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1.
The MP2 and CCSD(T) basis set limit binding energies of various hydrogen-bonded clusters were estimated via basis set extrapolation employing the correlation consistent aug-cc-pVDZ and modified aug-cc-pVDZ set containing extra polarization functions from cc-pVTZ set. By adopting the optimal interval for the difference between the cardinal numbers (X) corresponding to two basis sets in the X −3 type extrapolation scheme the estimated binding energies for (H2O)n and (HF)n (n=3−5) are shown to be close to the reference basis set limit values within the error bounds in many cases, manifesting the significance of these basis sets in studying the structures and binding of large hydrogen-bonded clusters.  相似文献   

2.
Possible geometrical structures and relative stabilities of (F2AlN3) n (n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F2AlN3) n (n = 2–4) possess cyclic structure containing Al–Nα–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F2AlN3) n (n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm−1, and the vibrational modes are N3 asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters (2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K.  相似文献   

3.
利用密度泛函理论在B3LYP/6-311G*水平上对碱土金属叠氮化合物(MgN6)n(n=1~5)团簇各种可能构型进行了几何优化,预测了各团簇的最稳定结构。并对最稳定结构的成键特性、电荷分布、振动特性及稳定性进行理论研究。结果表明,叠氮化合物中叠氮基以直线型存在,MgN6团簇最稳定结构为直线型;(MgN6)2团簇最稳定结构为Mg2N2四元环平面结构;(MgN6)n(n=3~5)团簇最稳定结构是由2个叠氮基与2个Mg原子首先构成近似菱形,再由近似菱形延伸形成的链状结构。叠氮基中间的N原子显示正电性,两端的N原子显示负电性,且与Mg直接作用的N原子负电性更强,金属Mg原子和N原子之间形成很强的离子键。(MgN6)n(n=1~5)团簇最稳定结构的IR光谱分为4个部分,其最强振动峰均位于2209~2313cm-1,振动模式为叠氮基中N-N键的反对称伸缩振动。稳定性分析显示,(MgN6)3和(MgN6)5团簇相对于其他团簇较为稳定。  相似文献   

4.
Connecting two discotic mesogens via a spacer not only stabilizes the columnar mesophase but also leads to the formation of glass columnar phase, and therefore improves the physical properties of discotic liquid crystals as organic semiconductor. Here, we report the synthesis of eight diacetylene-bridged triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)4(OMe)O2C-C8H16-C≡≡ C-]2, 3(n), (n = 4-8), [C18H6(OC6H13)5O2C-C8H16-C≡≡ C-]2, 6 and [C18H6(OC6H13)5O-(CH2)m-C≡≡ C-]2, 8(m), (m = 1, 3) by Eglinto...  相似文献   

5.
 The possible geometrical structures and relative stability of (SiS2) n (n=1–6) silicon–sulfur clusters are explored by means of density functional theory quantum chemical calculations. The effects of polarization functions and electron correlation are included in these calculations. The electronic structures and vibrational spectra of the most stable geometrical structures of (SiS2) n are analyzed by the same method. As a result, the regularity of the (SiS2) n cluster growth is obtained, and the calculation may used for predicting the formation mechanism of the (SiS2) n cluster. Received: 17 November 1999 / Accepted: 3 November 2000 / Published online: 3 May 2001  相似文献   

6.
Structures, binding energies, harmonic frequencies, dipole moments, HOMO–LUMO energy gaps and particularly atoms in molecules (AIM) analyses of some nanoannular carbon clusters (C4–C20) are investigated at B3LYP/6-31+G(d) level of theory. No correlation is found by plotting the calculated binding energies as a functional number of carbon atoms of carbon clusters. The calculated binding energies sharply increase from C4 to C10 while slowly from C10 to C20. The binding energies of C4n+2 clusters including C6, C10, C14, and C18 have a clear increase when compared with others indicating their aromatic characters which is confirmed by results of HOMO–LUMO energy gaps and geometrical parameters. AIM analyses show that most of our carbon clusters are topologically normal (non-conflict) with stable structures. Nevertheless, the topological networks of small antiaromatic rings, C4 and C8, at their equilibrium geometries may change via molecular vibrations. The existence of straight bond paths in 3D molecular graphs of carbon clusters with n > 10 implies that ring strains are decreased as the ring sizes grow. Except for C4 and C8, the ellipticity values for the remaining carbon clusters are small indicating that the C–C bond is conserved in these clusters. Dipole moments of even-numbered structures are negligible, whereas odd-numbered ones have μ values of 0.09−0.73 D.  相似文献   

7.
The structures, stability patterns of C26H n (n = 2) formed from the initial D 3h C26 fullerene were investigated by use of second-order-Moller–Plesset perturbation theory. The study of the stability patterns of hydrogenation reaction on C26 cage revealed that type (β) carbons were the active site and the analyses of π-orbital axis vector indicated that the reactivity of C26 was the result of the high strain and the hydrogenation reaction on C26 cage was highly exothermic. The calculated 13C NMR spectra of C26H n (n = 2) predicted that the two sp 3 hybridization carbons in C26H n (n = 2) obviously moved to high field compare with that in D 3h C26. Hence, the C26H2 should be obtained and detected experimentally. Similarly, the structures and reaction energies of C26H n (n = 4, 6, 8) were further studied at HF/6-31G*, B3LPY/6-31G* and MP2/6-31G* level. The results suggested the hydrogenation products of C26, C26H n (n = 4, 6, 8), were more stable than the C26 cage.  相似文献   

8.
Compounds (Bu4N)[2-B10H9{NH=C(NHR)CH3}] are obtained by reactions of the tetrabutylammonium salt of the [2-B10H9(N≡CCH3)] anion with aliphatic and aromatic primary amines RNH2 (R = n-C3H7, n-C4H9, cyclo-C5H9, C6H5, cyclo-C6H11, n-C6H13, C7H7, C8H8NH2, C6H4NO2, and C18H37) and identified by IR, ESI/MS, and NMR (1H, 11B, and 13C) spectroscopy. The structures of the amidine-type derivatives [2-B10H9{Z-NH=C(NH-cyclo-C5H9)CH3}] and [2-B10H9{Z-NH=C(NH-C7H7)CH3}] are determined by X-ray diffraction.  相似文献   

9.
Molecular structure and vibrational spectra of 1,2-tetramethylenediborane (B2C4H12), 1,2:1,2-bis(tetramethylene)diborane (B2C8H18), 1,1-tetramethylenediborane (B2C4H12) and 1,1:2,2-bis(tetramethylene)diborane (B2C8H18), have been studied using quantum computational density functional B3LYP and B3PW91 methods and 6-31G*, 6-31G** and 6-31++G** basis sets. Natural bond orbital analyses have been carried out to study in detail the nature of the B—C, C—C and B—H bonds in these molecules. This study showed that all these compounds are thermodynamically stable in the gas phase, but bicyclic structures are more stable than monocyclic structures.  相似文献   

10.
The fluorophobic effect of the semi-fluorinated chain of discotic molecules efficiently improves the stability of columnar mesophase.Low symmetric discogens exhibit decreased melting points and wide mesophase ranges.A series of triphenylene derivatives 1,C18H6(OCnH2n+1)4(OMe)(O2CC2H4C6F13),and their hydrocarbon analogues 2,C18H6(OCnH2n+1)4(OMe)(O2CC8H17),n = 4―8,were synthesized for the investigation of the influence of semi-fluorinated peripheral chain and molecular symmetry on mesomorphism.The structures ...  相似文献   

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