Direct Observation of Unstable Reaction Intermediates by Acid-Base Complex Formation

• Published in: Chemical record Vol. 13; no. 3; pp. 303 - 325
• Main Author: Ohashi, Yuji
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.06.2013; Wiley Subscription Services, Inc
• Subjects: acid-base complexes; Acids; crystal engineering; Crystals; photochemistry; reaction intermediates; Studies; X-ray analysis
• ISSN: 1527-8999; 1528-0691
• DOI: 10.1002/tcr.201300002

:  The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X‐ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single‐crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid‐base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid‐base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X‐ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid‐base complex crystals with various alkylammonium cations. The formation of acid‐base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X‐ray techniques. The formation of crystals of acid‐base complexes between reactant molecules or their anions and amines or their alkylammonium cations, the metastable structures of nitrenes and photochromic salicylideneanilines, and the unstable excited structures of a Pt complex have been investigated by using X‐ray techniques.