Molecular structure of nitrogen-linked methyltetrazole-saccharinates Amin Ismael a , José António Paixão b , Rui Fausto c,⇑ , Maria Lurdes S. Cristiano a,⇑ a CCMAR and Department of Chemistry and Pharmacy, F.C.T., University of Algarve, P-8005-039 Faro, Portugal b CEMDRX, Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal c Department of Chemistry, University of Coimbra, P-3004-535 Coimbra, Portugal article info Article history: Available online 16 April 2012 Keywords: Saccharin Tetrazole Tautomerism H-bonding X-ray crystallography Solid state infrared and Raman spectroscopies abstract The molecular structures of nitrogen-linked 1- and 2-methyltetrazole-saccharinates, were investigated in the crystalline phase using X-ray crystallography and infrared and Raman spectroscopies, complemented by quantum chemical calculations performed at the DFT(B3LYP)/6-31++G(d,p) level of theory for the iso- lated molecules. In the neat crystalline solid (space group P  1, a = 6.9763 Å, b = 8.3097 Å, c = 10.0737 Å, a = 96.517°, b = 107.543°, c = 99.989°; Z = 2), 1-methyltetrazole-saccharinate units assume the most sta- ble configuration for the isolated molecule, (1H)-1-methytetrazole iminosaccharin tautomeric form (1MTIS), with the N@C spacer linking the two heterocycles. On the other hand, neat crystalline 2-methyl derivative units (space group P  1, a = 7.8010 Å, b = 8.6724 Å, c = 9.4984 Å, a = 114.083°, b = 107.823°, c = 93.080°; Z = 2) exist in the (2H)-2-methytetrazole aminosaccharin tautomeric form (2MTAS), with the two heterocycles connected by an NH spacer. In both crystals, the structure consists of a packing of dimeric units, the dimers formed via hydrogen bonding involving either the NH group of the saccharyl system (1MTIS) or the spacer amine group (2MTAS). In the former, the hydrogen bond is bifurcated and the NH group acts as a donor both towards a neighbor molecule and an N atom of the tetrazole ring, form- ing an intramolecular hydrogen bond. The observed difference in the crystallographic basic units of the two compounds reveals the prevalence of the H-bond networks in determining the structural preferences of the tetrazole-saccharinates in the solid state. Such structural flexibility appears also to be of potential interest in the design of new ligands based on the tetrazole-saccharinate framework. The relative strengths of the H-bonds in the crystals of the two compounds were evaluated through inspection of their vibrational spectra and empirical correlations between spectroscopic data and the H-bond enthalpies and distances. Ó 2012 Elsevier B.V. All rights reserved. 1. Introduction Tetrazoles and benzisothiazoles (saccharins) have relevant applications in major areas such as medicine, agriculture and food chemistry [1], and are also important building blocks in organic synthesis. For instance, 5-chloro-1-phenyl-(1H)-tetrazole and 3- chloro-1,2-benzisothiazole 1,1-dioxides (saccharyl chlorides) are used as derivatizing agents for alcohols and phenols [2,3]. Because of the strong electron-withdrawing properties of both heterocy- cles, the resulting tetrazolyl and saccharyl ethers may then under- go easy and selective transition metal-catalyzed hydrogenolysis, affording the corresponding alkenes or arenes [4–7]. Furthermore, tetrazoles have been shown to be important intermediates for the synthesis of other heterocyclic compounds, through photolysis [8– 10]. Tetrazoles and saccharins have also important applications in coordination chemistry, as ligands [11,12]. The tetrazolyl ligand may coordinate through four nitrogen electron-donating atoms and may therefore act as a multidentate ligand or as a bridging building block in supramolecular assemblies, being known to be able to participate in at least seven distinct types of coordination modes with metal ions in the construction of metal–organic frame- works. Tetrazolyl-based coordination compounds have also been used in catalysis [13–16]. Similarly, the saccharinate anion (1,2- benzisothiazole-3-one 1,1-dioxide anion; deprotonated saccharin) interacts with metal centres in various ways, generating relatively strong interactions in crystalline environments, mostly through hydrogen bonding. As a polyfunctional ligand, it can be engaged in N, O(C@O) or O(SO 2 )-metal coordination, and can also act as a bidentate amidato-like bridging agent [17–20]. In fields such as supramolecular chemistry [21] and molecular magnetism [22], the design of bridging ligands is instrumental for controlling the molecular architectures required to define spe- cific physical properties in resulting coordination frameworks. In spite of their expectable capabilities as bridging ligands, mixed 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.04.018 ⇑ Corresponding authors. E-mail addresses: rfausto@ci.uc.pt (R. Fausto), mcristi@ualg.pt (M.L.S. Cristiano). Journal of Molecular Structure 1023 (2012) 128–142 Contents lists available at SciVerse ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc