Structural studies on co-ordinated macrocyclic ligands. Part II. Crystal and molecular structure of acetylacetonato-C-meso-(5,5,7,12,12,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate

Abstract

The title compound and the corresponding cobalt(III) compound have been prepared and the crystal and molecular structure of the former has been determined fromX-ray diffractometer data. Crystals are monoclinic,a= 16·190(8), b= 12·678(7), and c= 13·197(6)Å, β= 100·52(8). Space group Cc. The structure was solved by the heavy-atom method and refined to R0·0630 for 1580 independent reflections. The nickel(II) ion is in approximately octahedral co-ordination with the macrocycle folded at N(4) and N(11) to occupy four adjacent co-ordination sites, a symmetrical, planar acetylacetonato-chelate occupying the two remaining sites. In the structure the configuration of the amine is 1RS, 4RS, 7RS, 8RS, 11RS, 14SR. The five-membered chelate rings adopt unsymmetrical gauche conformations and the six-membered chelate ring including N(1) and N(11) adopts a chair conformation. That containing N(4) and N(8) adopts a twist-boat conformation which minimises non-bonded interactions of the methyl substituents. The strain inherent in this non-optimum geometry is considered to be responsible for the observed low stability of compounds in which the amine has this configuration.