SYNTHESIS AND MAGNETIC-PROPERTIES OF BIS(MU-HYDROXO)BIS[(2,2'-BIPYRIDYL)COPPER(II)] SQUARATE - CRYSTAL-STRUCTURE OF BIS(MU-HYDROXO)BIS[(2,2'-BIPYRIDYL)COPPER(II)] SQUARATE TETRAHYDRATE

The compound [Cu2(bipy)2(OH)2](C4O4)·5.5H2O, where bipy and C4O42- correspond to 2,2′-bipyridyl and squarate (dianion of 3,4-dihydroxy-3-cyclo- butene-1,3-dione) respectively, has been synthesized. Its magnetic properties have been investigated in the 2-300 K temperature range. The ground state is a spin-triplet state, with a singlet-triplet separation of 145 cm-1. The EPR powder spectrum confirms the nature of the ground state. Well-formed single crystals of the tetrahydrate, [Cu2(bipy)2(OH)2](C4O4)·4H2O, were grown from aqueous solutions and characterized by X-ray diffraction. The system is triclinic, space group P1, with a = 9.022(2), b = 9.040(2), c = 8.409(2) Å, α = 103.51(2), β = 103.42(3), γ = 103.37(2)°, V = 642.9(3) Å3, Z = 1, Dx = 1.699 g cm-3, μ(Mo Kα) = 17.208 cm-1, F(000) = 336 and T = 295 K. A total of 2251 data were collected over the range 1≤θ≤25°; of these, 1993 (independent and with I≥3σ(I)) were used in the structural analysis. The final R and Rw residuals were 0.034 and 0.038 respectively. The structure contains squarato-O1, O3-bridged bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] units forming zigzag one-dimensional chains. Each copper atom is in a square-pyramidal environment with the two nitrogen atoms of 2,2′-bipyridyl and the two oxygen atoms of the hydroxo groups building the basal plane and another oxygen atom of the squarate lying in the apical position. The magnetic properties are discussed in the light of spectral and structural data and compared with the reported ones for other bis(μ-hydroxo)bis[(2,2′-bipyridyl)copper(II)] complexes. © 1990.