ISSN:
0009-2940
Keywords:
Chromium(III) alkyls
;
Paramagnetism
;
Calculations, MO
;
Metal - Metal bonding
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The electronic structures of the edge-sharing bioctahedral chromium(III) dimers {C5H5Cr(CH3)(μ1-Cl)}2 (2) and {Me5C5Cr(CH3)(μ1-CH3)}2 (4* (Cp* derivative), 4 (Cp derivative)), the trinuclear complex {C5H5Cr(μ1-Cl)}3(μ1-CH) (3), and the face-sharing bioctahedral chromium(III) compounds {Me5C5Cr}2(μ1-CH2) (6*, 6) [{Me5C5Cr}2(μ1-CH3)3]+ (7*, 7) have been studied MO-theoretically by the extended Hückel method. Proceeding from 2 over 3 to 4*, or from 6* to 7* a 3-center/4-electron chloride or methylene bridge is replaced by a 3-center/2-electron methyl group (a methylidyne cap in the trimer). The 3c/2e bridges give rise to an increased metal - metal overlap population due to Cr - Cr bonding within the core levels. In the series of 2 - 3 - 4* this is accompanied by a decrease in the Cr - Cr distance (329 - 284 - 260 pm) and effective magnetic moment, μeff (2.53 - 2.05 - 1.53 μB per Cr at room temp.). The latter can be ascribed to an increased splitting within the chromium d-block because of the shorter metal-metal separation. The bioctahedra 6* and 7* feature even shorter Cr - Cr contacts than 4* (239 and 242 pm), primarily because of their face-sharing geometry. However, their effective magnetic moments (per Cr) are 2.33 and 1.32 μB at room temp. The high magnetic moment for 6* can be understood from the orbital interactions in the frontier orbital metal d block: A face-sharing bioctahedron shows one σ, two δ, and no π type overlap, while an edge-sharing bioctahedron (4) has σ, π, and δ interaction between the metals. In the former this destabilizes only σ* sufficiently to prevent occupation by electrons (leaving five orbitals for six electrons, possible spin multiplicities S=0, 1, 2) while for the latter both σ* and π* are destabilized beyond electron occupation (leaving four MOs for six electrons, possible spin multiplicities S=0, 1). 4*, 6* and 7* are unusual examples of metal - metal bonded complexes containing octahedral CrIII ions.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19931260313
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