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Trends in Inorganic Chemistry   Volumes    Volume 4 
Abstract
Survey of Cu(II) and Ni(II) complexes formed by 1,3 - diaminopropane. Similarities in their benzoate complexes
Markku R. Sundberg
Pages: 121 - 144
Number of pages: 24
Trends in Inorganic Chemistry
Volume 4 

Copyright © 1996 Research Trends. All rights reserved

ABSTRACT
 
The molecular structures of tn (tn = 1,3- diaminopropane) containing metal complexes were surveyed. The vast majority of them were bis- complexes with the six-membered chelate rings displaying chair conformation. More specifically, totally 26 molecular structures of M(ZbzO)2tn2 compounds (where M = Cu or Ni and ZbzO is a benzoate anion) were analyzed by statistical methods to establish similarities within the series. An ortho substituent in a benzoate anion seems to lead into crystallization in the orthorhombic system, whereas the meta or para substituents result in the crystallization in the monoclinic system almost without exception. Every compound contains a monomeric complex unit with a metal cation sitting at a centre of symmetry. The benzoate anions in the axial direction are all coordinated through one oxygen of a benzoate anion. If only bond lengths and angles were used in the comparison, the only highly significant difference was found in the axial bond lengths (Cu>Ni). Owing to weak axial bonding in the copper(II) complexes, both the coordination mode and coordination number can be chosen based upon the choice of a benzoate anion. In the nickel(II) complexes no variation has been found, yet. By making use of additional new structural parameters defined to describe the coordination more explicitly, new dissimilarities between the copper(II) and nickel(II) complexes were found in the bite size (Cu<Ni), inclination of a carboxylate group (Cu<Ni) and tilting of the axial bond (Cu>Ni). The dissimilarity of the copper(II) and nickel(II) complexes seems to manifest itself also in d-s mixing. Declination of a carboxylate group is probably affected by a hydrogen bond to a coordinated oxygen in some compounds. The statistical results suggest that a chair-to-chair interconversion may proceed via a half-boat conformation, where the metal atom lies on the plane. The proposed mechanism seems to be independent on the central metal cation. However, the easiness of a metal atom to approach planarity may well be metal-dependent. A deformation in the chelate ring manifests itself in the M-N-C angles, for which there is a clear correlation.
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