Unprecedented three-dimensional 10-connected bct nets based on trinuclear secondary building units and their magnetic behavior

Abstract

Three unprecedented metal-organic frameworks [M₃(tib)₂(CTC)₂]·nH₂O [M = Co(II), n = 2 (1); Mn(II), n = 2.92 (2) and Ni(II), n = 2 (3)] based on M₃(OCO)₆ trinuclear secondary building units (SBUs) have been successfully synthesized by reactions of corresponding metal salt with mixed flexible triacid of 1,3,5-cyclohexanetricarboxylic acid (H₃CTC) and rigid imidazol-containing ligand 1,3,5-tris(1-imidazolyl)benzene (tib) under hydrothermal conditions. In 1–3, the CTC³⁻ ligands link the SBUs to form two-dimensional (2D) ‘hxl’ (hexagonal lattice) networks and the tib ligands further pillar the 2D layers leading to the formation of three-dimensional frameworks, which are firstly reported uninodal 10-connected bct nets. The magnetic measurements showed that 1 and 3 exhibit ferromagnetic coupling interactions between the adjacent metal centers with g = 2.63, D = 66.69 cm⁻¹, zJ = 0.68 cm⁻¹ and g = 2.22, J = 6.25 cm⁻¹, zj′ = −0.053 cm⁻¹, respectively, while 2 has antiferromagnetic interaction between the Mn(II) ions with g = 2.01, J = −0.57 cm⁻¹, zj′ = 1.3 × 10⁻⁴ cm⁻¹.