STRUCTURAL MOTIFS IN DINUCLEAR D8 METAL-COMPLEXES - STRUCTURAL AND SPECTROSCOPIC CHARACTERISTICS OF AN ALTERNATIVE UNSYMMETRICAL 3-5 LIGAND DISTRIBUTION AS COMPARED TO THE SYMMETRICAL 4-4 OR FACE-TO-FACE ARRANGEMENT

Addition of [Rh(CNCH3)4](BPh4) to an acetone solution of [Pt(dMP)2]Cl2(dpm is bis(diphenylphosphino)methane) followed by addition of methanolic ammonium hexafluorophosphate yields ivory [(CH3NC)PtRh(CNCH3)3(mu-dpm)2](PF6)3. Crystals of [(CH3NC)PtRh(CNCH3)3(mu-dpm)2](PF6)3.0.46(CH3CH2)2O.0.54CH3CN form in the monoclinic space group P2(1)/n (No. 14) with a = 15.724 (6) angstrom, b = 18.157 (5) angstrom, c = 25.13 (3) angstrom, and beta = 97.52 (5)-degrees at 130 K with Z = 4. Refinement of 492 parameters and 7788 reflections gave R = 7.3% and R(w) = 7.6%. The cation contains a three-coordinate Pt(II) center datively bonded to a five-coordinate Rh(I) center at a distance of 2.708 (2) angstrom. Similarly, addition of Rh(CO)Cl(AsPh3)2 and 3 equiv of methyl isocyanide to [Pt(dpm)2]+ followed by addition of ammonium hexafluorophosphate leads to formation of yellow [(CH3NC)PtRhCl(CNCH3)2(mu-dpm)2](PF6)2. Yellow crystals of [(CH3NC)PtRhCl(CNCH3)2(mu-dpm)2](PF6)2.0.5CH3CN form in the triclinic space group P1BAR (No. 2) with a = 11.465 (4) angstrom, b = 14.832 (6) angstrom, c = 19.712 (10) angstrom, alpha = 87.71 (4)-degrees, beta = 79.43 (4)-degrees, and gamma = 67.98 (3)-degrees with Z = 2 at 130 K. Refinement of 473 parameters and 6461 reflections gave R = 4.1% and R(w) = 4.2%. This complex is structurally similar to [(CH3NC)PtRh(CNCH3)3(mu-dpm)2]3+, except a chloride is residing in the axial position on the rhodium in place of a methyl isocyanide. Addition of I2 to solutions of [(CH3NC)PtRh(CNCH3)3(mu-dpm)2](PF6)3 does not lead to oxidative addition across the metals but to direct attack on a coordinated methyl isocyanide to produce [(CH3NC)PtRhI(CNCH3)2(mu-dpm)2](PF6)2. Yellow crystals of [(CH3NC)PtRhI(CNCH3)2(mu-dpm)2](PF6)2.CH3CN are essentially isostructural with [(CH3NC)PtRhCl(CNCH3)2(mu-dpm)2](PF6)2 and crystallize in the triclinic space group P1BAR (No. 2) with a = 11.531 (5) angstrom, b = 14.682 (6) angstrom, c = 19.849 (14) angstrom, alpha = 86.21 (5)-degrees, beta = 78.26 (5)-degrees, and gamma = 68.77 (3)-degrees with Z = 2 at 130 K. Refinement of 438 parameters and 6057 reflections gave R = 4.2% and R(w) = 4.4%. The optical properties of the above three compounds show broad absorbances in the UV region and no photoluminescence. On the basis of their coordination geometry, these three structures are categorized as 3:5 complexes and are contrasted to the well-studied, face-to-face 4:4 complexes. The 4:4 complex, [(NC)PtRh(CNBu(t))2(mu-dpm)2](PF6) is made by addition of 2 equiv of sodium cyanide to [Pt(dpm)2]Cl2 followed by addition of [Rh(CNBut)4](PF6) and ammonium hexafluorophosphate. Red crystals of [(NC)2PtRh(CNBut)2(mu-dpm)2](PF6).0.5CH3OH.0.5(CH3CH2)2O crystallize in the orthorhombic space group Pnma (No. 62) with a = 35.723 (11) angstrom, b = 15.214 (7) angstrom, and c = 12.542 (5) angstrom with Z = 4 at 130 K. Refinement of 244 parameters and 3082 reflections gave R = 6.5% and R(w) = 6.5%. The cation contains a square planar RhP2(CNR)2 unit and a square planar PtP2(CN)2 unit connected through the two dpm bridges at a separation of 3.079 (2) angstrom. The complex in dichloromethane shows a strong absorbance at 470 nm (epsilon = 12 300 M-1 cm-1) and photoemissions at 530 nm (fluorescence) and 645 nm (phosphorescence).