Ethylenediamine, ligand structure

All attempts to produce optical isomers of [Co(en)3]3+ based upon a trigonal prismatic structure are shown below. The ethylenediamine ligand appears as an arc in each diagram below ... 

Both 1- and 1 -A -alkylated ethylenediamine ligands are prochiral and coordination completes the asymmetry at the nitrogen atom. Under favorable conditions, such complexes can be resolved and the absolute configuration determined by X-ray or other methods. Structures (17)-(22) show some representative configurations. 

H2O [172] (153 4 H2O) resembles that in the ammine complex, including the detail of intramolecular hydrogen bonding from amine donors to alkoxide acceptors. The structure determination demonstrates that the stronger ethylenediamine ligand is also replaced by the lyxose anions. 

It is noteworthy that metallomicelles of Ni(II) complexes with long-chain N-al-kylated ethylenediamine ligands catalyze the epimerization of aldoses in an aqueous dispersion [24]. A reexamination of the effect of metallomicelles on the hydrolysis of phosphate and carboxylate esters was given by Scrimin et al. [25], Acceleration in second-order reactions are often to interpret as a local concentration increase of the reactants. The catalytic effect of metallosurfactants in enzyme-related reactions has been investigated by Nolte s working group [26], also carefully considering the assembly structure [27]. The wide field of artificial enzymes was recently reviewed by Murakami et al. [28]. 

For Class B (substitution labile) metal complexes, reequilibration to more thermodynamically favorable coordination modes will be very rapid relative to immobilization. Such behavior is typical of first-row TM complexes. In addition, these ions are usually very oxophilic, so the metal complexes are typically subject to ICC interactions with oxide materials. Since these metal ions are generally immobilized under conditions of thermodynamic control, all pertinent speciation equilibria, including ICC reactions (Section III.B), must be considered in order to understand or predict the outcome of immobilization reactions. It is essential to understand the relevant equilibria if direct imprinting of active site structures is to be successful. The studies of Klonkowski et al. (210-213), for example, underscore this point Sol-gel immobilization of copper complexes bearing silylated amine and ethylenediamine ligands were shown by EPR to result in multiple copper environments, suggesting competition between immobilization and ICC reactions. 

The effects of ligand structure, such as N-alkylated chain length, degree of N-substitution, and the distance between the two amino groups, that is, methylene-diamine (mn), ethylenediamine (en), trimethylenediamine (tn) and some kinds of polymethylenediamine (bn, hn), were extensively studied. In addition, ethylenediamine derivatives containing ether linkages and polyamines such as triamine and tetramine are also mentioned. Scheme 2 depicts the relationships between the abbreviations and the structure of representative ligands studied in this work. 

Some ligands have more than one atom with an unshared pair of electrons and hence can form more than one bond with a central metal atom. Ligands of this type are referred to as chelating agents the complexes formed are referred to as chelates (from the Greek chela, crab s claw). Two of the most common chelating agents are the oxalate anion (abbreviated ox) and the ethylenediamine molecule (abbreviated en), whose Lewis structures are... 

Coordination compounds containing bidentate ligands are often thermally more stable than those comprised of related monodentate ligands, e.g. ethylenediamine (en) complexes dissociate at a higher temperature than those of ammonia or pyridine. Compounds containing a ring structure, such as coordinated salicylaldehyde (sal) and acetyl-acetonate (acac), are particularly stable, and may often be sublimed... 

A chelating ligand contains two or more donor atoms in a structure that allows the ligand to wrap around the metal. Examples featured in Chapter 18 are the bidentate ligand ethylenediamine (en, chemical formula H2 NCH2 CH2 NH2) and the hexadentate ethylenediaminetetraacetate (EDTA). 

Titrations of Zn11 ions with ethylenediamine-N,9-ethyladenine, 8, followed by H NMR, show line broadening for H2, indicative of a ligand exchange at N3 (58). However, this behavior is anion dependent. Thus line broadening is seen with NOJ and CIO4 (Fig. 15), but not with CP ions. Structural data obtained on compounds isolated from these reac-... 

The complex [Co(NH3)5(OS02CF3)]2+ undergoes triflate substitution by cyanate and condensation with acetone to form the unusual bis-bidentate imine complex (213)917 in a reaction reminiscent of the classic Curtis condensation of acetone with ethylenediamine. Apart from the novelty of the synthesis, the reported crystal structure was only the second of a CoN6 complex bearing a cyanate ligand. 

Amine adducts of Ni11 diphenyldithiophosphinate with substituted ethylenediamins have been prepared and characterized. A dimeric pentacoordinate structure was proposed for [Ni2(S2PPh2)4(tmeda)].91s One crystal structure of a square planar Ni11 complex (351) with an aminophosphonate ligand has been reported.916... 

Other polydentate ligands are polyamines and related ligands. Stability constants of silver(I) complexes with polyamines in dimethyl sulfoxide,419 A-methyl-substituted 4-methyldiethylene-triamines,420 or ethylene- or N- or C-methylated ethylenediamine in aqueous solution have been reported.421 The structure of the silver 1,3-diaminopropane complex, [Ag NH2(CH2)3NH2 ]-C104,422 and complex formation with 1,4-diaminobutane and 1,5-diaminopentane have been reported.423 A dinuclear silver(I) compound with ethylenediamine [(enH)Ag(en)Ag(enH)2]4+ has... 

Bis(ethylenediamine)gold(III) chloride reacts with /3-diketonates in aqueous base via Schiff base condensation to form complexes of gold(III) with a 14-membered macrocyclic tetraaza ligand such as (292).1711-1713 The X-ray structure showed the cation to be nearly planar. Delocalization of -electrons within the six-membered /3-diketonate rings was indicated by the observed pattern of C—C and C—N distances. Open-chain tetraaza ligand complexes in which condensation of only one /3-diketonate has occurred, can be isolated as intermediates in this reaction. They may be used for further condensation with a different /3-diketonate. Oxidation of this complex with trityl tetrafluoroborate introduces a double bond in position C2C3.1712,1714... 

Open chain polyamine ligands have been widely studied. Often the coordination of zinc is compared with other first row transition metals and factors, such as behavior across a pH range, studied. The protonation patterns and stability constants are of particular interest. Octahedral zinc tris(ethylenediamine) structures have been characterized by X-ray diffraction with a number of different counter anions.94 The X-ray structure of zinc tris(ethylenediamine) with fluoride counter ions reveals extensive hydrogen bonding.95... 

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