engleski

Temperature Infleunce on Disorder of a Coordinated Dimethylsulphoxide Molecule

If some fragment, usually relatively small, of the crystal structure cannot be assigned the same equilibrium position in all unit cells of the crystal or it's equilibrium position changes in time, it is said that such fragment is disordered. In the former case disorder is refered to as static whereas in the latter as dynamic. Disordered crystal structures are latively often encountered, and a dimethylsulphoxide (dmso) molecule is particuralely often found to be disordered. In the dimethylsulphoxide adduct of bis(1, 3-diphenyl-1, 3-propanedion)cadmium(II) complex the two dmso molecules are ligated to cadmium(II) ion through oxygen atoms in cis geometry [1]. Electronic density of one of the two dmso molecules was modeled assuming positional disorder of that molecule over two positions. In order to gain deeper insite into the nature of the disorder, variable temperature diffraction experiment was perfomed with one single crystal. The temperature of the sample was in the interval from 100 K to 330 K. It was found that disorder was completely diminished at 100 K and became more expressed as temperature was raised. For this reasons disorder was interpreted as dynamic, that is, the results indicate that the position of the dmso molecule changes with time. At 300 K refined occupancies of major and minor orientations are 0.82 and 0.18, respectively. Based on data measured at four temperatures, in the interval from 150 K to 300 K (quality of data collected at 330 K was quite poor), the enthalpy difference [2] of the two orientations was estimated at 4.9 kJ mol− 1. The disordered dmso molecule is situated in a cavity between two phenyl rings which are leaving enough space for the orientation to change without significant energy increase.

dimethylsulphoxide; disorder; temperature

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