STRUCTURE OF THE ERGOLINE DERIVATIVE 1,1- ,8S,10S)-2,3-DIHYDRO-2,6-DIMETHYL-8-ERGOLINYL]UREA AT 3 DIFFERENT TEMPERATURES (295-K, 50-K AND 15-K)

The structure of the ergoline derivative 8S,10S)-2,3-dihydro-2,6-dimet hyl-8-ergolinyl]-urea has been determined by X-ray single crystal diff raction at three temperatures: 295, 50 and 15 K. Large displacement pa rameters of the diethyl-urea side group atoms cause rather improper bo nd distances at room temperature which, after cooling, adopt normal va lues. An inspection of the displacement parameters expressed in U(eq)' s, shows that even the temperature reduction from 50 to 15 K causes an average decrease of U(eq)'s by 33%. At room temperature, the individu al displacement parameters depend strongly on the atomic distances fro m the molecular center of gravity. This dependence disappears almost c ompletely at 15 K.