Ferromagnetic CuII4, CoII4, and NiII6 Azido Complexes Derived from Metal-Assisted Methanolysis of Di-2,6-(2-pyridylcarbonyl)pyridine

Abstract

Reaction of copper(II) perchlorate with di-2,6-(2-pyridylcarbonyl)pyridine (pyCOpyCOpy, dpcp) in the presence of sodium azide yields complex [Cu(4)(N(3))(2){pyC(OMe)(O)pyC(OMe)(O)py}(2)(MeOH)(2)](ClO(4)) x 2 MeOH (1 x 2 MeOH), which crystallizes in the monoclinic P2(1)/c space group. Similar reaction of cobalt(II) nitrate yields complex [Co(4)(N(3))(2)(NO(3))(2){pyC(OMe)(O)pyC(OMe)(O)py}(2)] x 0.5 MeOH (2 x 0.5 MeOH) which crystallizes in the monoclinic I2/m space group. Reaction of nickel(II) perchlorate yields complex [Ni(6)(CO(3))(N(3))(6){pyCOpyC(O)(OMe)py}(3)(MeOH)(2)(H(2)O)][Ni(6)(CO(3))(N(3))(6){pyCOpyC(O)(OMe)py}(3) (MeOH)(3)](ClO(4))(2) x 1.8 MeOH (3 x 1.8 MeOH), which crystallizes in the triclinic P1 space group, as a mixed salt of two similar Ni(II)(6) cations, differing only in one terminally coordinated solvate molecule. The cation of 1 consists of four Cu(II) ions in a rhombic topology, while complex 2 consists of four Co(II) ions in a defective double cubane topology. Each of the two cations in 3 contains six Ni(II) 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 Cu(II) 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-N(azido)-M and M-O(alkoxo)-M angles between 90-105 degrees. The magnetic susceptibility data of 1 and 3 were analyzed with appropriate spin Hamiltonian models (H =- 2J(ij)S(i)S(j) 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.