| Abstract
| - A heavy-atom effect on the surprisingly nonfolded MoS2C2 metallacycle of the d1 Cp2Mo(dmit)•+ in [Cp2Mo(dmit)•+][AsF6-] is investigated in the corresponding salts with Cp2W(dmit), Cp2Mo(dsit), and Cp2W(dsit). Only introduction of both W and dsit affords a novel structure for [Cp2W(dsit)•+][AsF6-], with a folded metallacycle and a spin-ladder behavior. This variety of folding angles and molecular structures is attributable to a very low energy cost (<1 kcal mol-1) for folding, as determined by DFT calculations.
- Cp2M(dithiolene) (M = MoIV, WIV) d2 complexes exhibit a folding (θ) of the MS2C2 metallacycle along the S−Saxis upon oxidation to the d1 paramagnetic cation. The evolution of the peculiar unfolded structure (θ = 0°) ofCp2Mo(dmit)•+ (dmit2-, 2-thioxo-1,3-dithiole-4,5-dithiolate) in its AsF6- salt toward the introduction of heavyatoms (W, Se) is examined here by substituting dsit2- (dsit2-, 2-thioxo-1,3-dithiole-4,5-diselenolate) for dmit2-and/or W for Mo in those AsF6- salts. While [Cp2Mo(dsit)•+][AsF6-] (orthorhombic, Cmcm, a = 9.071(2), b =20.868(4), c = 10.243(2) Å, V = 1938.9(7) Å3, Z = 4) and [Cp2W(dmit)•+][AsF6-] (orthorhombic, Cmcm, a =9.0295(15), b = 20.568(2), c = 10.2641(12) Å, V = 1906.2(4) Å3, Z = 4) crystallize with an unfolded geometryand are isostructural with [Cp2Mo(dmit)•+][AsF6-], the introduction of both W and dsit2- in Cp2W(dsit) stabilizesa fully different structure for [Cp2W(dsit)•+][AsF6-] (monoclinic, P21/c, a = 6.8442, b = 15.9923(13), c = 17.6594(16) Å, β = 90.934(11)°, V = 1932.6(3) Å3, Z = 4) with the Cp2W(dsit)•+ cation in a folded geometry (θ =30.1(1)°). DFT calculations show that the variety of folding angles and hence of molecular structures found inthose open-shell d1 Cp2M(dithiolene)•+ complexes is attributable to a very low energy cost (<1 kcal mol-1) forfolding around the minimal energy folding angle. The molecular geometry of those complexes and hence theirfrontier orbitals are therefore highly related to the actual crystal structure they adopt. The unfolded complexesexhibit, in their AsF6- salts, a three-dimensional set of intermolecular interactions in the solid state, confirmed bythe presence of an antiferromagnetic ground state (TNéel = 3.5(5) K in [Cp2W(dmit)•+][AsF6-]). On the otherhand, the folding of Cp2W(dsit)•+ in [Cp2W(dsit)•+][AsF6-] leads to the formation of a rare spin-ladder systemwith a spin gap of 90−100 K, as deduced from the temperature dependence of its magnetic susceptibility.
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