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Issue 45, 2013

Two new polar coordination polymers with diamond networks: interpenetration and thermal phase transition

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Abstract

Two new polar coordination polymers, [Cu(Hmpc)2] (1) and [Cu2(mpc)2(DMA)] (2), were synthesized by solvothermal reactions of a ligand 3,5-dimethyl-1H-pyrazole-4-carboxylic acid (H2mpc) with Cu(NO3)2. Single-crystal X-ray analysis reveals that 1 crystallizes in the orthorhombic, polar space group Fdd2. Each square-planar coordinated Cu2+ ion is linked to four adjacent Cu2+ ions by mono-deprotonated Hmpc ligands, resulting in a severely distorted 4-connected diamond network, inside which the methyl groups of the ligands are densely packed. In 2, non-centrosymmetric binuclear Cu2+ units serve as 4-connecting nodes, forming a non-porous polar structure consisting of 2-fold-interpenetrated diamond networks. A thermal structural phase transition was detected in 2 at around 323 K. At 298 K, 2 crystallizes in the tetragonal chiral space group P41 (), with a = 10.9931 (6) Å, c = 18.0850(9) Å, and Z = 4, whereas at a higher temperature (438 K) it is transferred to the tetragonal non-centrosymmetric space group P42nm (), with a = 10.9857(5) Å, c = 9.1031(9) Å, and Z = 2. By repeating in situ single-crystal X-ray diffraction, this phase transition was found to be reversible between a non-twinning non-centrosymmetric crystal () and a racemic-twinning chiral crystal (). The symmetry of the diamond network was increased from C1 to D2d in the heating process, so that two fold interpenetrated networks become strictly parallel along the c-axis at about 323 K, and the c-axis was halved in . At the same time, 2-fold disordered coordinated DMA molecules in were found to be 8-fold disordered in . According to aizu notation, 2 can be classified as 4mmF4 species, which are potentially secondary ferroic.

Graphical abstract: Two new polar coordination polymers with diamond networks: interpenetration and thermal phase transition

Supplementary files

Article information


Submitted
12 Jun 2013
Accepted
23 Jul 2013
First published
29 Jul 2013

CrystEngComm, 2013,15, 9530-9536
Article type
Paper

Two new polar coordination polymers with diamond networks: interpenetration and thermal phase transition

X. Qi, C. Zhang, B. Wang, W. Xue, C. He, S. Liu, W. Zhang and X. Chen, CrystEngComm, 2013, 15, 9530 DOI: 10.1039/C3CE41111G

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