Magneto-structural studies on a number of doubly end-on cyanate and azide bridged dinuclear nickel(II) complexes with {N₃O} donor Schiff base ligands

Two new doubly mu(1,1)-N-3 bridged (1 and 3) and six new doubly mu(1,1)-NCO bridged Ni-II complexes (2, 4-8) with six different N3O donor Schiff base ligands have been synthesized and magneto-structurally characterized. All these neutral complex molecules are isostructural and constitute edge sharing bioctahedral structures. Magnetic studies revealed that all these complexes exhibit ferromagnetic interaction through bridging pseudohalides with ferromagnetic coupling constant J being significantly higher for azide-bridged complexes than that of the cyanate analogues. This is consistent with the literature reported data and also the presence of polarizable p systems and two different N and O donor atoms in cyanate ion, rendering it a poor magnetic coupler in comparison to azide analogues. Although, the magneto-structurally characterized doubly mu(1,1)-N-3 bridged Ni-II complexes are abundant, only few such complexes with mu(1,1)-bridging NCO- ions are reported in the literature. Remarkably, addition of these six new examples in this ever-growing series of doubly mu(1,1)-NCO bridged systems gives us an opportunity to analyse the precise magneto-structural correlation in this system, showing a general trend in which the J value increases with an increase in bridging angles. Therefore, the high degree of structural and magnetic resemblances by inclusion of six new examples in this series is the major achievement of the present work. An elaborate DFT study was performed resulting in magneto-structural correlation showing that nature and value of the J-parameter is defined not only by Ni-N-b-Ni bond angles, but an important role is also played by the Ni1-Ni2-N-b-X-t dihedral angle (N-b and X-t are bridging N and terminal N or O atom of bridging ligands, respectively).