Experimental Determination of Scan-truncation Losses from Low-temperature (16 K) Single-crystal X-ray Measurements

Abstract

Model intensity profiles have been obtained for biscarbonyl[ 14]annulene by convoluting the Mo Ka spectral distribution with two functions derived from experimental measurements at 16(1) K, up to 26Mo = 110�, of a spherical crystal mounted on a four-circle diffractometer equipped with the Samson low-temperature apparatus. The process includes accurate measurement of the inherent background, treatment of the profiles by numerical Fourier methods, and least-squares fitting. Owing to the instrumental configuration of the diffractometer used in this investigation, the first step of the process has required a careful determination of the X dependence of the background, besides the usual 26 dependence. Truncation losses for the crystal under study, evaluated for several scan ranges, are far larger than usually assumed or predicted.