Solvent-controlled three families of Zn( ii ) coordination compounds: synthesis, crystal structure, solvent-induced structural transformation, supramolecular isomerism and photoluminescence

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 44; no. 13; pp. 6052 - 6061
• Main Authors: Han, Lu-Lu, Hu, Tuo-Ping, Mei, Kai, Guo, Zhi-Min, Yin, Chen, Wang, Ya-Xin, Zheng, Jun, Wang, Xing-Po, Sun, Di
• Format: Journal Article
• Language: English
• Published: England 07.04.2015
• Subjects: Coordination compounds; Networks; Photoluminescence; Self assembly; Solvents; Symbols; Topology; Transformations
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/C4DT03868A

This work reports the assembly, topological structure, supramolecular isomerism and luminescence of three solvent-controlled families of coordination compounds, [Zn(bpz) 2 (H 2 O) 3 ·2Hpta] ( 1 ), [Zn(bpz)(pta)] n ( 2 ), [Zn(bpz)(tpa)(H 2 O)] n ( 3 ), [Zn(bpz)(tpa)·4H 2 O] n ( 4 ), and [Zn(bpz)(npa)·H 2 O] n ( 5 and 6 ) (bpz = 3,3′,5,5′-tetramethyl-4,4′-bipyrazole, H 2 pta = phthalic acid, H 2 tpa = terephthalic acid, H 2 npa = 4-nitrophthalic acid). The six transition metal compounds reported in this study were definitely characterized by X-ray crystallography to reveal how networks with different topologies are constructed around the same four-connected metal centers. Compound 1 is a 0D discrete molecule, in which Zn( ii ) is in a trigonal bipyramidal coordination geometry, whereas the guest Hpta − as counteranion is hydrogen-bonded with the [Zn(bpz) 2 (H 2 O) 3 ]. In compound 2 , the Zn( ii ) center is linked by two bpz and two pta; thus, a 4-connected dia network with the point symbol {6 6 } is formed. In 3 , the Zn( ii ) center is six-coordinated, but in fact it is also a 4-connected node in the whole network due to the terminal aqua ligand and bidentate chelating carboxylate group thus, the resultant network has a 4-connected cds topology with the point symbol {6 5 ·8}. Compound 4 exhibits a chiral two-fold interpenetrated 4-connected qtz network with the point symbol {6 4 ·8 2 }. Compounds 5 and 6 are a pair of genuine supramolecular isomers with identical 4-connected dia topology. The three families of compounds, namely, 1 / 2 , 3 / 4 , and 5 / 6 , are structurally controlled by the solvent systems H 2 O/CH 3 OH–H 2 O, H 2 O/DMF–CH 3 OH, and CH 3 OH–H 2 O/CH 3 CN–H 2 O, respectively. Except for the discrete molecule 1 , the other five compounds have the same 4-connected coordination networks, but with different topologies ranging from dia ( 2 , 5 , 6 ), cds ( 3 ) to qtz ( 4 ), suggesting the important influences that the linkage orientations of the ligand and different geometries of the 4-connected node exert in self-assembly. Interestingly, discrete 1 can be irreversibly transformed from a 0D discrete molecule to an infinite 3D structure ( 2 ) by heating it in CH 3 OH–H 2 O solvent, indicating a solvent-induced structural transformation. In addition, results about thermal stabilities and photoluminescence spectra are also discussed in detail.