2,2′-Bipyrimidine (bipym)-bridged dinuclear complexes. Part 4. Synthesis, crystal structure and magnetic properties of [CO₂(H₂O)₈(bipym)][NO₃]₄, [CO₂(H₂O)₈(bipym)][SO₄]₂·2H₂O and [CO₂(bipym)₃(NCS)₄]

Abstract

Three new dinuclear cobalt(II) complexes [Co2(H2O)8(bipym)][NO3]41, [Co2(H2O)8(bipym)]-[SO4]2·2H2O 2 and [Co2(bipym)3(NCS)4]3(bipym = 2,2′-bipyrimidine) have been synthesised and their crystal structures determined by X-ray diffraction methods. Crystals of 1 and 3 are triclinic, space group P, Z= 1 with a= 7.511(1), b= 8.844(2), c= 9.514(1)Å, α= 79.67(1), β= 88.54(1) and γ= 82.46(1)° for 1 and a= 9.045(2), b= 9.149(2), c= 11.621(2)Å, α= 74.73(2), β= 80.67(2) and γ= 61.17(1)° for 3. Crystals of 2 are monoclmic, space group P21/c with a= 8.115(1), b= 11.596(2), c= 11.823(3)Å, β= 91.57(2)° and Z= 2. The structures of 1 and 2 are made up of dinuclear cations [Co2(H2O)8(bipym)]4+ with nitrate counter ions for 1 and water of crystallization and sulfate groups for 2. The structure of 3 consists of dimeric neutral [Co2(bipym)3(NCS)4] units. Bipyrimidine bridges the cobalt atoms in this series of complexes in a bis(chelating) fashion and a crystallographically imposed inversion centre is located halfway between its two pyrimidyl rings. It is present also as a terminal ligand in 3. The two equivalent cobalt atoms of 1and 2 are each bound to four water oxygens and two cis nitrogens of bipym in a slightly distorted octahedral environment. Each cobalt atom in 3 is bound to six nitrogen atoms belonging to two thiocyanate groups in cis position and to two bipym ligands, one terminal and the other bridging. The intramolecular metal–metal separation varies between 5.761(1) and 5.942(2)Å. The magnetic properties of 1–3 have been investigated in the temperature range 4.2–300 K. They all exhibit antiferromagnetic exchange with susceptibility maxima at 13.0–16.4 K. Fits of the magnetic data through the Lines model and the simpler lsing spin-only formalism are compared.