Emilio Tedesco

The effect of the counter ion on M–H···H–X (X=O, N) interactions in crystalline transition metal hydrides

The relationship between molecular and crystal structures of organometallic complexes showing intramolecular interactions of the M–H···H–X type (M=transition metal, X=O, N, and S) has been investigated by a combined use of molecular orbital calculations and crystal packing analysis. Molecular and crystal structures determined by neutron and/or X-ray diffraction data of coordination complexes and clusters showing intramolecular (M–H···H–X) interactions within the range 1.5–2.5 A have been retrieved from the Cambridge Structural Database. DFT calculations were performed for the majority of compounds in order to determine the nature of the H···H interaction. The optimized geometries obtained by DFT are usually in good agreement with the experimentally determined ones, short H···H distances being also found. Most of the systems analysed, such as cis-[IrH(OH)(PMe3)4][PF6], involve cationic complexes. It has been found that the counter ion exerts a strong influence in bringing together the two hydrogens. When it is included in the calculations, the agreement between the observed and the calculated structures is much better.

A variable temperature study of Ru3(CO)12 in the solid state and the generation of alternative crystal structures

SummaryThe molecular and crystal structure of Ru3(CO)12 has been reinvestigated on single-crystal X-ray diffraction data collected at 100 and 150 K. Thermal motion analysis on high-order diffraction data have been used to characterize the motion about equilibrium positions of the molecule as a whole and of groups of atoms. It has been shown that, while the molecule undergoes an almost isotropic rigid-body librational and translational motion, the three Ru(CO)4 units undergo different librational motions about the axes passing between each Ru atom and bisecting the opposite 615-01 bond. Packing potential energy calculations and computer graphics have been used to show that the most favoured packing motif in the experimental crystal is based on interlocking between tetracarbonyl units formed by two pairs of CO ligands at right angles along a 615-02 edge. Starting from the structure of Ru3(CO)12, alternative crystal arrangements have been generated and compared with the experimental crystal structure in terms of packing efficiency and cohesive energy.

CRYSTALLINE DIHYDROGEN COMPLEXES. INTRAMOLECULAR AND INTERMOLECULAR INTERACTIONS AND DYNAMIC BEHAVIOR

Abstract The molecular and crystal structure of complexes containing the ‘non-classical’ η 2 -H 2 ligand have been examined. The solid-state dynamical behavior of the ligand has been investigated by atom-atom potential energy barrier calculations, and the results compared with the available spectroscopical and theoretical information. Electronic barriers to reorientation have also been evaluated by molecular orbital extended Huckel calculations in the cases of Ru( η 2 -H 2 )(C 5 Me 5 )(dppm)BF 4 and of OsCl( η 2 -H 2 )(H 2 bim)(P- 1 Pr 3 ) 2 Cl. The existence of hydrogen-bonding interactions involving the η 2 -H 2 ligand has also been analyzed.

THE FIRST AMINE DERIVATIVES OF IR4(CO)12 SYNTHESIS AND X-RAY CHARACTERIZATION OF IR4(CO)10(1,10-PHENANTHROLINE) AND IR4(CO)10(4,4'-ME2-2,2'-BIPYRIDINE )

Abstract The reaction of NEt 4 [Ir 4 (CO) 11 X] (X = Br, I) with aromatic diamines, N-N, in the presence of Ag + salts affords the first examples of diamino-carbonyl complexes Ir 4 (CO) 10 (N-N), (N-N) = 1,10-phenanthroline ( 1 ), 4,7-dimethylphenanthroline ( 2 ), 5,6-dimethylphenanthroline ( 3 ), 3,4,7,8-tetramethylphenanthroline ( 4 ), 2,2′-bipyridine ( 5 ), 4,4′-dimethyl-2,2′-bipyridine ( 6 ). The crystal and molecular structures of 1 and 6 show that the diamine ligands chelate a basal iridium atom in the cluster.

Crystal construction and molecular recognition for [Cr(CO)6]

The molecular organization in crystals of the prototypical organometallic molecule [Cr(CO)6] has been investigated by means of packing-potential-energy calculations and computer graphics analysis. The atom–atom pairwise-potential-energy method has been used to study the interaction energy between molecular pairs and the molecular self-recognition process which leads to crystal construction. Alternative crystal structures have been generated and compared with the experimentally observed structure in terms of packing cohesion.

C–H · · · OHydrogen bonding in crystalline complexes carrying methylidyne(µ3-CH) and methylene (µ-CH2) ligands: adatabase study

The relationship between the molecular and crystal structures of organometallic complexes carrying methylidyne (µ 3 -CH) and methylene (µ-CH 2 ) ligands has been investigated on data retrieved from the Cambridge Structural Database. It has been shown that µ 3 -CH and µ-CH 2 groups participate in intermolecular hydrogen-bonding networks of the C–H · · · O type involving, in most cases, the oxygen atoms of CO ligands as acceptors. The order of decreasing acidity, judged on purely geometrical grounds from the average length of the hydrogen-bonding interactions, is roughly µ 3 -CH > µ-CH 2 . These ligands establish C–H · · · O interactions which are comparable in length to those established by hydrogen atoms bound to sp- and to sp 2 -hybridized carbon atoms consistent with experimental and theoretical evidence.

Molecular structure and crystal structure generation for [Fe3(CO)12]

The electronic structure of [Fe3(CO)12] has been investigated by means of extended-Huckel calculations and compared to that of [Ru3(CO)12], showing that the bridged structure, observed in the solid state, arises because of electronic reasons, namely a weaker metal–metal repulsion in the case of the lighter cluster. This is associated with the bridge-formation process and becomes determining for the energetic balance in compounds of heavier metals. The possible existence of crystal structures which are alternative to the observed disordered one known for [Fe3(CO)12] has been explored by means of the atom–atom pairwise potential-energy method. Alternative ordered molecular arrangements have been generated and compared with the experimental crystal structure in terms of packing efficiency and cohesive energy.