Some cyclic tetra-amines and their metal-ion complexes. Part VI. The crystal structure of acetato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate

Abstract

The structure of acetato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)nickel(II) perchlorate has been investigated by single-crystal three-dimensional X-ray methods. The blue prismatic crystals are monoclinic, space group P2₁/c, with a= 9·39, b= 30·67, c= 9·57 Å, β= 119·3°, Z= 4. The structure was solved by Patterson and Fourier syntheses, and refined by least-squares methods to a final R of 0·120 for the 2753 visually estimated independent reflexions.

The cyclic tetra-amine is folded, with the four secondary amine groups co-ordinated to adjacent octahedral sites of the nickel (II) ion. The acetate ion functions as a symmetric chelate, occupying the two remaining sites. The cyclic tetra-amine is the C-rac-modification, and both pairs of asymmetric nitrogens also have the racemic arrangement, but the pairs are of opposite helicity.

The relative energies of the 36 configurations of the co-ordinated 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane macrocycles, arising from the pair of asymmetric carbon centres and two pairs of asymmetric nitrogen centres, are discussed in terms of the conformational energies of the chelate ring systems and methyl substituent interaction energies.

The space-group determination of cis-oxalato-C-rac-(5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane)cobalt(III) perchlorate is also reported: Pccn, with a= 16·03, b= 9·61, c= 15·12 Å, Z= 4.