scholarly journals The Ultrafast Photoisomerizations of Rhodopsin and Bathorhodopsin Are Modulated by Bond Length Alternation and HOOP Driven Electronic Effects

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

A New Class of Cyanine-like Dyes with Large Bond-Length Alternation

2009 ◽  
Vol 131 (17) ◽  
pp. 6099-6101 ◽  
Author(s):  
Shino Ohira ◽  
Joel M. Hales ◽  
Karl J. Thorley ◽  
Harry L. Anderson ◽  
Joseph W. Perry ◽  
...  
Keyword(s):  
Bond Length ◽  
Bond Length Alternation ◽  
New Class

scholarly journals An investigation of the interrelationships between linear and nonlinear polarizabilities and bond-length alternation in conjugated organic molecules

1993 ◽  
Vol 90 (23) ◽  
pp. 11297-11301 ◽  
Author(s):  
C B Gorman ◽  
S R Marder
Keyword(s):  
Bond Length ◽  
Organic Molecules ◽  
Computational Method ◽  
Bond Length Alternation ◽  
Conjugated Molecules ◽  
Conjugated Organic Molecules ◽  
Alpha Beta ◽  
Relationship Of ◽  
The Relationship ◽  
Observable Parameter

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.

Bond length alternation and aromaticity in large annulenes

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

scholarly journals Bond-Length Distributions for Ions Bonded to Oxygen: Results for the Transition Metals and Quantification of the Factors Underlying Bond-Length Variation in Inorganic Solids

2020 ◽  
Author(s):  
Olivier Charles Gagné ◽  
Frank Christopher Hawthorne
Keyword(s):  
Transition Metal ◽  
Bond Length ◽  
A Priori ◽  
Bond Formation ◽  
Length Variation ◽  
Electronic Effects ◽  
Coordination Polyhedra ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Non Local

Bond-length distributions are examined for 63 transition-metal ions bonded to O2- in 147 configurations, for 7522 coordination polyhedra and 41,488 bond distances, providing baseline statistical knowledge of bond lengths for transi-tion metals bonded to O2-. A priori bond valences are calculated for 140 crystal structures containing 266 coordination poly-hedra for 85 transition-metal ion configurations with anomalous bond-length distributions. Two new indices, Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡, are proposed to quantify bond-length variation arising from bond-topological and crystallographic effects in extended solids. Bond-topological mechanisms of bond-length variation are [1] non-local bond-topological asymmetry, and [2] multi-ple-bond formation; crystallographic mechanisms are [3] electronic effects (with inherent focus on coupled electronic-vibra-tional degeneracy in this work), and [4] crystal-structure effects. The Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡 indices allow one to determine the primary cause(s) of bond-length variation for individual coordination polyhedra and ion configurations, quantify the dis-torting power of cations via electronic effects (by subtracting the bond-topological contribution to bond-length variation), set expectation limits regarding the extent to which functional properties linked to bond-length variations may be optimized in a given crystal structure (and inform how optimization may be achieved), and more. We find the observation of multiple bonds to be primarily driven by the bond-topological requirements of crystal structures in solids. However, we sometimes observe multiple bonds to form as a result of electronic effects (e.g. the pseudo Jahn-Teller effect); resolution of the origins of multiple-bond formation follows calculation of the Δ𝑡𝑜𝑝𝑜𝑙 and Δ𝑐𝑟𝑦𝑠𝑡 indices on a structure-by-structure basis. Non-local bond-topological asymmetry is the most common cause of bond-length variation in transition-metal oxides and oxysalts, followed closely by the pseudo Jahn-Teller effect (PJTE). Non-local bond-topological asymmetry is further suggested to be the most widespread cause of bond-length variation in the solid state, with no a priori limitations with regard to ion identity. Overall, bond-length variations resulting from the PJTE are slightly larger than those resulting from non-local bond-topological asym-metry, comparable to those resulting from the strong JTE, and less than those induced by π-bond formation. From a compar-ison of a priori and observed bond valences for ~150 coordination polyhedra in which the strong JTE or the PJTE is the main reason underlying bond-length variation, the Jahn-Teller effect is found not to have a symbiotic relation with the bond-topo-logical requirements of crystal structures. The magnitude of bond-length variations caused by the PJTE decreases in the fol-lowing order for octahedrally coordinated d0 transition metals oxyanions: Os8+ > Mo6+ > W6+ >> V5+ > Nb5+ > Ti4+ > Ta5+ > Hf4+ > Zr4+ > Re7+ >> Y3+ > Sc3+. Such ranking varies by coordination number; for [4], it is Re7+ > Ti4+ > V5+ > W6+ > Mo6+ > Cr6+ > Os8+ >> Mn7+; for [5], it is Os8+ > Re7+ > Mo6+ > Ti4+ > W6+ > V5+ > Nb5+. We conclude that non-octahedral coordinations of d0 ion configurations are likely to occur with bond-length variations that are similar in magnitude to their octahedral counterparts. However, smaller bond-length variations are expected from the PJTE for non-d0 transition-metal oxyanions.<br>

Approximate Molecular Orbital Theory: The Hückel/Tight-binding Model

2020 ◽  
pp. 231-245
Author(s):  
Jochen Autschbach
Keyword(s):  
Bond Length ◽  
Molecular Orbital ◽  
Tight Binding ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Bond Length Alternation ◽  
Binding Model ◽  
Linear Polyenes ◽  
Benzene Structure ◽  
Cyclic Polyenes

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.

scholarly journals Coordination compounds containing bis-dithiolene-chelated molybdenum(IV) and oxalate: comparison of terminal with bridging oxalate

2017 ◽  
Vol 73 (8) ◽  
pp. 1202-1207
Author(s):  
Agata Gapinska ◽  
Alan J. Lough ◽  
Ulrich Fekl
Keyword(s):  
Oxalic Acid ◽  
Bond Length ◽  
Coordination Compounds ◽  
Bond Length Alternation ◽  
Acta Cryst ◽  
Oxalate Ligand ◽  
Length Determination ◽  
The Difference ◽  
Complex Anions ◽  
Rare Opportunity

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].

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
Keyword(s):  
Bond Length ◽  
Bond Length Alternation ◽  
Alternant Hydrocarbons
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