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Topic: Pi backbonding

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	VOH // Questions and Answers for 171
		Backbonding is the ability of a metal and ligand to transfer electron density in the pi system.
		Cl- as a ligand does "negative" pi backbonding in that it donates electron density into the metal d orbitals raising the t2g levels and weaking the metal Cl- bond.
		Yes, basically strong pi bonding ligands make the t2g levels bonding and therefore favorable to be filled leading to 18 electrons, otherwise 1st row TM can have 12-22 electrons and 2nd and 3rd row TM can have 12-18 electrons (since eg* becomes very antibonding and less accessible).
	voh.chem.ucla.edu /vohtar/fall01/171/qa.html (13869 words)

	Encyclopedia: Pi backbonding (Site not responding. Last check: 2007-10-30)
		Ï backbonding, also called Ï backdonation, is a concept from chemistry, that refers to the flow of electrons from an atomic orbital on one atom to a Ï anti-bonding orbital that belongs to other atoms.
		It is especially common in the coordination of multi-atomic ligands to metal centres, where electrons from the metal flow towards the bond between the ligand atoms, thereby relieving the metal from excess negative charge and allowing it to bond with the ligands.
		Because Ï backbonding usually places electrons in the anti-bonding molecular orbital of the ligand, it can cause the respective bond order to decrease.
	www.nationmaster.com /encyclopedia/Pi-backbonding (372 words)

	electronic1
		The donation of electron density from the CO to the metal results in a slight strengthening of the CO bond (electron density is being removed from a slightly antibonding orbital).
		The importance of this, is that the amount of pi donation to the carbonyl ligand is usually dependent on the amount of electron density at the metal center.
		In a typical MLCT transition, an electron from one of the metal orbitals is transferred to a pi* orbital of one of the ligands on the metal.
	www.chem.vt.edu /chem-dept/brewer/chem-ed/4414/tutorials/electronic/ELECTRON.HTML (1658 words)

	RuTrisBpy
		Carbonyl groups can also be used to report on the extent of metal-ligand backbonding, which is dependent on the electron population or density of the metal center.
		The backbonding occurs through a molecular orbital that has pi anti-bonding character with respect to the C-O bond.
		This orbital is not populated in a free carbonyl group, but in the metal complex this orbital has the proper symmetry to overlap with a populated metal d orbital resulting in the transfer of some electrons from the metal to the ligand.
	antoine.frostburg.edu /chem/simon/chm411/lab/Molybdenum.htm (747 words)

	Metal carbonyl Information
		Carbon monoxide bonds to transition metals using synergic pi back-bonding.
		A full d orbital overlaps with a pi antibonding orbital on the carbon monoxide which has the effect of weakening the carbon-oxgyen bond compared with free carbon monoxide.
		The coordination of carbon monoxide to these metals is based on Π backbonding of filled d-orbital electrons to the Π
	www.bookrags.com /wiki/Metal_carbonyl (550 words)

	Chem 32 Virtual Manual (Site not responding. Last check: 2007-10-30)
		Backbonding: The carbonyl has antibonding pi orbitals that are optimally situated for backbonding.
		electron density available for backbonding to the second CO. Hence the second CO is less tightly bound than the first.
		Therefore it is high spin and the binding of the second pyridine, since it does not disrupt any stabilizing interactions, is strong.
	kalee.tock.com /chem32/coor/7s.html (202 words)

	Pi Kappa Alpha - Encyclopedia Glossary Meaning Explanation Pi Kappa Alpha (Site not responding. Last check: 2007-10-30)
		Pi Kappa Alpha - Encyclopedia Glossary Meaning Explanation Pi Kappa Alpha.
		Here you will find more informations about Pi Kappa Alpha.
		Pi Kappa Alpha is a social fraternity with 280 chapters and colonies in the United States and Canada.
	www.encyclopedia-glossary.com /en/Pi-Kappa-Alpha.html (254 words)

	Dictionary of Meaning www.mauspfeil.net
		{{wrongtitletitle=π backbonding}} '''π backbonding''', also called π backdonation, is a concept from chemistry, that refers to the flow of Electron electrons from an atomic orbital on one atom to a π anti-bonding Molecular orbital orbital that belongs to other atoms.
		It is especially common in the Complex_%28chemistry%29 coordination of multi-atomic Ligand ligands to metal centres, where electrons from the metal flow towards the Chemical bond bond between the ligand atoms, thereby relieving the metal from excess negative Electric charge charge and allowing it to bond with the ligands.
		Because π backbonding places electrons in the anti-bonding molecular orbital of the ligand, it causes the respective Bond order bond order to decrease.
	www.mauspfeil.net /Pi_backbonding.html (191 words)

	Chemical Reactivity
		This leaves the double bond function electron deficient, a condition that may be remedied by the sharing of a d-electron pair with the empty antibonding-pi-orbital (a pi-like backbonding).
		If the sigma bond is weak, backbonding will also be weak, and the structure of the double bond component of the complex will not be significantly perturbed.
		As noted in the following diagram, the metal of a Schrock alkylidene is electrophilic, and is stabilized by electron donating ligands as well as backbonding from an occupied p-orbital of the carbon atom.
	www.cem.msu.edu /~reusch/VirtualText/orgmetal.htm (6204 words)

	Organometallic HyperTextBook: Alkene Complexes
		The bonding in alkene complexes is described by the Dewar-Chatt-Duncanson model, which provides us with a bonding picture not unlike that seen in carbonyl or phosphine complexes.
		A sigma-type donation from the C=C pi orbital with concomitant pi-backbonding into an empty pi* orbital on the ethylene presents us with a synergistic bonding situation: the greater the sigma donation to the metal, the greater the pi-backbonding:
		The greater the electron density back-donated into the pi* orbital on the alkene, the greater the reduction in the C=C bond order.
	www.ilpi.com /organomet/alkene.html (530 words)

	Information Archive at NNYTech (Site not responding. Last check: 2007-10-30)
		This is because of relatively poor shielding of the nuclear charge by electrons in d and especially f orbitals.
		As the result, their affinity for the pi electrons in the forming of organometallic complexes should be greater.
		As a result, electronic pi backbonding > effect in pt complex are more significant tha in pd > complex.
	archive.nnytech.net /sgroup/thechemistrycluster/2604/1 (333 words)

	[No title]
		The electronic structure analysis reveals that C equivalent to C bond is an efficient ''relay'' of pi- electrons and that it supports inter-ring conjugation.
		An explicit form of the fifth order equation, the solutions of which determine the dispersion relations for five pi electron bands and closed expressions of molecular orbitals, is obtained.
		Ten band-edge energies of five pi bands of heterocyclic polymers are found as analytical functions of system parameters.
	morris.umh.ac.be /Biblio/171197 (17295 words)

	Organometallic HyperTextBook: Carbonyl Complexes
		The first component is a two electron donation of the lone pair on carbon (coordination exclusively through the oxygen is extremely rare) into a vacant metal d-orbital.
		Notice that although this involves the occupation of a pi* orbital on the CO, it is still a bonding interaction as far as the metal center is concerned.
		This occupation of the pi* on CO does lead to a decreased bond order in the carbon monoxide molecule itself.
	www.ilpi.com /organomet/carbonyl.html (681 words)

	Superconductivity in Layered Structures of Rare-Earth Carbide Halides
		This backbonding is already indicated by shortened C-C distances.
		They show density of states at the Fermi edge, and their COOP (Crystal Orbital Overlap Population) confirmed the C-C antibonding (C pi*) and the Gd-C bonding character of these states.
		The electrons are delocalized in covalently mixed p-d band states and have a tendency to pairwise occupation of the molecular pi* states of the
	www.fkf.mpg.de /simon/publications/jb91/simon.html (662 words)

	organometallic chemistry
		The electronic structure of these newly synthesized compounds was elucidated with the aid of DFT calculations.
		In contrast to the common assumption that NHCs are pure sigma donor ligands, our calculations reveal the existence of both pi- and sigma-type interactions between the metal ions and the carbenoid carbons.
		It was found that pi-backbonding interactions in electron-rich diaminocarbene metal complexes typically contribute to approximate 15 - 30% of the complexes' stability.
	www.inorganic-chemistry.net /kmpages/organometallic2.html (569 words)

	Processes and compositions for electroless metallization - Patent 5500315
		For example, 3-mercaptopropyltriethoxysilane, 2-(diphenylphosphino)ethyltriethoxysilane, and cyanomethylphenyl trimethoxysilane should serve as suitable catalyst ligating groups in accordance with the invention.
		Also preferred are ligating groups with antibonding (pi*) orbitals in the ligand, for example aromatic heterocycles such as pyridine and other nitrogen containing aromatics.
		Such groups give rise to dpi.fwdarw.pi* backbonding interactions that favor complex formation.
	www.freepatentsonline.com /5500315.html (12619 words)

	[No title]
		To my understanding, the theory states that in the transition metal complexes, the combination of multiple ligand orbitals can provide better interaction with metal than a single ligand orbital does.
		For example, nitrosyl is a good backbonding ligand with metal.
		With appropriate symmetry, the combination of (pi)* orbital of dinitrosyl can be even stronger backbonding ligand because the combinated orbital lows its energy from single NO and close to Metal orbitals.
	www.ccl.net /cgi-bin/ccl/message.cgi?1999+10+12+006+raw (193 words)

	Superconductivity in Yttrium carbide halides
		The metallic conductivity of these compounds is due to backbonding from occupied pi* orbitals of the C
		According to our hypothesis the pairwise attractive interaction between conduction electrons originates from a tendency towards (pairwise) localization in the pi* states at the Fermi level.
		unit offer an effective electron phonon coupling through dynamic variation of the energy of the pi* level and/or variation of the p-d overlap.
	www.fkf.mpg.de /simon/publications/jb94/baecker.html (503 words)

	Biophysical Journal: Imaging Neuronal Seal Resistance on Silicon Chip using Fluorescent Voltage-Sensitive Dye
		Cell-selective methods are required such as microinjection or genetic labeling, both not yet developed for these dyes.
		We thank Bernd Kuhn for advice on the voltage-sensitive dye, Bernhard Straub for his expertise with backbonding of chips, Helge Vogl and Christian Figger for help in chip fabrication, Martin Maass from Olympus for the fruitful cooperation, and Raimund Gleixner and Hanna Salman for critical reading of the manuscript.
		The project was supported by a generous grant of the Bundesministerium für Bildung und Forschung.
	www.findarticles.com /p/articles/mi_qa3938/is_200408/ai_n9421102/pg_3 (1438 words)

	Ziegler-Natta catalyst Summary
		The transition metal's ligands restrict the incoming alkene's position with respect to the growing polymer chain to impose stereoregularity.
		Without any d-electrons, the titanium-alkene bond is not stabilized by backbonding, so the barrier to react and add to the growing polymer chain is decreased, increasing the activity of the catalyst.
		The length of a polymer chain is determined by two competing rate constants, the rate of chain propagation (transferring the alkene to the growing polymer chain) versus the rate of termination.
	www.bookrags.com /Ziegler-Natta_catalyst (1376 words)

	ETD-db: ETD database
		¡@¡@The natural populations in the carbonyls¡¦ antibonding pi (2p) orbitals have been calculated by Natural Bond Orbital (NBO) method.
		For groups 6B and 7B, the order of backbonding extend acquired is 5d > 3d > 4d (Class A).
		For the rest series, 4B, 5B and 8B, however, the tendency of backbonding obtained is as expected 5d > 4d > 3d (class B).
	etdncku.lib.ncku.edu.tw /ETD-db/ETD-search/view_etd?URN=etd-0626104-154702 (319 words)

	Sundar's Thesis
		The argument, therefore, was that the protein imposed steric hindrances on the binding of CO ligand, forcing it to bind in a bent fashion.
		As a bent binding structure is not favorable for backbonding between the Fe dxy and CO [[pi]]
		As it is energetically less demanding than the bending motion of the ligand bound to the porphyrin, the stretching frequency itself is below that of the bending motion.
	community.middlebury.edu /~chem/chemistry/students/sundar/vikthesis/SundarThesis.html (17820 words)

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