Heterometallic Oximato-Bridged Linear Trinuclear NiII-MIII-NiII (MIII = Mn, Fe, Tb) Complexes Constructed with the fac-O3 [Ni(HL)3]- Metalloligand (H2L=pyrimidine-2-carboxamide oxime): A Theoretical and Experimental Magneto-Structural Study

Three oximato-bridged linear trinuclear heterobimetallic complexes of formula [{Ni(HL)3}2M]X center dot nS [M = Mn3+, X = ClO4, n = 9, S = H2O (1); M = Fe3+, X = ClO4, n = 9, S = H2O (2); M = Tb3+, X = NO3, n = 11, S = CH3OH (3); H2L = pyrimidine-2-carboxamide oxime] were prepared from the reaction of the in situ generated [Ni(HL)3] complex with the corresponding M2+ salts for 1 and 2 (which are oxidized to M3+ during the course of the reaction) and the Tb3+ salt for 3. The heterometallic trinuclear [NiMNi]+ cationic entities are formed by the coordination of two [Ni(HL)3] metalloligands to the central M3+ metal ion through three facially arranged oxime oxygen atoms belonging to the H2L ligands. Therefore the HL ligand acts in a 2-N1,N8:-O9 bidentate bridging mode. Compounds 1 and 2 exhibit antiferromagnetic interactions, whereas for 3 the spin-orbit coupling and the effects of the crystal-field on the 2S+1LJ states of the Tb3+ ion encumbers the determination of the nature of the magnetic exchange interaction between the Ni2+ and Tb3+ ions through the oximato bridging group. DFT calculations carried out on the solid-state structures predict J values that match well with the experimental ones. The experimental J values were compared with those observed for analogous NiMNi complexes and their differences justified on the basis of structural parameters such as the NiNOM torsional angle and the distortion from the OC-6 octahedral to the TPR-6 trigonal prismatic geometry.