Self-assembly, crystal structures, and properties of metal-2-sulfoterephthalate frameworks based on [M4(μ3-OH)2]6+ clusters (M = Co, Mn, Zn and Cd)

Abstract

Hydro- and solvo-thermal reactions of d-block metal ions (Mn²⁺, Co²⁺, Zn²⁺ and Cd²⁺) with monosodium 2-sulfoterephthalate (NaH₂stp) form six 3D coordination polymers featuring cluster core [M₄(μ₃-OH)₂]⁶⁺ in common: [M₂(μ₃-OH)(stp)(H₂O)] (M = Co (1), Mn (2) and Zn (3)), [Zn₂(μ₃-OH)(stp)(H₂O)₂] (4), [Zn₄(μ₃-OH)₂(stp)₂(bpy)₂(H₂O)]·3.5H₂O (5) and [Cd₂(μ₃-OH)(stp) (bpp)₂]·H₂O (6) (stp = 2-sulfoterephthalate, bpy = 4,4′-bipyridine and bpp = 1,3-di(4-pyridyl)propane). All these coordination polymers were characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetric and elemental analysis. Complexes 1–3 are isostructural coordination polymers with 3D frameworks based on the chair-like [Zn₄(μ₃-OH)₂]⁶⁺ core and the quintuple helixes. In complex 4, there exist double helixes in the 3D framework based on the chair-like cluster cores. Complex 5 possesses a 2-fold interpenetration structure constructed from boat-like cluster core and the bridging ligands stp and bpy. For complex 6, the chair-like cluster cores and stp ligands form a 2D (4,4) network which is further pillared by bpp linkers to a 3D architecture. Magnetic studies indicate that complex 1 exhibits magnetic ordering below 4.9 K with spin canting, and complex 2 shows weak antiferromagnetic coupling between the Mn(II) ions with g = 2.02, J_wb = −2.88 cm⁻¹, J_bb = −0.37 cm⁻¹. The fluorescence studies show that the emissions of complexes 3–6 are attributed to the ligand π–π* transition.