Tetrahedral versus square planar arrangement of cyclopentadienyl ligands in bimetallic organosamarium complexes. X-ray crystal structure of [(C5H4Me)2(THF)Sm(μ-Cl)]2

The effects of cyclopentadienyl ring size on the geometry of bimetallic organosamarium complexes have been studied by comparing the X-ray crystal structure of [(C₅H₄Me)₂(THF)Sm(μ-Cl)]₂, prepared from KC₅H₄Me and SmCl₃ in THF, with C₅Me₅ analogs. The complex crystallizes from THF at −30°C in space group Pbcn with a = 20.312(5), b = 9.626(2), c = 16.225(3) Å, V = 3172.5(12) ų and D_calc = 1.74 g cm⁻³ for Z = 4. Least-squares refinement of the model based on 1759 reflections [|F_o| > 2.0σ(|F_o|)] converged to a final R_F = 5.0%. The complex adopts a geometry which has a molecular two-fold rotation axis perpendicular to the Sm₂Cl₂ plane and a crystallographic inversion center. Hence, both methyl groups of each (C₅H₄Me)₂Sm unit are located on the side opposite of the THF ligands, which are trans to each other, and the four C₅H₄Me ring centroids define a square plane. The Sm---Cl distances are 2.759(3) and 2.819(3) Å.     

Ab initio calculation of the potential functions for internal rotation around the CS bonds in simple ethene thiols

Ab initio calculations with complete geometry optimisation have been used to study internal rotation in compounds of the type XCH = CHSH, X = CN, H, CH₃ and F, with X located trans to the sulphur atom. Potential functions for the CS torsion have been obtained for each case and it has been established that the dominant framework changes accompanying internal rotation in these molecules involve the CCS angle and CS bond length. Furthermore, it has been shown that the nature of the substituent X significantly affects the molecular conformation of the SH group. The observed trends are discussed in terms of a simple model.     

Exocyclic push–pull conjugated compounds. Part 3. An experimental NMR and theoretical MO ab initio study of the structure, the electronic properties and barriers to rotation about the exocyclic partial double bond in 2-exo-methylene- and 2-cyanoimino-quinazolines and -benzodiazepines

The structure of a number of 2-exo-methylene substituted quinazolines and benzodiazepines, respectively, 1, 3a,b, 4 (X=–CN,–COOEt) and their 2-cyanoimino substituted analogues 2, 3c,d (X=–CN,–SO₂C₆H₄–Me(p) was completely assigned by the whole arsenal of 1D and 2D NMR spectroscopic methods. The E/Z isomerism at the exo-cyclic double bond was determined by both NMR spectroscopy and confirmed by ab initio quantum chemical calculations; the Z isomer is the preferred one, its amount proved dependent on steric hindrance. Due to the push–pull effect in this part of the molecules the restricted rotation about the partial C²,C¹¹ and C²,N¹¹ double bonds, could also be studied and the barrier to rotation measured by dynamic NMR spectroscopy. The free energies of activation of this dynamic process proved very similar along the compounds studied but being dependent on the polarity of the solvent. Quantum chemical calculations at the ab initio level were employed to prove the stereochemistry at the exo-cyclic partial double bonds of 1–4, to calculate the barriers to rotation but also to discuss in detail both the ground and the transition state of the latter dynamic process in order to better understand electronic, inter- and intramolecular effects on the barrier to rotation which could be determined experimentally. In the cyanoimino substituted compounds 2, 3c,d, the MO ab initio calculations evidence the isomer interconversion to be better described by the internal rotation process than by the lateral shift mechanism.     

Photochemical E/Z isomerization of aryl-substituted methanimines. AM1-CI potential energy curves along the CN double bond twisting and the N atom in-plane inversion

Potential energy curves of aryl-substituted methanimines along the C = N bond twisting and the in-plane inversion of the N atom were obtained by AM1-SDCI calculations, and the photochemical E/Z isomerization paths were elucidated. An aromatic group introduced at the C atom of the C = N group has little effect on the S₀ surface for the inversion and rotation paths, while it has a significant effect on the shape of the T₁ curve along the rotation path. It is suggested that phenylmethanimine and 2-anthrylmethanimine undergo photoisomerization by the rotation mechanism. The methoxy group introduced at the N atom raises the inversion barrier on the S₀ state, while it lowers the 90°-twistedT₁ energy. TheT₁ potential energy curves of N-methoxy-1-phenylethanimine and N-methoxy-1-(2-anthryl)ethanimine indicate that the former undergoes a two-way isomerization and the latter a one-way isomerization by the rotation mechanism, which is in accordance with experiment.     

Crystal structure of a novel Hg(II) complex, [Hg(tri-2-furylphosphine)2(tri-2-furylphosphinoxide)3] [ClO4]2

The Hg(II) complex [Hg(TFP)₂(OTFP)₃][ClO₄]₂ with TFP=tri-2-furyl-phosphine and OTFP=tri-2-furylphosphinoxide has been prepared and characterised. It crystallises in the hexagonal P6₃/m space group with Z=2, a=13.308(3), c=21.092 (4) Å, V=3235(1) Å³. The structure of the complex cation consists of independent molecules with Hg pentacoordinated in exact trigonal bipyramidal geometry.     

Organoplatinum(IV) compounds : II. Preparation and characterization of trimethylplatinum(IV) compounds with chelating nitrogen donor ligands. The crystal and molecular structure of iodotrimethyl[bis(3,5-dimethyl-1-pyrazolyl)methane]platinum(IV)

Compounds of the types Me₃PtX(NN) (where X = Cl, I, OAc, NO₃; NN = bis(1-pyrazolyl)methane (pz₂CH₂), bis(3,5-dimethyl-1-pyrazolyl)methane ((Me₂pz)₂CH₂), or bis(2-pyridyl)methane (py₂CH₂)), [Me₃Pt(NNN)][PF₆] (where NNN=tris(1-pyrazolyl)methane (pz₃CH), or tris(2-pyridyl)methane (py₃CH)), and [Me₃Pt((Me₂pz)₂CH₂(py)][PF₆] have been prepared and characterized by elemental analyses and ¹H and ¹³C NMR spectroscopy; the structure of Me₆PtI[(Me₂pz)₂CH₂] (1) has also been determined by X-ray crystallography. Crystals of 1 are orthorhombic, space group Pcmn with four molecules in a unit cell of dimensions a 11.936(5), b 14.462(4), c 10.138(5) Å. The structure was solved by the heavy-atom method and refined by full-matrix least-squares calculations to R = 0.022 for 1719 observed data. The molecule has crystallographic mirror symmetry. The Pt atom has octahedral geometry with one methyl group trans to iodine and two methyl groups trans to the N atoms of the bidentate ligand (Pt---I 2.843(1), Pt---N, 2.236(4), Pt---C 2.077(6) (trans to I) and 2.032(5) Å (trans to N)).     

Autoassociates and tautomerism of 2-oxo-5-halogenopyrimidines: theoretical and experimental investigations

Theoretical calculations (on a semi-empirical level) of energy and geometry of the autoassociates of two tautomeric forms of 2-oxo-5X-pyrimidines (X = H, Cl, Br) are presented. On the basis of the calculated energies of autoassociates it is possible to explain the enol—keto tautomeric transition between the gas phase and condensed phases. We propose a double-proton transfer reaction as a possible mechanism for the tautomeric transition.

Infrared absorption spectra of 2-oxo-5X-pyrimidines in the v(NH …) and v(C=O) regions in solid phases and in low-temperature argon matrices are also presented and discussed. Comparison of IR spectra and results of the theoretical calculations with known crystallographic structures of 2-oxo-5X-pyrimidines (X = H, F, Cl) lead to the conclusion that the crystal structure of the 5-bromo derivative should be similar to that of the 5-chloro derivative.     

Copper(I) coordination compounds with two bidentate chelating pyrazole ligands. X-ray crystal structures of DI-μ-chloro-bis[[N,N-bis(1- pyrazolylmethyl)aminoethane]copper(I)] and [bis(N,N-bis(1-pyrazolylmethyl)aminoethane]copper(I) triflate

The pyrazole derivatives of aminoethane N,N-bis(3,5-dimethyl-1-pyrazolyl- methyl)aminoethane (aebd) and N,N-bis(1-pyrazolylmethyl)aminoethane (aebp) form co- ordination compounds with copper(I) of stoichiometry [Cu(L)X], with X = Cl, Br, I and SCN, and [Cu(L)₂X], with X = CF₃SO₃ and BF₄. The ligands chelate in a bidentate manner, with only the pyrazole groups coordinating. The crystal structures of two representative examples have been determined: [Cu(aebp)Cl]₂ is triclinic, space group P , with a = 8.711(2), b = 9.351(1) and c = 9.528(1) Å, = 68.57(1)°, β = 61.47(1)° and γ = 77.82(1)°, and Z = 2. Standard least-squares refinement gave R = 0.029 (R_w = 0.038) for 1804 reflections. [Cu(aebp)₂]CF₃SO₃ is monoclinic, space group P2₁/n, with a = 13.352(5), b = 14.663(3) and c = 15.752(4) Å, β = 117.49(3)°, and Z = 4. Standard least-squares refinement gave R = 0.029 (R_w = 0.032) for 1786 reflections. In both cases the copper environment is slightly-distorted tetrahedral. The chloride compound is dimeric with one ligand molecule (Cu---N distances of 2.011(2) and 2.047(2) Å) and two bridging chlorides per copper (Cu---Cl distances of 2.3874(8) and 2.4094(8) Å). With the non- coordinating triflate anion, a monomeric compound with two ligand molecules per copper was obtained (Cu---N distances of 2.018(4), 2.028(4), 2.049(4) and 2.050(4) Å).     

Thione complexes of group IIB dihalides. X-ray crystal structure of Cd(ETTC)2I2

Complexes having the empirical formulae M(ETTC)₂X₂ (M = Zn or Hg, X = Br or I, ETTC = ethylene trithiocarbonate), Cd(ETTC)₂I₂ and Hg(ETTC)X₂ (X = Cl, Br or I) were obtained by the reaction of zinc, cadmium or mercury dihalides in dichloromethane or ethanol with ETTC. The structures of the compounds were characterized by ¹H NMR and IR spectrometry, conductance measurements and elemental analysis. The X-ray crystal structure of Cd(ETTC)₂I₂ has been determined using counter data and refined to an R value of 0.045. The unit cell constants are a = 1586.3(2), b = 699.7(1) and c = 724.9(3) pm, the space group is Pmn2₁ and Z = 2. Coordination about the cadmium atom is tetrahedral.     

Electronic structure and conformational properties of (carboxy-alkenyl)-phosphonic acids

The general conformational properties and electronic structure of (carboxy-alkenyl)-phosphonic derivatives were determined at RHF/STO-3G^* level. In all the series, low rotation barriers were found for the two C=C/P=O conformers. In the compounds in which the interactions between the carboxylic and phosphonic moieties are smaller, the most stable conformers are the C=C/P=O s-cis ones. In most of the conformers, the C=C/C=O system presents the disposition s-cis. The Z-(2-carboxy-vinyl) and Z-(2-carboxy-propenyl) phosphonic acids present intramolecular hydrogen bonds, existing in at least four conformer with internal hydrogen bonds. These last compounds were more rigorously studied at RHF/3-21G^* and RHF/6-31G^** levels. The most stable conformer shows a trans structure for the C=C/P=O angle, with an intramolecular hydrogen bond located between the hydroxylic hydrogen of phosphonic group and the carbonyl oxygen of carboxylic moiety. A secondary conformer is found with a double intramolecular hydrogen bond between two hydroxylic hydrogens of the phosphonic moiety and the oxygen of carboxylic bond. Another secondary conformer appears with an intramolecular hydrogen bond between the oxygen of the phosphoryl bond and the hydroxylic hydrogen of the carboxylic group. A study of the topology of charge densities is carried out. This analysis reveals bonds with an ionic participation. A very weak π conjugation, variable with the conformers, is found in the C=C/P=O system, as well as a strongly polarized P=O partial triple bond. The intramolecular hydrogen bonds give rise to cyclic structures.     

Steric effects in conjugated systems : Part V. methylvinyl ketone and methyl-β-N,N-dimethylaminovinyl ketone

Based on the earlier results on methylated butadienes and acroleins, the conformational analysis of methylvinyl ketone was performed using the Wiberg method. The effect of nonbonded interactions involving the methyl group on the molecular geometry was estimated. In agreement with experimental findings the larger amount of the s-cis than s-trans conformer in methylvinyl ketone vs. acrolein is thought to be due to steric hindrance. Contrary to the situation for other unsaturated compounds, the rotation of the methyl group in the s-trans conformer of methylvinyl ketone seems to be determined mainly by nonbonded interactions. The barrier to internal rotation of the methyl group in the s-cis compared to the s-trans conformation seems to be considerably less. The present analysis of the steric properties of methylvinyl ketone seems to indicate that the spectral arguments in favour of nonplanarity of β-N,N-dimethylaminovinyl ketone are equivocal.     

Use of ab initio computational results and experimental frequencies to construct the internal rotational potential function for acrolein

Ab initio optimizations of the complete acrolein molecular geometry accomplished using analytical gradient methods at the 6-31G* SCF level at ten points during rotation from the planar trans- to the planar cis-form (rotation about the single C---C bond) are used to calculate the values of the Pitzer function F(φ), the coefficients of its Fourier expansion, and the coefficients in the potential energy expansion. The theoretical potential expansion coefficients are then adjusted using the experimental torsional frequencies and their overtones for the trans- and cis-forms of CH₂=CH---CH=O and CH₂=CH---CD=O. For the cis-conformer two different sets of experimental frequencies are employed. The dependence of the slope of the acrolein potential energy curve on the experimental frequency set used for the cis-rotamer is discussed.     

Control of selected physical properties of MX solids: an experimental and theoretical investigation

A series of eight materials of stoichiometry [Pt(L-L)₂X₂][Pt(L-L)₂]Y₄ (X is Cl, Br; L-L is 1,2-diaminoethane (en) or 1,2-diaminocyclohexane (chxn); Y is ClO⁻₄, X⁻) were synthesized. Crystal structures were determined for the compounds [Pt(chxn)₂Cl₂][Pt(chxn)₂](ClO₄)₄ 1, [Pt(chxn)₂Br₂][Pt(chxn)₂](ClO₄)₄2, and [Pt(chxn)₂Br₂][Pt(chxn)₂]Br₄ 4. All three of these compounds crystallize in the orthorhombic space group I222. Compound 1 has a = 5.711(1) Å, b = 7.804(1) Å, c = 24.101(7) Å, Z = 1, d_x = 2.033 g cm⁻³. Compound 2 has a = 5.781(1) Å, b = 7.720(1) Å, c = 24.036(5) Å, Z = 1, d_x = 2.174 g cm⁻³. Compound 4 has a = 5.379(1) Å, b = 7.028(1) Å, c = 23.884(4) Å, Z = 1, d_x = 2.440 g cm⁻³. These solids contain pseudo one-dimensional chains with a charge-density-wave (CDW) ground state structure: X-Pt(IV)-X···Pt(II)···X. Single crystal resonance Raman experiments were performed on all compounds to measure the symmetric X---Pt---X stretching frequency v₁ and the band edge. It is shown that the optical and electronic properties and, therefore, the CDW strength of these one-dimensional materials may be systematically varied over a wide range by employing different combinations of L-L and Y; templates composed of hydrogen bonded networks of L-L and Y were found to control the metal-metal separation, thereby controlling the X---Pt(IV)---X…Pt(II)…X chain geometry. Relationships between the CDW strength, measured as the ratio of the short M(IV)---X distance to the long M(II)---X distance, the band gap energy v₁ and the Pt---Pt separation are developed. The reaction coordinate is found to be dominated by changes in the M---M and Pt(II)---X separations over most of the range studied, with contributions from changes in the Pt^IV---X bonds becoming important only at the smallest M---M separations. Direct evidence demonstrating that MX systems are true Peierls distorted systems is also presented. These results are consistent with modeling based on Peierls-Hubbard hamiltonians. This work explains the unusual pressure and temperature dependences that have been observed for the structures and optical properties of this class of materials and also provides a wealth of information to benchmark many-body theoretical calculations modeling electron-electron and electron-phonon interactions in one-dimensional materials.     

Synthesis, characterization, and X-ray crystal structures of W(VI) alkyl complexes with chelating diamide and imido co-ligands

The complex W(NPh)Cl₂[o-(NSiMe₃)₂C₆H₄] 3 was synthesized from PhN = WCl₄ · OEt₂ and N,N′-(Li₂[o-(NSiMe₃)₂C₆H₄] and reacts with Lewis bases to form the adducts W(NPh)Cl₂[o-(NSiMe₃)₂C₆H₄](L) (L = PMe₃, THF, 3-picoline, ^tBuNC, MeCN) 4a–e. Crystals of 4a are triclinic, space group P1¯, with a = 9.562(1), b = 10.277(1), c = 14.920(2) Å, = 82.15(1), β = 80.18(1), γ = 80.41(1)°, and Z = 2. The structure was solved by the heavy atom method and refined to R = 0.0408 for 4224 observed (I > 2σ(I)) reflections. The dialkyl complexes W(NPh)R₂[o-(NSiMe₃)₂C₆H₄] (R = Me, Et, CH₂Ph, CH₂CMe₃, CH₂CMe₂Ph) 5–9 are formed through subsequent reactions of 3 with the corresponding Grignard reagent. Crystals of complex 5 are monoclinic, space group P2(1)/n, with a = 10.3545(2), b = 17.9669(1), c = 13.3168(1) Å, β = 103.826(1)°, and Z = 4. The structure of complex 5 was solved by direct methods in SHELXTL5 and refined to R = 0.0247 for 4572 observed reflections. Compound 5 has a square pyramidal geometry in which the imido ligand occupies the apical position and reacts with PMe₃ to form the adduct W(NPh)Me₂[o-(NSiMe₃)₂C₆H₄](PMe₃) 5a. Crystals of complex 5a are monoclinic, space group C2/m, with a = 13.5336(1), b = 14.4291(1), c = 15.3785(1) Å, β = 110.365(1)°, and Z = 4. The structure of compound 5a was solved by direct methods in shelxtl5 and refined to R = 0.0272 for 3057 observed reflections. Crystals of the bis-neopentyl complex 8 are monoclinic, space group P2(1)/n, with a = 10.6992(4), b = 18.3144(7), c = 16.0726(6) Å, β = 92.042(1)°, and Z = 4. The structure of 8 was solved by direct methods in shelxtl5 and refined to R = 0.0261 for 5881 observed reflections. Complex 8 has a trigonal bipyramidal geometry with both neopentyl groups and one amido nitrogen in the equatorial plane.     

Transition metal coordination compounds of a chelating imidazole-thioether ligand. The X-ray crystal structure of (1,6-bis(4(5)-imidazolyl)-2,5-dithiahexane)bis(nitrato)copper(II)

Transition metal coordination compounds with the novel N₂S₂-donor ligand 1,6-bis(4(5)-imidazolyl)-2,5-dithiahexane (abbreviated bhdhx) with general formulae M(bhdhx)(NO₃)₂(M = Co, Ni, Cu) and M(bhdhx)(H₂O)₂(BF₄)₂ (M = Cu, Zn) have been isolated. In all compounds the ligand is tetradentate with both thioether sulphurs and imidazole nitrogens coordinating. In all compounds the metal ions are six-coordinated in a distorted octahedral geometry with either nitrates or water molecules as the fifth and sixth ligands. This is confirmed by the ligand field spectra, which agree with a distorted octahedral coordination. The distortion from octahedral, indicated by the ligand field spectrum of the cobalt nitrate compound is such that the S atoms of the ligands must be at a very large distance from the metal ion. A single crystal of Cu(bhdhx)(NO₃)₂ was used in a structure determination: orthorhombic space group Pbcn, a = 14.351(5), b = 8.554(3), c = 13.057(4) Å, Z = 4, and T = 293 K. The structure was solved by heavy atom techniques and refined by least-squares methods to a residual R value of 0.033 for 847 significant reflections. The copper ion is at a special position on a two-fold axis, which causes a two-fold symmetry in the ligand. The coordination geometry of the copper atom is distorted octahedral with the two nitrates and the two thioether sulphurs in a cis position, and the imidazole nitrogens trans. The copper to nitrogen distances are 1.933(4) Å, the copper to sulphur distances are 2.495(1) Å, and the copper to oxygen distances are 2.280(3) Å.     

Some complexes of nickel (II) with morpholine

The compounds NiX₂M_x[M = morpholine; X = C₆F₅ (x = 2), NO₃(x = 3), Br(x = 2 or 3), and I(x = 4)] have been prepared and investigated. Magnetic and spectral studies have been carried out to determine the mode of coordination and stereochemistry of the complexes. Except for NiBr₂M₃, which appears to contain bridging morpholine, in all other compounds the neutral ligand acts as a monodentate N-donor group.     

A highly regio- and stereo-selective hydrostannation reaction of various fluorine-containing internal acetylene derivatives

The hydrostannation reaction of various fluoroalkylated acetylene derivatives with tributyltin hydride was investigated using a variety of catalysts in toluene. Among them, the Et₃B-induced hydrostannation reaction gave the highest regio- and stereo-selectivity. Their selectivity was mostly influenced upon the difference of the substituent X at the aromatic ring of the aryl-substituted internal acetylenes. Thus, the acetylenes having a halogen atom or an electron-donating group as X reacted smoothly with tributyltin hydride, affording the vinylstannane 4Z exclusively, while the acetylenes having an electron-withdrawing group (X=CO₂Et, NO₂) resulted in the preferential formation of 5E. The plausible mechanism of the formation of these products was discussed.     

A rationalization of orientation and reactivity in the nucleophilic replacement reactions of aromatic polyhalo-compounds

C₆F₅X compounds react with nucleophiles at the position para to X in some cases (X = H, CH₃, NMe₂, SMe, CF₃), meta in others (X = NH₂, O⁻) and occasionally at both meta and para in comparable amounts (X = OMe, NHME); significant amounts of ortho-replacement also occur (X = Cl, OMe). These orientations, and those in polychloro-aromatics and polyfluoro-polynuclear aromatics, can be rationalized by considering the relative stabilities of the Wheland-type intermediates involved (I, II, III), provided the halogens are taken as electron-repelling in π-systems. Reactivities can be rationalized if ground state stabilities are considered as well. A number of predictions have been made on the basis of these arguments.     

The crystal and molecular structure of bis(indazol-1-yl)pyridin-2′-ylmethane (BIPM) and [Rh(BIPM)(NBD)]PF6

The syntheses of a new tripodal ligand bis(indazol-1-yl)pyridin-2′-ylmethane (BIPM) and of a cationic complex (Rh(BIPM)(NBD)]PF₆, (NBD = 2,5-norbornadiene) are reported. Both compounds were characterized by infrared, ¹H, and ¹³C NMR spectroscopy and by single crystal X-ray analysis. BIPM crystallizes in the monoclinic system in space group P2₁/n with an β helical conformation. The [Rh(BIPM)(NBD)]PF₆ complex crystallizes in the monoclinic space group C/2c, the rhodium atom being pentacoordinate with a distorted trigonal bipyramidal geometry.     

三环已基锡L-扁桃酸酯配合物的合成、结构及性质

三环己基氢氧化锡与L-扁桃酸(物质的量比1:1)在苯和乙醇混合溶剂中反应合成了三环己基锡L-扁桃酸酯。 经X射线衍射方法测定了其晶体结构,配合物属斜方晶系,空间群为P2₁2₁2₁,晶体学参数a=0.80825(4) nm,b=1.77151(8) nm,c=1.8385(2) nm,α=β=γ=90°,V=2.6324(2) nm³,Z=4,D_c=1.310 g/nm³,μ(MoKα)=9.92 cm^-1,F(000)=1080,R₁=0.0472,wR₂=0.1341。 中心锡原子与环己基碳原子和氧原子构成畸型四面体。 对其结构进行量子化学从头计算,探讨了配合物的稳定性、分子轨道能量以及一些前沿分子轨道的组成特征。 研究了配合物的热稳定性、电化学性能、圆二色谱和体外抗癌活性。