The elusive structure of CrCl(2): a combined computational and gas-phase electron-diffraction study
Brian Vest1, Zoltán Varga, Magdolna Hargittai
1Centre of Theoretical Chemistry and Physics (CTCP), The New Zealand Institute for Advanced Study, Massey University (Auckland Campus), North Shore MSC, Auckland, New Zealand.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|May 21, 2008
Summary
Chromium dichloride (CrCl2) clusters exhibit chain-like structures similar to the solid state. Calculations reveal early nucleation of these chains, with minimal energy changes between magnetic couplings.
Area of Science:
- Inorganic Chemistry
- Computational Chemistry
- Solid-State Chemistry
Background:
- Chromium dichloride (CrCl2) presents structural complexity due to vibronic interactions.
- Observed distortions include Renner-Teller in monomers, Jahn-Teller in crystals, and pseudo-Jahn-Teller in oligomers.
Purpose of the Study:
- To investigate the low-energy structures of monomeric CrCl2 and its clusters (Cr2Cl4, Cr3Cl6, Cr4Cl8).
- To elucidate the structural motifs and energetic properties of CrCl2 aggregation.
- To aid in the re-analysis of high-temperature electron-diffraction data.
Main Methods:
- Unrestricted Kohn-Sham (broken-symmetry) density functional calculations.
- Higher-level computations including coupled-cluster and state-average CASSCF.
- Analysis of vibrational spectra and thermodynamics of cluster formation.
Main Results:
- Gas-phase clusters form 2D antiferromagnetically coupled chains of CrCl2 units, resembling alpha-CrCl2 solid-state structure.
- Each Cr atom in chains has S=2 spin; minimal energy difference between antiferromagnetic and ferromagnetic coupling.
- Monomeric CrCl2 is bent (149(10) degrees), consistent with Renner-Teller distortion of the (5)Pi(g) state to a (5)B(2) ground state.
Conclusions:
- CrCl2 nucleation begins early, forming chain motifs similar to the solid state.
- Weak spin-coupling between metal centers is indicated.
- Thermodynamics of cluster formation were examined over 1000-2000 K.
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