Syntheses, structures and luminescent properties of zinc(ii) and cadmium(ii) coordination complexes based on new bis(imidazolyl)ether and different carboxylate ligands

Abstract

A series of mixed-ligand coordination complexes, namely [Zn(CA)₂(BIE)] (1), [Zn(OX)(BIE)]·H₂O (2), [Zn₂(m-BDC)₂(BIE)₂] (3), [Cd(m-BDC)(BIE)] (4), [Cd(5-OH-m-BDC)(BIE)] (5), [Zn(5-OH-m-BDC)(BIE)] (6), [Zn₂(p-BDC)₂(BIE)₂]·2.5H₂O (7), [Cd₃(p-BDC)₃(BIE)] (8), [Cd₃(BTC)₂(BIE)₂]·0.5H₂O (9) and [Zn(BTCA)_0.5(BIE)] (10), where CA = cinnamate anion, OX = oxalate anion, m-BDC = 1,3-benzenedicarboxylate anion, 5-OH-m-BDC = 5-OH-1,3-benzenedicarboxylate anion, p-BDC = 1,4-benzenedicarboxylate anion, BTC = 1,3,5-benzenetricarboxylate anion, BTCA = 1,2,3,4-butanetetracarboxylate anion, and BIE = 2,2′-bis(1H-imidazolyl)ether, were synthesized under hydrothermal conditions. In 1, a pair of BIE ligands bridge adjacent Zn(II) atoms to give a centrosymmetric dimer. In 2 and 3, BIE ligands connect Zn(II)–carboxylate chains to form hexagonal honeycomb 6³-hcb and square 4⁴-sql layers, respectively. In 4 and 5, m-BDC and 5-OH-m-BDC bridge Cd(II) atoms to give dimeric units, respectively, which are further linked by BIE ligands to form sql nets. In 6, the BIE ligands extend the Zn(II)–carboxylate chains into 2D sinusoidal-like sql nets. The undulated sql nets polycatenate each other in the parallel manner with DOC (degree of catenation) = 2, yielding a rare 2D → 3D parallel polycatenation net. In 7, the BIE and p-BDC ligands link the Zn(II) atoms to give a rare 3-fold interpenetrated 3-connected 10³-ths net. 8 contains unusual edge-sharing polyhedral rods formed by [Cd₃(CO₂)₆] clusters. Each rod is connected by the benzene rings of p-BDC in four directions into a simple α-Po topology. In 9, two kinds of different 2D Cd–BTC layers are alternately linked to each other by sharing Cd(II) centers to form a 3D framework, which is further linked by two kinds of BIE ligand to produce a complicated 3D polymeric structure. 10 possesses a unique (3,4)-connected 3D framework with (8³)₂(8⁵·10) topology. The structural differences described indicate the importance of carboxylate ligands and metals in the framework formation of coordination complexes. The infrared spectra, thermogravimetric and luminescent properties were also investigated in detail for the compounds.