A series of multi-dimensional metal–organic frameworks with trans-4,4′-azo-1,2,4-triazole: polymorphism, guest induced single-crystal-to-single-crystal transformation and solvatochromism

• Published in: CrystEngComm 2015-01, Vol.17 (29), p.5396-5409
• Main Authors: Ding, Bin, Wang, You You, Liu, Shi Xin, Wu, Xiang Xia, Zhu, Zhao Zhou, Huo, Jian Zhong, Liu, Yuan Yuan
• Format: Article
• Language: English
• Subjects: Color; Construction; Ligands; Metal-organic frameworks; Nanostructure; Single crystals; Three dimensional; Transformations; Two dimensional
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/C5CE00724K

In this work, a flexible multi-dentate trans-4,4'-azo-1,2,4-triazole (atrz) ligand has been employed, and a series of novel coordination polymers, namely [Fe( mu -atrz)(NCS) sub(2)(H sub(2)O) sub(2)]n (1), [Fe( mu -atrz)(NCS) sub(2)(H sub(2)O) sub(2)]n (2), {[Fe( mu -atrz)( mu -Cl)(H sub(2)O) sub(2)].Cl.H sub(2)O}n (3), {[Fe( mu -atrz)(atrz) sub(2)(H sub(2)O) sub(2)].2Br.4H sub(2 )O}n (4), {[Fe( mu -atrz)(atrz) sub(2)(H sub(2)O) sub(2)].(BF sub(4)) sub(2).2H sub(2)O} n (5), {[Cu( mu -atrz) sub(3)].(BF sub(4 )) sub(2).2H sub(2)O}n (6), {[Cu( mu -atrz) sub(3)].(BF sub(4 )) sub(2)}n (7), {[Cu sub(2)( mu sub(4)-atrz) ( mu sub(2)-OH) sub(2)(H sub(2)O) sub(4)].SO sub(4 ).3.75H sub(2)O}n (8), {[Zn( mu -atrz)(NCS) sub(2)].0.5H sub(2)O}n (9) and {[Zn( mu -atrz)(NCS) sub(2)]}n (10) have been isolated. 1 and 2 present one-dimensional (1D) polymorphic iron(ii)-triazole frameworks, in which bicycle-pedal motion of the azo moieties of atrz can be observed. Further, when different iron(ii) salts are used, 1D iron(ii)-triazole frameworks 3-5 with different 1D bridging motifs can be isolated. 6 has a 3D nano-porous Cu super(II) framework with dimensions of 11.709(1) Aa 12.201(1) Aa. Interestingly, 6 exhibits guest induced single-crystal-to-single-crystal (SC-SC) structural transformation to obtain another 3D nano-porous Cu super(II) framework 7 with dimensions of 11.621(6) Aa 16.674(1) Aa. 8 has a 2D cationic Cu super(II) framework constructed with infinite (CuO)n chains and unique mu sub(4)-bridging atrz ligands. Anion exchange experiment indicates an anion-induced structural transformation from the 3D Cu super(II) framework 6 to the 2D Cu super(II) framework 8 confirmed by PXRD patterns. Further, when Zn(NCS) sub(2) is used in the reaction system, 9 can be isolated which exhibits guest induced SC-SC transformation to obtain 10 accompanied by a color change from red (9) to pale pink (10). Variable temperature magnetic susceptibility measurements (2-300 K) reveal anti-ferromagnetic interactions between central iron(ii) ions for 1-5. The polymorphic iron(ii) frameworks, guest induced single-crystal-to-single-crystal transformation and solvatochromism also reveal great potential for the construction of flexible frameworks employing 4,4'-azo-1,2,4-triazole as basic building blocks.