155 Acta Chim. Slov. 1999, 46(2), pp. 155-160 STRUCTURAL IDENTIFICATION OF TRANS-[MomBr2py4]Br3 (py=PYRIDINE,C5H5N)s J.V.Brenčič , A.N.Chernega and R.Rotar Fac.of Chem. and Chem. Technology, University of Ljubljana, P.O.Box 537, 1001 Ljubljana, Slovenia, jurij.brencic@UNI-LJ.SI Chem. Cryst. Laboratory, 9 Park Road, Oxford, OX1 3PD, United Kingdom (Received 30.3.1999) Abstract Trans-[MoniBr2py4]Br3 crystallizes in the orthorhombic, Pcnm space group, with a=7.670(2), b=22.063(3) and c=15.237(l)Â. Unit cell contains 4 formula units. Mo-Br and Mo-N(pyridine) bonds are 2.552(1) and 2.210(7), 2.222(8)Â. Trans located pyridine rings are staggered. Tribromide ion is symmetrical, but not linear. The compound is isostructural with trans-[MoniCl2py4]Br3 Introduction Trans-[MomBr2py4]Br3 is the product of the oxidative decomposition of trans, trans-[MoBr2py4][MoBr4py2] [1]. Several other halo-pyridine compounds of Molybdenum(III) are known. The first among them mer-MoX3py3 (X=Cl,Br) were prepared long time ago [2]. Later several compounds containing trans and cis-[MoX4py2]"and [MoX5py]2" (X=Cl,Br), were characterised [3,4]. Trans-[MomBr2py4]Br3 was expected to be isostructural with trans-[MomCl2py4]Br3 [5], and the crystal structure analysis was undertaken to prove this hypothesis. Dedicated to the memory of Prof.Dr.Jože Šiftar 156 Results and Discussion Trans-[MoIIIBr2py4]Br3 and trans- [MoIIICl2py4]Br3 are the only examples of the monomeric coordination compounds in which four pyridine ligands are coordinated to molybdenum(III). Trans located pyridine rings are in staggered conformation. Almost identical cation geometry was found before in the structures of trans-[IrIIICl2py4]Cl.6H2O [6], trans-[RhIIICl2py4][H(ONO2)2] [7] and trans-[RuIIICl2py4]- lH(ONO2)2] [8]. On the contrary pyridine rings in trans-[CrF2py4](PF6) are in eclipsed conformation[9]. Eclipsed conformation was found as well in the cationic part of trans,trans-[MoX2py4][MoX4py2] [1]. Cation and anion are located on the two-fold axis. Mo-Br and Mo-N(pyridine) bonds have expected values around 2.55 and 2.20A (see Table 3.). Molybdenum atom has octahedral coordination with octahedral angles close to 900 and 1800. Acute angles between the equatorial plane defined by molybdenum and two nitrogen atoms and the pyridine rings are 45.6(4) and 47.5(4)0. Pyridine rings are planar within 0.01A. All bonds and angles are normal. Angles between the planes of the trans located pyridine rings are 86.0(4) and 93.8(4)A. The tribromide ion is symmetrical and close to linear. As observed before, large cations favour symmetrical structure [10] IIIT Table 1. Crystal data for trans-[Mo Br2py4]Br3 Formula C20H20Br5MoN4 Volume(A3) 2578.1(1) Formula weight 811.86 Dc(mg/m3) 2.09 Space group Pbcn (^(MoKa)mm-1 8.19 Z 4 Indep.refl. 2261 a(Â) 7.670(2) Observ.refl. 1234 b 22.064(3) R, I>3g(I) 0.045 c 15.237(1) wR 0.054 157 Fig. 1. ORTEP view of the molecule with the atomic numbering scheme. Displacement ellipsoids are plotted at the 30% probability level Experimental Trans-[MoIIIBr2py4]Br3 was crystallized from the acetonitrile solution which was concentrated above sulfuric acid at room temperature. Yellow single crystals of square shape were used for X-ray structural analysis. Enraf-Nonius CAD4 diffractometer and co -29 scan mode was used for collecting the data. Reflections were corrected for Lorenz, polarization effects and absorption. Important crystal data are collected in Table 1. Tables 2 and 3 contain atomic positions and dimensions. Figure 1 shows cation and anion with the numbering scheme. The phase problem was solved by direct methods. All nonhydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms were placed in calculated 158 positions and included in the final refinement with the fixed positional and displacement parameters. Crystallographic calculations were carried out using CRYSTALS[11] and NRCVAX [12] program packages. Table 2. Fractional atomic coordinates and equivalent displacement parameters(A2). Ueq is defined as one third of the trace of the ortohgonalized Uij tensor. Atom x y z Ueq Mo 0.00 0.38507(5) 0.25 0.0330(2) Br1 0.24819(2) 0.38553(5) 0.36161(7) 0.0514(3) Br2 0.00 0.64161(7) 0.25 0.0625(3) Br3 0.2131(2) 0.63952(7) 0.3768(1) 0.0874(3) N1 0.133(1) 0.3135(3) 0.1740(5) 0.034(1) N2 0.141(1) 0.4549(3) 0.1727(5) 0.036(1) C11 0.305(1) 0.3167(5) 0.1588(7) 0.042(2) C12 0.392(1) 0.2739(5) 0.1111(8) 0.051(2) C13 0.301(2) 0.2257(6) 0.0772(8) 0.059(2) C14 0.129(2) 0.2221(5) 0.0939(8) 0.055(2) C15 0.046(1) 0.2664(5) 0.1418(7) 0.044(2) C21 0.151(1) 0.4499(4) 0.0852(1) 0.044(2) C22 0.242(2) 0.4909(6) 0.0357(7) 0.059(2) C23 0.326(2) 0.5378(5) 0.0762(8) 0.062(2) C24 0.318(2) 0.5422(5) 0.1649(8) 0.053(2) C25 0.222(2) 0.5001(5) 0.2107(7) 0.055(2) Tables of observed and calculated structure factors, anisotropic displacement parameters and hydrogen atoms positions are available from the authors on request. 159 Table 3. Selected geometric parameters (A,o) Mo - N1 2.210(7) Mo - Br1 2.552(1) Mo - N2 2.222(8) Br2 - Br3 2.531(2) N1 - -Mo- - N2 89.6(3) N1 - Mo - N1i 88.7(3) N1 - ¦Mo- Br1 90.4(2) N2 - Mo - N2i 92.1(3) N2 - Mo- - Br1 89.3(2) N1 - ¦Mo - N2i 178.1(3) N1i - Mo - Br1 89.9(2) B r1 - Mo - Br1i 179.55(6) N2i - Mo - Br1 90.4(2) Br3 - Br2 - Br3i 177.91(9) Symmetry code: (i) -x, y, 1 -z References [1] J. V. Brenčič , L. Golič, I. Leban, R. Rotar, J.Sieler, Z. anorg. allg. Chem. 1996, 622, 2124-2128. [2] A. Rosenheim, G. Abel, R. Levy, Z. anorg. allg. Chem. 1931, 197, 189-211. [3] D. W. DuBois, R. T. Iwamoto, J. Kleinberg, Inorg. Chem. 1969, 8, 815-819. [4] J. V. Brenčič,Acta Chim. Slov. 1997, 44, 131-141. [5] R. Rotar, I. Leban, J. V. Brenčič, Acta Cryst. 1996, C52, 2155-2157. [6] R. S. Gillard, S. H. Mitchell, P. A. Williams, R. S. Vagg, J. Coord. Chem. 1984, 13, 325-330. [7] G. C. Dobson, R. Mason, R. D. Russel, J. Chem. Soc. Chem. Commun. 1967, 62. [8] N. S. Al-Zamil, E. H. M. Evans, R. D. Gillard, T. E. James, T. E. Jenkins, R. T. Lancashire, P. A. Williams, Polyhedron 1982, 1, 523-534. [9] G. Fochi, J. Strähle, F. Gingl, Inorg. Chem.,1981, 30, 4669. [10] J. L. Atwood, P. C. Junk, M. T. May, R. D. Robinson, J. Chem. Crystallogr. 1994, 24, 243-245. [11] D. J. Watkins, J. R. Caruthers, P. W. Betteridge, Crystal user guide, Chemical Crystallography Laboratory, University of Oxford, 1985. [12] E. J. Gabe, Y. Le Page, J. P. Charland, F. C. Lee, P. S. White, NRCVAX-An Iteractive Program System for Structure Analysis, J. Appl. Crystallogr. 1989, 23, 384. 160 Povzetek Trans-[MomBr2py4]Br3 kristalizira v ortorombski prostorski skupini Pcnm z a=7.67(2), b=22.063(3) in c=15.237(l)Â. V osnovni celici so 4 formulske enote. Razdalje Mo-Br in Mo-N(piridin) so 2.552(1) in 2.210(7), 2.222(8)Â. Piridinski obroči, ki so v trans položajih drug napram drugem, tvorijo med seboj pravi kot. Tribromidni anion je simetričen, vendar ni linearen. Spojina ima enako strukturo kot trans-[MomCl2py4]Br3. 161