Magnetic and spectroscopic properties of a series of linear homo- and heterotrinuclear clusters with asymmetric 3,4-disubstituted 1,2,4-triazoles as ligands.

The syntheses, spectroscopic and magnetic properties are described of a series of transition metal(II) tetrafluoroborate and perchlorate compounds with the asymmetric ligands 3-methyl-4-ethyl-1,2,4-triazole (metz) and 3-methyl-4-phenyl-1,2,4-triazole (mptz). A series of coordination compounds have been obtained with the general formula [M₃L₆(H₂O₆] (anion)₆(H₂O)_x (L = metz, anion = ClO₄⁻, M = Mn (x = 1.5), Fe (x = 0), Co (x = 3), Ni (x = 1.5), anion = BF₄⁻, M = Mn (x = 6), Co (x = 3), Ni (x = 0); L = mptz, anion = ClO₄⁻, M = Mn (x = 1.5), Fe (x = 0), Co (x = 1.5), Ni,Zn (x = 0), Cd (x = 5), anion = BF₄^-, M = Mn (x = 1.5, Co, Ni, Zn, Cd (x = 0). A linear trinuclear structure is proposed for these compounds, in which the metal (II) ions are linked to each other by two pairs of three N1, N2 bridging 1,2,4-triazole ligands. The coordination sphere around the terminal metal (II) ions is completed by water molecules. The two unequal coordination sites present in these compounds allow a route to the synthesis of heterotrinuclear species. Pure samples of the heterotrinuclear Mn(II)-Ni(II)-Mn(II) compounds have been obtained. The magnetic susceptibilities of the compounds have been recorded and were fitted to theoretical expressions for linear trimers. For all compounds the interaction between neighbouring metal(II) ions appeared to be antiferromagnetic and rather weak. Fitting of the magnetic susceptibility for the heteronuclear MnNiMn compound results in the values; J = −1.88 cm⁻¹, g_Mn = 1.99 andg_Ni = 2.30 (based on the spin Hamiltonian): ∧H = −2J[∧S_Mn−a · ∧S_Ni) + (∧S_Mn−b · ∧_SNi)).