Preparation and Axial Ligation Behavior of a (2, 3, 11, 12- Tetramethyldibenzo [b,i] [l, 4, 8, 11] Tetraaza-Cyclotetradecinato) Coba (II)

The cobalt (II) complex (Co (L-2)) of 5, 14-dihydro-2, 3, l, 11, 12-tetramethyldi-benzo [b, i] [l, 4, 8, 11] tetraazacyclotetradecine was prepared. The interaction of various substituted pyridines with the cobalt (II) complex was investigated by measuring electronic spectra. The cobalt (II) complex became the penta-coordi-nated complex by taking up a pyridine base in the axial position: Co (L-2) + B → B-Co (L-2). For the interaction of 4-substituted pyridines with the cobalt-(II) complex, the general behavior of the equilibrium constants was interpreted in terms of the pyridine basicity and the Hammett equation. The weaker coordination tendency of hindered pyridines toward the cobalt (II) complex was dependent on the steric effect of 2- and/or 6-methyl groups of substituted pyridines in the coordination process.