Anisotropic displacement parameters (ADPs) are commonly used in crystallography, chemistry, and related fields to describe and quantify thermal motion of atoms. Within the very recent years, these ADPs have become predictable by lattice dynamics in combination with first-principles theory. Here, we study four very different molecular crystals, namely, urea, bromomalonic aldehyde, pentachloropyridine, and naphthalene, by first-principles theory to assess the quality of ADPs calculated in the quasi-harmonic approximation. In addition, we predict both the thermal expansion and thermal motion within the quasi-harmonic approximation and compare the predictions with the experimental data. Very reliable ADPs are calculated within the quasi-harmonic approximation for all four cases up to at least 200 K, and they turn out to be in better agreement with the experiment than those calculated within the harmonic approximation. In one particular case, ADPs can even reliably be predicted up to room temperature. Our results also hint at the importance of normal-mode anharmonicity in the calculation of ADPs.

The reaction o f appropriate amounts of BH3 with diazadiboretidines (RBNtBu), (la-e; R = Et, Pr, Bu, tBu, tBu(Me3Si)(4), or into an acyclic product RBH-NtBu-BH-NtBu-BHR (2e). The structure of 3c is characterized by a planar N2B3 ring skeleton with an unsymmetrical double-hydrogen bridge. RESULTSThe diazadiboretidines la-c [ 1-41 readily react with the borane thf . BH3 in a 1 : 1 ratio to give the five-1042-7163/90/$3.50 + .25 a Numbers in parentheses are estimated standard deviations in the least significant digit.

ChemInform Abstract The reactions of (I) with Ag salts of non-coordinating anions yield the clusters (III) which are characterized by X-ray analyses (both space group R3c with Z = 6).

TlI3(CH3C5H4NO)2 is obtained in acetonitrile by the reaction of TlI with iodine and 3-methyl- pyridine-N-oxide. It crystallizes monoclinic in the centrosymmetric space group C2/c with lattice parameters at 190 K, a = 1756.5(8), b = 780.7(5), c = 1397.1(4) pm, β = 110.26(3)° and Z = 4. The structure consists of monomeric complexes, in which the Tl atom shows a fivefold coordina­tion in form of a slightly distorted trigonal bipyramid, the I atoms being located in the equatorial plane. The symmetry of the complex is C2 whereby the Tl atom and one of the I atoms occupy the twofold axis.

Nahezu gleichseitige ineinander einbeschriebene Dreiecke aus den Atomen der beiden Metallsorten kennzeichnen die Strukturen von 1, deren Zentralteil damit der (111)‐Ebene einer dichtgepackten Metallstruktur stark ähnelt. 1a und 1b sind die ersten strukturell charakterisierten Nb0‐bzw. Ta0‐Cluster ohne Brükkenliganden (dmpe = Me2PCH2 CH2PMe2) [AgM(CO)4 (dmpe)]3 1a M = Nb, 1b M = Ta