Sandwich Complexes of the As_4～(2-) Aromatic Ring with Some Transition Metals

The equilibrium geometries,energies,harmonic vibrational frequencies,and nucleus independent chemical shifts(NICS) of the new type sandwich structures [As4MAs4]n-(M = Fe,Co,Ni,Ru,Rh,Pd,Os,Ir and Pt;n = 0,1 or 2) are investigated at the B3LYP level.All the [As4MAs4]n-species adopt staggered(D4d) conformations as their stable structures and eclipsed(D4h) conformations as their transition states,and once the sandwich complexes are formed,the As42- square properties remain unchanged.The NICS calculation confirms that the complexes of Fe,Co,and Ni are aromatic with negative NICS values,and those of Ru,Rh,and Ir exhibit slight aromaticity,while those of Pd,Os,and Pt show slight antiaromaticity.     

E_4~(2-),[CoE_4]~+和[P_4CoE_4]~-(E=N～Bi)结构和芳香性的理论预测

用密度泛函理论杂化密度泛函B3LYP方法研究了E24-,[CoE4]+和[P4CoE4]-(E=N,P,As,Sb,Bi)几何结构、键能及芳香性.结果表明,E42-,[CoE4]+和[P4CoE4]-的基态结构分别具有D4h,C4v和C4v(交错型)对称性.三明治配合物中,金属与配体间存在σ,π和δ三种成键方式,P4与E4间相互影响较小.E4对P4中的P—P键长影响随着N,P,As,Sb,Bi顺序逐渐变长,中心Co离子与E4间的键合能随N,P,As,Bi,Sb的顺序增大.N42-的环外具有弱芳香性,其它E42-环中心及环外均为反芳香性.除[CoN4]+外,其它[CoE4]+中的E4环均具有较强的中心和内芳香性及弱的外反芳香性.[P4CoE4]-中的P4和E4均具有较大的中心、内和外芳香性,且P4环芳香性随N,P,As,Sb,Bi顺序逐渐递增.     

D_(3d)[E_3ME_3]~(2-)(E=P,As;M=Ni,Pd,Pt):含η~3-P_3~-和η~3-As_3~-配体的最小无机三明治配合物

C4H42-、C5H5-(Cp-)及C6H6(Ar)等有机配体可以与过渡金属形成典型的三明治夹心化合物.作为CH的等电子体,P可以取代CH与过渡金属形成混合型三明治配合物,例如:CpNiP3,CpFeP5,[CpMPnMCp]等.2002年,Schleyer等首次成功地合成了以η5-P5-为配体的不含碳的无机三明治配合物[P5TiP5]2-;2007年,Chen等采用密度泛函方法预测了含P4四元环的[P4MP4]n-三明治结构.本文采用密度泛函和从头计算方法首次系统地研究了含η3-P3-和η3-As3-三元环配体的过渡金属三明治配合物D3d[E3ME3]2-(E=P,As;M=Ni,Pd,Pt)(图1),对该系列化合物进行了结构优化、频率分析、自然轨道分析和光谱性质预测.结果表明,三元环状P3-和As3-与五元环状P5-和As5-具有类似的芳香性,可能作为新颖配位形成一大类过渡金属夹心化合物.[E3ME3]2-满足18电子规则,交错型单重态D3d[E3ME3]2-是该七原子体系的全局极小,而重叠型单重态D3h[E3ME3]2-在能量上略高(2.0kcal/mol),其他二维和三维结构则远非稳定(24kcal/mol).作为体系的全局极小,D3d[E3ME3]2-是在实验上可能合成的最小无机三明治夹心结构.在[E3ME3]2-系列配合物中,配位中心M携带的电荷为+0.07|e|～+0.27|e|,Wiberg键级为1.84～2.22;配体E原子携带的电荷为-0.35|e|～-0.38|e|,Wiberg键级为2.93～2.98.配体原子间以单键(WBIE-E=1.03-1.07),配体E和配位中心M间的Wiberg键级为WBIM-E=0.31-0.37,体现典型的配位成键特点.显然,与实验已知的[P5TiP5]2-类似,在[E3ME3]2-体系中配位中心M向配体E3发生了部分电荷转移,E3三元环表现为电子受体.轨道分析表明,该夹心化合物体系存在典型的离域π键(图1).体系存在较大NICS(-18.1～-24.8ppm),表明其芳香性本质.引进Li+阳离子可以有效稳定[E3ME3]2-二价阴离子,形成含交错型Cs[E3ME3]Li-和C2h[E3ME3]Li2.Cs[E3ME3]Li-的第一计算电子剥离能介于2.7～2.9eV,位于355nm激发光能量(3.496eV)范围之内.     

Carbon-free D_(3d) [E_3ME_3]~(2-) (E=P,As;M=Ni,Pd,Pt):The smallest inorganic sandwich complexes with aromatic η~3-P_3~- and η~3-As_3~- ligands

A density functional theory and wave function theory investigation on the possibility of carbon-free phosphametallocenes [P3MP3]2-and arsenametallocenes [As3MAs3]2- (M=Ni, Pd, Pt) is presented in this work. Staggered singlet D3d [E3ME3]2- (E=P, As)-the smallest inorganic metallocenes possible to construct-proved to be the global minima of the heptaatomic sys- tems and may be targeted in future experiments. Cyclo-P3- and cyclo-As3- turned out to possess similar aromaticity to cyclo-P5- and cyclo-As5- and may...     

杂苯C5H5X（X=N,P,As,Sb,Bi）芳香性的核独立化学位移（NICS）与异构体稳定化能（ISE）研究

应用量子化学方法,通过核独立化学位移(NICS)和异构体稳定化能(ISE)的计算,研究了苯及第五主族元素取代杂苯分子C5H5X(X=N,P,As,Sb,Bi)的芳香性与稳定性.局域轨道定位函数局部最大值的计算结果表明,分子中C—X成键强度与实验稳定性顺序一致.从头算与密度泛函理论对分子的化学位移计算结果各异,计算值与实验值相关分析表明,Hartree-Fock方法对所研究体系的NICS比密度泛函理论具有更好的相关性.在分子环平面上方0.8～0.9处的NICS是芳香性判据的最佳选择,由自然定域分子轨道分解NICS最大处的zz张量值,结果显示π键对分子的芳香性起主要贡献.异构体稳定化能与NICS(max)的zz张量及π键(NICS(max)zzπ)均有很好的相关性,可以表征杂苯分子C5H5X全局芳香性,其顺序为:苯>吡啶>磷杂苯>砷杂苯>锑杂苯>铋杂苯.特别地,对这类分子π轨道的研究发现不包含X原子的π轨道将产生异常大的π键芳香性,这一现象可为分子磁性设计提供理论指导.     

钛锆钒异核双金属配合物[Cp2V(μ-η2:η4-PhC4Ph)MCp2′](M=Ti,Zr; Cp′=C5H5,C5H4SiMe3)的合成与表征

室温下, [Cp2Ti(C≡CPh)2], [Cp2Zr(C≡CPh)2]和[(C5H4SiMe3)2Zr(C≡CPh)2]分别与二茂钒作用, 合成了[Cp2V(μ-η2∶η4-PhC4Ph)MCp2′] (1, M=Ti, Cp′=C5H5; 2, M=Zr, Cp′=C5H5; 3, M=Zr, Cp′=C5H4SiMe3). 用元素分析、质谱、核磁共振谱、磁矩、红外和拉曼光谱对配合物进行了表征. 3个配合物具有相似的磁化率, 配合物3的晶体结构分析表明PhC4Ph通过内部2个碳原子键合到Cp2V上, 内部2个碳原子和外部2个碳原子均与Cp2′Zr键合, 丁二烯骨架内部的2个碳原子都具有四配位的平面结构.     

(1,3,5-C3P3H3)M与(1,3,5-C3P3H3)2M (M=Ti,V, Cr)配合物的结构与芳香性

运用密度泛函理论研究了(1,3,5-C3P3H3)M和(1,3,5-C3P3H3)2M (M=Ti,V,Cr)的结构、键合能以及芳香性.结果表明:低自旋的(1,3,5-C3P3H3)M和(1,3,5-C3P3H3)2M基态结构分别具有C3v和D3h对称性.金属与配体间为共价作用,二者之间存在σ、π和σ三种成键方式.V的三明治配合物的解离方式与Ti和Cr的三明治配合物不同,前者为分步解离,后两者则为一步解离.其中(1,3,5-C3P3H3)2Cr(D3h)的第一解离能最大,配合物最稳定.这些三明治和半三明治配合物都具有中心芳香性、内芳香性和外芳香性,且中心芳香性均大于自由配体(1,3,5-C3P3H3)的中心芳香性,芳香性主要贡献来源于π键和金属原子的孤对电子.内芳香性按照Ti、V、Cr的顺序依次增大,且内芳香性明显要大于外芳香性.高自旋的半三明治(1,3,5-C3P3H3)Ti(C3,5A1)与单重态(1,3,5-C3P3H3)Ti (C3v,1A1)相比,配体的变形性增大,稳定性增加,且C平面中心芳香性和内芳香性均增大,但P平面的中心芳香性却降低.     

Lindqvist型[M6-nMonO19]p-阴离子（M=W,Nb,Ta）电子性质的密度泛函理论研究

采用密度泛函理论方法探讨了取代Mo原子对[W6-nMonO19]2-,[Nb6-nMonO19]p-和[Ta6-nMonO19]p-体系的M—Ot(M=W,Nb,Ta)键的活化作用.计算结果表明,随着取代Mo原子数的增多,[M6-nMonO19]2-(M=W,Nb,Ta)中M—Ot键的键能逐渐减小,因此Mo原子的引入使M—Ot键活化.在[W6-nMonO19]2-中,Mo—Ot键的键能小于W—Ot键的键能,因此,Mo—Ot键比W—Ot键易断裂,与实验结果一致.而在[Nb6-nMonO19]p-和[Ta6-nMonO19]p-体系中,Mo—Ot键的键能大于M—Ot(M=Nb,Ta)键的键能.Nb和Ta原子的端氧Ot的电荷大于Mo原子的端氧Ot的电荷,初步预测,当[Nb6-nMonO19]p-和[Ta6-nMonO19]p-与有机胺反应时,Nb—Ot和Ta—Ot键优先断裂,易与有机胺的氮原子成键.     

钛锆钒异核双金属配合物[Cp2V（μ—η^2：η^4—PhC4Ph）MCp2‘]（M=Ti,Zr;Cp’=C5H5,C5H4SiMe3）的合成与表征

室温下，[Cp2Ti(C≡Cph)2],[Cp2Zr(C≡CPh)2]和[C5H4SiMe3)2Zr(C≡CPh)2]分别与二茂钒作用，合成了钛锆钒异核双金属配合物[Cp2V(μ-η^2:η^4-PhC4Ph)MCp2‘](M=Ti,Zr;Cp‘=C5H5,C5H4SiMe3)。用元素分析、质谱、核磁共振谱、磁矩、红外和拉曼光谱对配合物进行了表征。3个配合物具有相似的磁化率。配合物3的晶体结构分析表明PhC4Ph通过内部2个碳原子键合到Cp2V上，内部2个碳原子和外部2个碳原子均与Cp2‘Zr键合，丁二烯骨架内部的2个碳原子都具有四配位的平面结构。     

铍-铍金属链夹心配合物D4d [Ben(C4H4)2]2- 及[Ben(C4H4)2]Li2 (n=2–8)

中文：采用密度泛函理论方法(B3LYP和BP86)在6-311+G(d,p)基组水平上系统研究了新颖的铍-铍金属链夹心配合物[Ben(C4H4)2]2- 及 [Ben(C4H4)2]Li2 (n=2–8) 的几何结构、电子结构、成键特征及热力学稳定性。结果表明,具有交错式D4d 对称性的[Ben(C4H4)2]2-及[Ben(C4H4)2]Li2 为体系势能面上的真正极小。自然键轨道(NBO)、分子中的原子(AIM)及分子轨道分析表明该系列夹心配合物中铍-铍间主要以共价键为主,而配体与铍-铍链之间则主要以离子键为主。核独立化学位移(NICS)分析表明配体在该系列配合物中具有π芳香性。稳定的夹心配合物锂盐[Ben(C4H4)2]Li2 (n=2–8)有望通过C4H4Li2/C5H5-配体交换反应进行制 备,该系列配合物将进一步丰富多核夹心配合物研究领域。     

Theoretical study on structures and aromaticities of P5(-) anion, [Ti (eta(5)-P5)]- and sandwich complex [Ti(eta(5)-P5)2]2-

The equilibrium geometries, energies, harmonic vibrational frequencies, and nucleus independent chemical shifts (NICSs) of the ground state of P5(-) (D(5h)) anion, the [Ti (eta(5)-P5)]- fragment (C(5v)), and the sandwich complex [Ti(eta(5)-P5)2]2- (D(5h) and D(5d)) are calculated by the three-parameter fit of the exchange-correlation potential suggested by Becke in conjunction with the LYP exchange potential (B3LYP) with basis sets 6-311+G(2d) (for P) and 6-311+G(2df) (for Ti). In each of the three molecules, the P-P and Ti-P bond distances are perfectly equal: five P atoms in block P5(-) lie in the same plane; the P-P bond distance increases and the Ti-P bond distance decreases with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. The binding energy analysis, which is carried out according to the energy change of hypothetic reactions of the three species, predicts that the three species are all very stable, and [Ti (eta(5)-P5)]- (C(5v)), more stable than P5(-) and [Ti(eta(5)-P5)2]2- synthesized in the experiment, could be synthesized. NICS values, computed for the anion and moiety of the three species with GIAO-B3LYP, reveal that the three species all have a larger aromaticity, and NICS (0) of moiety, NICS (1) of moiety, and minimum NICS of the inner side of ring P5 plane in magnitude increase with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. By analysis of the binding energetic and the molecular orbital (MO) and qualitative MO correlation diagram, and the dissection of total NICS, dissected as NICS contributions of various bonds, it is the main reason for P5(-) (D(5h)) having the larger aromaticity that the P-P sigma bonds, and pi bonds have the larger diatropic ring currents in which NICS contribution are negative, especially the P-P sigma bond. However, in [Ti (eta(5)-P5)]- (C(5v)) and [Ti(eta(5)-P5)2]2- (D(5h), and D(5d)), the reason is the larger and more negative diatropic ring currents in which the NICS contributions of P-P pi bonds and P5-Ti bonds including pi, delta, and sigma bonds, especially P5-Ti bonds, are much more negative and canceled the NICS contributions of P and Ti core and lone pair electrons.     

Sandwich Complexes of the As42-Aromatic Ring with Some Transition Metals

The equilibrium geometries, energies, harmonic vibrational frequencies, and nuc- leus independent chemical shifts (NICS) of the new type sandwich structures [As4MAs4]n- (M = Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt; n = 0, 1 or 2) are investigated at the B3LYP level.All the [As4MAs4]n- species adopt staggered (D4d) conformations as their stable structures and eclipsed (D4h) conformations as their transition states, and once the sandwich complexes are formed, the As42- square properties remain unchanged.The NICS calculation confirms that the complexes of Fe, Co, and Ni are aromatic with negative NICS values, and those of Ru, Rh, and Ir exhibit slight aromaticity, while those of Pd, Os, and Pt show slight antiaromaticity.     

Achieving Adaptive Aromaticity in Cyclo[10]carbon by Screening Cyclo[n]carbon (n=8−24)

Discovery of species with adaptive aromaticity (being aromatic in both the lowest singlet and triplet states) is particularly challenging as cyclic species are generally aromatic either in the ground state or in the excited state only, according to Hückel's and Baird's rules. Inspired by the recent realization of cyclo[18]carbon, here we demonstrate that cyclo[10]carbon possesses adaptive aromaticity by screening cyclo[n]carbon (n=8?24), which is supported by nucleus‐independent chemical shift (NICS), anisotropy of the current‐induced density (ACID), π contribution of electron localization function (ELF_π) and electron density of delocalized bonds (EDDB) analyses. Further study reveals that the lowest triplet state of cyclo[10]carbon is formed by in‐plane ππ* excitation. Thus, the major contribution to the aromaticity from out‐of‐plane π molecular orbitals does not change significantly in the lowest singlet state. Our findings highlight a crucial role of out‐of‐plane π orbitals in maintaining aromaticity for both the lowest singlet and triplet states as well as the aromaticity dependence on the number of the carbon in cyclo[n]carbon.     

Local aromaticity of [n]acenes, [n]phenacenes, and [n]helicenes (n = 1-9)

The local aromaticity of the six-membered rings in three series of benzenoid compounds, namely, the [n]acenes, [n]phenacenes, and [n]helicenes for n = 1-9, has been assessed by means of three probes of local aromaticity based on structural, magnetic, and electron delocalization properties. For [n]acenes our analysis shows that the more reactive inner rings are more aromatic than the outer rings. For [n]phenacenes, all indicators of aromaticity show that the external rings are the most aromatic. From the external to the central ring, the local aromaticity varies in a damped alternate way. The trends for the [n]helicene series are the same as those found for [n]phenacenes. Despite the departure from planarity in [n]helicenes, only a very slight loss of aromaticity is detected in [n]helicenes as compared to the corresponding [n]phenacenes. Finally, because of magnetic couplings between superimposed six-membered rings in the higher members of the [n]helicenes series, we have demonstrated that the NICS indicator of aromaticity artificially increases the local aromaticity of their most external rings.     

Aromaticity and electron affinity of Carbo(k)-[3]radialenes, k=0, 1, 2

Aromaticity enhancement is a possible driving force for the low reduction potentials of buta-1,3-diynediyl-expanded [N]radialenes: this hypothesis is theoretically analyzed for the expanded [3]radialene prototype. This study is undertaken within a more general prospect, namely the evaluation of the variation of aromaticity with endocyclic and peripheral carbomeric expansion of [3]radialene and its mono- and dianions. The structures, denoted as [C-H](6) (h)[C-C](3) (k)carbo-[3]radialene(q) (h=0, 1; k=0, 1, 2; q=0, -1, -2), were optimized in relevant singlet, doublet, or triplet spin states at the B3PW91/6-31G** level. They were found to be all planar. The structural aromaticity was measured through the average bond length d(av) over the [C-C](3) (k)carbo-[3]radialene core, and by the corresponding bond-length equalization parameter sigma(d), related to Krygowski's GEO. The magnetic aromaticity was measured by Schleyer's NICS values at the center of the rings. Regarding the relative variation of NICS and sigma(d), two classes of species can be distinguished according to their endocyclic expansion level. The species with a nonexpanded (k=0) or doubly expanded (k=2) ring constitute the first class: they exhibit D(3h) symmetry and a strong correlation of NICS with sigma(d). The species with a singly expanded ring (k=1) fall far from the correlation line, and constitute the second class. This class distinction is related to the degeneracy scheme of the frontier orbitals of the neutral representative. A finer appraisal of the electron (de)localization is brought by the ELF (Electron Localization Function) analysis of the electron density. It allows for a weighting of relevant resonance forms. Unsubstituted species are well described by the superimposition of two or three resonance forms. For (doublet spin state) monoanionic species, their respective weights are validated by comparison with AIM spin density. The weighted mean, n, of the formal numbers of paired pi(z) electrons in the resonance forms was calculated and compared with the closest even integer of either forms 4m+2 or 4m. A density-based continuous generalization of the orbital-based discrete Hückel rule is then heuristically proposed through an analytical correlation of NICS versus sigma(d), n, and S, the spin of the species. The frontier-orbital-degeneracy pattern of neutral species is discussed with respect to structural and magnetic aromaticity criteria. A decreasing HOMO-LUMO gap versus endocyclic expansion is obtained, but [C-C](3) (1)carbo-[3]radialene possesses the highest HOMO and LUMO energies. Vertical and adiabatic electron affinities of neutral and monoanionic species were also computed and compared with related experimental data.     

Dicyclobuta[de,ij]naphthalene and dicyclopenta[cd,gh]pentalene: a theoretical study

The structures, energetics, and aromatic character of dicyclobuta[de,ij]naphthalene, 1, dicyclopenta[cd,gh]pentalene, 2, dihydrodicyclobuta[de,ij]naphthalene, 3, and dihydrocyclopenta[cd,gh]pentalene, 4, have been examined at the B3LYP/6-311++G//B3LYP/6-31G level of theory. All molecules are bowl-shaped, and the pentalene isomers, 2 and 4, are most stable. A comparison with other C(12)H(6) and C(12)H(8) isomers indicates that 2 is approximately 25 kcal/mol less stable than 1,5,9-tridehydro[12]annulene and 4 is approximately 100 kcal/mol higher in energy than acenaphthylene, both of which are synthetically accessible. The transition state structure for bowl-to-bowl inversion of 1 is planar (D(2)(h)()) and lies 30.9 kcal/mol higher in energy than the ground state; the transition state for inversion of 2 is C(2)(h)() and lies 46.6 kcal/mol higher in energy. Symmetry considerations, bond length alternations, and NICS values (a magnetic criterion) all indicate that the ground states of 1, 3, and 4 are very aromatic; however, HOMA values (a measure of bond delocalization) indicate that 3S and 4S are aromatic but that 1S is less so. NICS values for the ground state of 2 strongly indicate aromaticity; however, bond localization, symmetry, and HOMA values argue otherwise.     

Experimental and theoretical characterization of MSi16(-), MGe16(-), MSn16(-), and MPb16(-) (M = Ti, Zr, and Hf): the role of cage aromaticity

Silicon (Si), germanium (Ge), tin (Sn), and lead (Pb) clusters mixed with a group-4 transition metal atom [M = titanium (Ti), zirconium (Zr), and hafnium (Hf)] were generated by a dual-laser vaporization method, and their properties were analyzed by means of time-of-flight mass spectroscopy and anion photoelectron spectroscopy together with theoretical calculations. In the mass spectra, mixed neutral clusters of MSi(16), MGe(16), and MSn(16) were produced specifically, but the yield of MPb(16) was low. The anion photoelectron spectra revealed that MSi(16), MGe(16), and MSn(16) neutrals have large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps of 1.5-1.9 eV compared to those of MPb(16) (0.8-0.9 eV), implying that MSi(16), MGe(16), and MSn(16) are evidently electronically stable clusters. Cage aromaticity appears to be an important determinant of the electronic stability of these clusters: Calculations of nucleus-independent chemical shifts (NICSs) show that Si(16)(4-), Ge(16)(4-), and Sn(16)(4-) have aromatic characters with negative NICS values, while Pb(16)(4-) has an antiaromatic character with a positive NICS value.     

Synthesis and catalysis of di- and tetranuclear metal sandwich-type silicotungstates [(gamma-SiW10O36)2M2(mu-OH)2]10- and [(gamma-SiW10O36)2M4(mu4-O)(mu-OH)6]8- (M = Zr or Hf)

The di- and tetranuclear metal sandwich-type silicotungstates of Cs10[(gamma-SiW10O36)2{Zr(H2O)}2(mu-OH)2] x 18 H2O (Zr2, monoclinic, C2/c (No. 15), a = 25.3315(8) A, b = 22.6699(7) A, c = 18.5533(6) A, beta = 123.9000(12) degrees, V = 8843.3(5) A(3), Z = 4), Cs10[(gamma-SiW10O36)2{Hf(H2O)}2(mu-OH)2] x 17 H2O (Hf2, monoclinic, space group C2/c (No. 15), a = 25.3847(16) A, b = 22.6121(14) A, c = 18.8703(11) A, beta = 124.046(3) degrees, V = 8974.9(9) A(3), Z = 4), Cs8[(gamma-SiW10O36)2{Zr(H2O)}4(mu4-O)(mu-OH)6] x 26 H2O (Zr4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.67370(10) A, c = 61.6213(8) A, V = 9897.78(17) A(3), Z = 4), and Cs8[(gamma-SiW10O36)2{Hf(H2O)}4(mu4-O)(mu-OH)6] x 23 H2O (Hf4, tetragonal, P4(1)2(1)2 (No. 92), a = 12.68130(10) A, c = 61.5483(9) A, V = 9897.91(18) A(3), Z = 4) were obtained as single crystals suitable for X-ray crystallographic analyses by the reaction of a dilacunary gamma-Keggin silicotungstate K8[gamma-SiW10O36] with ZrOCl2 x 8 H2O or HfOCl2 x 8 H2O. These dimeric polyoxometalates consisted of two [gamma-SiW10O36](8-) units sandwiching metal-oxygen clusters such as [M2(mu-OH)2](6+) and [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). The dinuclear zirconium and hafnium complexes Zr2 and Hf2 were isostructural. The equatorially placed two metal atoms in Zr2 and Hf2 were linked by two mu-OH ligands and each metal was bound to four oxygen atoms of two [gamma-SiW10O36](8-) units. The tertanuclear zirconium and hafnium complexes Zr4 and Hf4 were isostructural and consisted of the adamantanoid cages with a tetracoordinated oxygen atom in the middle, [M4(mu4-O)(mu-OH)6](8+) (M = Zr or Hf). Each metal atom in Zr4 and Hf4 was linked by three mu-OH ligands and bound to two oxygen atoms of the [gamma-SiW10O36](8-) unit. The tetra-nuclear zirconium and hafnium complexes showed catalytic activity for the intramolecular cyclization of (+)-citronellal to isopulegols without formation of byproducts resulting from etherification and dehydration. A lacunary silicotungstate [gamma-SiW10O34(H2O)2](4-) was inactive, and the isomer ratio of isopulegols in the presence of MOCl2 x 8 H2O (M = Zr or Hf) were much different from that in the presence of tetranuclear complexes, suggesting that the [M4(mu4-O)(mu-OH)6](8+) core incorporated into the POM frameworks acts as an active site for the present cyclization. On the other hand, the reaction hardly proceeded in the presence of dinuclear zirconium and hafnium complexes under the same conditions. The much less activity is possibly explained by the steric repulsion from the POM frameworks in the dinuclear complexes.     

第一过渡系金属硅烯配合物的理论研究

以HF/6-311+G^*基组研究了硅烯SiH₂同第一过渡系金属的配合物MSiH₂的分子轨道特征及键解离能.MSiH₂为共平面构型.其中基态的3TiSiH₂和4CoSiH₂带有明显的双键特征.M-Si键具有共价性质.M-Si的键解离能,从Sc到Cu呈现周期性变化,这种变化趋势同M的金属离子激发能之间存在近似的线性关系.