Synthesis and Characterization of Phenolate-Bridged Copper Dimers with a Cu-Cu Separation of >3.5 Angstroem. Models for the Active Site of Oxidized Hemocyanin Derivatives

Article abstract of DOI:10.1021/ja00300a020

Described are the synthesis and characterization of the new binucleating ligand 2,6-bis(bis<2-(1-pyrazolyl)-ethyl>amino)-p-cresol (Hbpeac) and two of its copper(II) derivatives.The ligand provides four donors, including a bridging phenoxide, to each metal ion.An "exogenous" ligand completes the coordination sphere of each copper.Both the μ-acetato (1a) and the μ-1,3-azido (1b) copper(II)complexes have been characterized by X-ray crystallography.In both structures, the coordination spheres of the copper(II) ions are distorted from a square-pyramidal geometry toward a trigonal-bipyramidal arrangement.The distortion is more pronounced in the acetato complex and accounts for the difference between the two compounds in terms of their magnetic behavior.Variable temperature magnetic susceptibility measurements demonstrate strong antiferromagnetic coupling (2J=-1800 cm^-1) for the azido derivative but negligable magnetic interaction between the copper ions in the acetato complex.The magnetic behavior, electronic spectrum, and structure of the azide derivative suggest that this complex is an excellent structural model for the oxidized azide derivative of hemocyanin.Crystal data for C32H42Cl2Cu2N10O12 (1a) are as follows: orthorhombic, a=13.999 (5) Angstroem, b=23.046 (9) Angstroem, c=12.523 (5) Angstroem, V=4043 Angstroem³, Z=4, space group=P2₁2₁2₁2₁.Crystal data for C31H41Cl2Cu2N13O13 (1b) are as follows: orthorhombic, a=12.977 (2) Angstroem, b=13.1888 (3) Angstroem, c=22.033 (6) Angstroem, V=3771 Angstroem³, Z=4, space group=P2₁2₁2₁.