Influence of the Coordination of Donor Solvent Molecules to 1,4,7,10-Tetramethyl-1,4,7,10- tetraazacyclododecanenickel(II) and Analogous Nickel(II) Complexes on Their Steric Factors

Abstract

Coordination equilibrium constants (K NiS) of some donor solvent molecules to 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecanenickel(II) ([Ni(Me4[12]aneN4)]2+) were determined in nitrobenzene (a noncoordinating bulk solvent). The first (K NiS1) and second stepwise coordination equilibrium constants (K NiS2) for 1,4,7,10-tetraazacyclododecanenickel(II) ([Ni([12]aneN4)]2+), 1,4,8,11-tetraazac yclotetradecane- nickel(II) ([Ni([14] aneN4)]2+), 1,4,8,11-tetrathiacyclotetra-decanenickel(II) ([Ni([14]aneS4)]2+) were also reinvestigated. The K NiS values for [Ni(Me4[12]aneN4)]2+ were compared to those of [Ni([12]aneN4)]2+, (1R,4S, 8R,11S)-1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) (R,S,R,S-[Ni(Me4[14]aneN4)]2+), R,R,S,S-[Ni(Me4[14]aneN4)]2+, [Ni([14]aneN4)]2+, and [Ni([14]aneS4)]2+. Coordination of pyridine (Py), N,N,N′,N′-tetramethylurea (TMU), and N,N-dimethylacetamide (DMA) to [Ni(Me4[12]aneN4)]2+ was observed, although these donor solvent molecules did not coordinate to R,S,R,S-[Ni(Me4[14]aneN4)]2+. The K NiS values for Py, TMU, and DMA are 7.9, 2.8, and 9.0 dm3⋅mol−1, respectively. Some hydrogen-bonding waters were coordinated to R,S,R,S-[Ni(Me4[14]aneN4)]2+, but such waters did not coordinate to [Ni(Me4[12] aneN4)]2+. Also, the K NiS2 values were larger than the corresponding K NiS1 values for [Ni([14]aneS4)]2+. Furthermore, the K NiS1 values for [Ni([12]aneN4)]2+ were the largest among these nickel(II) complex cations. The K NiS, K NiS1, and K NiS2 values are discussed in terms of properties of the donor solvents and steric strains of these nickel(II) complex cations.