- Monocyclopentadienyl compounds of manganese(II). Synthesis, structure, magnetism, and NMR spectra
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A series of 13 manganese(II) half-sandwich compounds [(RnCp)MnXL]2, type L, and (Rcp)MnXL2, type K, have been prepared on different routes. These routes include the new starting materials Mn(DME)2I2 and [Mn3I6(AsEt3)4n. In general, K is favored only when small powerful donor ligands are used. In solution K and L are in equilibrium when R = Me, X = I, and L = PMe3. Byproducts of low solubility may force the equilibrium entirely to K, e.g., for R = H, X = I, and L = PMe3. A systematic paramagnetic NMR study shows that the compounds may be characterized easily. In particular, the distinction between K and L, the delocalization of unpaired electrons, and hyperconjugative effects in the phosphine-transition-metal bonding are shown. According to the NMR data and to solid-state magnetic measurements all compounds have five unpaired electrons per manganese at room temperature. For [Mecp)MnX(PEt3)]2 (X - Cl (2), X = Br (3), = I (4)) the magnetism has been followed down to 1.25 K, and antiferromagnetic interaction with J = -4.8, -5.0, and -4.7 cm-1 has been found. The J values are shown to be typical for superexchange in high-spin maganese(II) dimers. As determined by X-ray crystallography 2, 3, and 4 are halogen-bridged centrosymmetric dimers with pseudotetrahedral metal centers. Crystals of 2 and 3 are orthorhombic, space group Pbca, with a = 13.691 (3)/13.869 (1) ?, b = 15.314 (2)/15.248 (1) ?, c = 14.402 (3)/14.640 (1) ?, V = 3019.6/3074.8 ?3, and dcalcd = 1.265/1.435 g cm-3 for Z = 4. Refinement converged at R = 0.055/0.046 for 156/136 refined parameters and 1611/1572 observables. 4 is monoclinic, space group P21/c, with a = 15.099 (4) ?, b = 15.365 (3) ?, c = 14.576 (4) ?, β = 108.11 (2)°, V = 3214.1 ?3, and dcald = 1.567 g cm-3 for Z = 4. Refinement converged at R = 0.071 for 227 refined parameters and 2697 observed reflections. There is a clear halogen dependence for the geometry of the central Mn2X2 unit. All distances and the angle X-Mn-X increase on going from Cl to I while Mn-X-Mn* decreases. The latter effect is attributed to increasing halogen repulsion.
- K?hler, Frank H.,Hebendanz, Nikolaus,Müller, Gerhard,Thewalt, Ulf,Kanellakopulos, Basil,Klenze, Reinhard
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p. 115 - 125
(2008/10/08)
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