CHARACTERIZATION OF PROTONATED TRANS-BIS(DIOXIME)RUTHENIUM COMPLEXES - CRYSTAL-STRUCTURES OF TRANS-RU(DPGH)2(NO)CL, TRANS-[RU(DMGH)(DMGH2)(NO)CL]CL, AND TRANS-RU(DMGH)2(NO)CL

Single-crystal X-ray diffraction studies were carried out on trans-Ru(DPGH)2(NO)Cl (1), trans-[Ru(DMGH)(DMGH2)(NO)Cl]Cl (2), and trans-Ru(DMGH)2(NO)Cl (3) (DMGH = dimethylglyoxime monoanion, DPGH = diphenylglyoxime monoanion). These represent the first crystal structures of trans-bis(dioxime) complexes containing ruthenium. Complex 1 crystallizes in the monoclinic space group C2/c, with a = 10.459 (5) angstrom, b = 10.148 (4) angstrom, c = 26.673 (13) angstrom, beta = 98.25 (4) angstrom, Z = 4, V = 2802 (2) angstrom 3, and R = 4.83%. Complex 2 crystallizes in the monoclinic space group P2(1)/c, with a = 13.8100 (10) angstrom, b = 10.095 (2) angstrom, c = 11.898 (2) angstrom, beta = 100.780 (10) angstrom, Z = 4, V = 1629.4 (4) angstrom 3, and R = 3.05%. Complex 3 crystallizes in the orthorhombic space group P2(1)2(1)2(1), with a = 7.9920 (10) angstrom, b = 14.251 (2) angstrom, c = 24.666 (2) angstrom, Z = 8, V = 2809.1 (5) angstrom 3, and R = 3.84%. The crystal structure determinations include the location and refinement of hydrogen atoms associated with the oxime oxygens. The existence of two types of hydrogen bonds (O-H--Cl hydrogen bonds and a symmetric O-H--O oxime bridge) associated with the oxime oxygen atoms of trans-[Ru(DMGH)(DMGH2)(NO)Cl]Cl can be clearly demonstrated. Furthermore, the crystal structures of both trans-Ru(DPGH)2(NO)Cl and trans-Ru(DMGH)2(NO)Cl display a third type of hydrogen bonding (asymmetric O-H--O oxime bridge) involving the oxime oxygen atoms. Thus, three types of hydrogen bonding that were previously proposed for trans-bis(dioxime) transition metal complexes can be directly observed within these three structurally similar bis(dioxime)ruthenium complexes. In addition, we can now unambiguously assign the O-H stretching IR bands to the proper modes of hydrogen bridging. Temperature-dependent H-1 NMR spectroscopy of trans-[Ru(DMGH)-(DMGH2)(NO)Cl]Cl was used to measure rate constants of proton exchange, which demonstrated that the solid-state structure is maintained in solution. Finally, the cyclic voltammograms of complexes 2 and 3 and the pK(a) values for the stepwise removal of two protons from complex 2 were measured.