Structural, magnetic and spectroscopic characterization of novel di-μ-carboxylato-bridged binuclear copper(II) complexes with 1,10-phenanthroline

Bis(μ-carboxylato-O,O')-diaquabis(1,10-phenanthroline)dicopper(II) dinitrate tetrahydrates, [Cu(RCOO)(phen)(H₂O)]₂(NO₃)₂4H₂O, where R=H, CH₃, and (CH₃)₃C, were prepared and characterized by elemental analyses, electronic spectra, magnetic susceptibilities, and X-ray structure analysis. The magnetic susceptibility data conform to the usual dimer equation. The -2J values are 125 cm^-1 for formate, 86 cm^-1 for acetate, and 99 cm^-1 for 2.2-dimethylpropanoate. The crystal structures of [Cu(HCOO)(phen)(H₂O)]₂(NO₃)₂4H₂O(1) and [Cu(CH₃COO)(phen)(H₂O)]₂(NO₃)₂4H₂O (2) were determined by the single-crystal X-ray diffraction method. The crystallographic data are: Compound 1, monoclinic, 12/a, a=18.850(2), b=9.775(2), c=17.752(2) A, β=99.03(1)°, V=3230.4(8) A³, Z=4, R=0.055 for 2511 observed unique reflections; Compound 2, monoclinic, C2/c, a=18.563(4), b=14.272(5), c=14.126(3) A, β=106.72(2)°, V=3584(2) A³, Z=4, R=0.082 for 2092 reflections. The complexes consist of dimeric [Cu(RCOO)(phen)(H₂O)]^{2 +}₂ cations with five-coordinated copper ions linked by two carboxylato ions in a syn-syn bridging arrangement. The Cu...Cu distances are 3.103(2) A for 1 and 3.063(3) A for 2.