SYNTHESIS AND ELECTROCHEMISTRY OF MO[BH(ME(2)PZ)(3)](NO)[S(CH2)(2)CONH(CH2)(2)S] AS A PROBE OF THE EFFECTS OF N-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-S HYDROGEN-BONDING ON REDOX POTENTIALS

A series of bidentate alkanethiolate compounds Mo[BH(Me(2)pz)(3)](NO)[SRS], [SRS](2-) = [S(CH2)(2)CONH(CH2)(2)S](2-) (1), [S(CH2)(5)S](2-) (2), and [S(CH2)(6)S](2-) (3), have been synthesized in order to determine the effects of N-H...S hydrogen bonding on redox potentials in metal-thiolate complexes. Complex 1 was structurally characterized by X-ray crystallography. It crystallizes in the space group P2(1)/c with a = 11.878(2) Angstrom, b = 10.8040(10) Angstrom, c = 21,453(4) Angstrom, alpha = 90 degrees, beta = 105.54 degrees, gamma = 90 degrees, V = 2652.4(7) Angstrom(3), Z = 4, and R = 0.0374. Redox potentials of -0.793 V (1), -0.930 V (2), and -1.013 V (3) (relative to SCE) were measured in CH3CN by cyclic voltammetry. A comparison of complexes 1-3 by solution vibrational spectroscopy shows that the high redox potential of 1 may be attributed to the presence of N-H...S hydrogen bonds. The nitrosyl stretching frequency, v(NO), was assigned in the resonance Raman spectra of complexes 1-3. This band decreased in frequency in parallel with the decrease in redox potential. For complex 1 in solution the values of the amide N-H stretching frequency, v(NH), 3434 and 3308 cm(-1) indicates a hydrogen bonding equilibrium constant of K = [NHbonded]/[NHfree] = 6.7.