Structural and Magnetic Properties of a {GdCu₅}₂ Metallacrown Dimer with a Disulfonate Linker

The complex {Na-2(H2O)(8)[GdCu5(GlyHA)(5)(H2O)(4)L](2)}L-2 & sdot; 2.5DMF & sdot; 10.5H(2)O (1, where GlyHA(2-)= glycinehydroxamate, L2-= 4,4 '-bis(2-sulfonatostyryl)biphenyl) was obtained as the outcome of the metathesis reaction of previously reported [GdCu5(GlyHA)(5)(CO3)(NO3)(H2O)(5)] & sdot; 3.5H(2)O with an excess of the disulfonate's sodium salt. X-Ray analysis of 1 shows a dimeric structure in which 15-metallacrown-5 units {GdCu5}(3+) are arranged in an "edge-to-edge" manner by way of two linking disulfonates, L2-. Magnetic studies of polycrystalline 1 over a temperature range of 2-300 K revealed both Gd-Cu ferromagnetic and Cu-Cu antiferromagnetic interactions within the metallacrown unit. Experimental chi T-M vs. T data for 1 were fitted using different theoretical models. A two-J model, which takes into account both exchange interactions between adjacent copper(II) ions and the Gd-Cu exchange interactions allows fitting of the chi T-M vs. T data in the whole temperature range. The values obtained for the exchange parameters are in accord with previously reported parameters for Ln(III)-Cu(II) 15-metallacrowns-5. The 240 GHz powder EPR spectra for 1 were recorded between 30 and 150 K.