Magic clusters MAu4 (M=Ti and Zr) and their dimers: how magic are they?

The stability of closed shell bimetallic magic clusters MAu(4) (M=Ti and Zr) is investigated theoretically through ab initio molecular orbital calculations. Both these clusters have tetrahedral structures and are found to be associated with large values of the ionization potential, HOMO-LUMO gap as well as the binding energies, which are characteristic of the magic clusters. However, the cluster-cluster interaction energy corresponding to a dimer formation is found to be unusually high ( approximately 5-7 eV) in contradiction to the usual properties of a magic cluster and is attributed to a 3-center-2-electron M-Au-M type bridge bonding as well as aurophilic attraction. Gross geometrical features of the individual clusters are, however, mostly retained in the dimer, thus satisfying the basic requirements for the cluster-assembled materials. This work would have important implications in the design of novel cluster-based nanomaterials for various nanoscale applications.     

MX~4(M=Ti,Zr,Hf;X=Cl,Br)的电子结构研究

本文利用单电子非相对论Hartree-Fock-Slater和完全相对论Dirac-Fock-Slater两种离散变分局域密度泛函方法(DV-Xα), 对MX~4(M=Ti,Zr,Hf;X=Cl,Br)的电子基态和相应于低能UV光谱的激发态进行了计算, 结果与实验符合得较好。用Mulliken布居分析方法研究了分子的共价性质, 发现除HfBr~4外,相对论效应对金属与配体之间的键级影响很小。     

钛,锆和铪羰基化合物M(CO)_n(M=Ti,Zr,Hf;n=4～7)的理论研究

利用密度泛函方法对标题化合物的平衡几何、热化学及振动频率进行了理论预测,发现这3种金属原子都有相似的M(CO)n(n=4～7)结构.全局最低构型对M(CO)7都是单态C3v戴帽八面体7S-1,对M(CO)6都是三重态D3d畸变八面体6T(而对应的单重态M(CO)5仅比它低不到21 kJ·mol-1).对M(CO)n(n=5,4)都是三重态6S-1,其构型分别为从6T中移去1个或2个CO基的衍生物5T和4T.此外,五重态的D3h的三角双锥M(CO)5和单态的Td四面体M(CO)4以及能量更高的含有C和O同时与金属成键的独特配位CO基的M(CO)6和M(CO)3也被发现.最后,给出M(CO)7→M(CO)6+CO反应的离解能.并讨论了金属18价电子的Ti(CO)7存在的可能性.     

Filling a Gap: The Coordinatively Saturated Group 4 Carbonyl Complexes TM(CO)8 (TM=Zr,Hf) and Ti(CO)7

Homoleptic Group 4 metal carbonyl cation and neutral complexes were prepared in the gas phase and/or in solid neon matrix. Infrared spectroscopy studies reveal that both zirconium and hafnium form eight-coordinate carbonyl neutral and cation complexes. In contrast, titanium forms only the six-coordinate Ti(CO)₆⁺ and seven-coordinate Ti(CO)₇. Titanium octacarbonyl Ti(CO)₈ is unstable as a result of steric repulsion between the CO ligands. The 20-electron Zr(CO)₈ and Hf(CO)₈ complexes represent the first experimentally observed homoleptic octacarbonyl neutral complexes of transition metals. The molecules still fulfill the 18-electron rule, because one doubly occupied valence orbital does not mix with any of the metal valence atomic orbitals. Zr(CO)₈ and Hf(CO)₈ are stable against the loss of one CO because the CO ligands encounter less steric repulsion than Zr(CO)₇ and Hf(CO)₇. The heptacarbonyl complexes have shorter metal−CO bonds than that of the octacarbonyl complexes due to stronger electrostatic and covalent bonding, but the significantly smaller repulsive Pauli term makes the octacarbonyl complexes stable.     

Analysis of M···H-Si interactions in [{M(CpSiMe2H)Cl3}2], (M = Zr, Hf, Ti and Mo) complexes

For the d(0) complex [{Zr(CpSiMe(2)H)Cl(3)}(2)] which contains a linear Si-H···Zr interaction across the dimer, DFT calculations are in good agreement with X-ray structures. The BP86 functional shows a slightly stronger interaction than B3LYP but for qualitative purposes either functional is sufficient. QTAIM analysis shows a bond critical point (bcp) for the interaction, a small negative value for the total energy density [H((r))] and the H atomic basin decreases in energy, E(H), and atomic volume compared to the free ligand. NBO analysis showed E(2) for Si-H σ to Zr(dz(2)) donation at 42.8 kcal mol(-1) and a 34% spatial overlap for the interaction consistent with an inverse hydrogen bond. The Wiberg bond index for the interaction is 0.1735 (0.7205 for the Si-H bond), ν((Si-H)) and (1)J((Si-H)) at 2060 cm(-1) and 145.4 Hz compared to 2183 cm(-1) and 172.1 Hz in the free ligand. Using a "synthesis by computation" approach to forming like complexes, similar features were found for [{Hf(CpSiMe(2)H)Cl(3)}(2)]. The titanium complex [{Ti(CpSiMe(2)H)Cl(3)}(2)] does not contain any Si-H···Ti interaction as rotation about the C-Si bond of the ligand occurs to place the Si-H bond hydrogen closer to a terminal chloro ligand across the dimer. An increase in electron density on the metal in the d(2) complex [{Mo(CpSiMe(2)H)Cl(3)}(2)] results in a stronger interaction with a distinct QTAIM analysis bcp [ρ((r)) 0.0448 a.u.], a small negative value for H((r)) and a much reduced H atomic volume. NBO analysis shows E(2) for Si-H σ to Mo(dz(2)) donation at 143.1 kcal mol(-1) and a 29% spatial overlap. Mo(dz(2)) to Si-H σ* donation (back donation) is minimal [E(2) 1.3 kcal mol(-1), ~1% spatial overlap]. The Wiberg bond index is 0.3114 (0.5667 for the Si-H bond), ν((Si-H)) 2015 cm(-1) and (1)J((Si-H)) 120.6 Hz.     

The alkoxides of zirconium and hafnium: direct electrochemical synthesis and mass-spectral study. Do “M(OR)4”, where M=Zr,Hf, Sn,really exist?

The direct electrochemical synthesis of zirconium (1a) and hafnium (1b) alkoxides, M(OPrⁱ)₄·PrⁱOH, Zr(OBuⁱ)₄·BuⁱOH (4a) and M(OR)₄, where R=Et (2a,b), Buⁿ (3a), Bu^s (5a), C₂H₄OMe (6a,b) has been carried out by anodic oxidation of metals in anhydrous alcohols in the presence of LiCl as a conductive additive to give quantitative yields. The solubility polytherms and dissociation pressure of1a,b have been investigated. It has been proved by means of chemical analysis, X-ray powder, and IR spectral studies that the desolvation of 1a,b and Sn(OPrⁱ)₄·PrⁱOH (1c) is accompanied by the formation of amorphous oxocompounds M₃O(OPr_i)₁₀. On the basis of¹H NMR data it has been proved that the structure of the latter is analogous to that of known triangular cluster molecules M₃(₃-O)(₃-OR)(-OR)₃(OR)₆, where M=Mo, W, U. Mass-spectral data and the determined physicochemical characteristics of1–5 permit to conclude that the samples of composition M(OR)₄, where M=Zr, Hf, and2,3,5 contain tri- and tetranuclear oxocomplexes M₃O(OR)₁₀ and M₄O(OR)₁₄ respectively, along with Zr(OR)₄ oligomers of different molecular complexity.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 752–760, April, 1995.     

Hexacoordinated MIV (M=Ti,Zr, Hf) Tetrachlorido Complexes with Chelating Dithienylethane Based 1,2 Diketone Ligand – π-Conjugation as Decisive Factor for Axial Chirality Mode

1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione ( 1 , DTEthane) reacts with MCl₄ metal precursors of group four (M=Ti, Zr, Hf) via coordination of the carbonyl groups. The molecular structure of complex 2–4 were determined in scXRD studies in the solid state and characterized by means of multi-nuclear and multi-dimensional NMR spectroscopy in solution. While the resulting titanium complex [TiCl₄(DTEthane)] 2 shows a monomeric structure, where 1 binds in a bidentate fashion, complexes with a Zr ( 3 ) and Hf ( 4 ) center have dimeric scaffolds in which the ligands adopt a bridging mode. Quantum chemical calculations using density functional theory (G16, B97D3/def2-TZVP) were used to evaluate the general trend of dimer formation (Ti<Zr<Hf). The molecular structures derived from both scXRD and the DFT optimized structures reveal the carbonyl groups in conjugation with the adjacent thiophene substituent. As a result, they are coplanar and rotation about the two C−C axes (C1−C7; C8−C9) is restricted allowing for only one chiral axis along C7−C8. This gains special importance with respect to previously described complexes carrying the closely related 1,2-endiolato ligand (1,2-bis(2,5-dimethylthiophen-3-yl)ethene-1,2-diolate), in which no coplanarity of the thiophene rings to their neighboring metallacycle was observed allowing for two chiral axes. Noteworthy, further DFT calculations addressing the pathway of racemization found transition states, which are characterized by contrary rotations of both thiophene rings and a loss of conjugation rather than a direct rotation around the axis C7−C8.     

茂金属催化剂Cp_2~tMCl_2(Cp~t=~tBuC_5H_4,M=Ti、Zr、Hf)聚合丁烯-1的研究

探讨了茂金属催化剂 Cpt2 MCl2 ( Cpt=t Bu C5 H4,M=Ti,Zr,Hf)的合成以及用于聚合丁烯 -1的研究 ,研究了几种不同的茂金属催化剂和不同聚合条件下的催化行为 ,并通过 IR、1 H NMR、EI-MS、DSC、粘度法测分子量和正庚烷抽提等测试手段对催化剂和聚合物进行了表征 .结果表明 ,叔丁基取代的茂金属催化剂催化丁烯 -1聚合具有较高的催化活性 ,叔丁基的引入提高了聚合物的等规度和分子量     

Structures of MAu16 (-) (M=Ag, Li, Na, and K): how far is the endohedral doping?

The structural and electronic properties of MAu16 (-) (M=Ag, Li, Na, and K) have been studied by the scalar relativistic all-electron density-functional calculations, in which particular attention is paid to the stability of the endohedral Au16 (-) cage doped by different dopant atoms. It is found that only the smaller atoms, such as Cu, Li, and Na, can be stably encapsulated in the Au16 (-) cage, while the addition of the larger Ag or K atom prefers to locate in the surface or outside of the cage, which is inconsistent with the previous hypothesis that the Au16 (-) cage could act as a container to hold an arbitrary heterometal atom. The stable endohedral Li@Au16 (-) and Na@Au16 (-) have a large energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital gap, indicating that they are chemically stable and may be used as potential building blocks for designing cluster-assembled materials.     

OMS, OM(η2-SO), and OM(η2-SO)(η2-SO2) molecules (M = Ti, Zr, Hf): infrared spectra and density functional calculations

Infrared spectra of the matrix isolated OMS, OM(η(2)-SO), and OM(η(2)-SO)(η(2)-SO(2)) (M = Ti, Zr, Hf) molecules were observed following laser-ablated metal atom reactions with SO(2) during condensation in solid argon and neon. The assignments for the major vibrational modes were confirmed by appropriate S(18)O(2) and (34)SO(2) isotopic shifts, and density functional vibrational frequency calculations (B3LYP and BPW91). Bonding in the initial OM(η(2)-SO) reaction products and in the OM(η(2)-SO)(η(2)-SO(2)) adduct molecules with unusual chiral structures is discussed.     

层状晶体β-MNCl(M=Zr,Hf)的电子掺杂新方法及其性质研究

通过控制叠氮化物RN_3(R=Li, Na, K, Rb)与层状晶体β-MNCl (M = Zr, Hf) 反应的摩尔比，成功地对层状晶体β-MNCl(M=Zr, Hf)进行了电子掺杂，得到了转 变温度分别是13.5K和23.5K的超导体。实验结果还进一步表明，当摩尔比x=n (NaN_3)/n(β-ZrNCl)=0.3时，反应所得反插层化合物ZrNCl_(1-x)经450 ℃退火处 理后，其超导性质最好。作者同时利用XRD，TEM和SQUID测试结果，分析了化学反 应机理和电子掺杂原理，并研究了所得超导体在空气中的稳定性。     

Al促进SO~4^2^-/M~xO~y(M=Zr,Ti, Fe)固体强酸的研究

合成与表征了三个系列的Al促进固体强酸样品,并研究了对甲苯的苯甲酰化反应性能。实验表明,向SO~4^2^-/ZrO~2,SO~4^2^-/TiO~2和SO~4^2^-/Fe~2O~3中引入适量的Al~2O~3,有助于稳定样品表面的含硫物种,增加样品表面的有效酸位,提高样品的强酸性和对甲苯的苯甲酰化的反应活性。NH~3吸附微量热结果表明,Al促进样品的强酸性和催化活性的显著提高是由于样品表面的酸位强度分布发生了变化,有利于正丁烷异构化反应和苯甲酰化反应的中强酸位和强酸位的酸量显著增加。     

Al促进SO~4^2^-/M~xO~y(M=Zr, Ti, Fe)固体强酸的研究

合成与表征了三个系列的Al促进固体强酸样品,并研究了对甲苯的苯甲酰化反应性能.实验表明,SO_4~(2-)/ZrO_2,SO_4~(2-)/TiO_2和SO_4~(2-)/Fe_2O_3中引入适量的Al_2O_3,有助于稳定样品表面的含硫物种,增加样品表面的有效酸位,提高样品的强酸性和对甲苯的苯甲酰化的反应活性.NH_3吸附微量热结果表明,Al促进样品的强酸性和催化活性的显著提高是由于样品表面的酸位强度分布发生了变化,有利于正丁烷异构化反应和苯甲酰化反应的中强酸位和强酸位的酸量显著增加.     

Electronic structure and low temperature thermoelectric properties of In₂₄M₈O₄₈ (M = Ge(4+), Sn(4+), Ti(4+), and Zr(4+))

The electronic structure and transport properties of In₂₄M₈O₄₈ (M = Ge⁴⁺, Sn⁴⁺, Ti⁴⁺, and Zr⁴⁺) have been studied by using the full‐potential linearized augmented plane‐wave method and the semiclassical Boltzmann theory, respectively. It is found that the magnitude of powerfactor with respect to relation time follows the order of In₂₄Sn₈O₄₈ > In₂₄Zr₈O₄₈ > In₂₄Ge₈O₄₈ > In₂₄Ti₈O₄₈. The largest powerfactor is 2.7 × 10¹² W/K²ms for In₂₄Sn₈O₄₈ at 60 K, which is nearly thirty times larger than those of conventional n‐type thermoelectric materials. The origin of the different thermoelectric behavior for these compounds is discussed from the electronic structure level. It is found that, at low temperature, the dopant strongly affect the bands near the Fermi level, which consequently leads to their different thermoelectric properties. The electronic configuration and the difference in atomic number between the dopant and the host atom also play an important role on the thermoelectric properties of In₂₄M₈O₄₈. Our calculations give a valuable insight on how to enhance the thermoelectric performance of In₃₂O₄₈. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

不同碱金属叠氮化物对层状晶体β-MNCl(M=Zr,Hf)电子掺杂的影响

Layer-structured crystals of β-MNCl (M=Zr,Hf) could be electron-doped by reactions with different alkali metal azides RN3 (R=Li,Na,K,Rb), and controlling the amounts with the molar ratios of azides to β-MNCl. All the prepared compounds show superconductivity with the same transition temperatures at 13.5 K for β-ZrNCl and 23.5 K for β-HfNCl. However the different alkali metal azides RN3 show different reactivity with β-MNCl, and the properties of the products such as superconducting fractions, the lattice constant, and stability against thermal or air, are very dependent on the kinds of alkali metals used. Based on the the results of SQUID measurements, it can be concluded that NaN3 and KN3 are the best react agents for β-ZrNCl and β-HfNCl respectively.     

Chemical bonding in “early–late” transition metal complexes [(H2N)3M–M′(CO)4] (M = Ti, Zr, Hf; M′ = Co, Rh, Ir)

Quantum chemical DFT calculations at the BP86/TZ2P level have been carried out for the complex [HSi(SiH₂NH)₃Ti–Co(CO)₄], which is a model for the experimentally observed compound [MeSi{SiMe₂N(4-MeC₆H₄)}₃Ti–Co(CO)₄] and for the series of model systems [(H₂N)₃M–M′(CO)₄] (M = Ti, Zr, Hf; M′ = Co, Rh, Ir). The Ti–Co bond in [HSi(SiH₂NH)₃Ti–Co(CO)₄] has a theoretically predicted BDE of D _e = 59.3 kcal/mol. The bonding analysis suggests that the titanium atom carries a large positive charge, while the cobalt atom is nearly neutral. The covalent and electrostatic contributions to the Ti–Co attraction have similar strength. The Ti–Co bond can be classified as a polar single bond, which has only little π contribution. Calculations of the model compound (H₂N)₃Ti–Co(CO)₄ show that the rotation of the amino groups has a very large influence on the length and on the strength of the Ti–Co bond. The M–M′ bond in the series [(H₂N)₃M–M′(CO)₄] becomes clearly stronger with Ti < Zr < Hf, while the differences between the bond strengths due to change of the atoms M′ are much smaller. The strongest M–M′ bond is predicted for [(H₂N)₃Hf–Ir(CO)₄].     

Formation of M(4)Se(4) cuboids (M = As, Sb, Bi) via secondary pnictogen-chalcogen interactions in the co-crystals MX(3)·Se[double bond, length as m-dash]P(p-FC(6)H(4))(3) (M = As, X = Br; M = Sb, X = Cl; M = Bi, X = Cl, Br)

The reactions of the group 15 trihalides, MX(3) (M = As, Sb, Bi; X = Cl, Br), with the phosphine selenide SeP(p-FC(6)H(4))(3) result in the formation of co-crystals of formula MX(3)·SeP(p-FC(6)H(4))(3). No reaction was observed with MI(3) (M = As, Sb, Bi). The structures of MX(3)·SeP(p-FC(6)H(4))(3) (M = As, X = Br 2; M = Sb, X = Cl 3; M = Bi, X = Cl 5; M = Bi, X = Br 6) have been established, and are isomorphous, crystallising in the cubic I23 space group. All the structures feature a primary MX(3) unit, which has three weak secondary MSe interactions to SeP(p-FC(6)H(4))(3) molecules. However, each of these SeP(p-FC(6)H(4))(3) molecules bridges three MX(3) molecules, resulting in the generation of an M(4)Se(4) (M = As, Sb, Bi) distorted cuboid linked by the pnictogen-chalcogen interactions. Four opposing corners of the cuboid are occupied by the M atom (M = As, Sb, Bi) of an MX(3) pyramid, and the other four by the selenium atom of the phosphine selenide.     

α-Na3M2(PO4)3 (M = Ti, Fe): absolute cationic ordering in NASICON-type phases

The structure of the fully ordered α-Na(3)Ti(2)(PO(4))(3) NASICON compound was elucidated using high-quality single-crystal data. The cation/vacancy distribution forms a homogeneous 3D arrangement and could represent the absolute cationic ordering available in the full Na(3)M(2)(PO(4))(3) series, as verified for M = Fe. For M = Ti, the reversible α → γ transition was observed at 85 °C, leading to the standard disordered R ?3c γ model. Through JPDF analysis, the most probable Na(+) zigzag M(2)-M(1) diffusion scheme was directly deduced using our accurate crystallographic data.