engleski

Structure-properties relationship derived from X-ray charge density: unusual chemical bonds bordering intra- and intermolecular

Application of X-ray charge density to study of interesting chemical problems is illustrated on several examples involving electron delocalisation and charge transfer. Semiquinone radicals are stabilised by delocalisation of the unpaired electron and negative charge, and their electron structure is somewhere between aromatic (fully delocalised π electrons) and quinoid (distinguishable single and double bonds). In the solid state they form extended π-stacks, and the spin coupling can be diamagnetic (high electron density between the rings) or antiferromagnetic (low electron density between the rings). The border line between a weak covalent bond and a strong intermolecular interaction (such as a hydrogen or a halogen bond) is often a fuzzy one, and the borderline cases are illustrated on an H2O-H-OH2 fragment (Zundel ion) and N-Br-N fragment.

semiquinone ; pi-interactions ; proton transfer ; halogen bonding ; X-ray charge density

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