Divalent Metal 2,5-Thiophenedicarboxylate Coordination Polymers with the Conformationally Flexible Bis(4-pyridyl-formyl)homopiperazine Ligand

Divalent metal coordination polymers containing the rigid 2,5-thiophenedicarboxylate (tdc) ligand and the conformationally flexible dipyridylamide ligand bis(4-pyridylformyl)homopiperazine (bpfh) show different layer topologies and chirality. As determined by single-crystal X-ray diffraction, {[Cd(tdc)(bpfh)(H2O)]·3H2O}n (1) shows a twofold parallel interpenetrated centrosymmetric (4,4) layered grid structure. {[Zn(tdc)(bpfh)]·H2O}n (2) exhibits a similar system of twofold interpenetrated (4,4) grid-like layers, but in contrast to 1, it crystallizes in an acentric space group. {[Ni2(tdc)2(bpfh)2(H2O)]·2H2O}n (3) possesses {Ni2(μ-H2O)(OCO)2} dimeric units connected into a doubled layer motif by the full span of the tdc and bpfh ligands. Weak antiferromagnetic coupling is observed within the dimeric units in 3 [g = 2.172(6) and J = –0.79(1) cm–1]. Compounds 1 and 2 undergo blue-violet fluorescence upon ultraviolet irradiation; the cadmium derivative 1 shows potential as a sensor for the solution-phase detection of nitrobenzene although coordination polymer exfoliation likely occurs. Thermal decomposition behavior of the three new phases is also discussed.
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