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1.
The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo 3S 42Mo} 8+ and> Mo 3S 4]CuI> 4+, versus the prototype arene-metal sandwich (C 6H 6) 2Cr and half-sandwich complexes C 6H 6Cr(CO) 3. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo 3S 4] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo 3S 4] 4+ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo 3S 4] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo 3S 4] 4+ ligands. The analogy of the ligand [Mo 3S 4] 4+ in the clusters studied with the ligand benzene is also briefly discussed. 相似文献
2.
A structural study of odd-numbered n-alkane (C n) binary mixtures (C 21 : C 23) was carried out on powder samples using a Guinier-de Wolff camera with increasing concentration of n-C 23 at 293 K. Despite the reports in the literature, these molecular alloys do not form an orthorhombic continuous homogeneous solid solution to C21 from C23 at “low temperature”. Instead, as already observed in two even-numbered Cn systems, X-ray diffraction results show the existence of seven solid solutions as the molar concentration of C23 increases: four terminal solid solutions, denoted β0(C21)β0(C23), isostructural with the “low temperature” phase of pure C21 and C23 (Pbcm), β′0(C21) and β′0(C23), identical to the phase β′0 which appears in pure C23 above the δ transition, and three orthorhombic intermediate solid solutions, designated β″1, β′1 and β″2. On the basis of powder X-ray photographs, the phases β″1 and β″2 (C21 : C23) are indistinguishable, and they are isostructural with the intermediate solid solution β″ of the even-numbered Cn binary systems (C22 : C24) and (C24 : C26). The phase β′1(C21 : C23) is also isostructural with the two indistinguishable intermediate solid solutions β′1 and β′2 of the molecular alloys (C22 : C24) and (24 : C26). From this study and our other laboratory results, the sequences of appearance of the solid solutions and the structural identities between these phases are established at “low temperature” for all the binary molecular alloys of consecutive Cn (odd-odd, even-even or odd-even: 19 < n < 27) when increasing the solute concentration. 相似文献
3.
MNDO calculations were made for triethylboroxin (EtBO) 3 and triphenylboroxin (PhBO) 3 using both X-ray determined and optimized geometry of these molecules. The results were compared with hypothetical “monomeric” molecules R---B=O. Calculated energies of trimerization are about −200 kJ mol −1 for both compounds and confirm the much higher stability of the “trimer”. Ebulliometric determination of molecular weight of triphenylboroxin in 2-pentanone confirms its trimeric character. 相似文献
4.
Reaction of N,N′-butylenebis(2-pyridone) (BBP) with hydrated M(NO 3) 3 salts (M = Y or a lanthanide ion) affords the complexes M 2(BBP) 3(NO 3) 6. Thorium(IV) nitrate and dioxouranium(VI) nitrate give Th 2(BBP) 3(NO 3) 8·0.5Me 2CO and UO 2(BBP)(NO 3) 2, respectively. X-ray diffraction studies on the Nd complex show it to contain arrays of contiguous 66-membered macrocyclic rings arranged so as to form as unusual “bedspring”-like network structure. 相似文献
5.
Compartmental complexes [EuH 2(fsa) 2en]Cl·3H 2O and [CuH 2(fsa) 2en]·0.5H 2O have been synthesized and characterized. The compartmental ligand (H 4(fsa) 2en) is N, N′-bis(3-carboxysalicy- lidene)ethylenediamine. Spectral study indicates that Eu(III) and Cu(II) are coordinated by the ---O 2O 2 coordinating atoms (outside) and the ---N 2O 2 coordinating atoms (inside), respectively. Since there is a considerable difference in the ligand field strength between the “outside” and “inside” coordination spheres, their different fluorescence properties have been investigated by photoacoustic spectroscopy and fluorescence spectroscopy. 相似文献
6.
The addition of R 3SiCl to B(OTf) 3 gives “supersilylating agents” formulated as R 3SiB(OTf) 3Cl. The catalytic properties of these species are similar to those of the previously-described (but less accessible) R 3SiB(OTf) 4. 相似文献
7.
The reaction of trans-[Mo(N 2) 2(PPh 2Me) 4] with the tripodal phosphine tris(2-diphenylphosphinoethyl)phosphine, PP 3, in benzene has been studied. The product was recrystallized from a mixture of benzene and petroleum ether to give [Mo(PP 3) 2]·C 5H 10, whose crystal structure shows a distorted octahedral “MoP 6” coordination with both phosphines acting as tridentate ligands. 相似文献
8.
Interactions between ethylselenoglycollic, selenoglycollic and ethylene-bis- selenoglycollic acids and some “soft”, “borderline” and “hard” metallic ions have been studied. The interactions of [PdCl 4] aq2− with the three ligands were verified conductometrically and spectrophotometrically. The stability constants β 1 and β 2 for the system [PdCl 4] 2-- ethylene-bis-selenoglycollic acid have been determined at 25°C at ionic strength 3.0 M (NaCl). The stoichiometric ionization constant of the mentioned acid was also studied. 相似文献
9.
We report here an ab initio investigation of the cluster effect (i.e., the formation of four-member groups of nearly degenerate rotation-vibration energy levels at higher J and Ka values) in the H 2Te molecule. The potential energy function has been calculated ab initio at a total of 334 molecular geometries by means of the CCSD (T) method where the (1s-4f) core electrons of the Te atom were described by an effective core potential. The values of the potential energy function obtained cover the region up to around 10 000 cm −1 above the equilibrium energy. On the basis of the ab initio potential, the rotation-vibration energy spectra of H 2 130Te and its deuterated isotopomers have been calculated with the MORBID (Morse oscillator rigid bender internal dynamics) Hamiltonian and computer program. In particular, we have calculated the rotational energy manifolds for J40 in the vibrational ground state, the ν 2 state, the “first triad” (the ν 1/ν 3/2 ν 2 interacting vibrational states), and the “second triad” (the (ν 1 + ν 2)/(ν 2 + ν 3)/3 ν 2 states) of H 2130Te. We have also investigated the cluster formation in the vibrational ground state of H 2 130Te by first fitting the rotational data available from experiment with a modified Watson-type effective Hamiltonian and then using the optimized ground state constants to extrapolate the rotational structure to higher J values. Both the ab initio calculation and the prediction with the effective Hamiltonian show that the cluster formation in H 2Te is very similar to that in H 2Se and H 2S, which we have studied previously. However, contrary to semiclassical predictions, we do not determine any significant displacement of the clusters towards lower J values relative to H 2Se. Hence the experimental observation of the cluster states in H 2Te will be at least as difficult as in H 2Se. 相似文献
10.
The optical spectra of Er(BH 4) 3·3THF neat crystals and La, Gd, Y(BH 4) 3·3THF mixed crystals are reported and analyzed. Lanthanum borohydride is found to have a different room temperature crystal structure (triclinic) from Er, Gd, Y(BH 4) 3·3THF (Pbcn). At low temperature the Pbcn crystals undergo a phase transition to a structure with two crystallographically inequivalent sites in a unit cell. The optical spectra of Er(BH 4) 3·3THF in Er, Y, Gd(BH 4) 3·3THF crystals clearly evidence these two sites. Large vibronic intensity is observed at 1.6 K and 77 K and nine “molecular” vibrations are assigned. These modes are quite similar to those found for U(BH 4) 4. Er (BH 4) 3·3THF spectra are very different: no vibronic transitions are observed but many (often upwards of fifty for a given manifold) weak sharp “satellite” lines are found associated with pure electronic transitions. These data are discussed in terms of structural differences and comments on bonding and covalent character in lanthanide borohydrides are made. 相似文献
11.
The electronic structure of the truncated-icosahedral C 60 cluster (“footballene”) is theoretically examined by performing a linear muffin-tin orbitais (LMTO) calculation. 相似文献
12.
An investigation of the frontier molecular orbitais of o- and p-RC 6H 4NC (R=H, CH 3, NO 2, F, Cl, CF 3, OCH 3) was carried out so that a thorough understanding of the intricacies of σ donation and π acceptance could be developed and used to modify subtly the electron density on metal centers. The results of this study-Indicate that the substituent position (ortho vs. para ) does alter the electron density in the ligand appreciably and that substitution of the phenyl ring with the groups indicated has a smaller effect on the σ-donating ability than it does on the π-accepting ability of the isonitrile ligand. The π-accepting abilities of the isonitrile ligands increase in the order o-, p-CH3OC6H4NC, o-, p-CH3C6H4NC, o-, p-C6H5NC, o-, p-FC6H4NC, o-, p-CF3C6NC, o-, p-ClC6H4NC, o-, p-NO2C6H4NC while the σ-donating ability decreases in this order. The energies of the σ-donor and π-acceptor orbitais are shown to correlate well with observed E
values of Cr(RC6H4NC)6 and Mn(RC6H4NC)6+1 complexes. This demonstrates how the theoretical results can be useful in understanding the observed physical properties of isonitrile-metal complexes. 相似文献
13.
The crystal structure of the title compound, C 20H 34O 2, has been determined by single crystal X-ray diffraction methods at 295 K from diffractometer data using direct methods and refined by least squares to a residual of 0.06 for 2152 “observed” reflections. Crystals are orthorhombic, P2 12 12 1, a = 32.770(8), b = 10.960(3), c = 10.850(3) Å, Z=8. The asymmetric unit comprises two independent molecules, both of which confirm the structure proposed in the preceding paper. 相似文献
14.
Ethylene polymerization using in situ combinations between a chloroneodymocene precursor and a dialkylmagnesium reagent has been investigated to prepare tailor-made oligomers. Combinations of [Cp *2NdCl 2Li(OEt 2) 2] (1) with 40 equiv. of n-butylethylmagnesium (BEM) or di( n-hexyl)magnesium (DHM) gave oligoethylenes with Mn up to 2500 and narrow molecular weight distributions ( Mw/ Mn<1.10) in moderate activity ( A1 h=79 kg/(mol of Nd h atm) at 80 °C, 1 atm). Under these conditions, ethylene polymerization proceeded in a controlled fashion, with a linear growth of Mn vs monomer conversion, ascribed to an effective chain transfer between the Nd and Mg centers. Combinations of [ rac-{Me 2Si(η 5-2-SiMe 3-4- t-Bu-C 5H 2) 2}Nd(μ-Cl) 2Li(THF) 2] (2) with either BEM or DHM (20–40 equiv.) showed decreased activity, suggesting possibly a different rate-determining-step for ethylene polymerization than for that of higher -olefins. The oligoethylenes obtained from combinations based on 2 have narrow molecular weight distributions ( Mw/ Mn<1.2) but higher contents of vinyl terminations. Monitoring of the reactions showed also a non-linear growth of Mn vs monomer conversion, especially marked when DHM was used as co-reagent. The 2/DHM combination behaves as a “self-correcting” catalyst system that deviates from the calculated Mn values for a controlled-living polymerization in the early stage of the reaction and re-approach them progressively in the second stage. 相似文献
15.
A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ ji,Δ(ν r) for rotationally inelastic collisions from level ji to ji + Δν 1 = 8,22,42) in 7Li *2 A 1Σ +u)—Xe. The σ jν±2(ν r) are strongly attenuated at a smaller ν r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ jiΔ = ν r−n (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited. 相似文献
16.
An X-ray crystallographic study, the first of a complex containing a chelating bidentate isonitrile (DiNC) ligand, reveals that [Rh(t-BuDiNC) 2]BPh 4·1.5CH 3CN crystallizes as a “slipped-stacked” face-to-face dimer of two approximately planar [Rh(t-BuDiNC) 2] + cations with a Rh-Rh distance of 3.384 Å, and an angle of 22.7° between the stacking axis and the Rh---Rh vector. The syntheses of two new bidentate isonitrile ligands, SiNC-2 and SiNC-3 are also described. These ligands contain bulky trimethylsiloxy groups ortho to each isonitrile group and differ only in that the SiNC-3 ligand contains an additional CH 2 unit in its backbone. Each reacts with [Rh(COD)Cl] 2 to afford, after metathesis with KPF 6, a complex of the empirical formula [Rh(SiNC- n) 2]PF 6. Spectroscopic results suggest the SiNC-2 complex is dinuclear, with four SiNC-2 ligands bridging the two rhodium atoms. The SiNC-3 complex is mononuclear, but unlike most other mononuclear [Rh(CNR) 4] + complexes, shows no tendency to self-associate in solution. The different structures of these two complexes and the solution behavior of the SiNC-3 complex are attributed to the bulkiness of the trimethylsiloxy groups. 相似文献
17.
The gas-phase stabilities of cluster ions SF +m (SF 6) n with m = 0−5 were determined by using a high pressure mass spectrometer. The bond energies of SF +m (SF 6) 1 were found to be less than 10 kcal/mol and to decrease with m = 0 → 5. There appear to be rather large gaps in the bond energies between n = 1 and 2 for the clusters SF +m (SF 6) n with m = 0−4. The structures of SF +5, SF + (SF 6) 1, SF +3 (SF 6) 1, and SF +5 (SF 6) 1 were investigated by ab initio molecular orbital calculations. For SF +5, the D3h geometry is found to be most stable and C4v is a transition state of the Berry pseudorotation. For the ion-molecule complexes, the “on-top hat” models were found to be the most stable structures. 相似文献
18.
Three lanthanide “ate” complexes L 2YbM(THF) n supported by amine bis(phenolate) ligand [L=Me 2NCH 2CH 2N{CH 2-(2-O-C 6H 2-Bu t2-2,4)} 2; M=Li, n=2 (1); M=Na, n=2 (2); M=K, n=3 (3)] were synthesized by the metathesis reactions of LM 2 with anhydrous YbCl 3 in 2:1 molar ratio in high yield. All the complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The influence of the alkali metal ions on the molecular structure of these lanthanide complexes has been elucidated. 相似文献
19.
Isopinocamphyl-tosylate (2) was treated with indenyllithium to yield 3-(neoisopinocamphyl)-indene (3). Treatment of 3 with methyllithium gave 1-(neoisopinocamphyl)indenyllithium (4) which was then treated with 0.5 molar equivalents of ZrCl 4(thf) 2 to give a 52:48 mixture of one of the “ racemic-like” isomers of bis[1-(neoisopinocamphyl)indenyl]ZrCl 2 (5A) and its “ meso-like” diastereomer 5C. Hydrogenation of the 5A/5C mixture (50 bar H 2, Pt) furnished a mixture of the corresponding tetrahydroindenylzirconium complexes 6A and 6C, from which the “ meso-like” bis[1-(neoisopinocamphyl)-4,5,6,7-tetrahydroindenyl]zirconium dichloride diastereoisomer (6C) was isolated. Treatment of 6C with an excess of methylalumoxane in toluene/propene generated an active -olefin polymerization catalyst. At −30°C partly isotactic polypropylene (
η = 39000) was obtained. The catalyst derived from the chirally-substituted “ meso-like” metallocene complex 6C produced polypropylene predominantly under enantiomorphic site control. 相似文献
20.
Electron paramagnetic resonance techniques are used to determine the phase transition temperature Tc of Ni(NH 3) 6I 2 as a function of hydrostatic pressure. The hydrostatic pressure causes Tc to increase and the value of the pressure coefficient d Tc/d p is (10 ± 2) K/GPa. Tc and d Tc/d p for hexammine halides is calculated on the basis of the “rigid-sphere model” and good agreement with the experimental data is obtained. 相似文献
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