Lawrence F. Dahl

Synthesis and characterization of Di-π-cyclopentadienyl- metal pentasulfides of titanium(IV) and vanadium (IV):an operational test of the influence of an unpaired electron on the molecular geometry

Our preparation of Ti( h 5 −C 5 H 5 ) 2 S 5 by the reaction of elemental sulfur with Ti( h 5 −C 5 H 5 ) 2 (CO) 2 in hexane and of V( h 5 −C 5 H 5 ) 2 S 5 − H 2 O by the reacti of V( h 5 −C 5 H 5 ) 2 Cl 2 with Na 2 S 5 in THF and structural analyses by single crystal X-ray diffraction (together with infrared, solution EPR, and temperaturedependent magnetic susceptibility measurements) represent an extension of our previous work on M( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 (M = Ti, V). The crystallographic results provide further support of our previous conclusions that the Ballhausen—Dahl model is not valid for M( h 5 −C 5 H 5 ) 2 L 2 systems. The structuralfeatures of the chair-like titanium and vanadium pentasulfide molecules are compared to the corresponding phenylmercapto analogs and to the chair-like cyclohexasulfur molecule in rhombohedral sulfur. Ti( h 5 −C 5 H 5 ) 2 S 5 was isolated as a mixture of monoclinic and orthorhombic Crystalline phases-which were both characterized by preliminary X-ray data. A complete Structural determination and refinement of the monoclinic phase, which contains two independent molecules in a cell of dimensions a 22.843(2), b 7.958(1), c 14.465(1) A, β 90.074(4)° and symmetry P 2 1 / c , yielded R 1 5.3 % and R 2 5.9 % for 2168 independent diffractometry-collected data with I ≥ 2.5o( I ). V( h 5 −C 5 H 5 ) 2 S 5 - H 2 O contains four V( h 5 −C 5 H 5 ) 2 S 5 molecules and two water molecules of hydration (of crystallographic site symmetry C 2 -2) in onorthorhombic unit cell of symmetry P 2 1 2 1 2 and of dimensions a 13.491(1), b 12.748(1), c 7.715(1) A. Least-squares refinement of 750 diffractometry data with I ≥2.0σ( I ) gave R 1 2.4% and R 2 3.0% Both of these compounds were independently synthesized and Spectroscopically characterized by Kopf and co-workers, and-a Complete X-ray diffraction study was performed by Epstein and Bernal on a different monoclinic phase of Ti( h 5 −C 5 H 5 ) 2 S 5 (isolated by-Kopf). An extraction of V( h 5 −C 5 H 5 ) 2 S 5 with re fluxing benzene under nitrogen atmosphere in a Soxhlet apparatus led to the formation of the previously reported [V 2 ( h 5 −C 5 H 5 ) 2 S 5 ] n compound which was characterized by physical measurements including a preliminary X-ray diffraction study.

Structure of and bonding in [(C3H5)PdCl]2

Abstract The molecular configuration of [(C3H5)PdCl]2 has been elucidated from a three-dimensional X-ray analysis. The yellow molecular crystals are monoclinic with a = 7.46; 0.02 A, b = 7.43 ± 0.02 A, c = 8.61 ± 0.02 A, and β = 93.6 ± 0.012; the unit cell of symmetry P21/n(C52h) contains two dimeric molecules. The structure has been refined to R1 and R2 values of 6.9 and 8.8% respectively, by the application of an anisotropic-isotropic least-squares method. The dimeric molecule of idealized point symmetry C2h2/m (i.e., the required crystallographic molecular symmetry is Ci− 1 ) consists of a (PdCl)2 rhombus with each palladium symmetrically bonded to an allylic group. The overall crystallographic results of Rowe1 based on two-dimensional data are substantiated with the notable exception that our more precisely determined atomic coordinates (which provide more refined molecular parameters) reveal that the plane of the three allylic carbons is not perpendicular to the plane of the (PdCl)2 bridge system; the dihedral angle between these two planes is 108° (e.s.d. ± 4°) with the central allylic carbon tipped away from the palladium; the palladium, however, is closer to this central carbon (PdC = 2.02 ± 0.04 A) than to the two terminal carbons (mean PdC = 2.15 ± 0.02 A). The allylic carbons possess a bond angle of 128.6 ± 3.3° and an average CC distance of 1.36 ± 0.03 A. The structure and bonding of [(C3H5)PdCl]2 are discussed with respect to other related organometallic complexes.

Preparation of V(h5−C5H5)2(SC6H5)2 and stereochemical characterization of M(h5−C5H5)2(SC6H2)2 (M = Ti, V): the geometrical effect of an unpaired electron on a M(h5−C5H5)2L2 complex

The synthesis of the d 1 vanadium(IV) compound V( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 from the reaction of V( h 5 −C 5 H 5 ) 2 with (C 6 H 5 ) 2 S 2 and its stereochemical characterization from X-ray diffraction data (as well as from infrared, solution EPR, and temperature-dependent magnetic susceptibility, data were performed in conjunction with a previous structural determination by X-ray diffraction of the corresponding d ° titanium(IV) compound Ti( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 in order to provide an operational test of the qualitative bonding model proposed by Ballhausen and Dahl and widely utilized by others for d 1 and d 2 metal(IV) complexes (M( h 5 −C 5 H 5 ) 2 L 2 ). The isomorphous Ti( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 and V( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 compounds crystallize with eight molecules in a monoclinic unit cell of symmetry C 2/c and of dimensions a 31.76(10), b 7.97(2), c 15.45(5) A, β 104.87(17)° for the titanium compound and a 31.454(5), b 7.835(1), c 15.545(2) A, β 104.35(1)° for the vanadium compound. The molecular configuration, comprised of a distorted tetrahedral array of the two cyclopentadienyl rings and two phenylmercapto sulfur atoms about the central metal atom, conforms closely to C 2 −2 symmetry. The crystallographic results, which show the SVS bond angle of 94.1(1)° to be 5° less than the STiS bond angle of 99.3(3)°, are taken as Strong evidence for the nonvalidity of the Ballhausen—Dahl model applied to M( h 5 −C 5 H 5 ) 2 L 2 systems. The structural determination and rigid-body least-squares refinement of the titanium compound were based on 1048 observed maxima collected by photographic methods, while the corresponding refinement of the vanadium compound utilized 1793 reflections above background obtained with a four-circle diffractometer. Efforts to obtain V( h 5 −C 5 H 5 ) 2 (SC 6 H 5 ) 2 from the reaction of V( h 5 −C 5 H 5 ) 2 CI 2 with thiophenol led instead to the V 2 ( h 5 −dC 5 H 5 ) 2 (μ 2 −SC 6 H 5 ) 4 dimer, which is presumed on the basis of its determined magnetic moment of μ eff 300 1.15 BM to be structurally similar to the previously reported methylmercapto homolog.

Nonparameterized MO calculations of ligand-bridged M2(CO)8-(U2-X)2-type dimers containing metalmetal interactions: Evidence for dictation of stereochemistry by one-electron and two-electron metalmetal σ-type bonds☆

Nonparameterized MO calculations performed on the (edge-bridged)-bioctahedral metal dimers of the Dessy-characterized [Cr2(CO)8(μ2-PR2)2](n-2) series and of the [Mn2(CO)8(μ2-PR2)2]n series (n = 0, +1, +2) have revealed that the corresponding dimeric pairs with n = 0, +1, and +2 have two, one, and no electrons, respectively, in the antibonding 2b3u MO corresponding to a “net” no-electron metalmetal bond, a “net” one-electron metalmetal bond, and a two electron metalmetal bond. Of prime significance is that this 2b3u MO, which is the LUMO in both electron-pair (metalmetal)-bonded dimers (n = +2) and the HOMO in the corresponding dimers to which one or two electrons have been added, is found to be largely composed of in-plane antibonding σ★-type dimetal orbital character rather than either out-of-plane π★-type dimetal antibonding orbital character or bridging-ligand orbital character. These MO results are also shown to be completely compatible with the available spectral and X-ray data.

Molecular structure of the MoMo triple-bonded pentamethylcyclopentadienylmolybdenum dimer, Mo2(η5-C5Me5)2(CO)4, and its geometrical relationship with the nonmethylated cyclopentadienyl analogue (MoMo) and corresponding chromium dimers (CrCr)

Abstract In order to determine whether the strikingly different chemical behavior of Mo 2 (η 5 -C 5 Me 5 ) 2 (CO) 4 ( 1 ) vs. Mo 2 (η 5 -C 5 H 5 ) 2 (CO) 4 ( 2 ) is possibly linked to unusual variations in molecular structure, an X-ray crystallographic investigation of 1 has been carried out. This study revealed that the solid-state configuration of 1 is indeed distinctly different from that of 2 but that its MoMo bond lengthis analogously short (at the high end of the triple-bond range). The centrosymmetrically-required geometry of 1 possesses a nonlinear C 5 Me 5 (c)Mo′ bond angle (where C 5 Me 5 (c) denotes the ring centroid) of 168.3° and two markedly different pairs of linear-type semibridged carbonyls with one pair comparable to those in 2 but with the other pair much more asymmetric (corresponding to a considerably weaker interaction with the second molybdenum atom). In contrast, 2 experimentally conforms to a C 2 h -2/ m geometry with a linear (C 5 H 5 (c)MoMo′C 5 H 5 (c) axis and with its four carbonyl ligands equivalently bent back over the MoMo bond in a linear-type semibridged arrangement. A crystal disordering in 1 of the less asymmetric-bridged carbonyl pair occurs in a similar fashion to that previously found and resolved for both asymmetric-bridge carbonyl pairs in 2 . The MoMo triple-bond length of 2.488(3) A in 1 is only 0.04 A longer than that of 2.448(1) A in 2 but 0.75 A shorter than the weak, unbridged MoMo single-bond distance of 3.235(1) A in Mo 2 (η 5 C 5 H 5 ) 2 (CO) 6 . A comparative analysis of the geometrical variations in 1 and 2 is made with the corresponding structurally analogous Cr 2 (η 5 -C 5 R 5 ) 2 (CO) 4 dimers (R  H, Me) and other semibridged carbonyl clusters in an effort to provide additional insight in assessing the current conflicting views on the bonding nature of the semibridged carbonyls in the M 2 (η 5 -C 5 R 5 ) 2 (CO) 4 dimers (M  Cr, Mo).

The molecular and crystal structure of thallium (I) methoxide

Abstract An X-ray single-crystal structural study of thallium (I) methoxide, TlOCH3, has yielded the thallium arrangement along with a proposed over-all configuration of the molecule. Thallium (I) methoxide is orthorhombic with a = 13·80 A , b = 6·98 A , and c = 13·66 A . The probable space grou[ is Pca21; the unit cell contains sixteen TlOCH3 species. Two-dimensional Patterson and Fourier projections and least squares analyses gave the atomic positions of the heavy thallium atoms; the X-ray data were not sufficient to allow detection of the methoxide positions. Crystalline thallium (I) methoxide consists of tetrameric molecules in which the thallium atoms are at the corners of a regular tetrahedron. In this structure the average TlTl distance is 3·84 A. A structure is proposed for (TlOCH3)4 in which thallium and methoxide groups each occupy the corners of two interpenetrating concentric tetrahedra of different size resulting in a distorted cube such that the TlOTl angle is > 90° and the OTlO angle is

Syntheses, structures and properties of primarily nanosized homo/heterometallic palladium CO/PR3-ligated clusters.

Syntheses, properties and structures of nanosized palladium CO/PR3-ligated homo- and heterometallic clusters containing up to 165 metal atoms are the focus of this review. The work discussed is primarily that of the authors and their coworkers. We propose that the unparalleled variety of structural types and the distinctive reactivities of neutral Pdn(CO)x(PR3)y clusters composed of zerovalent Pd atoms are a consequence of relatively weak Pd–L(ligand) and Pd(0)–Pd(0) interactions that result from the stable 5s04d10 closed-shell electron configuration of atomic Pd in its ground state.

Structure of and bonding in I,5-cyclooctadiene-duroquinone nickel

Abstract The structure of I,5-cyclooctadiene-duroquinone-nickel, C8H12NiC10H12O2, has been determined from a three-dimensional X-ray analysis. The compound crystallizes in a monoclinic unit cell of symmetry P2/n and dimensions a = 14.26 A, b = 7.95 A, c = 14.17 A, and β = 94°27′. There are four molecules per unit cell with each molecule located on a crystallographic two-fold axis. A three-dimensional least-squares refinement yielded a final unweighted discrepancy factor of R1 = 101%. Each discrete monomeric molecule consists of a nickel atom sandwiched between a boat- form I,5-cyclooctadiene ring and a duroquinone ring. The two sets of parallel double bonds in the cyclooctadiene and duroquinone rings are perpendicular; the nickel therefore can be considered to possess an idealized tetrahedral configuration. The cyclooctadiene ring of C2 symmetry shows significant skeletal skewing similar to that present in free I,5-cyclooctadiene, whereas the idealized D2h symmetry of free duroquinone is reduced to C2c in the nickel-complexed duroquinone due to a deformation of the carbonyl groups out of the plane of the ring. The detailed geometry of the rings, and the nature and implications of the bonding are discussed with respect to related complexes.

Synthesis and stereochemical analysis of the cubane-like Fe4(CO)12(μ3-S)4 and Fe4(CO)12(μ3-Se)4 tetramers: conversion of the tetrametal-bonding Fe4X4 cores in Fe4(NO)4(μ3-X)4 (where X - S, Se) into tetrametal-nonbonding cores by substitution of carbonyl for nitrosyl ligands

Abstract )). A qualitative structural-bonding analysis of the presume cubane-like “tetramethylplatinum” points to its possible existence in that it is an electronically equivalent analog of the cubane-like Re4(CO)12(μ3-H)4; however, it is Pt-Pt distances vs. expected bonding ones for such an electron-deficient 56-electron system that its true composition is indeed the previously suggested Pt4Me12(μ3-OH)4.

Neutron diffraction study of (Et/sub 4/N)/sup +/(Cr/sub 2/(CO)/sub 10/(. mu. /sub 2/-H))/sup -/: a (M/sub 2/(CO)/sub 10/(. mu. /sub 2/-H))/sup -/ monoanion with a pseudo D/sub 4h/ nonhydrogen geometry together with a disordered, bent symmetric metal--hydrogen--metal bond

The results of a single-crystal neutron diffraction study of the chromium-hydrogen-chromium bond in (Et/sub 4/N)/sup +/(Cr/sub 2/(CO)/sub 10/(..mu../sub 2/-H))/sup -/ was reported. The Cr-H-Cr bond in the (Cr/sub 2/(CO)/sub 10/(..mu../sub 2/-H))/sup -/ monoanion of the tetraethylammonium salt was found to be non-linear with the bridging hydrogen atom randomly disordered between two centrosymmetrically related sites each equidistant from the two chromium atoms and displaced ca. 0.3 A from the crystallographic center of symmetry. (DDA)