19F nuclear magnetic resonance spectra of some trisubstituted metal trifluorophosphine complexes. Examples of [AX3]3 nuclear spin systems

The ¹⁹F NMR spectra of π-allyl-tris(trifluorophosphine)rhodium(I), [A], benzene-tris(trifluorophosphine)chromium(0), [B], and nitrosyl-tris(trifluorophosphine) rhodium(-I), [C], are presented. These are examples of [AX₃]₃ nuclear spin systems (A = phosphorus, X = fluorine). The spectra of [A] and [B] have been completely analysed to afford values of ¹J(PF), ²J(PP′), ³J(PF′) and ⁴J(FF′).     

Molecular structure and IR absorption spectra of perfluorinated aldehyde hydrates (n-CxF2x+1CH(OH)2, x = 1-4)

Structures and IR absorption spectra of the conformational isomers of perfluorinated aldehyde hydrates, n-C_xF_2x+1CH(OH)₂, (x = 1-4) have been calculated using density functional theory (DFT) and compared to experimental FT-IR measurements. Two absorption peaks around 3600-3700 cm⁻¹ were observed and are assigned to OH stretching modes of OH groups with, and without, intramolecular hydrogen bonding. For n-C₃F₇CH(OH)₂, two absorption bands around 900-1000 cm⁻¹ were observed in the experimental spectra, whereas only a single in-phase stretching mode of the (CF₃)(C₂F₄CH(OH)₂) and (C₃F₇)(CH(OH)₂) bonds was calculated for each conformer. The experimental spectra were well described by composite spectra of the thermal equilibrium mixture of different conformational isomers of n-C_xF_2x+1CH(OH)₂ calculated by DFT.     

Inelastic neutron scattering spectra of alkali metal (Na,K) bifluorides: The harmonic overtone of v3

Inelastic neutron scattering spectra of MFHF (M  Na and K) have been measured up to energy transfers of ca. 4000 cm^?1 Both 0 → 1 and 0 → 2 transitions of the bending (v₂), and antisymmetric stretching (v₃) modes were observed. A normal harmonic (i.e. no quartic contribution) model for the dynamics of the bifluoride ion is entirely consistent with our observations. Evidence of phonon dispersion was observed in the band shape of v₃, but no structure attributable to the LO mode could be found. The similarity of the band shapes of v₃ for both NaFHF and KFHF is interpreted in terms of a very short range coupling mechanism.     

Synthesis and characterization of three new fluorovanadate complexes: N(C2H5)4[VOF4], N(CH3)4[VOF3Cl], N(C4H9)4[VOF3Br] and theoretical calculations of VOF4, VOF3Cl and VOF3Br ions

The reaction of VOF₃ with (C₂H₅)₄NF, (CH₃)₄NCl and (C₄H₉)₄NBr salts in anhydrous CH₃CN produced new complexes with the anion general formula [VOF₃X]⁻ in that (X = F⁻, Cl⁻, Br⁻). These were characterized by elemental analysis, IR, UV/Visible and ¹⁹F NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the VX (X = F, Cl, Br) bond length values for the [VOF₃X]⁻ in compounds 1-3 are 1.8247, 2.4031 and 2.5595 Å, respectively. Also, the VF₅ bond length values in [VOF₃X]⁻ are 1.824, 1.812 and 1.802 Å, respectively. These results reveal that the bond order for VX bonds decrease from compounds 1 to 3, while for VF₅ bonds, the bond orders increase. It can be concluded that the decrease of VX bonds lengths and the increase of VF₅ bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF₄⁻, VOF₃Cl⁻ and VOF₃Br⁻ are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site.     

Vibrational spectra of the peroxotantalates (NH4)3[Ta(O2)4], K3[Ta(O2)4], Rb3[Ta(O2)4] and Cs3[Ta(O2)4] and the crystal structure of Rb3[Ta(O2)4]

The compounds (NH₄)₃[Ta(O₂)₄], K₃[Ta(O₂)₄], Rb₃[Ta(O₂)₄] and Cs₃[Ta(O₂)₄] have been prepared and investigated by X-ray powder methods as well as Raman- and IR-spectroscopy. In the case of Rb₃[Ta(O₂)₄] the structure has been solved from single crystal data. It is shown that all these compounds are isotypic and crystallize in the K₃[Cr(O₂)₄] type (SG , No. 121). The infrared- and Raman spectra (recorded on powdered samples) are discussed with respect to the internal vibrations of the peroxo-group and the dodecahedral [Ta(O₂)₄]³⁻ ion. Symmetry coordinates for the [Ta(O₂)₄]³⁻ ion are given from which the vibrational modes of the O-O stretching vibrations of the O₂²⁻ groups, the Ta-O stretching vibrations and the Ta-O bending vibrations are deduced.     

Blue-shifted hydrogen-bonded complexes. II. CH3F(HF)1 n 3 and CH2F2(HF)1 n 3

The equilibrium structures, binding energies, and vibrational spectra of the clusters CH₃F(HF)_{1 n 3} and CH₂F₂(HF)_{1 n 3} have been investigated with the aid of large-scale ab initio calculations performed at the Møller–Plesset second-order level. In all complexes, a strong C–FH–F halogen–hydrogen bond is formed. For the cases n = 2 and n = 3, blue-shifting C–HF–H hydrogen bonds are formed additionally. Blue shifts are, however, encountered for all C–H stretching vibrations of the fluoromethanes in all complexes, whether they take part in a hydrogen bond or not, in particular also for n = 1. For the case n = 3, blue shifts of the ν(C–H) stretching vibrational modes larger than 50 cm⁻¹ are predicted. As with the previously treated case of CHF₃(HF)_{1 n 3} complexes (A. Karpfen, E. S. Kryachko, J. Phys. Chem. A 107 (2003) 9724), the typical blue-shifting properties are to a large degree determined by the presence of a strong C–FH–F halogen–hydrogen bond. Therefore, the term blue-shifted appears more appropriate for this class of complexes. Stretching the C–F bond of a fluoromethane by forming a halogen–hydrogen bond causes a shortening of all C–H bonds. The shortening of the C–H bonds is proportional to the stretching of the C–F bond.     

Vibrational spectra and structural features of carbene analogs ElII(OCH2CH2NMe2)2 and ClElIIOCH2CH2NMe2 (ElII = Ge, Sn, Pb)

Vibrational spectra of compounds of divalent Group 14 elements El^II(OCH₂CH₂NMe₂)₂ with El^II = Ge (1), Sn (2), Pb (3) and ClEl^IIOCH₂CH₂NMe₂ with El^II = Ge (4) and Sn (5) were measured for the first time and analyzed within the framework of DFT calclations. Monomeric compounds 1 and 2 whose molecules are stabilized only through intramolecular coordination were confirmed to be isostructural. Unlike 1 and 2, plumbylene 3 is a polymer in both solution and the crystalline state; the latter was confirmed by X-ray diffraction analysis. The ν^s _C-N stretching frequency in the CH₂NMe₂ fragment was shown to decrease by 80–100 cm⁻¹ owing to the formation of the coordination bond El←N. To elucidate the mechanism of a dynamic flip-flop process suggested earlier based on the broadening of some signals in the NMR spectra of compounds 1 and 4, the Raman spectra of solutions of compounds 1 and 2 in THF and Py were obtained. These experiments revealed no equilibrium with participation of a stable form with one coordination bond El←N cleaved along with the starting molecule. This is consistent with the results of the corresponding quantum chemical calculations of thermo-dynamic parameters. A somewhat different, more probable mechanism of the dynamic process was proposed, which involves an overturn of the CH₂NMe₂ fragment with cleavage of the El←N bond in the transition state only.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

Synthesis, crystal structure, infrared and Raman spectra of Sr5(As2O7)2(AsO3OH)

The new compound Sr₅(As₂O₇)₂(AsO₃OH) was synthesized under hydrothermal conditions. It represents a previously unknown structure type and belongs to a group of a few compounds in the system SrO-As₂O₅-H₂O; (As₂O₇)⁴⁻ besides (AsO₃OH)²⁻ groups have not been described yet. The crystal structure of Sr₅(As₂O₇)₂(AsO₃OH) was determined by single-crystal X-ray diffraction (space group P2₁/n, a=7.146(1), b=7.142(1), , β=93.67(3)°, , Z=4). One of the five symmetrically unique Sr atoms is in a trigonal antiprismatic (Inorg. Chem. 35 (1996) 4708)—coordination, whereas the other Sr atoms adopt the commonly observed (“Collect” data collection software, Delft, The Netherlands, 1999; Methods Enzymol. 276 (1997) 307)—coordination. The position of the hydrogen atom was located in a difference Fourier map and subsequently refined with an isotropic displacement parameter. Worth mentioning is the very short hydrogen bond length O_h-H?O(1) of 2.494(4) Å; it belongs to the shortest known examples where the donor and acceptor atoms are crystallographically different. This hydrogen bond was confirmed by IR spectroscopy. In addition, Raman spectra were collected in order to study the arsenate groups.     

Vibrational spectra and normal coordinate analysis of germylazide-do and -d3

The infrared spectra (4000–20 cm^?1) of gaseous and solid GeH₃NNN and GeD₃NNN and the Raman spectra (3000–0 cm^?1) of liquid and solid GeH₃NNN and GeD₃NNN have been recorded. The vibrational spectrum has been assigned on the basis of C_s symmetry. The GeNN bend was observed in the Raman spectrum of the gas at ~150 cm^?1; however, the frequency of the GeH₃ torsion could not be determined. A normal coordinate calculation has been carried out by utilizing a modified valence force field. The GeN stretching force constant was found to have a significantly smaller value than the corresponding force constant in GeH₃NCO and GeH₃NCS. A considerable amount of mixing was found between the GeN stretch and the NNN in-plane bend. The frequencies of the normal modes and the normal coordinate analysis of GeH₃NNN are discussed in view of the recent results reported for GeH₃NCO and GeH₃NCS.     

CN stretching and NO2 deformation vibrations and normal coordinate analysis of m-dinitrobenzene and m-dinitrobenzene-d4

Two bands appear for each CN stretching and nitro deformation vibration in the infrared and Raman spectra of m-dinitrobenzene and m-dinitrobenzene-d₄. The 907 cm^?1 bending mode in the vibrational spectra of m-dinitrobenzene undergo 30 cm^?1 upward shift upon d₄ substitution. A normal coordinate analysis pointed out that the 937 cm^?1 bending and 727 cm^?1 CN stretching vibrations as well as 18b CD in-plane deformation are mixed to a great extent. The other nitro bending mode undergo also an inverse isotopic effect (2 cm^?1 upward shift) due to coupling with the 18a CD in-plane deformation vibration.     

Energy analysis of metal-metal bonding in [RM-MR] (M = Zn, Cd, Hg; R = CH3, SiH3, GeH3, C5H5, C5Me5)

The metal-metal bonds of the title compounds have been investigated with the help of energy decomposition analysis at the DFT/TZ2P level. In good agreement with experiment, computations yield Hg-Hg bond distance in [H₃SiHg-HgSiH₃] of 2.706 Å and Zn-Zn bond distance in [(η⁵-C₅Me₅)Zn-Zn(η⁵-C₅Me₅)] of 2.281 Å. The Cd-Cd bond distances are longer than the Hg-Hg bond distances. Bond dissociation energies (-BDE) for Zn-Zn bonds in zincocene −70.6 kcal/mol in [(η⁵-C₅H₅)₂Zn₂] and −70.3 kcal/mol in [(η⁵-C₅Me₅)₂Zn₂] are greater amongst the compounds under study. In addition, [(η⁵-C₅H₅)₂M₂] is found to have a binding energy slightly larger than those in [(η⁵-C₅Me₅)₂M₂]. The trend of the M-M bond dissociation energy for the substituents R shows for metals the order GeH₃ < SiH₃ < CH₃ < C₅Me₅ < C₅H₅. Electrostatic forces between the metals are always attractive and they are strong (−75.8 to −110.5 kcal/mol). The results demonstrate clearly that the atomic partial charges cannot be taken as a measure of the electrostatic interactions between the atoms. The orbital interaction (covalent bonding) ΔE_orb is always smaller than the electrostatic attraction ΔE_elstat. The M-M bonding in [RM-M-R] (R = CH₃, SiH₃, GeH₃, C₅H₅, C₅Me₅; M = Zn, Cd, Hg) has more than half ionic character (56-64%). The values of Pauli repulsions, ΔE_Pauli, electrostatic interactions, ΔE_elstat, and orbital interactions, ΔE_elstat are larger for mercury compounds as compared to zinc and cadmium.     

Thermodynamics of BaNd2Fe2O7(s) and BaNdFeO4(s) in the system BaNdFeO

Two compounds, BaNd₂Fe₂O₇(s) and BaNdFeO₄(s) in the quaternary system BaNdFeO were prepared by citrate-nitrate gel combustion route and characterized by X-ray diffraction analysis. Heat capacities of these two oxides were measured in two different temperature ranges: (i) 130-325 K and (ii) 310-845 K, using a heat flux type differential scanning calorimeter. Two different types of solid-state electrochemical cells with CaF₂(s) as the solid electrolyte were employed to measure the e.m.f. as a function of temperature. The standard molar Gibbs energies of formation of these quaternary oxides were calculated as a function of temperature from the e.m.f. data. The standard molar enthalpies of formation from elements at 298.15 K, ΔfHm° (298.15 K) and the standard entropies, Sm° (298.15 K) of these oxides were calculated by the second law method. The values of ΔfHm° (298.15 K) and Sm° (298.15 K) obtained for BaNd₂Fe₂O₇(s) are: −2756.9 kJ mol⁻¹ and 234.0 J K⁻¹ mol⁻¹ whereas those for BaNdFeO₄(s) are: −2061.5 kJ mol⁻¹ and 91.6 J K⁻¹ mol⁻¹, respectively.     

Infrared Photodissociation Spectroscopy of Ti+(CO2)2Ar and Ti+(CO2)n(n=3-7) Comple xes (cited: 1)

Ti⁺(CO₂)₂Ar and Ti⁺(CO₂)_n(n=3-7) complexes are produced by laser vaporization in a pulsed supersonic expansion. The ion complexes of interest are each mass-selected in a time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy. For each complex, a sharp band in the CO stretching frequency region is observed, which confirms the formation of the OTi⁺CO(CO₂)_n-1 oxide-carbonyl species. Small OTi⁺CO(CO₂)_n-1 complexes (n≦5) exhibit CO stretching and antisymmetric CO₂ stretching vibrational bands that are blue-shifted from those of free CO and CO₂. The experimental observations indicate that the coordination number of CO and CO₂ molecules around TiO⁺ is five. Evidence is also observed for the presence of another electrostatic bonding Ti⁺(CO₂)₂ structural isomer for the Ti⁺(CO₂)₂Ar complex, which is characterized to have a bent OCO-Ti⁺-OCO structure stabilized by argon coordination     

Vibrational spectroscopy of the sorosilicate mineral hemimorphite Zn4(OH)2Si2O7 · H2O

Raman spectroscopy complimented by infrared spectroscopy has been used to study the mineral hemimorphite from different origins. The Raman spectra show consistently similar spectra with only one sample showing additional bands due to the presence of smithsonite. Raman bands observed at 3510–3565 and 3436–3455 cm⁻¹ are assigned to OH stretching vibrations. Using a Libowitzky type formula, these OH bands provide hydrogen bond distances of 0.2910, 0.2825, 0.2762 and 0.2716 pm. Water bending modes are observed in the Raman spectrum at 1633 cm⁻¹. An intense Raman band at 930 cm⁻¹ is attributed to SiO symmetric stretching vibration of the Si₂O₇ units. Raman bands observed at 451 and 400 cm⁻¹are attributed to out-of-plane bending vibrations of the Si₂O₇ units. Raman bands at 330, 280, 168 and 132 cm⁻¹ are assigned to ZnO and OZnO vibrations.     

[Pt2(P2O4H2)4]4-和[Pt2(P2O4CH4)4]4-基态和激发态性质的理论研究

采用从头计算MP2和CIS方法分别优化等电子双核d⁸配合物[Pt₂(P₂O₄H₂)₄]^4-和[Pt₂(P₂O₄CH₄)₄]^4-的基态和激发态结构。结果表明基态Pt-Pt距离分别为0.290 5和0.298 7 nm，与实验的0.292 5和0.298 0 nm符合。NBO计算的Pt-Pt键级以及Pt原子间伸缩振动说明Pt-Pt相互作用具有吸引本质。CIS计算揭示电子激发到Pt-Pt的σ(p_z)成键轨道使得相互作用增强。保持激发态几何，含时密度泛函理论(TD-DFT)计算的溶液发射分别为449和475 nm，与实验值512和510 nm接近。     

The reaction of copper(II) and 2-hydrazino-2-imidazoline leading to the in situ formation of bisimidazoline (biz). Crystal structure and vibrational spectroscopy of mixed-valence [Cu(biz)2][Cu2Br4] complex

The reaction of Cu(OH)₂ and 2-hydrazino-2-imidazoline hydrobromide surprisingly resulted in complex compound where Cu(II) ions are chelated by a new ligand, namely bisimidazoline (biz). As has been found in the X-ray analysis, the [Cu(biz)₂]²⁺ cations are accompanied by [Cu₂Br₄]²⁻ anions, which makes the whole compound of metal-mixed-valency type. Both ions are centrosymmetric and quasi-planar. The Cu(II) coordination environment is a rectangle with almost equal Cu–N bond lengths (1.984(3), 1.987(3) Å). The electrostatic interaction of both complex ions is strengthened by two strong N–H···Br and four weaker (C–H···Br, C–H···N) hydrogen bonds. The relatively simple IR and Raman spectra were interpreted with help of quantum calculations carried out at the B3LYP/LanL2DZ level. The characterization of computed normal vibrations and correlating observed bands is given in terms of approximate D_2h symmetry. The most intense band resulting from the Cu–N stretching vibration (B_3u) was located at 342 cm⁻¹, by ⁶³Cu and ⁶⁵Cu isotope substitution. The chemical reactions leading to the formation of presented compound are also proposed.     

Alkynyl Ti-M complexes based on M(CO)4 and MO2 building blocks (M = Mo, W)

The synthesis and properties of heterobimetallic Ti-M complexes of type {[[Ti](μ-η¹:η²-CCSiMe₃)][M(μ-η¹:η²-CCSiMe₃)(CO)₄]} (M = Mo: 5, [Ti] = (η⁵-C₅H₅)₂Ti; 6, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = W: 7, [Ti] = (η⁵-C₅H₅)₂Ti; 8, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) and {[Ti](μ-η¹:η²-CCSiMe₃)₂}MO₂ (M = Mo: 13, [Ti] = (η⁵-C₅H₅)₂Ti; 14, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti). M = W: 15, [Ti] = (η⁵-C₅H₅)₂Ti; 16, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) are reported. Compounds 5-8 were accessible by treatment of [Ti](CCSiMe₃)₂ (1, [Ti] = (η⁵-C₅H₅)₂Ti; 2, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) with [M(CO)₅(thf)] (3, M = Mo; 4, M = W) or [M(CO)₄(nbd)] (9, M = Mo; 10, M = W; nbd = bicyclo[2.2.1]hepta-2,5-diene), while 13-16 could be obtained either by the subsequent reaction of 1 and 2 with [M(CO)₃(MeCN)₃] (11, M = Mo; 12, M = W) and oxygen, or directly by oxidation of 5-8 with air. A mechanism for the formation of 5-8 is postulated based on the in-situ generation of [Ti](CCSiMe₃)((η²-CCSiMe₃)M(CO)₅), {[Ti](μ-η¹:η²-CCSiMe₃)₂}-M(CO)₄, and [Ti](μ-η¹:η²-CCSiMe₃)((μ-CCSiMe₃)M(CO)₄) as a result of the chelating effect exerted by the bis(alkynyl) titanocene fragment and the steric constraints imposed by the M(CO)₄ entity.The molecular structure of 5 in the solid state were determined by single crystal X-ray diffraction analysis. In doubly alkynyl-bridged 5 the alkynides are bridging the metals Ti and Mo as a σ-donor to one metal and as a π-donor to the other with the [Ti](CCSiMe₃)₂Mo core being planar.     

Structural changes accompanying negative thermal expansion in Zr2(MoO4)(PO4)2

Zr₂(MoO₄)(PO₄)₂ is orthorhombic (Sc₂W₃O₁₂ structure) from 9 to at least 400 K, and shows anisotropic volume negative thermal expansion (α_a=−8.35(4)×10⁻⁶ K⁻¹; α_b=3.25(3)×10⁻⁶ K⁻¹; α_c=−8.27(5)×10⁻⁶ K⁻¹ in the range 122-400 K) similar in magnitude to A₂M₃O₁₂ (M—Mo or W) with large A³⁺. The contraction on heating is associated with a pattern of Zr-O-Mo/P bond angle changes that is somewhat similar, but not the same as that for Sc₂W₃O₁₂. On heating, the most pronounced reductions in the separation between the crystallographic positions of neighboring Zr and P are not associated with significant reductions in the corresponding Zr-O-P crystallographic bond angles, in contrast to what was seen for Sc₂W₃O₁₂.     

Synthesis and crystal structures of two (cyclopentadienyl)titanium(III) hydroborate complexes, [CpTiCl(BH4)]2 and Cp2Ti(B3H8)

Treatment of Cp^∗TiCl₃ and Cp₂TiCl₂ with NaB₃H₈ affords the titanium(III) hydroborate compounds [Cp^∗TiCl(BH₄)]₂ and Cp₂Ti(B₃H₈), respectively. The former compound arises by means of a new reaction, the metal-induced fragmentation of the B₃H₈ anion, and can also be made by treating Cp^∗TiCl₃ with LiBH₄. The latter compound has been previously described, but not characterized crystallographically. Both compounds have been studied by single crystal X-ray diffraction. Dimeric [Cp^∗TiCl(BH₄)]₂ has bridging chloride ligands and terminal Cp^∗ and BH₄ ligands. The Ti-Ti distance is 3.452(1) Å, which indicates that there is no metal-metal bonding interaction. The Ti-Cl distances are 2.440(2) Å and the Ti-Cl-Ti and Cl-Ti-Cl angles of 89.97(8) and 90.03(8)° so that the Ti₂Cl₂ unit is nearly a perfect square. The BH₄ groups are each tridentate, with a Ti-B distance of 2.220(9) Å and an average Ti-H distance of 1.98(5) Å. In Cp₂Ti(B₃H₈), the B₃H₈ ligand is bidentate, as is usually seen, and the Ti-B and Ti-H distances are 2.600(3) and 1.96(2) Å. The dihedral angle between the Ti-B(1)-B(2) plane and the B(1)-B(2)-B(3) plane is 123.4°. The Ti-B distances are 0.04 Å longer than those in niobium analog, Cp₂Nb(B₃H₈), despite the fact that the single bond metallic radius of Ti is 0.02 Å smaller than that of Nb. This lengthening of the bond is probably a consequence of the presence of one fewer skeletal bonding electron in Cp₂Ti(B₃H₈).