Synthesis of some pentagonal-bipyramidal complexes of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), and zinc(II) with a heptadentate Schiff-base ligand and the crystal and molecular structures of a copper(II) complex

Abstract

Complexes of the type [ML]X₂.xH₂O, where M is a divalent metal ion (Mn, Fe, Co, Ni, CU, Zn), X = ClO₄- or BPh₄-, x= 0 or 1, and L is a potentially heptadentate Schiff base derived from the condensation of one molecule of 2,6-diacetylpyridine with two molecules of diethylenetriamine, are reported. The complexes were prepared by metal exchange from corresponding alkaline-earth metal complexes. By means of a single-crystal X-ray analysis of [CuL][ClO₄]₂, comparisons of X-ray powder patterns, and various physical properties it is shown that the complexes have a pentagonal-bipyramidal structure in the solid state and also, nickel(II) complexes excepted, in acetonitrile solution. Crystals of [CuL][ClO₄]₂, are monoclinic, with a= 12.18(1), b= 13.78(1), c= 14.92(1)Å, β= 98.3(1)°, Z= 4, space group P2₁/n. 1 486 Reflections above background have been measured by diffractometer and refined by full-matrix least squares to R 0.079. The three nitrogen atoms of the trimethine group together with the two secondary amine nitrogen atoms define the equatorial plane of a distorted pentagonal bipyramid, the primary amine nitrogen atoms occupying the axial positions. The Cu–N_ax. bonds [1.993(19), 1.997(20)Å] are notably shorter than the Cu–N_eq. bonds (average 2.356 Å). The transition-metal complexes are all high spin. Electronic spectra are reported, as well as the e.s.r. spectrum of [CuL][BPh₄]₂.