Characterization of a new non-centrosymmetric polymorph of diphenyl-1,3,4-oxadiazole Olga Franco a , Gu ¨nter Reck b , Ingo Orgzall c, * , Burkhard W. Schulz b , Burkhard Schulz c a Institut fu ¨r Physik, Universita ¨t Potsdam, Physik Kondensierter Materie, IFZ-DOBS, Am Neuen Palais 10, D-14469 Potsdam, Germany b Bundesanstalt fu ¨r Materialforschung und-pru ¨fung (BAM), Richard-Willsta ¨tter-Straße 11, D-12489 Berlin, Germany c Universita ¨t Potsdam, Interdisziplina ¨res Forschungszentrum ‘Du ¨nne Organische und Biochemische Schichten’ Am Neuen Palais 10, D-14469 Potsdam, Germany Received 1 July 2002; revised 18 October 2002; accepted 18 October 2002 Abstract Diphenyl-1,3,4-oxadiazole (DPO) crystallization experiments from solutions clearly reveal the polymorphism of the substance. Besides the formerly known centrosymmetric monoclinic structure with space group P2 1 /c (DPO I) a new monoclinic structure with the non-centrosymmetric space group Cc is found (DPO II): a ¼ 2.4134(4) nm, b ¼ 2.4099(3) nm, c ¼ 1.2879(2) nm, b ¼ 110.048(3)8, and V ¼ 7.0363(17) nm 3 . The asymmetric unit contains six independent molecules in a complex packing motif. A re-determination of the crystal structure of DPO I at room temperature gives lattice parameters a ¼ 0.51885(6) nm, b ¼ 1.8078(2) nm, c ¼ 1.21435(14) nm, b ¼ 93.193(3)8, and V ¼ 1.1373(2) nm 3 . X-ray measurements at 363 K show a significant increase of the unit cell volume by 1.6%. Differences between both structures concerning morphology and characteristic Raman bands are outlined in detail. DSC investigations show an irreversible transition from DPO I to DPO II at 97 8C. DPO II does not show any transition in the temperature range up to the melting point at 141 8C. The non- centrosymmetric DPO II structure shows triboluminescence. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Diphenyl-1,3,4-oxadiazole; X-ray structure; Polymorphism; Non-centrosymmetric structure 1. Introduction The rapid technological development requires the search for advanced materials with tailor-made properties. Organic substances may easily be modified by chemical syntheses thus tuning the properties and therefore have attracted increasing attention as high performance materials for instance in sensoric applications, optical and display techniques, new electronic devices, batteries etc. [1,2]. But, tailoring of the properties requires the exact knowledge of the relationship between structures and properties of the materials and their mutual dependence. Based on a model where complex structures are built from small and relatively simple units like the synthonic approach [3–5] it is assumed that some of the properties of a basic unit are preserved in the final product while others may change in a systematic manner. Therefore, the knowledge of structure and properties of more or less simple starting materials is 0022-2860/03/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S0022-2860(02)00569-0 Journal of Molecular Structure 649 (2003) 219–230 www.elsevier.com/locate/molstruc * Corresponding author. Tel.: þ49-331-9772915; fax: þ 49-331- 9772985. E-mail address: orgzall@rz.uni-potsdam.de (I. Orgzall).