INCREASED BASICITY AND HYDROGEN-BONDING DONOR ABILITY OF WATER BY HYDROGEN-BONDING TO DIMETHYL-SULFOXIDE AND ITS COORDINATION TO 1,4,8,11-TETRAMETHYL-1,4,8,11-TETRAAZACYCLOTETRADECANENICKEL(II) IN NITROBENZENE

The axial coordination of the four-coordinated 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) cation ([Ni(tmc)]2+) by water which is hydrogen-bonded to dimethyl sulphoxide (DMSO) has been investigated spectrophotometrically in nitrobenzene (NB) containing < 0.05 mole fraction DMSO at 25-degrees-C. Although water in NB is only weakly coordinated to the cation, water which is hydrogen-bonded to DMSO in NB can be easily coordinated to form the five-coordinated [Ni(tmc)(WS)]2+ cation with a coordination constant of 24.0 dm3 mol-1, where W is water, S is DMSO, and WS is the 1:1 water-DMSO species H-O-H...S. (-O- is the coordinating oxygen atom and the formation constant for WS was determined by using NMR methods.) The residual hydrogen atom of the coordinated water in WS can be hydrogen-bonded to further species, including additional DMSO and either WS or NB-solvated water, to form two additional kinds of five-coordinated complexes: [Ni(tmc)(WS-S)]2+ and either [Ni(tmc)(WS-WS)]2+ or [Ni(tmc)(WS-WS)]2+, where WS-S is S...H-O-H...S, WS-WS is S...H-O-H...OH-H...S, and WS-W is S...H-O-H...OH-H. The corresponding equilibrium constants for the hydrogen bonding of water were 1.5 dm3 mol-1 for WS, 12.3 for [Ni(tmc)(WS-S)]2+, 8.6 for [Ni(tmc)(WS-WS)]2+ and 1.3 for [Ni(tmc)(WS-W)]2+. The increased hydrogen-bonding donor ability and basicity are discussed in terms of polarization of the O-H bond through hydrogen bonding and coordination.