Title

Isolation, Characterization, and Computational Studies of the Novel [Mo₃(μ₃-Br)₂(μ-Br)₃Br ₆]²⁻ Cluster Anion

Abstract

The novel trimolybdenum cluster [Mo3(μ3-Br) 2(μ-Br)3Br6]2- (1, {Mo 3}9- 9 d-electrons) has been isolated from the reaction of [Mo(CO)6] with 1,2-C2H4Br2 in refluxing PhCI. The compound has been characterized in solution by electrospray ionization mass spectrometry (ESI-MS), UV-vis spectroscopy, cyclic voltammetry, and in the solid state by X-ray analysis (counter-cations: (η-Bu)4N+ (1), Et4N+, Et3BzN+), electron paramagnetic resonance (EPR), magnetic susceptibility measurements, and infrared spectroscopy. The least disordered (η-Bu)4N+ salt crystallizes in the monoclinic space group C2lc, a = 20.077(2) Å b = 11.8638(11 ) Å c = 22.521 (2) Å α = 90 deg, β = 109.348(4) deg, γ = 90 deg, V= 5061.3(9) Å3, Z= 4 and contains an isosceles triangular metal arrangement, which is capped by two bromine ligands. Each edge of the triangle is bridged by bromine ions. The structure is completed by six terminal bromine ligands. According to the magnetic measurements and the EPR spectrum the trimetallic core possesses one unpaired electron. Electrochemical data show that oxidation by one electron of 1 is reversible, thus proceeding with retention of the trimetallic core, while the reduction is irreversible. The effective magnetic moment of 1 (μeff, 1.55μB, r.t.) Is lower than the spin-only value (1.73 μB) for S = 1/2 systems, most likely because of high spin-orbit coupling of Mo(III) and/or magnetic coupling throughout the lattice. The ground electronic state of 1 was studied using density functional theory techniques under the broken symmetry formalism. The ground state is predicted to exhibit strong antiferromagnetic coupling between the three molybdenum atoms of the core. Moreover, our calculated data predict two broken symmetry states that differ only by 0.4 kcal/mol (121 cm-1). The antiferromagnetic character is delocalized over three magnetic orbitais populated by three electrons. The assignment of the infrared spectra is also provided.

Department(s)

Chemistry

Sponsor(s)

European Union
Generalitat Valenciana
National Institute of Health (U.S.)
Spanish Ministerio de Educacion y Ciencia

Library of Congress Subject Headings

Coordination compounds
Molybdenum

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2010 American Chemical Society (ACS), All rights reserved.


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