Structures and magnetic properties of tetranuclear nickel(II) complexes with unusual μ3-1,1,3 azido bridges

Pyrazolate-based dinucleating ligands with thioether-containing chelate arms have been used for the synthesis of a family of novel tetranuclear nickel(II) complexes [L2Ni4(N-3)(3)(O2CR)](ClO4)(2) that incorporate three azido bridges and one carboxylate (R = Me, Ph). Molecular structures have been elucidated by Xray crystallography in four cases, revealing Ni-4 cores with a unique topology in which two of the azido ligands adopt an unusual mu(3)-1,1,3 bridging mode. The compounds were further characterized by mass spectrometry, IR spectroscopy, and variable-temperature magnetic susceptibility measurements. Magnetic data analyses indicate a combination of significant intramolecular ferromagnetic and antiferromagnetic exchange interactions that give rise to an overall S-T = 0 ground state. The sign and the magnitude of the individual couplings have been rationalized in the framework of the common magnetostructural correlations for end-to-end and end-on azido linkages, suggesting that these correlations also remain valid for the respective fragments of multiply bridging mu(3)-1,1,3 azido ligands.