A series of coordination polymers based on reduced Schiff base multidentate anions and bis(imidazole) ligands: syntheses, structures and photoluminescence

Abstract

Eleven new coordination polymers, namely, [Zn(L¹)(bbi)]·0.5H₂O (1), [Co(L¹)(bbi)]·0.5H₂O (2), [Cd(L¹)(bbi)]·0.5H₂O (3), [Zn(L²)(bbi)]·H₂O (4), [Co(L²)(bbi)]·1.25H₂O (5), [Cd(L²)(bbi)_0.5(H₂O)] (6), [Zn(L³)(bbi)]·H₂O (7), [Co(L³)(bbi)]·H₂O (8), [Cd(L³)(bbi)_0.5(H₂O)]·2H₂O (9), [Zn(HL⁴)(bbi)] (10) and [Cd(HL⁴)(bbi)(H₂O)]·1.5H₂O (11), where H₂L¹ = 4-carboxy-phenylene-methyleneamino-2-benzyl acid, H₂L² = 4-carboxy-phenylene-methyleneamino-3-benzyl acid, H₂L³ = 4-carboxy-phenylene-methyleneamino-4-benzyl acid, H₃L⁴ = 4-carboxy-phenylene-methyleneimino-3,5-dibenzyl acid and bbi = 1,4-bis(1H-imidazol-1-yl)butane, have been synthesized under hydrothermal conditions. Compounds 1–3 are isomorphous, and show 2D two-fold interpenetrating 6³-hcb networks. Compound 5 is isomorphous with 4. Compound 4 displays a 2D undulated layer structure. Adjacent layers are connected through hydrogen bonds to generate a 3D supramolecular architecture. The structure of compound 6 is an unusual 2D 2-fold parallel interpenetrating network with both polyrotaxane and polycatenane characters. 7 and 8 show 2D undulated sheet structures. The sheets are penetrated by each other to give rise to 3D polycatenations. The structure of compound 9 is an intriguing 2D self-penetrating network. Further, the π–π interactions among the L³ anions link the 2D networks into a 3D supramolecular assembly. Compound 10 displays a corrugated 2D (4,4) sheet with dangling arms. Each sheet is threaded by the dangling arms of two others, leading to an unusual 3D polythreading framework. The structure of compound 11 is a 3D (3,4)-connected framework with (4²·6)(4²·6·12³) topology. The thermogravimetric and luminescent properties have also been studied for the compounds.