Crystal spectra of chromium tris-acetyl acetone
01 Oct 1960-Journal of Chemical Physics (American Institute of Physics)-Vol. 33, Iss: 4, pp 1266-1266
About: This article is published in Journal of Chemical Physics.The article was published on 1960-10-01. It has received 10 citations till now. The article focuses on the topics: Chromium.
TL;DR: The spin Hamiltonians of Cr(en)33+ and trans−CrCl2(en)-2+ ion were determined from the ESR spectra in this article, where the major axis for the spin-spin interaction lay along the C2 axis which is in the plane of the nitrogen atoms and rotates one ethylenediammine ring into the other.
Abstract: The spin Hamiltonians of Cr(en)33+ and trans‐CrCl2(en)2+ in single crystals of Co(en)3Cl3·3H2O, Co(en)3Cl3·NaCl·6H2O and trans‐[CoCl2(en)2]Cl·HCl·2H2O have been determined from the ESR spectra. In the case of the trans‐CrCl2(en)2+, ion it was found that the major axis for the spin—spin interaction lay along the C2 axis which is in the plane of the nitrogen atoms and rotates one ethylenediammine ring into the other. D and E for trans‐CrCl2(en)2+ were calculated from both a crystal field model and from the results of an extended Huckel molecular orbital calculation. It was found that both calculations give comparable results and give the best results when the spin—orbit coupling parameter of the free ion is used. In the case of the MO calculation, the results agree with experiment when the N–Cr–N bond angle in the ethylenediammine ring is chosen to be 84°. For trigonal complexes of Cr III, D was also calculated using a crystal field model and again it was found that the best results were obtained when the s...
TL;DR: In this article, the optical crystal spectrum of chromium acetylacetonate has been measured and the trigonal field splitting K is found to be +530 cm-1, which is attributed to covalency.
Abstract: The optical crystal spectrum of chromium acetylacetonate has been measured. The trigonal field splitting K is found to be +530 cm—1. The ionic model can account for the sign of the trigonal field and intensity ratios of Cr(C2O4)3—3 but not of the acetylacetonate. This failure is ascribed to covalency, particularly π covalency in the acetylacetonate ring.
TL;DR: In this paper, it was shown that ligand field theory and the angular overlap model are not able to account for the trigonal level splitting of Cr(acac)3 for which the coordination sphere of oxygen atoms is nearly octahedrally arranged.
Abstract: The varying π-bonding contributions in the title compounds caused by the different electronic and molecular structure of the chelate rings are used for explaining the large band splittings in the absorption spectra by trigonal symmetry. It is shown that usual ligand field theory and the angular overlap model are not able to account for the trigonal level splitting of Cr(acac)3 for which the coordination sphere of oxygen atoms is nearly octahedrally arranged. The experimental finding can, however, be rationalized by an extended angular overlap model which considers the phase coupling of π-orbitals in the ligands leading to non-additive contributions to the metal-ligand bond energy.
TL;DR: In this article, the symmetry of the field perturbing the metal ion is predominantly axial and the axial potential is negative for the complexes of Ti+3 and of Ru+3.
Abstract: Paramagnetic‐resonance absorption has been observed in complexes of acetylacetone with the trivalent transition metals titanium, chromium, iron, molybdenum, and ruthenium. The symmetry of the field perturbing the metal ion is predominantly axial. For the complexes of Ti+3 and of Ru+3, the axial potential is negative. Energy‐level splittings by the ligand field and g factors were obtained for the various complexes. Resonance was also observed in complexes of trifluoroacetylacetone with chromium and iron and in the complex chromium (III) hexafluoroacetylacetonate. Resonance could not be detected in the complexes vanadium (III) acetylacetonate, manganese (III) acetylacetonate and ferric (III) hexafluoroacetylacetonate, although magnetic‐susceptibility measurements on the last two compounds indicated that they were paramagnetic.
TL;DR: In this article, the absorption spectrum of a microscopic crystal of copper-ethylene-diamine-bis (acetylacetone) was shown to consist of three bands as predicted by the ligand field theory.
Abstract: IN a previous communication1 it was shown that the absorption spectrum of a microscopic crystal of copper-ethylene- diamine-bis(acetylacetone) consists of three bands as predicted by the ligand field theory. Copper biguanides form transparent reddish crystals2, very convenient for measurement in our experimental arrangement. In Fig. 1 are given the spectrophotometric optical density (O.D.) vs. wave-length (λ) curves for a thin crystal of copper bis-biguanide dibromide dihydrate with light polarized along the long axis of the crystal and at right angles to it, respectively. It is evident that the first curve consists of three bands, but the sharpness and fine structure are not as well defined as was the case with copper-ethylene-diamine-bis(acetylacetone). The decomposition of the curve into its component bands shows three peaks at 485 mµ, 540–550 mµ and 600 mµ. When the light was polarized at right angles to the long axis of the crystal, the absorption spectrum was found to consist of two bands, with peaks at 485 mµ and 550 mµ, the peak at 600 mµ being missing. If we associate the band of longest wave-length with the transition d z 2 → d xy, then the result may mean that the z-axis of the molecular field coincides with the long axis of the crystal.