RELATIONSHIPS BETWEEN METAL-METAL FORCE-CONSTANTS AND METAL-METAL SEPARATIONS FOR AG2 AND PD2 SYSTEMS - CRYSTAL AND MOLECULAR-STRUCTURES OFAG2(DMB)2X2 (X = CL, BR, I DMB = 1,8-DIISOCYANO-P-MENTHANE) AND CIS-PD(CNC(CH3)3)2CL2 COMPLEXES

The complexes Ag2(dmb)2X2 (X = Cl, Br, I; dmb = diisocyano-p-menthane) have been characterized by X-ray diffraction at 233 K (X = CI), 293 K (X = Br), and 243 K (X = I). The silver complexes are found to contai n Ag2(dmb)2(2+) core structures with two silver atoms bridged by dmb l igands to give Ag2N4C14 rings. The halogen atoms are doubly bridging t he silver metals, with Ag-X bond distances of 2.685(3) and 2.719(3) an gstrom (x = Cl), 2.736(3) and 2.836(3) angstrom (X = Br), and 2.904(1) and 2.935(1) angstrom (X = I). The Ag-Ag separations are 3.452(2), 3. 347(3), and 3.379(2) angstrom for X = Cl, Br, and I, respectively. The cis-Pd(CNC(CH3)3)2Cl2 complex has also been synthesized and character ized by X-ray crystallography; the molecules pack as four quasi-face-t o-face dimers, where very weak Pd-Pd interactions are observed (Pd(1)- Pd(1), 4.441(3) angstrom; Pd(2)-Pd(2), 4.359(3) angstrom; Pd(3)-Pd(3), 4.056(3) angstrom; Pd(4)-Pd(4), 4.463(3) angstrom). The low-frequency (10-400 cm-1) vibrational spectra of these compounds and of four othe r related complexes containing Ag-Ag and Pd-Pd units in the solid stat e have been analyzed. Including literature results, for the metal-meta l stretching frequencies (nu(M2)), data banks of nine and twelve point s are accumulated for the silver and palladium compounds, respectively , where reparametrized Herschbach-Laurie type relationships (H-L) betw een r(M2) and F(M2), as applied to Ag2 or Pd2 systems, are designed. C rystal data: Ag2(dmb)2Cl2.2CHCl3, monoclinic, P2(1)/n, a = 10.8291 (11 ) angstrom, b = 14.1991 (11) angstrom, c = 12.9318(17) angstrom, beta = 106.437-9-degrees, V = 1907.2(3) angstrom3, Z = 2; Ag2(dmb)2Br2, Mon oclinic, P2(1)/n, a = 9.6030(7) angstrom, b = 17.7394(8) angstrom, c = 17.2335(10) angstrom, beta = 102.932(6)-degrees, V = 2861.3(3) angstr om3, Z = 4; Ag2(dmb)2I2.CH3CH2OH, monoclinic, P2(1)/n, a = 9.1781(12) angstrom, b = 14.9731(15) angstrom, c = 12.1882(12) angstrom, beta = 9 6.799(9)-degrees, V = 1663.2(3) angstrom3, Z = 2; cis-Pd(CNC(CH3)3)2-C l2, triclinic, P1BAR, a = 12.2675(10) angstrom, b = 12.334(13) angstro m, c = 21.211(4) angstrom, alpha = 99.663(12)-degrees, beta = 99.985(1 2)-degrees, gamma = 90.433(7)-degrees, V = 3113.9(7) angstrom3, Z = 8.