd2Se4, orange-red plate fragment, M = 2099.73, triclinic, space group P1� , a = 11.004(2), b = 12.939(3), c = 14.452(3) Å, a = 70.27(3), b = 76.32(3), g = 82.27(3)8, V = 1878.6(7) Å3, at 200(2) K, Z = 1, Dc = 1.856 g cm23, m = 6.432 mm21, 2qmax = 45.008, 3693 independent reflections measured (Rint = 0.0732) on a STOE IPDS diVractometer.All C, Au, O, P, Pd, and Se atoms were refined anisotropically, to yield R = 0.0747, wR2 = 0.1826, S = 1.011 for 2657 data [Fo > 4sFo]. CCDC reference number 186/1205.See http:// www.rsc.org/suppdata/dt/1998/3901/ for crystallographic files in .cif format. 1 J. F. Corrigan and D. Fenske, Chem. Commun., 1997, 1837; S. Dehnen and D. Fenske, Chem. Eur. J., 1996, 2, 1407; S. Dehnen, A. Schäfer, R. Ahlrichs and D. Fenske, Chem. Eur. J., 1996 2, 429; S. Dehnen and D. Fenske, Angew. Chem., Int. Ed. Engl., 1994, 33, 2287; H. Krautscheid, D. Fenske, G. Baum and M. Sewmelmann, Angew. Chem., Int. Ed. Engl., 1993, 32, 1303; F. 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