Applied Crystallography

Biography

Biography: Gerd Kaupp

Abstract

Crystal structures of organic solid-state reactions are decisive for their occurrence and selectivity. While Schmidts topochemistry concentrates on a distance limit between reacting centers by denying molecular migrations within the crystal, too many positive and negative failures pose unsurmountable problems for predictions. Conversely, AFM, SNOM, GID, and nano-scratching indicate anisotropic molecular migrations, enforced by the internal pressure upon chemical change by reaction that requires release. This holds for intra- and inter-crystalline and for gas-solid reactions also with formerly "too large" distances, explains nonreactivities at very small distances, and intercrystalline reactions. Required are crystallographic possibilities for molecular migrations within slip-planes and channels, or to sufficiently wide crystallographic voids. Such migrations are anisotropic and they are face-specific. Slip-planes or channels end on the reactive crystal faces, not on the unreactive ones. For intracrystalline reactions molecules move out and for intercrystalline ones reactants move also in. Solid-state reactions profit from the bargain of favorable crystallinity with respect to the same melt reactions (the latter require up to about 100K higher temperature and are less selective). This opposes undue beliefs that solid-state reactions require melts, or claims that these should require "help by some solvent". Such widely proposed beliefs restrict to reactions that proceed around room temperature as liquid-state reactions, mostly loosing completeness and/or specificity. In the case of non-reactive polymorphs one may try to generate and use different modifications. The pseudo-problems of topochemistry are easily removed by applying the full structural content. New applications for molecular and polymer (including large-scale) chemistry ensue.