A ferromagnetically coupled single hydroxido bridged tetranuclear nickel(II) Schiff base complex incorporating a Ni4O4 cubane core: Crystal structure and magnetic study

• Published in: Polyhedron 2013-09, Vol.61, p.73-79
• Main Authors: Shit, Shyamapada, Nandy, Madhusudan, Rosair, Georgina, Gómez-García, Carlos J., Borras Almenar, Juan J., Mitra, Samiran
• Format: Article
• Language: English
• Subjects: Characterization; Cubane core; Ferromagnetic coupling; Nickel(II) Schiff base complex; Single μ3-hydroxido bridge; X-ray structure
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2013.05.029

The ligating properties of a multidentate Schiff base ligand have been explored to synthesize a new tetranuclear nickel(II) complex incorporating a Ni4O4 cubane moiety. The presence of single μ3-hydroxido bridged oxygen occupying one vertex of the Ni4O4 cubane core is rare in Ni4O4 cubanes. The magnetic properties reveal the presence of ferromagnetic interactions between the nickel(II) atoms in the cluster, which have been fitted with two different exchange pathways (g=2.058, J1=+17.2cm−1 and J2=+6.6cm−1), in agreement with previous magneto-structural correlations in doubly oxido-bridged nickel(II) complexes. The new tetranuclear nickel(II) complex [Ni4(OH)(L)(HL)2(CH3OH)1.5(H2O)1.5]·9H2O (1) has been synthesised by the reaction of NiCl2·6H2O and the Schiff base ligand H3L (H3L=(CH3O)(OH)C6H3CHN–C(CH3)(CH2OH)2), prepared by the 1:1 condensation of 2-amino-2-methyl-1,3-propanediol and o-vanillin, and characterized by different physicochemical methods. Single crystal X-ray structural determination identifies a Ni4O4 cubane moiety as the central part of the complex unit. The presence of a single μ3-hydroxido bridged oxygen occupying only one vertex of the Ni4O4 cubane core is rare in Ni4O4 cubanes (ca. 5% of occurrence). Structural analysis also reveals two similar alkoxido oxygen atoms of the Schiff base coordinating the metals in two different modes; one in the μ3-bridging mode whilst the other binds in a monodentate fashion. The metal centers display distorted octahedral geometries with two different coordination environments. The magnetic properties reveal the presence of ferromagnetic nickel(II)–nickel(II) interactions in the cluster with two different exchange pathways. The magnetic data can be fitted to a Ni4O4 cubane model with g=2.058, J1=+17.2cm−1 and J2=+6.6cm−1. Isothermal magnetization measurements confirm the S=4 spin ground state. Both J values agree with previous magneto-structural correlations in doubly oxido-bridged nickel(II) complexes.