Quantitative crystal structure analysis of fluorinated porphyrins Rahul Soman, Subramaniam Sujatha, Chellaiah Arunkumar * Bioinorganic Materials Research Laboratory, Department of Chemistry, National Institute of Technology Calicut, Kozhikode 673 601, Kerala, India 1. Introduction The well-known definition of crystal engineering is quoted by Desiraju as ‘‘the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in design of new solids with desired physical and chemical properties’’ [1]. Intermolecular interactions in organic/inorganic compounds play an important role in the crystal packing of molecules which attracts intense attention in various research fields including supramolecular chemistry [2–4]. Such interactions involving fluorine are of mainly three kinds, namely C–F  H, F  F and C– F  p which provides stability to form molecular self-assemblies especially in the absence of strong intermolecular forces [5–8]. Even though these individual interactions are energetically weak, the net result may become considerably strong due to the co- operative effect and thus may provide a higher stability to the crystalline lattice. In addition, supramolecular assembly is framed by suitable combination of various types of weak intermolecular interactions like C–H  p and the geometrical preference of the metal ion. Owing to the high electronegativity of fluorine, it renders the C–F bond highly polar and by introducing the fluorine atoms into the organic moieties result in significant changes in the physical properties and biological activities compared with non- fluorinated precursors [9–11]. It is well known that the fluorinated drugs are innumerable and the study of weak intermolecular interactions involving fluorine is essential in the field of medicinal chemistry. Porphyrins and their metal derivatives have been widely studied due to their distinct spectral, electrochemical properties and novel biological activities. Synthetic porphyrin analogues are considered to be the ligands of choice to mimic natural processes, because of their close resemblance to natural systems in both structure and properties [12]. Study of weak interactions involving halogenated porphyrins offers an emerging field of research in crystal engineering [13]. A diverse range of self- assembly patterns of porphyrin have been discovered, held together by van der Waals interactions, hydrogen bonding, or metal coordination [14–16]. In order to explore the better understanding of intermolecular interactions to the supramolecu- lar assembly, it is crucial to get quantitative measurements of these interactions. Hirshfeld surface analysis [17,18] is becoming a valuable tool for elucidating molecular crystal structures quanti- tatively and such quantitative measures of weak interactions in porphyrins are poorly documented in the literature [16,19]. In this context, we hereby report the crystal structures and Hirshfeld surface analysis of 5,10,15,20-tetrakis(2 0 ,6 0 -difluorophenyl) por- phyrin, H 2 T(2 0 ,6 0 -DFP)P and its metal complexes (Fig. 1). And also, the effect of 2,6-difluorphenyl groups is discussed on the evaluation of intermolecular interactions. 2. Experimental 2.1. Materials and synthetic procedures All the chemicals employed here for the synthesis were commercially available reagents of analytical grade and were used without further purification. Solvents used for the synthesis Journal of Fluorine Chemistry 163 (2014) 16–22 A R T I C L E I N F O Article history: Received 18 February 2014 Received in revised form 31 March 2014 Accepted 2 April 2014 Available online 13 April 2014 Keywords: Supramolecular chemistry Metalloporphyrins Crystal structure analysis Intermolecular interactions Hirshfeld surface analysis A B S T R A C T Herein, we report a series of fluorinated porphyrins, 5,10,15,20-tetrakis(2 0 ,6 0 -difluorophenyl)porphyrin, MT(2 0 ,6 0 -DFP)P where M = 2H, 1; Co(II)(MeOH) 2 , 2; Cu(II), 3; Zn(II)(MeOH) 2 , 4 and Zn(II)(THF) 3 , 5 have been structurally characterized by single crystal X-ray diffraction analysis. All the compounds are crystallized in monoclinic crystal system and the crystal structures of 2, 4 and 5 features octahedral geometry whereas 3 exhibits square planar geometry. The compounds 1, 3 and 2, 4 are isostructural, show similar molecular crystal packing and comparable intermolecular interactions. The supramolecu- lar self assembly of compounds 1–5 is dominated by a variety of intermolecular interactions such as C– H  F, C–H  p, C–F  p and F  F. Furthermore, the role of weak intermolecular interactions in the crystal packing has been analysed and quantified using Hirshfeld surface analysis. ß 2014 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +91 9746244507; fax: +91 495 228 7250. E-mail address: arunkumarc@nitc.ac.in (C. Arunkumar). Contents lists available at ScienceDirect Journal of Fluorine Chemistry jo ur n al h o mep ag e: www .elsevier .c om /loc ate/f luo r http://dx.doi.org/10.1016/j.jfluchem.2014.04.002 0022-1139/ß 2014 Elsevier B.V. All rights reserved.