First Example of Equatorial−Equatorial Disposition of End-to-End Thiocyanate Bridges in a Polynuclear Copper(II) Complex and Its Relation to the Very Efficient Transmission of the Magnetic Interaction

The preparation, X-ray structure, and spectroscopic and magnetic properties of [Cu(NCS)(μ-NCS)(Hmtpo)(H 2 O)] 2 (where Hmtpo= 4 H,7 H -5-methyl-7-oxo[1,2,4]triazolo[1,5- a ]pyrimidine) are described. This compound crystallizes in triclinic space group P 1̄, with unit cell dimensions a = 8.408(2) Å, b = 10.581(3) Å, c = 7.927(2) Å, α = 89.45(2)°, β = 77.44(2)°, γ = 69.75(2)°, and Z = 1 (binuclear unit). The structure was refined to final R = 0.033 for 2143 data with I ≥ 3.0σ( I ). The structure is comprised of polymeric 1-D copper(II) complexes supported by two different kinds of thiocyanate bridges. The coordination geometry around each of the metal centers is a distorted octahedron (N 3 S + O + S*). The equatorial positions are occupied by a monodentate Hmtpo ligand, coordinated via N3, two bridging thiocyanate groups coordinated in a “symmetric” end-to-end fashion, and the N-donor atom of an asymmetric end-to-end thiocyanate bridge. Finally, a water molecule and a weakly bonded S-donor atom from the asymmetric end-to-end thiocyanate bridge, with a Cu···S separation of 2.959(1) Å, occupy the apical sites. The presence of two “symmetric” thiocyanate bridges with short Cu−SCN and Cu−NCS distances of 2.402(1) and 1.938(3) Å, respectively, results in a Cu−Cu separation of 5.499(1) Å. The magnetic susceptibility data measured in the 11−290 K temperature range shows a strong antiferromagnetic coupling between the copper ions through the “symmetric” thiocyanate bridges. Fitting the data to the Bleaney−Bowers equation gives the exchange parameter 2 J = −148.2 cm - 1, which is many times higher than those previously found in other copper(II) thiocyanate bridged complexes, and g = 2.20. The unprecedented equatorial−equatorial disposition of the thiocyanate bridging entities appears to be responsible for the magnetic behavior of this compound.