title: Supramolecular structures and columnar mesophase induction in nondiscoid pyrazoles by complexation to rhodium(I).
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.
authors.affiliation: Departamento de Química OrgAnica, Facultad de Ciencias-Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain. rgimenez@unizar.es
authors.forename: Raquel
authors.initials: R
authors.lastname: Giménez
authors.forename: Anabel
authors.initials: A
authors.lastname: Elduque
authors.forename: José Antonio
authors.initials: JA
authors.lastname: López
authors.forename: Joaquín
authors.initials: J
authors.lastname: Barbera
authors.forename: Emma
authors.initials: E
authors.lastname: Cavero
authors.forename: Ignacio
authors.initials: I
authors.lastname: Lantero
authors.forename: Luis A
authors.initials: LA
authors.lastname: Oro
authors.forename: José Luis
authors.initials: JL
authors.lastname: Serrano