The crystal structure of 1,1-bis(η5-cyclopentadienyl)-2,3,4,5-tetraphenylzirconole

The crystal and molecular structure of (η⁵-C₅H₅)₂Zr[C₄(C₆H₅)₄] has been determined by single crystal X-ray diffraction methods. The compound is isostructural with its titanium and hafnium analogues, and crystallizes in the monoclinic space group P2₁/n with unit cell parameters a = 13.790(5), b = 11.136(5), c = 18.692(7) », β = 92.82(4)°, and ?_calc = 1.34 g cm^?3 for Z = 4. Full-matrix least-squares refinement converged with a conventional R value of 0.049 for 2986 observed reflections. The metallocyclic ring is planar to within 0.05 », and the π-electron density is largely localized. The two independent ZrC(σ) bond lengths are 2.250(5) and 2.265(6) ». The ZrC(η⁵) distances range from 2.482(6) to 2.546(7) », and average 2.521(20) ». A comparison of zirconium- and hafnium-carbon bonds based on the data available shows that for M = Hf the MC bonds are shorter for all cases: C(sp), C(sp²), C(sp³), C(η⁵).     

Inorganic Chemistry in Liquid Ammonia : by David Nicholls,Elsevier Scientific Publ. Co., Amsterdam/Oxford/New York, 1979, x + 238 pp., Dfl. 110.00, $ 49.00.

Substitution of the hydrogen atoms of the cyclopentadienyl ring of (N, N-dimethylaminomethyl)cymantrene by deuterium changes the direction of orientation of metalation of this amine.     

Stoffwechselprodukte von Mikroorganismen. 177. Mitteilung. Avilamycin C

From cultures of the Avilamycin (Avilamycin A) producing organism, Streptomyces viridochromogenes, strain ETH 23575, a second antibiotic, Avilamycin C, C₆₁H₉₀Cl₂O₃₂ could be isolated in crystalline form. Both Avilamycins belong to the group of the Orthosomycins. By IR., ¹H- and ¹³C-NMR. spectroscopy and by transformation to a common derivative it could be proven that Avilamycin A is a methyl ketone, Avilamycin C the corresponding methyl carbinol.     

CNDO/2 calculations of some polyazaindenes

The theoretically estimated dipole moments of indolizine, imidazo[1,2-a]pyridine, imidazo-[1,5-a]pyridine and of pyrazolo[ 1,5-a]pyridine obtained by the CNDO/2 approximation have been compared with the experimental values. The bond angles and bond distances for these polyazaindenes have been estimated.     

Molecular orbital theory of the properties of inorganic and organometallic compounds. 3. STO-3G basis sets for first- and second-row transition metals

STO -3G minimal basis sets for first- and second-row transition metals have been formulated and applied to the calculation of equilibrium geometries for a variety of inorganic systems, metal carbonyls, and organometallic compounds. While the overall level of agreement with experiment is not as good as that previously noted for main-group compounds, most trends and many subtle features in geometries are reproduced.     

Calculation of Gurney parameters for aqueous tetraalkylammonium halides based on Friedman's cosphere-overlap model

Recalculations of the Gurney free-energy parameters A_ij based on the cosphereoverlap model of Friedman and co-workers have been made using more recent experimental data. Our procedure for calculation seems to be more systematic than those previously reported. The excess energy, entropy, and volume parameters (E_ij, TS_ij, and V_ij) were also recalculated for some aqueous tetraalkylammonium halides. In addition, the excess-heat-capacity parameters C_ij are also reported here for the first time. These data are discussed briefly in terms of the structural implications.     

Bis(1,2-bis(diphenylphosphino)ethane)tungsten(0) Complexes Containing Electron-Saturated Metal Centers and Singly-Coordinated Bridging Ligands

Reaction of 1,4-diisocyanobenzene or 4-isocyanobenzonitrile with trans-W(N(2))(2)(DPPE)(2) (DPPE = 1,2-bis(diphenylphosphino)ethane) produced cis-WL(2)(DPPE)(2), where L = 1,4-diisocyanobenzene or 4-isocyanobenzonitrile. cis-(CNC(6)H(4)NC)(2)W(DPPE)(2) crystallizes in the triclinic space group P&onemacr;, with a = 12.848(3) ?, b = 13.596(3) ?, c = 19.072(3) ?, alpha = 78.99(2) degrees, beta = 70.66(2) degrees, gamma = 65.26(2) degrees, V = 2849.8(11) ?(3), and Z = 2. cis-(NCC(6)H(4)NC)(2)W(DPPE)(2) crystallizes in the triclinic space group P&onemacr;, with a = 12.712(3) ?, b = 13.700(3) ?, c = 19.109(3) ?, alpha = 77.91(2) degrees, beta = 70.63(2) degrees, gamma = 64.76(2) degrees, V = 2830.7(13) ?(3), and Z = 2. Both compounds possess a distorted octahedral geometry about the metal center, with the two isocyanide ligands cis to one another. The isocyanide ligands are substantially bent along the CNC axis of the isocyanide group coordinated to tungsten. For the complex containing the symmetric ligand, CNC(6)H(4)NC, the mean CNC angle for the coordinated end of the isocyanide is 139.1(11) degrees, the average W-C bond length is 1.86(1) ?, and the C&tbd1;N bond lengths have a mean value of 1.30(2) ?. These data indicate substantial back-donation from an electron-saturated tungsten atom. This is supported spectroscopically, with substantial shifts to lower wavenumbers for the C-N stretching frequencies of the coordinated isocyanide groups. Similar trends are observed in cis-(NCC(6)H(4)NC)(2)W(DPPE)(2). Both compounds contain electron-rich metals surrounded by large ligands which apparently protect the metals from atmospheric oxidation. The isocyanide ligands in both complexes contain a second coordinating group pointing away from the metal into the environment surrounding the molecules, providing the potential for polymetallic complexes containing metals in a variety of oxidation states.     

Synthesis of mixed metal decaosmium carbido clusters: The X-ray structures of the monoanions [Os10C(CO)24Cu(NCMe)]− and [Os10C(CO)24AuPPh3]−

The high nuclearity mixed metal cluster monoanions [Os₁₀C(CO)₂₄Cu(NCMe)]^? (I) and [Os₁₀C(CO)₂₄AuPPh₃]^? (II) have been obtained by reaction of the carbido-dianion [Os₁₀C(CO)₂₄]^2? (III) with one equivalent of [Cu(NCMe)₄] [BF₄] and Ph₃PAuCl, respectively, in CH₂Cl₂. X-ray analysis of the [PPh₃Me]⁺ salts of I and II show that the Cu and Au ligands have added to capping tetrahedra of the dianion III in μ₃- and μ₂-bridging positions, respectively.     

The amperometric detection of thyroid hormones following reverse-phase high-performance liquid chromatography

The principle of an assay of the major thyroid hormones by an electrochemical technique is demonstrated. The separation of 3,3',5-triiodothyronine, 3,3',5'-triiodothyronine, and thyroxine, by reverse-phase high-performance liquid chromatography is followed by their electrochemical oxidation in a thin-layer electrochemical detection cell with a low-temperature isotropic carbon working electrode. The limits of detection found were in the subnanogram range with linear response in the ranges 0–125 ng for T₃ and 0–500 ng for T₄. The approach makes the simultaneous assay of total serum thyroid hormones feasible.     

Methyl displacements from cyclopentadienyl ring planes in sterically crowded (C5Me5)3M complexes

The displacements of the methyl substituents away from the metal and out of the cyclopentadienyl ring plane are compared in sterically crowded (C(5)Me(5))(3)M complexes vs sterically normal f-element complexes in an attempt to evaluate the utility of this parameter in predicting unusual (C(5)Me(5))(1-) ring reactivity. The out-of-plane displacements of 16 sterically crowded tris(cyclopentadienyl) complexes of general formula (C(5)Me(5))(3)M, (C(5)Me(4)R)(3)M (R = Et, (i)Pr, (t)()Bu, SiMe(3)), (C(5)Me(5))(3)MX (X = anion), and (C(5)Me(5))(3)ML (L = neutral ligand) are compared with [(C(5)Me(5))(2)U](2)(C(6)H(6)), (C(5)Me(5))(2)Sm(PC(4)H(2)(t)Bu(2)), and 33 representative examples of f-element bis(cyclopentadienyl) complexes with normal cyclopentadienyl behavior and coordination numbers ranging from 6 to 10. In general, the methyl displacement values of sterically crowded complexes overlap with those in the other complexes, which demonstrates that the basis of the structural distortions is complex. However, if the most extreme out-of-plane displacement in each of the sterically crowded complexes is examined vs the analogous maximum out-of-plane displacement in less crowded systems, there appears to be a basis for predicting cyclopentadienyl reactivity.