The synthesis, vibrational spectroscopy, and crystal and molecular structure of [H3NCH2CH2NH3][PdBr6]

The complex [H₃NCH₂CH₂NH₃][PdBr₆] has been isolated as well-formed brown crystals. The Raman (single crystal) and FTIR (wax disc) spectra of the complex have been recorded but the band assignments are complicated by extensive factor group splitting and resonance effects. The crystal belongs to space group Pnnm, with Z = 2, each ion occupying sites of 2/m (C_2h) symmetry. The [PdBr₆]²⁻ ion is very close to octahedral, the two unique PdBr distances, 2.466(3) and 2.470(3) Å, being equal within experimental error and the BrPdBr angles being 90 ± 0.8°. The diammonium cation has an extended, planar, trans structure.     

Beryllocene, (C5H5)2Be. The He(I) photoelectron spectrum and ab initio molecular orbital calculations

Ab initio molecular orbital calculations with a double-ζ basis have been carrried out on five models of beryllocene, Cp₂Be, with fixed geometries. The lowest energies are obtained for the π-Cp, σ-Cp and D_5d models.

The He(I) photoelectron spectrum of Cp₂Be was recorded and the ionization potentials of the first bands were compared with the orbital energies obtained from the molecular orbital calculations. A satisfactory fit between experiment and calculations was obtained for a slip sandwich model of C_s symmetry. A model of C_5v symmetry is only compatible with the PE spectrum if the Jahn—Teller splitting of the lowest ²E₁ state of the molecular ion is exceptionally large, 1.0 eV.     

Velocity map imaging of the photolysis of n-C4H9Br in UV region

Using velocity map ion imaging technique, the photodissociation of n-C₄H₉Br in the wavelength range 231–267 nm was studied. The results and our ab initio calculations indicated that the absorption of n-C₄H₉Br in the investigated region originated from the excitations to the lowest three repulsive states, as assigned as 1A″, 2A′ and 3A′ in C_s symmetry. Dissociations occurred on the PES surfaces of the three states, terminating in C₄H₉+Br (²P_3/2) or C₄H₉ + Br^* (²P_1/2) as two channels, and being impacted by an avoided crossing between the PES surfaces of the 2A′ and 3A′ states. The transition dipole to the 1A″ state was perpendicular to the symmetry plane, so perpendicular to the C–Br bond. The transitions to the 3A′ state was polarized parallel to the symmetry plane, and also parallel to the C–Br bond. While the transition dipole to the 2A′ state was in the symmetry plane, but formed an angle of about 53.1° with the C–Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways, for the photolysis of n-C₄H₉Br near 234 nm and 267 nm.     

Synthesis and characterization of (C5H9C9H6)2Yb(THF)2(II) (1) and [(C5H9C5H4)2Yb(THF)]2O2 (2), and ring-opening polymerization of lactones with 1

Reaction of YbI₂ with two equivalents of cyclopentylindenyl lithium (C₅H₉C₉H₆Li) affords ytterbium(II) substituted indenyl complex (C₅H₉C₉H₆)₂Yb(THF)₂ (1) which shows high activity to ring-opening polymerization (ROP) of lactones. The reaction between YbI₂ and cyclopentylcyclopentadienyl sodium (C₅H₉C₅H₄Na) gives complex [(C₅H₉C₅H₄)₂Yb(THF)]₂O₂ (2) in the presence of a trace amount of O₂, the molecular structure of which comprises two (C₅H₉C₅H₄)₂Yb(THF) bridged by an asymmetric O₂ unit. The O₂ unit and ytterbium atoms define a plane that contains a C_i symmetry center.     

Formation of [C60C5H5] adduct cations and theoretical study of the isomers

We study here the reactions between C₆₀ and planar C₅H₅⁺ cations that lead to the formation of [C₆₀C₅H₅]⁺ adduct cations in the chemical ionization source of the mass spectrometer. The structures, stabilities and charge locations of some possible isomers of [C₆₀C₅H₅]⁺: σ-adduct, π-complex, [1,4]- and [l,2]-addition cations, are studied by AM1 semiempirical molecular orbital calculations. We find that the most stable is the σ-addition cation. Another interesting and stable structure is the π-complex cation which is bonded by the electrostatic interaction at the inter-ring distance of 1.589 Å with the C_5v symmetry. The C₅H₅⁺ cyclopentadienium cation seems to be an “inverted umbrella” sitting on a five-membered ring of the C₆₀ cage.     

A study of electronic structures of some C9H9- carboanions

The electronic structures of five C₉H₉^-, carboanions have been studied by ab initio STO-3G calculations, and some general conclusions on related C₉H₉^- and C₉H₉⁺ structures are presented. Large antibonding interactions in one occupied MO make barbaral-9-yl anion (2) unstable as its cationic counterpart (8). The proposed D_9h-symmetrical cation and D_3h-symmetrical anion (3) do not exist due to Jahn-Teller distortions. A study of the MO correlations confirms that the two tetracyclic anions with C_2v symmetry (5 and 6) are the results of the Jahn-Teller distortions of 3. Anion 5 is identified as the proper intermediate of the Cope rearrangement of anion 2.     

Interaction of titanium and tin chlorides in tetrahydrofuran. The X-ray crystal structure of [trans-TiCl2(THF)4][SnCl5(THF)]

The direct reaction between [TiCl₄(THF)₂] and SnCl₂ in tetrahydrofuran (THF) yields the green paramagnetic salt [trans-TiCl₂(THF)₄][SnCl₅(THF)]. The same compound is also formed in the reaction between [TiCl₃(THF)₃] and SnCl₄ in THF. Crystals of the title compound are monoclinic with a = 8.442(4), b = 21.589(9), c = 9.262(5) Å, β = 107.91(5)°, Z = 2, space group P2₁/m. Both metal ions are in an octahedral environment. The titanium atom in the cation [TiCl₂(THF)₄]⁺ lies on the symmetry centre. The tin atom in [SnCl₅(THF)]⁻ is located on the mirror plane.     

Copper thioether chemistry: The synthesis and single crystal X-ray structures of [Cu2([18]aneS6)(NCMe)2](ClO4)2 and [Cu([9]aneS3)(AsPPh3)](ClO4)

Reaction of [18]aneS₆ with two molar equivalents of [Cu(NCMe)₄](ClO₄) in CH₂Cl₂-MeCN affords the binuclear copper(I) complex [Cu₂([18]aneS₆)(NCMe)₂](ClO₄)₂. The single crystal X-ray structure of the complex shows a centrosymmetric cation with two tetrahedral copper(I) centres each coordinated to three thioether S-donors of [18]aneS₆,Cu---S(1) = 2.3200(15), Cu---S(4) = 2.3415(16), Cu---S(7) = 2.3250(15) Å, and to one MeCN molecule, Cu---N(1) = 1.939(5) Å, to give an overall NS₃-donation at the metal centres. Additionally, S(7′) shows a long-range interaction, Cu …S(7′) = 3.318(2) Å thus distorting the coordination geometry of the metal ion towards trigonal bipyramidal. The metal-metal separation of 4.428(2) Å suggests that there is no significant interaction between the copper centres of the dimer. Reaction of [9]aneS₃ with one molar equivalent of [Cu(NCMe)₄](ClO₄) in refluxing MeCN in the presence of ligands, L, affords the adducts [Cu([9]aneS₃)L]⁺ (L = PPh₃, AsPh₃). The single crystal X-ray structure of the complex [Cu([9]aneS₃)(AsPh₃)](ClO₄) shows tetrahedral AsS₃ coordination at copper(I) with [9]aneS₃ bound facially to the metal centre, Cu---S = 2.303(6), Cu---As = 2.322(4) Å.     

Coordination geometry of chromium(VI) species. The first example of cis-bridging chromate ions in helically structured catena(μ-CrO4-O,O′)[Ni(HIm)3H2O]

Nickel(II) chromate complex with imidazole (HIm) was isolated from the [Ni²⁺–HIm–CrO₄²⁻] system in various experimental conditions, i.e. reagent molar ratios and nickel(II) salts. The catena(μ-CrO₄-O,O′)[Ni(HIm)₃H₂O] (1) crystallizes in monoclinic crystal system—space group P2₁/n with cell parameters: a=11.784(2), b=8.899(2), c=13.934(3) (Å), β=95.19(3) (°). The unit cell contains two independent helixes, left- and right-handed, stabilized by intrahelical and interhelical hydrogen bonds (HB) and π–π interactions. The cis coordination of the CrO₄²⁻ anions and the HB systems appeared to be the main determinants of the helical architecture. To the best of our knowledge the cis-chromate coordination was observed for the first time. The cis coordination causes the distortion of the nickel octahedron, which was analysed by 4 K single crystal electronic spectra with D_4h symmetry approximation (gaussian resolution and crystal field parameters). This symmetry was also confirmed with the polarised electronic spectra. The magnetic properties of the complex suggest the occurrence of weak intrachain antiferromagnetic interactions between the magnetic Ni^II center. The computational DFT studies of complex 1 assuming three possible isomers mer[(HIm)₃]–cis[(CrO₄²⁻)₂], mer–trans and fac–cis suggested that the main contribution to the stability of 1 might have interhelical and intrahelical hydrogen bonds.     

以笼烯为接头的球棒式碳纳米管的电子结构

按照Hamada构造一维至三维球棒式碳纳米管,构造了一些球棒式的笼烯接头的具有C₃/C₅旋转轴的单层碳纳米管.在Hückel近似下,利用群论约化定理计算了它们的π电子结构,并对其稳定性进行了探讨.     

Local density functional study of the structural and electronic properties of C60 and XC60 (X=K, Rb, Cs)

Results of first principles local density total energy and atomic force calculations carried out for free C₆₀ and XC₆₀ (X=K, Rb, Cs) molecular clusters are reported. The optimization of the geometry results in the bond lengths between adjacent carbon atoms being 1.387 and 1.445 Å, which are in very good agreement with the latest X-ray diffraction values. Energy levels, charge distributions, and wavefunction characteristics are obtained and discussed. The results for C₆₀ are in very good agreement with recently measured photoemission energy distribution curves (EDC) for the valence band states. The highest occupied molecular orbitals (HOMO) are found to be fully occupied H_u states and are 1.7 eV below the lowest unoccupied molecular orbitals (LUMO) which are of T_1u symmetry. Similar results obtained for the XC₆₀ clusters show that rigid-band-like behavior is found in the electronic structures after putting an alkali atom at the center of a C₆₀ ball. In each case, the alkali atom is almost fully ionized with the transferred electron distributed over the surface shell of C₆₀; the center region of the ball has very low charge density.     

Synthesis and crystal structure of the novel trimanganese tetrathiolate incomplete cubane: [Mo(η-C5H5)2(H)CO][Mn3(CO)9(μ-SC6H5)4]

An unexpected trimanganese(I) tetrathiolate-bridged complex, [Mn₃(CO)₉(μ-SC₆H₅)₄]⁻, with an incomplete cubane structure, was obtained by thermal reaction of [Mn₂(CO)₁₀] with [Mo(η⁵-C₅H₅)₂(SC₆H₅)₂]. The structure, established by single-crystal X-ray diffraction studies, shows the cation, [Mo(η⁵-C₅H₅)₂(H)CO]⁺, directed towards the vacant site of the cubane structure. Possible routes by which the anion and the cation could be formed are discussed.     

Normal co-ordinate analyses and structural considerations of TeCl4, TeBr4 and TeCl2Br2

The molecular structure of TeCl₂Br₂ in the vapour phase is reconsidered in the light of the recently published X-ray crystal structure for TeCl₄. Normal coordinate calculations are performed on molecular TeCl₂Br₂ in its three possible symmetries using force fields derived from the parent molecules TeCl₄ and TeBr₄. The calculations indicate that the data for molecular TeCl₂Br₂ can best be interpreted as arising from a mixture of at least the two high symmetry conformers rather than just the low symmetry C₁ molecule as previously reported.     

Synthesis and crystal structures of (C8h8)Nd(C5H9C5H4) (THF)2 and [(C8H8)Gd(C5H9C4H4(THF)][(C8H8)GD(C5H9C5H4(THF)2]

LnCl₃ (Ln=Nd, Gd) reacts with C₅H₉C₅H₄Na (or K₂C₈H₈) in THF (C₅H₉C₅H₄ = cyclopentylcyclopentadienyl) in the ratio of 1 : to give (C₅H₉C₅H₄)LnCl₂(THF)_n (orC₈H₈)LnCl₂(THF)_n], which further reacts with K₂C₈H₈ (or C₅H₉C₅H₄Na) in THF to form the litle complexes. If Ln=Nd the complex (C₈H₈)Nd(C₅H₉C₅H₄)(THF)₂ (a) was obtained: when Ln=Gd the 1 : 1 complex [(C₈H₈)Gd(C_%H₉)(THF)][(C₈H₈)Gd(C₅H₉H₄)(THF)₂] (b) was obtained in crystalline form.

The crystal structure analysis shows that in (C₈H₈)Ln(C₅H₉C₅H₄)(THF)₂ (Ln=Nd or Gd), the Cyclopentylcyclopentadieny (η⁵), cyclooctatetraenyl (η⁸) and two oxygen atoms from THF are coordinated to Nd³⁺ (or Gd³⁺) with coordination number 10.

The centroid of the cyclopentadienyl ring (Cp′) in C₅H₉C₅H₄ group, cyclooctatetraenyl centroid (COTL) and two oxygens (THF) form a twisted tetrahedron around Nd³⁺ (or Gd³⁺). In (C₈H₈)Gd(C₅H₉C₅H₄)(THF), the cyclopentyl-cyclopentadienyl (η⁵), cyclooctatetraenyl (η⁸) and one oxygen atom are coordinated to Gd³⁺ with the coordination number of 9 and Cp′, COT and oxygen atom form a triangular plane around Gd³⁺, which is almost in the plane (dev. -0.0144 Å).     

Caractéristiques spectroscopiques des liaisons hydrogène N-H-N très fortes. Études des acides A3(CN)6, (A=H,D; M=Fe,Co) par spectroscopie de vibration

Infrared and Raman spectra of the polycrystalline complex cyanide acids H₃M^III(CN)₆ (M=Fe,Co) and their deutero analogues were investigated at 300 and 90K in the region 4000-100 cm⁻¹. The spectra indicate clearly that the site symmetry of the M(CN)₆³⁻ ion is C_3v for M=Fe and D_3d for M=Co. These conclusions are consistent with an asymmetric N-H·N bond in H₃Fe(CN)₆ and with a symmetric one in H₃Co(CN)₆. The N-H stretching frequencies are assigned as ca. 1100 cm⁻¹ (Fe) and as 560 cm⁻¹ (Co), the shift being related to the difference in the hydrogen bonding strength, 2.665 Å (Fe) and 2.582 Å (Co). The spectroscopic behaviour of these very short N-H·N bonds appears to be similar to that of the strong O-H·O bonds in type A (for M=Co) or type pseudo-A compounds (for M=Fe).     

Cation–anion interactions in triphenyl telluronium salts. The crystal structures of (Ph3Te)2[MCl6] (M=Pt, Ir), (Ph3Te)[AuCl4], and (Ph3Te)(NO3)·HNO3

Triphenyltelluronium hexachloroplatinate (1), hexachloroiridate (2), tetrachloroaurate (3), and tetrachloroplatinate (4) were prepared from Ph₃TeCl and potassium salts of the corresponding anions. Upon recrystallization of 4 from concentrated nitric acid, K₂[PtCl₆] and (Ph₃Te)(NO₃)·HNO₃ (5) were obtained. The crystal structures of 1–3 and 5 are reported. Compounds 1 and 2 are isostructural. They are triclinic, P , Z=2 (the asymmetric unit contains two formula units). Compound 1: a=10.7535(2), b=17.2060(1), c=21.4700(3) Å, =78.9731(7), β=77.8650(4), γ=78.8369(4)°. Compound 2: a=10.7484(2), b=17.1955(2), c=21.4744(2) Å, =78.834(1), β=77.649(1), γ=78.781(1)°. Compound 3 is monoclinic, P2₁/c, Z=4, a=8.432(2), b=14.037(3), c=17.306(3) Å, β=93.70(3)°. Compound 5 is monoclinic. P2₁/n, Z=4, a=9.572(2), b=14.050(3), c=13.556(3) Å, β=90.76(3)°. The primary bonding in the Ph₃Te⁺ cation in each salt is a trigonal AX₃E pyramid with Te---C bond lengths in the range 2.095(8)–2.14(2) Å and the bond angles 94.1(6)–100.9(5)°. The weak TeCl (1–3) and TeO (5) secondary interactions expand the coordination sphere. In 1 and 2 the cation shows a trigonal bipyramidal AX₃YE coordination with one primary Te---C bond and the shortest secondary TeCl contact in axial positions and the two other Te---C bonds and the lone-pair in equatorial positions. The cation in 3 shows a distorted octahedral AX₃Y₃E environment and that in 5 is a more complex AX₃Y₃Y′₂ arrangement. In both latter salts the structure is a complicated three-dimensional network of cations and anions.     

Heteroleptic platinum(II) complexes of macrocyclic thioethers and halides: the crystal structures of [Pt(9S3)Cl2], [Pt(9S3)Br2], and [Pt(9S3)I2]

The synthesis, spectroscopic, and crystal structures of three heteroleptic thioether/halide platinum(II) (Pt(II)) complexes of the general formula [Pt(9S3)X₂] (9S3=1,4,7-trithiacyclononane, X=Cl⁻, Br⁻, I⁻) are presented. All three 9S3/dihalo complexes form very similar structures in which the Pt(II) center is surrounded by a cis arrangement of two halides and two sulfur atoms from the 9S3 ligand. The third sulfur from the 9S3 forms a long distance interaction with the Pt center resulting in an elongated square pyramidal structure with a S₂X₂+S₁ coordination geometry. The distances between the Pt(II) center and axial sulfur shorten with larger halide ions (Cl⁻=3.260(3) Å>Br⁻=3.243(2) Å>I⁻=3.207(2) Å). These distances are consistent with the halides functioning as π donor ligands, and their Pt---S axial distances fall intermediate between Pt(II) thioether complexes involving π acceptor and σ donor ligands. The ¹⁹⁵Pt NMR chemical shift values follow a similar trend with an increased shielding of the platinum ion with larger halide ions. The 9S3 ligand is fluxional in all of these complexes, producing a single carbon resonance. Additionally, a related series of homoleptic crown thioether complexes have been studied using ¹⁹⁵Pt NMR, and there is a strong correlation between the chemical shift and complex structure. Homoleptic crown thioethers show the anticipated upfield chemical shifts with increasing number of coordinated sulfurs. Complexes containing four coordinated sulfur donors have chemical shifts that fall in the range of −4000 to −4800 ppm while a value near −5900 ppm is indicative of five coordinated sulfurs. However, for S₄ crown thioether complexes, differences in the stereochemical orientation of lone pair electrons on the sulfur donors can greatly influence the observed ¹⁹⁵Pt NMR chemical shifts, often by several hundred ppm.     

On the electronic structure of [W(WS4)2]

The ground-state electronic structure of W₃S₈²⁻ has been calculated using the relativistic SCF-MS-X method. The results confirm a formal oxidation state of +2 for the central tungsten atom and a + 6 oxidation state for the terminal ones. A W---|W σ bond is detected within the 7a_1g molecular orbital leading to a W---|W bond order of 1/2. The energy order of the X MOs of ligand field interest, localized on the central metal ion, is explained based on the simple angular overlap approach taking into consideration the W---|W interactions.     

Syntheses and structures of dimesitylbismuth(III) bromide, Mes2BiBr, and bis(diphenyldithiophosphinato)mesitylbismuth(III), MesBi(S2PPh2)2

Addition of BiBr₃ to Mes₃Bi (Mes = 2, 4, 6-Me₃C₆H₂) in Et₂O gives 86% of Mes₂BiBr (1) as yellow crystals. Reaction of 1 with Ph₂PS₂NH₄ in a 1 : 1 molar ratio gives a quantitative yield of MesBi(S₂PPh₂)₂ (2) rather than the expected dimesitylbismuth compound. The crystal and molecular structures of 1 and 2 were determined at 153 K and 173 K, respectively. They contain Mes₂BiBr molecules with trigonal pyramidal coordination around Bi. The mean Bi---C bond distance is 2.27 Å and the Bi---Br bond distance is 2.690(2) Å. The angles around Bi vary between 89.4 and 106.4°. Intermolecular Bi…Br contacts of 3.795 Å, indicating weak secondary bonding, give rise to zig-zag shaped (Bi---Br)_x chains. In the polymeric chain the coordination geometry around bismuth atoms can be described as pseudo-trigonal bipyramidal. The crystals of 2 consist of discrete monomeric MesBi(S₂PPh₂)₂ molecules with a symmetry plane containing the metal atom and the aromatic ring of the attached mesityl group. The dithiophosphinato ligands exhibit an anisobidentate coordination pattern with long and short phosphorus—sulfur bonds, i.e. P(1)---S(1) 2.051(31) Å and P(1)---S(2) 1.980(3) Å, related to short and long bismuth—sulfur distances, respectively, i.e. Bi---S(1) 2.662(2) Å and Bi---S(2) 3.123(3) Å. This leads to a square-pyramidal geometry around the bismuth atom, with the metal lying 0.33 Å above the basal plane formed by the four sulfur atoms.     

Crystallographic evidence for different modes of interaction of BF3/BF4 species with water molecules and 18-crown-6

We report the crystal and molecular structures of the complex of 18-C-6 with H₃O⁺BF₄⁻ (I) and the complex of 18-C-6 with BF₃OH₂·H₂O (II). The different modes of appearance of the “BF₃” species as BF₃, BF₃OH₂, BF₃OH₂·H₂O and BF₄⁻, as well as their structurally significant intermolecular and intramolecular interactions, are discussed. In complex I the oxonium ion is bound at the centre of the 18-C-6 macrocycle. The oxonium oxygen is located practically equidistant (2.68–2.73 Å) from the six macrocyclic ethereal oxygens. The BF₄⁻ counter-ion is positioned 7.3 Å away from the oxonium ion in the same general plane of the crown ether. This anion is not involved in any direct intermolecular contacts, a fact that may explain why it is spherically disordered. In complex II there is no guest molecule (or ion) present in the “cavity” of the macrocycle, but there are two hydrogen-bonded systems of BF₃OH₂·H₂O that are interacting with the crown ether on either side of the general macrocyclic plane. Complex II features three types of hydrogen bonds—the O(water)-HO(crown) bonds (2.83 and 2.85 Å), the O(water)H-O(BF₃) bond (2.49 Å) and the O(BF₃)-HO(crown) bond (2.65 Å). The strong intermolecular O(crown)O(water)O(BF₃) and O(crown)O(BF₃) interactions stabilize the normally unstable BF₃OH₂·H₂O species.