Structural studies of organometallic compounds in solution: II. Magnesium bromide and iodide in diethyl ether and tetrahydrofuran; an extended X-ray absorption fine structure (EXAFS) and large angle X-ray scattering (LAXS) study

Abstract

The structures of the magnesium iodide complexes formed in concentrated diethyl ether and tetrahydrofuran solutions have been determined by the large angle X-ray scattering (LAXS) technique. Those of the more dilute solutions of magnesium bromide in diethyl ether and tetrahydrofuran solutions have been determined by the extended X-ray absorption fine structure (EXAFS) method. The investigation of the MgI 2 diethyl ether solution was carried out at 44°C since this solution crystallizes at about 30°C. This solution is probably best considered a melt, the structure of which can be regarded as a close-packing of iodide ions with magnesium ions occupying some of the holes. The coordination around a specific magnesium ion depends on whether it occupies a tetrahedral or an octahedral hole. The average MgI bond distance is 2.75 Å. Solvated MgI + is the dominating complex in MgI 2tetrahydrofuran solution. Magnesium is probably six-coordinate in this complex, and the MgI bond distance is 2.52(5) Å. The MgBr bond distance is 2.49 and 2.66 Å in diethyl ether and tetrahydrofuran, respectively.