Ligand bonding parameters in some macrocyclic, seven-coordinate complexes of nickel(II) and cobalt(II)

Abstract

Single crystal polarized electronic spectra and paramagnetic susceptibilities throughout the temperature range 20–300 K are reported for the complexes [M(H 2O) 2(tdmmb)][BF 4] 2; M = Ni(II, Co(II); tdmmb = 7,15-dihydro-7,9,13,15-tetramethylpyrido-[2′,1′,6′:12,13,14][1,2,4,7,9,10,13]-heptaazacyclopentadeca [3,4,5,6,7,8- aklmn][1,10] phenanthroline. The electronic properties of these formally pentagonal bipyramidal macrocyclic, complexes are analysed within a global, axial model — shown to be wholely inappropriate for the nickel complex — and within the angular overlap model. The ligand fields are dominated by the phenanthroline-type ligator as a strong σ donor and π donor, presumably reflecting the presence of electron rich nitrogen atoms substituted in the phenanthroline aortho positions. By contrast the two imine groups of the macrocycle act as a weak σ donors in line with the much longer MN bond lengths. Despite the ligand field asymmetry in the macrocycle plane, the molecular magnetic susceptibility tensor is calculated to be essentially axial with respect to the normal to this plane.