Structural aspects of reversible molecular oxygen uptake.

The system IrX(CO)[P(C(6)H(5))(3)](2) in benzene solution adds mo lecular oxygen reversibly if X is chlorine and irreversibly if X is iodine. The crystal structure of the complex IrIO(2)(CO)[P(C(6)H(5))(3)](2) * CH(2)Cl(2) is reported here and compared with a previous study of the structure of IrClO(2)(CO)[P(C(6)H(5))(3)](2). The O-O bond length is 1.47 +/- 0.02 angstroms in the irreversibly oxygenated iodo-compound and 1.30 +/- 0.03 angstroms in the reversibly oxygenated chloro compound

STRUCTURE OF A CARBON-MONOXIDE ADDUCT OF A CAPPED PORPHYRIN - FE(C2-CAP)(CO)(1-METHYLIMIDAZOLE)

The structure of Fe(C2-Cap)(CO)(1-Melm) has been determined by single-crystal X-ray diffraction methods. It consists of the packing of two crystallographically independent porphyrin molecules and solvate molecules. Both porphyrin molecules display the expected connectivity in which the benzene caps are slanted with respect to the mean porphyrin planes (dihedral angles of 15.5 and 11.5-degrees for molecules 1 and 2, respectively). The centroids of the cap atoms are 5.57 and 5.68 angstrom from the mean porphyrin planes. Since this distance is 3.96 angstrom in H-2(C2-Cap), the cap moves 1.6-1.7 angstrom further away from the porphyrin upon binding a CO ligand inside the cavity. The coordinated CO ligand is slightly but detectably distorted from linearity, being both bent and tilted off the axis normal to the porphyrin. The Fe-C-O bond angle and the off-axis displacements for the C and O atoms of CO are 173.1 (9)degrees, 0.17 angstrom, and 0.41 angstrom, respectively, for molecule 1, and 175.8 (8)degrees and 0.12 and 0.28 angstrom, respectively, for molecule 2. Crystallographic data: triclinic P1BAR, Z = 4, a = 18.022 (2) angstrom, b = 20.017 (1) angstrom, c = 20.691 (2) angstrom, alpha = 70.507 (7)degrees, beta = 76.232 (10)degrees, gamma = 82.549 (7)degrees at -150-degrees-C, 18 468 observations, 1740 variables, R(F) = 0.096 (F0(2) > 3-sigma(F0(2))).X1166sciescopu

PREPARATION AND STRUCTURES OF 2 STERICALLY PROTECTED RUTHENIUM PORPHYRIN COMPOUNDS OF THE TYPE-RU(POR)(H2O)(IN)(CO)(OUT)

Two sterically protected ruthenium porphyrin compounds of the type Ru(Por)(H2O)in(CO)out have been prepared, and their structures have been determined by single-crystal X-ray diffraction methods. Both compounds, Ru(beta-PocPivP)(H2O)in(CC)out (1), a ''pocket'' porphyrin, and Ru(OCCOPor)(H2O)in(CO)out (2), a ''capped'' porphyrin, pack as discrete porphyrin units with solvate molecules. In both compounds, the H2O ligand is inside the sterically protected region while the CO ligand is trans to the H2O molecule and is on the outside of the protected region. In Ru(beta-PocPivP)(H2O)in(CO)out, the H2O ligand is hydrogen-bonded to an amide oxygen atom, the O(H2O)-O(amide) distance being 2.688(4) angstrom; in Ru(OCCOPor)(H2O)in(CO)out, the H2O ligand, though not involved in traditional hydrogen bonding, may interact with the aromatic pi system of the benzene cap, the O(H2O)-cap centroid distance being 2.98 angstrom. The carbonyl groups have their normal, linear arrangement, with the Ru-C-O angles being 178.7(3) and 178.1(4)degrees in 1 and 2, respectively. In each structure, the porphyrin plane is slightly ruffled, with the Ru atom lying 0.20 and 0.26 angstrom below the porphyrin plane toward the carbonyl group in 1 and 2, respectively. In each structure, the cap is off-center and tilted. Each cap centroid lies 4.25 (1) and 4.79 A (2) above the porphyrin plane. These structures provide some useful insights info steric constraints in these encumbered porphyrins. Crystallographic data for Ru(beta-PocPivP)(H2O)in(CO)out.2CHCl3 (1): triclinic, C(i)l-P1BAR, Z = 2, a = 13.261(3) angstrom, b = 14.450(3) angstrom, c = 15.716(3) angstrom, alpha = 91.63(3)degrees, beta = 94.94(3)degrees, gamma = 94.40(3)degrees, 1 = -167-degrees-C, 11 611 unique reflections, 805 variables, R(F( (F(o))2 > 2sigma(F(o)2)) = 0.045, R(w)(F2) = 0.101. Crystallographic data for Ru(OCCOPor)-(H2O)in(CO)out-2CHCl3-1/2n-C6H12 (2): triclinic C(i)l-P1BAR, Z = 2, a = 9.651(2) A, b = 11.936(2) angstrom, c = 25.964(5) angstrom, alpha = 92.14(3)degrees, beta = 91.58(3)degrees, gamma = 104.99(3)degrees, t = -167-degrees-C, 15 970 unique reflections, 760 variables, R(F) (F(o)2 > 2sigma(F(o)2)) = 0.086, R(w)(F2) = 0.183.X1116sciescopu

SYNTHESES AND CHARACTERIZATION OF THE RUTHENIUM CARBONYL PORPHYRIN COMPLEXES RU(TPP)(CO)(1-MEIM) AND RU(ALPHA-POCPIVP)(CO)(1-MEIM)

Ru(TPP)(CO)(1-MeIm) and Ru(alpha-PocPivP)(CO)(1-MeIm) (TPP = tetraphenylporphyrinato; PocPivP = 'pocket' porphyrin dianion) were prepared by metalation of the free-base porphyrins with Ru-3(CO)(12), followed by reaction with 1-MeIm. The structures of Ru(TPP)(CO)(1-MeIm) and Ru(alpha-PocPivP)(CO)(1-MeIm) have been determined by single-crystal X-ray diffraction methods. The compound Ru(TPP)(CO)(1-MeIm) packs as one crystallographically independent porphyrin molecule with toluene solvate, whereas Ru(alpha-PocPivP)(CO)(1-MeIm) crystallizes as two crystallographically independent porphyrin molecules, molecule A and molecule B, with disordered solvate, modeled as water. In Ru(TPP)(CO)(1-MeIm) the Ru atom lies 0.032 Angstrom out of the 24-atom porphyrin plane toward the CO ligand. The Ru-C-O bond angle is 179.3(2)degrees and the Ru-C(CO) and C-O bond distances are 1.828(2) Angstrom and 1.147(3) Angstrom, respectively. The Ru-N-ax(1-MeIm) distance is 2.187(2) Angstrom, compared with an average Ru-N-eq(porphine) distance of 2.058(3) Angstrom. The molecular structure of Ru(alpha-PocPivP)(CO)(1-MeIm), a sterically protected 'pocket' porphyrin, is more distorted than that of Ru(TPP)(CO)(1-MeIm). In molecule A the Ru atom lies 0.03 Angstrom out of the 24-atom porphyrin plane toward the 1-MeIm ligand whereas in molecule B the Ru atom lies 0.01 Angstrom out of the porphyrin plane toward the CO ligand. For molecule A the Ru-C(CO) and C-O bond distances are 1.82(3) Angstrom and 1.18(3) Angstrom, respectively, and the Ru-C-O bond angle is 168(3)degrees. Respective values for molecule B are 1.82(2) Angstrom, 1.16(3) Angstrom, and 159(3)degrees. The M-N-ax distances are 2.20(2) Angstrom and 2.16(2) Angstrom, respectively, for molecules A and B. The average M-N-eq distances are 2.03(3) Angstrom and 2.03(5) Angstrom. The CO stretching frequencies are 1939 cm(-1) for Ru(TPP)(CO)(1-MeIm) and 1933 cm(-1) for Ru(alpha-PocPivP)(CO)(1-MeIm). Crystallographic data for Ru(TPP)(CO)(1-MeIm): triclinic, C-i(1)-P (1) over bar, Z = 2, a = 9.796(2) Angstrom, b = 13.320(1) Angstrom, c = 17.618(2) Angstrom, alpha = 74.88(1)degrees, beta = 87.97(1)degrees, gamma = 83.23(1)degrees, T = 153 K, 9049 unique reflections, 579 variables, R(F) (F-o(2) > 2 sigma(F-o(2))) = 0.034, R(w)(F-2) = 0.094. Crystallographic data for Ru(alpha-PocPivP)(CO)(1-MeIm): orthorhombic, C-2v(9)-Pn2(1)a, Z = 8, a = 26.672(5) Angstrom, b = 32.243(6) Angstrom, c = 14.124(3) Angstrom, T = 150 K, 8006 unique reflections, 699 variables, R(F) (F-o(2) > 2 sigma(F-o(2))) = 0.113, R(w)(F-2) = 0.246.X1112sciescopu

An investigation of the rare-earth telluride system BaLn2Te4 (Ln = Sm-Tm, Y): Syntheses, crystal structures, and magnetic properties

Single crystals of BaLn2Te4 (Ln = Gd-Tm, Y) form as black needles from the stoichiometric reaction BaTe + 2Ln + 3Te at 1000°C. BaSm2Te4 forms as a by-product in the reaction BaTe + Sm+Zn + Te at 850°C with the aid of a BaBr2/KBr flux. The compounds crystallize with four formula units in the space group D2h16-Pnma (No. 62) in the CaFe2O4 (calcium ferrite) structure type. Unit cell constants range from a = 13.6883(10) Å, b = 4.5148(3) Å, and c = 16.3427(12) Å in the Sm compound to a = 13.5677(10) Å, b = 4.4058(3) A, and c = 15.9989(12) Å for Tm (t= -120°C). Ln atoms are coordinated by six Te atoms in an octahedral arrangement. These octahedra share corners and edges to form a three-dimensional channel structure. Ba atoms occupy the bicapped trigonal-prismatic sites within these channels. Magnetic susceptibility data for two representative compounds (Ln = Er and Tb) show paramagnetic behavior in the region 5-300 K. © 2000 Elsevier Science S.A. All rights reserved

Carbide-derived nanoporous carbon and novel core-shell nanowires

Carbide-derived carbon (CDC) nanowires (NWs) have been synthesized by the high-temperature treatment of small-diameter beta-SiC whiskers with Cl-2/H-2. A variety of physical measurements indicate that Si was extracted by exposure to Cl, and that the C in the carbon nanowires is primarily sp(2)-bonded. From BET measurements, the specific surface area of these carbon nanowires is 1.3 x 10(3) m(2)/g and they contain a network of nanopores. Nanoindentation measurements indicate that the SiC-derived C is not a stiff material, the elastic modulus being 5.0 +/- 1.2 GPa. High-temperature treatment of the CDC nanowires under an inert gas significantly increases the degree of graphitization. In addition, partial extraction was used to obtain core-shell structures having a thin and also very high surface area CDC shell; further treatment at high temperature was used to produce graphitized carbon shell-crystalline SiC core NWs