Ferromagnetic Cu^II₄, Co^II₄, and Ni^II₆ Azido Complexes Derived from Metal-Assisted Methanolysis of Di-2,6-(2-pyridylcarbonyl)pyridine

Reaction of copper(II) perchlorate with di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) in the presence of sodium azide yields complex [Cu4(N3)2{pyC(OMe)(O)pyC(OMe)(O)py}2(MeOH)2](ClO4)·2MeOH (1·2MeOH), which crystallizes in the monoclinic P21/c space group. Similar reaction of cobalt(II) nitrate yields complex [Co4(N3)2(NO3)2{pyC(OMe)(O)pyC(OMe)(O)py}2]·0.5MeOH (2·0.5MeOH) which crystallizes in the monoclinic I2/m space group. Reaction of nickel(II) perchlorate yields complex [Ni6(CO3)(N3)6{pyCOpyC(O)(OMe)py}3(MeOH)2(H2O)][Ni6(CO3)(N3)6{pyCOpyC(O)(OMe)py}3 (MeOH)3](ClO4)2·1.8MeOH (3·1.8MeOH), which crystallizes in the triclinic P1̅ space group, as a mixed salt of two similar NiII6 cations, differing only in one terminally coordinated solvate molecule. The cation of 1 consists of four CuII ions in a rhombic topology, while complex 2 consists of four CoII ions in a defective double cubane topology. Each of the two cations in 3 contains six NiII ions in a cyclic topology, adopting a chair conformation. In 1 and 2 the ligand has undergone complete methanolysis and full deprotonation, yielding its dianionic bis-gem-diol form. In 3 it has undergone only partial methanolysis. All complexes exhibit ferromagnetic intramolecular interactions. Ferromagnetism in 1 is caused by the structural constraints imposed by the {pyC(OMe)(O)pyC(OMe)(O)py}2− ligand on the CuII ions, while in the case of 2 and 3 it is the result of the combined effect of the end-on azido and alkoxo bridges of dpcp, which form M−Nazido−M and M−Oalkoxo−M angles between 90−105°. The magnetic susceptibility data of 1 and 3 were analyzed with appropriate spin Hamiltonian models (Ĥ =− 2JijŜiŜj formalism). For 1, a solution considering J = +26.8 cm−1 along the periphery of the rhombus was found. In 3 it was found that alternating exchange couplings of J = +6.1 cm−1 and J′ = +27 cm−1 were operative along the periphery of the ring.