PREPARATION AND CHARACTERIZATION OF PYRIDINIUM-N-CARBOXYLATE TRIOXOCHROMATE(VI) (N=3, 4) AND PYRIDINIUM-4-CARBOXYLIC PYRIDINE-4 CARBOXYLATE TRIOXOCHROMATE(VI) HEMIHYDRATE

摘要

Three chromium (VI) compounds have been synthesized at room temperature by reaction of CrO3 with pyridinium carboxylic acids in water. An X-ray diffraction study of pyridinium-3-carboxylate trioxochromate, [3-HNicCrO(3)] (1), indicates crystallization in the triclinic system, space group P (1) over bar (No. 2) with Z=2 and lattice parameters a=7.548(3) Angstrom, b=6.593(3) Angstrom, c=7.820(3) Angstrom, alpha=90.01(2)degrees, beta=91.65(2)degrees, gamma=89.91(2)degrees and V=389.0(3) Angstrom(3) at 25(2)degrees C. The chromium atom presents a distorted tetrahedral coordination, with the three Cr-O (terminal oxygen) bond lengths ranging from 1.588(6) Angstrom to 1.603(6) Angstrom, and the fourth Cr-O bond being 1.881(4) Angstrom long. The symmetry is C-s, all atoms lying in the same plane with the exception of two terminal oxygens. 3-HNicCrO(3) molecules interact by hydrogen bonds. This experimental work has been complemented with a theoretical study to discuss geometries, relative energies for the two possible isomers of compound 1, IR and UV-visible spectroscopic data, and electronic analyses. Powder data for pyridinium-4-carboxylic pyridine-4-carboxylate trioxochromate hemihydrate, [4-HNic] [4-NicCrO(3)] (2), and pyridinium-4-carboxylate trioxochromate, [4-HNicCrO(3)] (3), are also reported. [References: 69]