Design, Synthesis And Property Of Zn(Ⅱ)/Mn(Ⅱ)Coordination Polymers

In recent years, metal-organic coordination networks have attracted considerableinterest because of their diverse structures and potential applications inphotoluminescence, magnetic, nonlinear optical materials, catalysis, ion exchange,semiconductor, molecular recognition, selective guest inclusion and so on. Success inproducing such networks depends on a good understanding of the connection betweenthe organic ligands and metal ions.The bridging ligands with multi-carboxylic and multi-N-donor ends are most widelyinvestigated. Whereas in recent years, a group of new bridging ligands, such as poly-imidazole/pyrazole, polyphosphines and N-P or N-O hybrids, have been designed andsynthesized in order to explore the different coordination abilities and the diversemolecular conformations. In this thesis, two flexible polyimidazol ligands,1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb),1,3-bis(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bitmb) and a rigid dioxo-ligand4,4′-bipyridine-N,N′-dioxide (BPNO) were employed to react with Zn(II) and Mn(II)salts in the presence of several dicarboxylic ligands under hydrothermal conditions. Aseries of coordination polymers were isolated therefrom and their properties on cationexchange, thermal stability and photoluminescence investigated.1. Reactions of Zn(NO3)2·6H2O with titmb in the presence of1,4-H2BDC or1,3-H2BDC (H2BDC=benzenedicarboxylic acid) afforded two coordination polymers,namely,[Zn3(titmb)2(1,4-BDC)3(H2O)6](1) and [Zn2(titmb)(1,3-BDC)2(H2O)](2).Similar reactions of Zn(NO3)2·6H2O with bitmb and1,4-H2BDC gave rise tocoordination polymer [Zn2(bitmb)2(1,4-BDC)2](3). Compound1has a1D linear chainformed from linking24-membered [Zn2(titmb)2] metallomacrocycles and[Zn(1,4-BDC)(H2O)2] units via imidazolyl groups of titmb ligands. Compound2has a 2D network assembled from connecting spiral [Znn(1,3-BDC)n] chains with titmblinkers, while compound3also has a2D network formed by linking24-membered[Zn2(bitmb)2] metallomacrocycles via1,3-BDC bridges. The ligands titmb and bitmb incompounds1-3exhibit uncommon cis-trans-trans and cis-trans as stable conformationsbecause of they are less bulky. The emission maxima of compounds1and2arered-shifted relative to that of titmb, which may be ascribed to the zinc(II)-to-ligandcharge transfer (MLCT) with electrons being transferred from the Zn(II) to imidazolylgroups. Intriguingly, the emission peak of compound3is blue-shifted related to that ofbitmb, which may be tentatively assigned to the π–π*intraligand fluorescence due to itsclose resemblance to the emission band of the bitmb ligand. The thermogravimetricanalyses (TGA) under the nitrogen atmosphere was performed in order to verify thethermal stability of compounds1-3. The first step loss corresponding to the coordinatedand lattice water molecules. This is followed by the loss of the corresponding carboxylgroup.2. Reactions of Mn(NO3)2/Mn(OAc)2·4H2O with BPNO and1,4-H2BDC/1,3-H2BDC resulted in three coordination polymers, viz:Mn2(1,4-NDC)2(BPNO)2(H2O)6·(BPNO)3(1,4-NDC=1,4-naphthalic acid)(4,3D layernetwork), Mn2(BPNO)(1,4-NDC)2·MeOH (5,3D layer network), andMn2(NH2-BDC)2(BPNO)(DMF)2(NH2-BDC=5-aminoisophthalic acid,2D layernetwork)(6). In the case that the carboxylatic acids were absent, reactions of BPNO andMn(II) salts gave [Mn(BPNO)2(μ-O)]2·2H2O (7) and [Mn(BPNO)2(μ-O)]·2MeOH (8)with two different types of solvents in the pore. Compound4formed by linking[Mn(BPNO)(H2O)3] units via1,4-NDC bridges, with one free BPNO side. Compound4was found to absorb equivmolar transition metal ions, such as Zn2+, Ni2+, Cd2+, Cu2+and Pd2+.