XwHÉ É Ép (phenyl) is the interaction of a hydrogen atom with the p-system of an aromatic ring in either an intermolecular or an intramolecular fashion. Although the existence of these types of interaction has gained recent attention in the literature, the geometry is poorly understood. This paper attempts to investigate the preferred geometry and interaction strength for OwH, NwH, NwH`, SwH, sp2 CwH and sp1 CwH interactions with phenyl rings. This has been done through searches of the Cambridge Structural Database, combined with semi-empirical and ab initio molecular orbital calculations. It is found that the classical image of T-shaped geometry is rarely adopted and that the preferred geometry involves direct interaction of XwH with the carbon atoms of the phenyl ring. The binding energy associated with the interaction decreases with the electronegativity of the donor atom X.

The complex cation [Pt(1)2]2+ [(l) = 1,4,7-trithiacyclononane] shows a quasi square based pyramidal structure with one non-bonding sulphur donor atom; electrochemical oxidation at +0.5 V. vs. FcO/Fc+ (Fc = ferrocene) at 20 "C in MeCN affords a paramagnetic platinum(iri) species.

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The synthesis, characterization, and crystal chemistry of N,N′-diphenylisophthalamide (1) and pyridine-2,6-dicarboxylic acid bisphenylamide (2) are described. Through a combination of single-crystal X-ray diffraction and molecular orbital and crystal packing calculations, the important intermolecular interactions have been determined. The structures have been compared with the closely related structures, N,N′-bis(3-hydroxyphenyl)isophthalamide (3) and N,N′-dimethyl-N,N′-diphenylisophthalamide (4). Crystalline 1 and 2 are isostructural, but there are subtle differences in the conformations and packing as a consequence of intramolecular hydrogen bonding in 2. This reduces the deviation from planarity in the molecular conformation of 2 and consequently lengthens the intermolecular hydrogen bonding distances. This is reflected in the lattice energies of 1 and 2 (-40.9 and -38.7 kcal/mol, respectively) and in the stacking energies of these compounds. For the compounds that do not contain an N atom in the central ring the progression 3, 1, 4 represents a reduction in the hydrogen-bonding options, reflected in the respective lattice energies: -51.3, -40.9, and -33.3 kcal/mol. The difference between 3 and 1 is in excellent agreement with predictions based on group contributions in structure 3. In 4 there are no hydrogen bonding options and so C-H‚‚‚O interactions play a much more important role.

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