Carbonato-bridged heteronuclear NiII2LnIII2 (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu) complexes synthesized by fixation of atmospheric CO2 – Structural and magnetic studies

A series of carbonato-bridged heteronuclear NiII2LnIII2 complexes 2[(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·9H2O·8MeOH (Ln = Tb (1), Dy (2), Ho (3), Er, (4)), [(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·2H2O·4MeOH (Ln = Tm (5)) and [(μ4-CO3)2{NiLn(L)(MeOH)(CH3COO)}2]·4MeOH (Ln = Yb (6), Lu(7)) with N,N′-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine (L) are reported. The complexes were obtained by a one-pot reaction with spontaneous fixation of atmospheric CO2 into the coordination species during crystallization process. In each complex the NiII2LnIII2 metal core has a similar topology. The hexadentate Schiff base ligands chelate the Ni(II) and Ln(III) ions forming two binuclear units, that are linked by two CO32− ions giving a carbonato bridged (μ4-CO3)2{NiIILnIII}2 structures. Ferromagnetic interactions between 3d–4f metal centers have been observed for compounds 1 and 2. In complexes 3–6 both the isotropic exchange as well as of thermal depopulation of mJ sublevels and magnetic anisotropy are observed. In compound 7, due to the nonmagnetic nature of the ground state of Lu(III) ions, only a weak antiferromagnetic interaction between Ni(II) ions occurs.