Structural studies of organometallic compounds in solution: I. Magnesium iodide in diethyl ether and tetrahydrofuran

Abstract

The structure of 2.8 M MgI2 in diethyl ether solution and that of 1.7 M MgI2 in tetrahydrofuran solution have been determined by large angle X-ray scattering measurements. The measurement on the diethyl ether solution was performed at 44°C, on a phase crystallizing at approximately 30°C. In diethyl ether a dimeric structure is found, arranged in a square-planar fashion. The bond lengths are: MgI 2.652(2), II (diagonal) 3.75(2) and II (linear) 5.30 Å. Three diethyl ether molecules are probably coordinated to each magnesium to complete an octahedral arrangement. In tetrahydrofuran the ion MgI+ from a dissociated complex predominates. In the MgI2 complex a tetrahedral arrangement is found. In both the MgI+ and MgI2 complexes the MgI distance is 2.56(2) Å. In the MgI2 complex the II distance is 4.44(4) Å. In both solutions the MgO and MgC distances were kept fixed at 2.10 and 3.48 Å, respectively. The solubility of MgI2 in diethyl ether has been shown to be strongly dependent on the water content of the ether; 0.2 M was the highest concentration obtained in anhydrous diethyl ether.