RESONANCE-ENHANCED INTRALIGAND AND METAL-METAL RAMAN MODES IN WEAKLY METAL METAL-INTERACTING PLATINUM(II) COMPLEXES AND LONG-RANGE RELATIONSHIP BETWEEN METAL-METAL SEPARATIONS AND FORCE-CONSTANTS

The vibrational spectra (including resonance Raman) particularly in the low-wavenumber region (2-500 cm-1) were investigated in the solid state at 295 K for six compounds forming either linear chains or binuclear Pt species (with or without peak Pt...Pt interactions). The nu(Pt2) modes have been localized in the 5-55-cm-1 range. For the chain compounds the data are as follows: [Pt(bpy)2](NO3)2-3H2O, no nu(Pt2); [Pt(bpy)2](Pt(CN)4), nu(Pt2) = 54 cm-1? (from IR); [Pt(NH3)4](PtCl4), nu(Pt2) = 50 cm-1; PtCl3(DMSO), nu(Pt2) = 5 cm-1. For the binuclear compounds the data are as follows: [(Bu-t-NC)2ClPt(mu-CN)Pt(CN-t-Bu)Cl2][cis-Pt(CN-t-Bu)2Cl2], nu(Pt2) = 38 cm-1; [(CH3)ClPt(mu-Cl)(mu-Cl)(mu-Ph2PPy)Pt(CH3)(DMSO)].DMSO, nu(Pt2) = 43 cm-1. Using these data and 12 other literature data of compounds for which both nu(Pt2) and r(Pt2) are known, a reparametrized Herschbach-Laurie relationship was designed (r(Pt2) = -0.223 In F(Pt2) + 2.86, where F(Pt2) is the force constant in mdyn angstrom-1; sigma = 0.98 for 16 data points). The Pt2 data are compared with those known for the Ag2, Pd2, Rh2, and Au2 systems.