Synthesis, structure, EPR, and DFT calculation on dinuclear paddle wheel Cu(II) complexes with bis-chelate rings

A series of diester-dicarboxylic acids, (LH2)-H-1, (LH2)-H-2, (LH2)-H-3, (LH2)-H-4, and (LH2)-H-5 and their dinuclear Cu-2 complexes [Cu(L-1)CH3CN](2) (1), [Cu(L-2)H2O](2) (2), [Cu(L-3)CH3CN](2) (3), [Cu(L-4)EtOH](2) (4), and [Cu(L-5)CH3CN](2) (5), were synthesized. The crystal structures obtained for 1, 2, and 4 and the density functional theory optimized structures for 2, 3, and 5 illustrated the formation of tetracarboxylate "paddle wheel" complexes. The phthalyl and diphenyl head groups and the spacer moieties were appropriately altered and the size of the chelate ring expanded from 15-membered in 1 to 21-membered in 5. The dinuclear units have strong Cu-Cu interaction with EPR spectra exploring spin coupled features.