Many-particle effects in the bond length alternation of alternant hydrocarbons

1992 ◽  
Vol 75 (4) ◽  
pp. 961-973 ◽  
Author(s):  
Michael C. Böhm ◽  
Johannes Schütt
2009 ◽  
Vol 131 (17) ◽  
pp. 6099-6101 ◽  
Author(s):  
Shino Ohira ◽  
Joel M. Hales ◽  
Karl J. Thorley ◽  
Harry L. Anderson ◽  
Joseph W. Perry ◽  
...  

1993 ◽  
Vol 90 (23) ◽  
pp. 11297-11301 ◽  
Author(s):  
C B Gorman ◽  
S R Marder

A computational method was devised to explore the relationship of charge separation, geometry, molecular dipole moment (mu), polarizability (alpha), and hyperpolariz-abilities (beta, gamma) in conjugated organic molecules. We show that bond-length alternation (the average difference in length between single and double bonds in the molecule) is a key structurally observable parameter that can be correlated with hyperpolarizabilities and is thus relevant to the optimization of molecules and materials. By using this method, the relationship of bond-length alternation, mu, alpha, beta, and gamma for linear conjugated molecules is illustrated, and those molecules with maximized alpha, beta, and gamma are described.


1998 ◽  
Vol 108 (16) ◽  
pp. 6681-6688 ◽  
Author(s):  
Cheol Ho Choi ◽  
Miklos Kertesz

Author(s):  
Jochen Autschbach

Huckel molecular orbital (HMO) theory is a simple approximate parameterized molecular orbital (MO) theory that has been very successful in organic chemistry and other fields. This chapter introduces the approximations made in HMO theory, and then treats as examples ethane, hetratriene and other linear polyenes, and benzene and other cyclic polyenes. The pi binding energy of benzene is particularly large according to HMO theory, rationalizing the special ‘aromatic’ behaviour of benzene. But there is a lot more to benzene than that. It is shown that the pi bond framework of benzene would rather prefer a structure with alternating single and double C-C bonds, rather than the actually observed 6-fold symmetric structure where all C-C bonds are equivalent. The observed benzene structure is a result of a delicate balance between the tendencies of the pi framework to create bond length alternation, and the sigma framework to resist bond length alternation.


2011 ◽  
Vol 133 (10) ◽  
pp. 3354-3364 ◽  
Author(s):  
Igor Schapiro ◽  
Mikhail Nikolaevich Ryazantsev ◽  
Luis Manuel Frutos ◽  
Nicolas Ferré ◽  
Roland Lindh ◽  
...  

2017 ◽  
Vol 73 (8) ◽  
pp. 1202-1207
Author(s):  
Agata Gapinska ◽  
Alan J. Lough ◽  
Ulrich Fekl

Two coordination compounds containing tetra-n-butylammonium cations and bis-tfd-chelated molybdenum(IV) [tfd2− = S2C2(CF3)2 2−] and oxalate (ox2−, C2O4 2−) in complex anions are reported, namely bis(tetra-n-butylammonium) bis(1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)oxalatomolybdate(IV)–chloroform–oxalic acid (1/1/1), (C16H36N)2[Mo(C4F6S2)2(C2O4)]·CHCl3·C2H2O4 or (N n Bu4)2[Mo(tfd)2(ox)]·CHCl3·C2H2O4, and bis(tetra-n-butylammonium) μ-oxalato-bis[bis(1,1,1,4,4,4-hexafluorobut-2-ene-2,3-dithiolato)molybdate(IV)], (C16H36N)2[Mo2(C4F6S2)4(C2O4)] or (N n Bu4)2[(tfd)2Mo(μ-ox)Mo(tfd)2]. They contain a terminal oxalate ligand in the first compound and a bridging oxalate ligand in the second compound. Anion 1 2− is [Mo(tfd)2(ox)]2− and anion 2 2−, formally generated by adding a Mo(tfd)2 fragment onto 1 2−, is [(tfd)2Mo(μ-ox)Mo(tfd)2]2−. The crystalline material containing 1 2− is (N n Bu4)2-1·CHCl3·oxH2, while the material containing 2 2− is (N n Bu4)2-2. Anion 2 2− lies across an inversion centre. The complex anions afford a rare opportunity to compare terminal oxalate with bridging oxalate, coordinated to the same metal fragment, here (tfd)2MoIV. C—O bond-length alternation is observed for the terminal oxalate ligand in 1 2−: the difference between the C—O bond length involving the metal-coordinating O atom and the C—O bond length involving the uncoordinating O atom is 0.044 (12) Å. This bond-length alternation is significant but is smaller than the bond-length alternation observed for oxalic acid in the co-crystallized oxalic acid in (N n Bu4)2-1·CHCl3·oxH2, where a difference (for C=O versus C—OH) of 0.117 (14) Å was observed. In the bridging oxalate ligand in 2 2−, the C—O bond lengths are equalized, within the error margin of one bond-length determination (0.006 Å). It is concluded that oxalic acid contains a localized π-system in its carboxylic acid groups, that the bridging oxalate ligand in 2 2− contains a delocalized π-system and that the terminal oxalate ligand in 1 2− contains an only partially localized π-system. In (N n Bu4)2-1·CHCl3·oxH2, the F atoms of two of the –CF3 groups in 1 2− are disordered over two sets of sites, as are the N and eight of the C atoms of one of the N n Bu4 cations. In (N n Bu4)2-2, the whole of the unique N n Bu4 + cation is disordered over two sets of sites. Also, in (N n Bu4)2-2, a region of disordered electron density was treated with the SQUEEZE routine in PLATON [Spek (2015). Acta Cryst. C71, 9–18].


Sign in / Sign up

Export Citation Format

Share Document