Molecular Structure And Magnetic Characterization Of Structurally Reinforced Chiral Macrocyclic Poly- Amine-Based Dinuclear Copper(II) Complexes by x- and w- band ESR Spectroscopy and Squid Measurements

Abstract

An attempt has been made to synthesize structurally reinforced chiral B₂-18-membered hexaazamacrocyclic amine based dinuclear copper(?) complexes 2 and 2′ as models for studying the size-match selectivity of metal ions. These two dinuclear complexes have manifested a prominent difference in the electronic spin structure, although only apparent structural difference is subtle. The complex 2 is double-bridged with an oxygen and chloride atom while 2′ is single-bridged only with the oxygen atom of hydroxide ion and the fifth ligand Cl is missing. From cw ESR measurements of 2 and 2′ in polycrystalline solids a large zero-field splitting (ZFS) value has been determined for 2′ and a small ZFS value for 2, respectively. These findings have been in accordance with the results from the SQUID measurements. The ZFS values and isotropic exchange interaction have been theoretically estimated on the basis of molecular structural considerations of the complexes. The ground-state spin structures for the complexes 2 and 2′ have been discussed in connection with the geometry of the bridging oxygen linker.