6533b830fe1ef96bd1297920

RESEARCH PRODUCT

Crystal structures and magnetic properties of the squarate-O1,On-bridged dinuclear copper(II) complexes [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (n=2) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (n=3)

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Abstract Two dinuclear copper(II) complexes of the formula [Cu2(phen)4(C4O4)](CF3SO3)2 · 3H2O (1) and [Cu2(bipy)4(C4O4)](CF3SO3)2 · 6H2O (2) [phen=1,10-phenanthroline, bipy=2,2′-bipyridine and C4O4 2−=dianion of 3,4-dihydroxy-3-cyclobuten-1,2-dione (squaric acid)] have been synthesized and characterized by single-crystal X-ray diffraction. Their structures consist of [Cu2(phen)4(C4O4)]2+ (1) and [Cu2(bipy)4(C4O4)]2+ (2) dinuclear copper(II) cations, uncoordinated CF3SO3 − anions and crystallization water molecules. The copper is in a distorted square pyramidal environment: one squarate-oxygen atom and three phen- (1) or bipy- (2) nitrogen atoms of two phen (1) or bipy (2) terminal ligands form a distorted square plane around the copper whereas the axial position is occupied by the remaining phen- (1) or bipy- (2) nitrogen atom. The squarate adopts the μ-1,2- (1) and μ-1,3- (2) bis(monodentate) coordination modes, the intradimer copper–copper separation being 4.912(2) (1) and 7.310(1) (2) A, respectively. Variable temperature magnetic susceptibility measurements reveal the occurrence of significant intramolecular antiferromagnetic coupling, the relevant parameters being J=−26.4 cm−1 and g=2.14 for 1 and J=−8.6 cm−1 and g=2.07 for 2 (J being the exchange parameter in the isotropic spin Hamiltonian Ĥ=−JŜA · ŜB). The influence of both the symmetry of the copper(II) centered magnetic orbitals and the coordination modes of the bridging squarate on the magnitude of antiferromagnetic coupling in related squarate-bridged copper(II) complexes is analyzed and discussed.