Ivan Bernal

The crystal and molecular structures of di-π-cyclopentadienyltitanium pentachalcogenides (C5H5)2TiS5−xSex : I. The structural properties of π-(h5C5H5)2TiS5

Abstract The crystal and molecular structure of (C5H5)2TiS5 has been determined from diffractometry data. The cell constants are a = 9.019(3) A, b = 13.089(6) A, c = 11.294(3) A, β = 93.62(4)°; the space group is P21/n, and Z = 4. The molecule consists of a titanium atom which is part of a six-membered ring whose other members are the five sulfur atoms of the polysulfide chain. This ring has a cyclohexane-like chair configuration. The coordination polyhedron about the titanium comprises the two terminal sulfur atoms of the pentasulfide chain and the centroids of the π-cyclopentadienyl rings and is in the form of a distorted tetrahedron. The S-Ti-S angle is 94.6° while the (centroid)-Ti-(centroid) angle is 133.7°. The Ti-S distances are 2.422(1) A and 2.448(1) A. The four S-S distances range from 2.056 to 2.067 A (average e.s.d. 0.002 A) with an average value of 2.060 A. This average S-S distance is very close to the values found in the polysulfide chain S42− and in various allotropes of elementary sulfur. The narrow range of titanium-carbon distances, 2.341 to 2.398 A (average e.s.d. 0.005 A), establish a distinct pentahapto coordination mode for the five-membered rings with respect to the titanium atom. The titanium-ring centroid distances of 2.066 and 2.071 A are among the longest thus far found for cyclopentadienyl rings coordinated to transition metals.

The crystal and molecular structure of (1,1′-trimethylenedicyclopentadienyl)titanium dichloride ☆ ☆☆

Abstract The crystal and molecular structure of (1,1′-trimethylenedicyclopentadienyl)titanium dichloride, [(CH 2 ) 3 (C 5 H 4 ) 2 ]TiCl 2 , has been determined from three-dimensional X-ray data collected by counter techniques. The coordination about the titanium atom is a distorted tetrahedron comprised of the two chlorine atoms and the centroids of the π-cyclopentadienyl rings of the 1,1′-trimethylenedicyclopentadienyl group. The Cl-Ti-Cl bond angle is 93.69(5)° and the (centroid)-Ti-(centroid) angle is 132:64°. The Ti-Cl bond distances are 2.372(1) and 2.364(3) A . The titanium- (ring centroid) distances are 2.061 and 2.060 A and the range of the Ti-C distances associated with the π-cyclopentadienyl rings, 2.407(3) to 2.360(4) A , establishes the pentahapto coordination mode of these groups. Crystal data: a = 8.490(2), b = 14.209(4), c = 10.185(2) A , β = 90.43(2)°, space group P 2 1 / n , Z = 4, D o = 1.57(1) and D c = 1.57 g·cm -3 . The structure was refined by least-squares techniques, using 1668 independent reflections for which F 2 o > 3σ( F 2 o ), and the refinement converged to a conventional R factor (on F of 2.9%.

THE CRYSTAL AND MOLECULAR STRUCTURE OF AN OCTACOORDINATED IRON(II) COMPOUND—TETRAKIS(1,8-NAPHTHYRIDINE)Fe(II) PERCHLORATE

Abstract Recently, Hendricker and Bodner reported the synthesis of a series of first-row transition metal complexes of the type M(L)4(C1O4)2, where M is a metal of the 3d transition series and L = 1,8-naphthyridine. Preliminary space group determination indicates that all the perchlorates of the 3d-transition series from M = Mn2 + to M = Zn2 + are isomorphic. Single crystals suitable for X-ray diffraction studies were grown from methanol solutions of the perchlorate salts. Red, prismatic, crystals of the Fe(II) salt were found to be triclinic with the following cell dimensions: a = 9.163(3), b = 9.315(3), c = 20.116(8) A, α = 99.66(8), β = 77.37(8) and γ = 91.70(8)°; Z = 2 molecules/unit cell. V(obs) = 1651.62(A)3 D(exp) = 1.57; D(calc) = 1.56 gms/cc. It was assumed that the space group is PΓ, which was verified by structure solution and refinement. The intensity data were collected with MoKα radiation (λ = 0.71069 A) using a manually-operated Picker four-circle goniometer. In all 1969 non-zero, independe...

STRUCTURAL STUDIES AND MÖSSBAUER SPECTRA OF FE4S4 CLUSTER SYSTEMS: BIOLOGICAL IMPLICATIONS OF THESE RESULTS

Abstract The structural arrangement of the iron-sulfur centers in the non-heme iron-sulfur proteins has been the subject of extensive physical investigations.1–4 Particular emphasis has been placed on the “ferredoxins” which have seven or eight iron atoms and eight or more sulfur atoms per protein unit. Several workers5–7 have proposed that the iron-sulfur cluster compounds of composition [Fe4S4L4] n- , where L=S2C2(CF3)2, may be useful model systems for the ferrodoxins. We report here a brief description of the structural parameters for the Fe4S4L4 −2 cluster and the Mossbauer data for the three derivatives, n=0, 1, 2. The data are compared with that reported for inorganic cluster systems of known structure and with the available data on non-heme iron-sulfur proteins.

The crystal structure of K3Cu(NO2)3

Abstract The compound crystallizes in the orthorhombic system, space group D162h-Pbnm with cell constants of a = 21.70(4), b = 18.94(4) and c = 10.88(2) A. The unit cell volume, observed and calculated densities are, respectively, 4471.66 A3, 2.46(2) g cm−3 and 2.44 g cm−3. There are 16 molecules of Kt3Cu(N02)5 in the unit cell and the anions crystallize in the lattice as four independent Cu(NO2)53- species located at positions (c) of the space group. Molecularly, they are identical in pain inspite of being crystallographically independent from one another. One Cu(NO2)53- species is bound through the nitrogen of three NO−2 ligands and by two in a symmetrical, bidentate fashion (i.e., The other type of Cu(N02)53- species present in the lattice contains all modes of coordination of NO−2 when bound to a single metal center. That is, there are two monodentate CuNO2 bonds, two monodentate CuONO bonds and one symmetrical, bidentate attachement of the type described above. There are eight crystallographically independent potassium ions in the lattice: four sit at general positions while the other four are found at mirror planes. The coordination around the potassium ions is irregular and determined primarily by packing considerations dictated by the anions. The coordination number of the potassiums vary considerably and the exact number of ligands around each depends on the length of the radius one is willing to consider reasonable for bonding. Details are discussed in the text.

The neutron diffraction structure of [C5H4(CH2)3C5H4]TiCl2☆

Abstract The crystal structure of 1,1′-trimethylene-di-π-cyclopentadienyl titanium dichloride, [C 5 H 4 (CH 2 ) 3 C 5 H 4 ]TiCl 2 , was determined from three-dimensional neutron diffractometry data in order to obtain accurate information for those structural parameters involving hydrogen atoms. Also, we were interested in the effect on the CC bond lengths of shifting electron density from the C atoms and accumulating it in the regions of the π-bonds of the Cp rings. The substance crystallizes as deep red-brown parallelepipeds in the monoclinic space group P2 1 /n with a = 8.490(2), b = 14.209(4), c = 10.185(2) A, and β = 90.43(2)°. The cell volume is 1228.6 A 3 while the measured and calculated densities are 1.566(8) and 1.572 gm-cm −3 , respectively. The molecule consists of a planar TiCl 2 fragment sandwiched equidistantly between two eclipsed rings which are canted such that their normals make an angle of 133.1° and linked by a (CH 2 CH 2 CH 2 ) chain. The entire propyl chain is to one side of the vector bisecting the ClTiCl angle and the ring carbons connected to the terminal CH 2  groups of the propyl chain do not occupy the position of nearest approach between the two rings. The normal to the plane of each of the rings does not coincide with the Ti-(ring centroid) vector, the angle between the two being 0.80° for ring 1 and 0.70° for ring 2. The two TiCl distances are 2.368(8) and 2.365(9) A and the Cl(1)TiCl(2) angle is 93.2(3)°. The average CC distance for rings 1 and 2 are 1.416(7) and 1.402(7) A, respectively. The average Cp CH distance is 1.05(2) and 1.12(2) A for rings 1 and 2. The average CCC and CCH angles are 108.0(5) and 126.0(8)° for ring 1 and 107.9(5)° and 125.6(9)° for ring. 2. The average C(cp)C(H 2 ) distance is 1.494(7) A while the average C(H 2 )C(H 2 ) distance is 1.509(8) A. The average aliphatic CH distance is 1.06(2) A. Finally, the average values of the CCC, CCH, and HCH angles at the aliphatic chain are 115.1(5), 109.9(8), and 105.7(9)°, respectively. The normals to rings 1 and 2 make angles of 23.9 and 22.9° with the normal to the TiCl 2 plane. The Cl atoms 1 and 2 lie 1.703 and 1.736 A, respectively, above and below the plane defined by (ring 1 centroid)-Ti-(ring 2 centroid). The angles between the vectors (ring 1 centroid)-Ti and (ring 2 centroid)-Ti with the normal to the plane defined by the TiCl 2 , fragment are 23.4 and 23.5°, respectively. The perpendicular distances between the ring centroids and the TiCl 2 plane are 1.89 and 1.89 A, respectively, for the rings 1 and 2. Finally, the angles between the TiCl(1) and TiCl(2) vectors with the normal to the (ring 1 centroid)-Ti-(ring 2 centroid) plane are 135.9 and 137.1°. The maximum deviation of any carbon from planarity in rings 1 and 2 is 0.01 and 0.05 A, respectively. The maximum deviation from planarity of any hydrogen from the plane defined by the hydrogens of rings 1 and 2 is 0.03 and 0.02 A. The planes defined by the hydrogens do not coincide with the planes defined by the five carbons of the same Cp ring. There is a slight, very possibly insignificant, but consistent displacement of the ring hydrogens towards the Ti atom in both rings. A measure of this effect can be obtained from the following distances: Ti-(Plane of Carbons, Ring 1) = 2.06 A Ti-(Plane of Hydrogens, Ring 1) = 2.04 Ti-(Plane of Carbons, Ring 2) = 2.06 Ti-(Plane of Hydrogens, Ring 2) = 2.04 For each ring, the difference in pairs of these quantities probably do not exceed two standard deviations and, except for the consistency of the results for the two rings, are doubtful significance. All distances and angles involving heavy atoms are in excellent agreement with the results of an X-ray study reported elsewhere. The CC distances in the rings obtained by neutron diffraction are slightly larger than those obtained in the X-ray study, as expected. The final values of the discrepancy indices for the present study are R 1 = 0.053 and R 2 = 0.048, with an error of fit of 1.04.

Structure of a novel fluxional molecule: 1,2,3-trithia-[3]-ferrocenophane

The crystal and molecular structure of 1,2,3-trithia-[3]-ferrocenophane has been determined from three-dimensional X-ray data collected by counter techniques. The molecule consists of two nearly parallel, eclipsed cyclopentadienyl rings linked by an S3 bridge. The material crystallizes in the monoclinic space groupP21/c with unit cell parametersa = 9·628(3),b = 9·347(4),c= 11·408(4) Å, β = 96·70(3) °. The structure was solved by standard techniques and the least-squares refinement converged to a conventionalR factor of 9·6 %.

The crystal and molecular structure of bicyclo[2.2.1]-hept-2-en-5,6-dinitrosocobalt-η5-cyclopentadienide. Evidence for a nitroxyl diradical bidentate ligand

Abstract An accurate X-ray crystallographic structural study of a metal complex having a nitroxyl diradical as a bidentate ligand has been carried out. Bicyclo[2.2.1]-hept-2-en-5,6-dinitrosocobalt-η 5 -cyclopentadienide crystallizes in space group P 1 with Z 2, a 8.245 ± 0.007, b 10.285 ± 0.016, c 7.888 ± 0.008 A and α 59.276 ± 0.073, β 101.099 ± 0.053, γ 108.802 ± 0.067°. Intensities of 1831 independent reflections were used in the refinement of the structure to an R ( F ) of 4.6%. The bonding of the Co atom to the cyclopentadienyl ligand appears to be a normal pentahapto linkage. The lone double bond and the CC single bonds adjacent to the endo hydrogens of the norbornene fragment of the molecule are shorter than have previously been reported for this moiety. This study represents the first structural report of NO groups bridging to Co. The CoNO angles (129.4(3) and 128.9(3)°) and the NO stretching frequency (1357 cm −1 ) of the title compound resemble values found in nitroxyl free radical compounds more closely than values found in bridging NO group compounds.

Crystal and molecular structure of bis-tetraphenylarsonium-tris-(cis-1,2-dicyano-1,2-ethylenedithiolato)Fe(IV)

The crystal structure of bis-tetraphenylarsonium-tris-(cis-1,2-dicyano-1,2-ethylenedithiolato)Fe(IV), [(C6H5)3As]2Fe[S2C2(CN)2]3, has been determined using 3154 independent, non-zero reflexions collected by counter techniques. The substance crystallizes in the monoclinic system: space groupI2/a,a = 20·153(8),b = 13·411(5),c = 21·497(8) Å and β = 95·28(8) °;Dm = 1·41(2),Dc = 1·43 g cm−3 andZ = 4. The structure consists of Ph4As+ cations in general positions and tris-(cis-1,2-dicyano-1,2-ethylenediothiolato)Fe(IV) anions on two-fold axes. Although the coordination around the arsenic atom is tetrahedral, the overall symmetry of the cation is 1 (C1), probably because the phenyl rings are rotated to accommodate the requirements of packing. The coordination of the six sulphur atoms about the iron atom is trigonal antiprismatic, approximating closely to an octahedron: for any pair oftrans sulphur atoms, the S-Fe-S angle is about 171 °.

Crystal structure of the orange isomer of [(C6H5)3P]2[C2S2(CF3)2]RuCO

The structure of the title compound has been determined by X-ray analysis. It is monoclinic:a = 10.147,b = 10.081,c = 38.627 Å, β = 102.27 °,Z = 4,P21/c. The structure was solved by standard methods and refined by least squares to a (conventional)R-factor of 4.7%. The Ru atom is in square-pyramidal configuration: the Ru-S distances (2.286, 2.336Å) are significantly different, but the Ru-P distances average to 2.389 Å. Comparisons are made with the violet isomer.