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Two Independent Determinations of the Crystal and Molecular Structure of the Iodine Monochloride Complex of Pentamethylenetetrazole Norman C. Baenziger,la A. Dwayne Nelson,la A. Tulinsky,lb John H. B1oor,lb,cand Alexander I. Popovlb Contribution f r o m the Departments of Chemistry, University of Iowa, Iowa City, Iowa 52240, and Michigan State University, East Lansing, Michigan 48823. Received June 26, 1967 Abstract: Two independent structure determinations have been carried out on the iodine chloride complex of pentamethylenetetrazole (PMT) by the use of X-ray crystallographic techniques. The two structures agree in general and agree in particular on readily determined parameters (involving iodine and/or chlorine). Thus, the PMT acts as a unidentate ligand with the iodine of IC1 bound to N(2) of the tetrazole ring, the N . . . I-CI group is linear and coplanar with the tetrazole ring which is itself planar, and the seven-memberedring of PMT is in a chair conformation. The results of the independent determinations are compared with respect to one another and other related molecules.
structure of the PMT.IC1 complex would yield some int has been shown in several publications that 1,5-subformation on the bonding site of the tetrazole ring. stituted tetrazoles and, in particular, pentamethylenetetrazole (hereafter abbreviated as PMT, CGHION~, Coincidentally, the determination of the crystal structure of the PMT.IC1 complex was begun quite indesee Figure 1) behave as relatively strong electron pendently in two laboratories (University of Iowa and donors. A solid addition compound PMT.IC1 has Michigan State University) and only upon the complebeen prepared,2 and the formation constant of this comtion of the two studies did the two groups of investigaplex was determined in carbon tetrachloride solutions. tors become aware of each others’ results. In the inCorresponding complexes with iodine bromide and ioterest of brevity and to compare the independent results, dine could not be isolated in the solid state but their both determinations are reported here. The designaexistence in solutions was shown by spectrophotometric tion of BN will refer to the authors Baenziger and Nelson techniques and their formation constants were likewise determined. Recently, transition metal complexes of and the designation of TBP will refer to the authors Tulinsky, Bloor, and Popov. PMT, of the type M”(PMT)6(C104)2, where M” = Fe, Mn, Co, Ni, and Zn, have also been reported. It appears that in all of the above complexes PMT acts Structure Determination According to B N as a unidentate ligand. This leads one to conclude that Crystals of PMT IC1 recrystallized from chloroform either complexation with a halogen or a transition metal gave yellow prisms. Since the crystals appeared to ion at any of the four ring nitrogens deactivates the ring sublime at room temperature, a crystal (0.3 X 0.3 X toward further complexation or there is only one pre0.4 mm) sealed in a thin-walled glass capillary was used ferred bond site available for coordination. to obtain the intensity data. Precession film intensity It is interesting to point out that although PMT is a data (Mo K a ) , hkO to hk5 and h01 to h51, were estirelatively strong electron donor toward Lewis acids mated visually and 844 independent reflections were such as halogens and transition metal ions, it has very observed. Lorentz-polarization corrections were made, little affinity for protons. In fact, it has essentially no but absorption corrections were not applied ( p < 1 basic properties in aqueous solution and behaves only cm-l). The unit cell dimensions determined from as a weak base even in acetic acid solutions. back-reflection Weissenberg diagrams by a least-squares It has been suggested that tetrazoles may form coextrapolation method gave a = 13.087 i 0.002, c = ordinate compounds through the ir-electron system 8.339 & 0.002 A. The b cell dimension determined of the tetrazole rings5 A study of charge-transfer from precession diagrams is less accurately known: complexes of mono- and disubstituted tetrazoles with b = 18.83 & 0.02 A. From the systematic absences ir-electron acceptors has shown that, while such comthe space group is Pbca. plexes do exist in solutions, they are extremely unstable A three-dimensional Patterson map revealed the and are largely dissociated even in concentrated soluI-C1 group. Using the position parameters for I and tiom6 C1 (R = 0.28), the positions of the nonhydrogen atoms In view of the somewhat unusual donor properties of in the molecule were obtained from a three-dimensional PMT, it was thought that a detailed analysis of the electron density difference map. Least-squares refinement proceeded through steps using first isotropic tem( I ) (a) University of Iowa; (b) Michigan State University; (c) perature factors and then anisotropic temperature National Science Foundation Undergraduate Participant, 1965-1966. (2) A . I . Popov, C. C. Bisi, and M. Craft, J . Am. Chem. Soc., 80, factors. (Atom scattering factors were the neutral 6513 (1958). atom value’ corrected for dispersion.) The weighting (3) F. M. D’Itri and A . I. Popov, Inorg. Chem., 5, 1670 (1966). (4) A . I. Popov and R. D. Holm, J . Am. Chem. Soc., 81, 3250 (1959). scheme used was w‘’~ = l/sF where sF is the standard
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( 5 ) A . D. Harris, H. H. Herber, H. B. Jonassen, and G . K. Wertheim, ibid., 85, 2927 (1963). (6) 1.C. Wehman and A . I. Popov, J . Phys. Chem., 70, 3688 (1966).
(7) “International Tables for X-ray Crystallography,” Vol. 3, The Kynoch Press, Birmingham, England, 1962, pp 202, 211.
Baenziger, Nelson, Tulinsky, Bloor, Popov / Pentameth ylenetetrazole-IC1 Complex
6464 Table I. Atom Parameters0 (Values X lo4)
