XAS, ESR and Potentiometric Studies of Three Dinuclear <i>N</i>,<i>N</i>′<i>‐para</i>‐Xylylenebis(tetraazamacrocycle)copper(<scp>II</scp>) Complexes − X‐ray Crystal Structure of [<i>N</i>,<i>N</i>′‐<i>p</i>‐Xylylenebis(cyclen)]copper(<scp>II</scp>)

Abstract

Abstract Dicopper complexes with N , N′ ‐ p ‐xylylenebis(cyclam or cyclen) and with the heteroditopic N , N′ ‐ p ‐xylylenebis(cyclam‐cyclen) were synthesized. An X‐ray study of the N , N′ ‐ p ‐xylylenebis(cyclen)dicopper complex showed that the copper( II ) ion is five‐coordinate with an H 2 O molecule in apical position. With this ligand, a polymeric chain was also obtained in the presence of KSCN. The terminal donor atoms of the bridging NCS − anion are coordinated in apical position to the square‐pyramidal copper( II ) ion. Two alternating kinds of Cu 2 L 4+ moieties are present in the chain, the first with two N 4 S chromophores and the second with two N 5 chromophores. EXAFS and XANES results are in agreement with a five‐coordinate copper ion in the cyclen unit and a six‐coordinate copper ion in the cyclam unit. Thermodynamic constants were determined by potentiometry. The existence of dinuclear Cu 2 L 4+ species (ligand/metal ratio &lt; 1) and mononuclear CuLH n (2+ n )+ species (ligand/metal ratio &gt; 1) were confirmed by an ESR study at variable pH. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)