Dinuclear copper complexes of pyridylphenylphosphine ligands: Characterization of a mixed-valence Cu/Cu dimer

Homo bi-copper complexes [Cu₂{PhP(2-py)₂}₂(NO₃)₃] (1) and [Cu₂{P(2-py)₃}₂Cl₂] (2), were synthesized from the reaction of Cu(NO₃)₂·3H₂O and CuCl₂·2H₂O with their corresponding 2-pyridylphosphine ligands. Compound 1 has a mixed valence Cu(I)-Cu(II) core with electron acceptor phosphine atoms and two NO₃⁻ anions coordinated in a monodentate fashion to Cu(I), giving it a distorted tetrahedral geometry. The environment of Cu(II) in 1 is composed of four nitrogen atoms from pyridyl and another NO₃⁻ anion in a square pyramidal geometry. This complex shows luminescence and a low energy absorption band at 969 nm corresponding to intermetallic electron transfer between the copper centers. Complex 2 was prepared from the treatment of copper(II) chloride with tris(2-pyridyl)phosphine, producing a binuclear copper complex which possesses a crystallographic inversion center. The copper geometry in this complex is distorted tetrahedral with coordination of one Cl⁻, two nitrogens from one bridging tris(2-pyridyl)phosphine ligand and one P atom from the other bridging tris(2-pyridyl)phosphine ligand, in a similar way observed in related complexes. The products have been characterized by spectroscopic methods and also by the single-crystal X-ray diffraction method.