Assembly of the inorganic double helix Mg6(Et2NCO2)12 by fixation of carbon dioxide: Crystal and solution structure

M. T. Caudle, R. A. Nieman, Victor G Young

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Abstract

The homoleptic magnesium carbamato complex Mg6(Et2NCO2)12, 1 (Et2NCO2- = diethylcarbamato anion), was prepared by the reaction of dibutylmagnesium with diethylamine, followed by carboxylation using gaseous carbon dioxide. Crystallographic characterization demonstrated that 1 has the standard M6(R2NCO2)12 structure and is a double helix of MgOx(x = 5, 6) coordination polyhedra with δ or ?? stereochemistry arising from the configuration around the six-coordinate Mg2+ cations. It crystallized in the orthorhombic space group Ccca with two molecules of δ1 and two of ??1 per unit cell (a = 21.548 Å, b = 25.094 Å, c = 15.4485(11) Å, α = β = λ = 90°). Extensive solution characterization of 1 by 1-dimensional proton and 13C NMR spectroscopy and by two-dimensional 1H-{13C} NMR correlation techniques verified that the helical structure is maintained in solution. Moreover, these measurements indicated that the intramolecular dynamics of 1 relating to motions of the ethyl groups was substantially hindered in solution. Correlation of the crystallographic and NMR structural studies indicated that this arises from a combination of hindered rotation about the carbamato C-N bond and efficient packing of the ethyl groups around the Mg6O24 core. The result is an inverted-micelle-like structure for 1 in which the hydrophobic ethyl groups form a sheath largely restricting access to the hydrophilic Mg6O24 core.

Original languageEnglish (US)
Pages (from-to)1571-1575
Number of pages5
JournalInorganic Chemistry
Volume40
Issue number7
DOIs
StatePublished - Mar 26 2001

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