Spectroscopic and neutron diffraction investigation of structure, bonding, and molecular dynamics in bis(methylcyclopentadienyl) hafnium bis(tetrahydroborate), (n/sup 5/-CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf(BH/sub 4/)/sub 2//sup 1/
The complex (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf(BH/sub 4/)/sub 2/ can be prepared by the reaction of (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/CfCl/sub 2/ with LiBH/sub 4/ in benzene.The bonding, molecular dynamics, and structure of this compound have been studied by infrared and Raman vibrational spectroscopy, dynamic nuclear magnetic resonance spectroscopy, and single-crystal neutron diffraction. Vibrational spectra reveal the perturbation of the B-containing ligand from a free BH/sub 4//sup -/ ion to be less in this complex than in most covalent tetrahydroborate transition metal complexes. The compound crystallizes from toluene/pentane in the monoclinic space group C2/c with four molecules in a unit cell of dimensions a = 14.566 (3), b = 6.839 (1), c = 13.959 (3) A, and ..beta.. = 102.31 (2)/sup 0/. Full-matrix least-squares refinement gave a final value of R(F/sub 0//sup 2/) = 0.107 for 1022 reflections. The molecular structure consists of monomeric (eta/sup 5/-CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf(BH/sub 4/)/sub 2/ units having C/sub 2/ symmetry and bidentate tetrahydroborate ligands. The ring centroid--Hf--ring centroid angle is 128.5 (3)/sup 0/. The average Hf--C(ring) bond distance is 2.491 (9) A. The coordination of each tetrahydroborate group is markedly unsymmetrical with crystallographically independent Hf--H(bridge) distances of 2.069 (7) and 2.120 (8) A. The lengths of the two B--H(bridge) bonds mirror, inversely, the Hf--H distances:. The B--H(terminal) distances are 1.186 (16) and 1.198 (15) A, and the Hf--B distance is 2.553 (6) A. Important bond angles are B--Hf--B = 101.4 (3)/sup 0/, H(bridge)--B--H(bridge) = 108.4 (6)/sup 0/, and H(terminal)--B--H(terminal) = 115.4 (10)/sup 0/. The anisotropy of the hydrogen atom thermal parameters within the tetrahydroborate groups may reflect motion along the bridge-terminal hydrogen interchange reaction coordinate. The nature of the (CH/sub 3/C/sub 5/H/sub 4/)/sub 2/Hf--tetrahydroborate interaction can be understood in terms of those bonding factors which govern ligand-to-metal charge donation.
- Research Organization:
- Argonne National Lab., IL
- OSTI ID:
- 6756156
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 100:9; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400201* -- Chemical & Physicochemical Properties
ALKENES
BOROHYDRIDES
BORON COMPOUNDS
CHEMICAL BONDS
COHERENT SCATTERING
COMPLEXES
CRYSTAL STRUCTURE
CYCLOALKENES
CYCLOPENTADIENE
DIENES
DIFFRACTION
DISTANCE
ENERGY LEVELS
EXCITED STATES
HAFNIUM COMPLEXES
HYDROCARBONS
HYDROGEN COMPOUNDS
INFRARED SPECTRA
INTERATOMIC DISTANCES
LIGANDS
MAGNETIC RESONANCE
MOLECULAR STRUCTURE
NEUTRON DIFFRACTION
NUCLEAR MAGNETIC RESONANCE
ORGANIC COMPOUNDS
ORGANOMETALLIC COMPOUNDS
POLYENES
RAMAN SPECTRA
RESONANCE
SCATTERING
SPECTRA
TRANSITION ELEMENT COMPLEXES
VIBRATIONAL STATES