The [Cu2(O2CMe)4(btd)2] complex as a bridging unit: preparation, characterisation, X-ray structure and magnetism of the 2D coordination polymer {[Cu6(O2CMe)8(OMe)4(btd)2]}n (btd=2,1,3-benzothiadiazole)

A systematic investigation of the [Cu2(O2CMe)4(H2O)2]/btd reaction system is described, where btd=2,1,3-benzothiadiazole. Reaction of [Cu2(O2CMe)4(H2O)2] with 5–8 equiv. of btd in both MeCN and MeOH yields [Cu2(O2CMe)4(btd)2] (1) in 40–50% yields. Treatment of [Cu2(O2CMe)4(H2O)2] with 1.4 or 0.7 equiv. of btd in MeOH leads to the precipitation of the polymeric compound {[Cu6(O2CMe)8(OMe)4(btd)2]} (2) in 82% yield. Reaction of 1 with two equivalents of [Cu2(O2CMe)4(H2O)2] in MeOH under reflux provides an additional route to 2. The structure of 1 consists of centrosymmetric dinuclear [Cu2(O2CMe)4(btd)2] molecules of the paddle-wheel cage type. The two CuII ions are bridged by four η1:η1:μ2 acetates, while a monodentate btd is at the apex of the square pyramid of each metal centre. The 2D structure of 2 consists of chains of tetranuclear, planar Cu4(OMe)4(O2CMe)4 repeating units running along the a axis, which are connected along the cell body diagonal via Cu2(O2CMe)4(btd)2 paddle-wheel dinuclear units. The btd molecules behave as bidentate bridging ligands. Within the tetranuclear units, each CuII ion is connected via two acetate bridges with one neighbouring CuII ion and via two methoxo bridges with the other neighbouring CuII ion; intertetranuclear linking is provided by two monoatomic acetate bridges. The results of solid state magnetic susceptibility studies are described for complex 2 in the temperature range 3–300 K. The results reveal antiferromagnetic exchange interactions between the CuII ions. The complicated structure of 2 does not permit an exact treatment for the determination of the various exchange interactions. However, an approximate 3-J magnetic model was constructed, resulting in an excellent fit. An orbital interpretation of the J-trend derived is also attempted.