A semiempirical approach to hydrogen bonding networks. Application of the Cyclic Cluster Model to organic crystals

A semiempirical quantum chemical method combined with the Cyclic Cluster Mo del provides the opportunity to optimise hydrogen positions in organic crys tals. Quantification of their interactions is enabled by the correct geomet ry within the framework of the same method. Test calculations on systems co ntaining only weak C-H ... O contacts describe their relative stability rea sonably well. Selectivity in a diastereomeric salt formation, where both st ronger and weaker X-H ... Y interactions contribute to crystal formation, i s studied and rationalised on an energetical basis. (C) 1999 Elsevier Scien ce B.V. All rights reserved.