Supramolecular structures and columnar mesophase induction in nondiscoid pyrazoles by complexation to rhodium(I) |
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Authors: | Giménez Raquel Elduque Anabel López José Antonio Barbera Joaquín Cavero Emma Lantero Ignacio Oro Luis A Serrano José Luis |
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Institution: | Departamento de Química OrgAnica, Facultad de Ciencias-Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain. rgimenez@unizar.es |
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Abstract: | Several new cis-RhCl(CO)2(Ln)] complexes have been prepared using different polycatenar pyrazole ligands (Ln) in order to obtain columnar liquid crystalline arrangements. The topology of the ligand plays an essential role, and a mesophase is induced at room temperature from a nonmesogenic pyrazole only when it is symmetrically substituted with six decyloxy chains. The single-crystal structure of a methoxy-substituted analogue, 3,5-bis(3,4,5-trimethoxyphenyl)pyrazole, is formed by globular tetrameric structures held together by H-bonding. However, parallel dimers are present in the corresponding cis-chlorodicarbonylrhodium(I) complex, a situation that explains the induction of a columnar mesophase in the decyloxy-substituted complex. The XRD pattern of the mesophase is consistent with a hexagonal symmetry in which the columns are formed by molecules assembled in an antiparallel mode. The crystal-to-mesophase transition was also detected by spectroscopic techniques as a shift in the IR carbonyl stretching bands and the appearance of a charge-transfer band in the absorption spectrum with thermochromic behavior. |
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