Templated synthesis of Ni(ii) complexes of unsymmetrical Schiff base ligands derived from 1,3-diamino-2-propanol: structural diversity and magnetic properties†
Abstract
An attempt at the synthesis of complexes of unsymmetrical Schiff base ligands derived from 1,3-diamino-2-propanol, o-hydroxyacetophenone and salicylaldehyde or o-vanillin by a Ni(II) templated method resulted in the isolation of mononuclear [NiL1] (1) and tetranuclear [Ni4L22(μ3-OCH3)2(H2O)2]·10CH3OH (2) where H3L1 = N-(α-methylsalicylidene)–N′-(salicylidene)–1,3-diamino-2-propanol, and H3L2 = N-(3-methoxysalicylidene)–N′-(α-methylsalicylidene)–1,3-diamino-2-propanol. Complex 1 on reaction with Ni(NO3)2 yielded a hexa-nuclear complex, [Ni2Ni4L12L32(NO3)2]·23CH3OH (3). Ligand H2L3 was formed in situ by partial hydrolysis of H3L1 during the synthesis of 3. Single crystal X-ray diffraction studies revealed a square planar geometry of Ni(II) in complex 1 and a hexa-coordinated distorted octahedral geometry of all four Ni(II) centres, forming a defective dicubane core in complex 2. In hexa-nuclear complex 3, two square planar Ni(II) centres are connected to a distorted cubane core, formed by four octahedral Ni(II). Temperature dependent molar magnetic susceptibility measurements illustrated overall ferromagnetic coupling among the Ni(II) in complex 2 with exchange coupling parameters, J1 = 10.9(2) cm−1, J2 = −3.1(1) cm−1, J3 = 13.8(8) cm−1 and g = 2.200(1) and predominating anti-ferromagnetic coupling interactions among the four paramagnetic Ni(II) in the cubane core of complex 3 with exchange coupling parameters, J1 = −1.99(1) cm−1, J2 = 2.00(1) cm−1, J3 = −1.93(1) cm−1 and g = 2.359(1). Cyclic voltammetry measurements showed quasi-reversible and irreversible Ni(II)/Ni(I) couples for complexes 1 and 2, respectively, whereas complex 3 showed one irreversible and one quasi reversible reduction process for the octahedral and square planar Ni(II) centres, respectively.