Hexadentate ligand

EthylenediaminetetraaceticAcid. Ethylenediaminetetraacetic acid (EDTAH has six potential donor groups two nitrogen atoms and four carboxylate groups. If EDTA 4— acts as a hexadentate ligand to a metal, the resulting complex contains five five-membered chelate rings and has a charge that is four less than that of the metal ion. 

Eig. 2. Stmctural representations of chelates where (8) corresponds to M(acac)2 (9) to ML2, L = S-sulfo-S-hydroxyquiaoline (10) to M-Trien (11) to a tetracoordinate metal bound to the hexadentate ligand EDTA and (12) to the Ee(III) chelate of EHPG. Stmcture (13), which emphasizes the spatial... 

The most complex P ligand so far characterized is the astonishing hexadentate Pio unit in [ Cr( j5-C5H5)(CO)2 5Pio] (see ref. 62 for details). 

Multidentate ligands contain more than two coordinating atoms per molecule, e.g. 1,2-diaminoethanetetra-acetic acid (ethylenediaminetetra-acetic acid, EDTA),f which has two donor nitrogen atoms and four donor oxygen atoms in the molecule, can be hexadentate. 

A dinuclear iron(ll/Ill) complex bearing a hexadentate phenol ligand displayed moderate activity toward aziridination of alkenes with PhlNTs a large excess of alkene (2,000 equiv. vs PhlNTs) was required for good product yields (Scheme 22) [76]. It is noteworthy that complex 4 is active in the aziridination of aliphatic alkenes, affording higher product yields than copper (11) catalysts with tetradentate macrocyclic ligands [77]. 

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). 

Ligand abbreviations acacjtrien = hexadentate Schiff base from triethylenetetramine (trien) and acetylacetone (acac) Saljtrien = hexadentate Schiff base from triethylenetetramine (trien) and salicylaldehyde. 

Fe(acac2trien)]N03. For the iron(III) complex of the hexadentate Schiff-base ligand acac2trien, the barrier heights have been determined from ultrasonic relaxation [94] as AG[h = 6-28 kcalmoD = 2196 cm and AGJil = 5.85 kcalmol= 2046 cm The difference of zero-point energies has been obtained from equilibrium studies as AG° = 0.43 kcal mol =... 

Fe(6-Mepy)3tren](PF6)2- Within the series of iron(II) complexes of the type [Fe(6-Mepy)3 (py) tren](PFg)2 containing the hexadentate ligand tris[4-(6-R)-2-pyridyl]-3-aza-3-butenyl]amine, R = H or CH3, the compounds with X = 1, 2 show a similar HS <- LS transition in solution as well as in the solid state [170]. In solution, spin-state conversion rates have been obtained as shown in Table 3. The complex with x = 0 is pure HS in solution, whereas in the solid state a gradual transition is observed extending over the range... 

Complexation is a phenomenon that involves a coordinate bond between a central atom (the metal) and a ligand (the anions). In a coordinate bond, the electron pair is shared between the metal and the ligand. A complex containing one coordinate bond is referred to as a monodentate complex. Multiple coordinate bonds are characteristic of polydentate complexes. Polydentate complexes are also referred to as chelates. An example of a monodentate-forming ligand is ammonia. Examples of chelates are oxylates (bidentates) and EDTA (hexadentates). 

The encapsulating hexadentate ligand (148) forms [Ni(148)]2+ with a distorted octahedral geometry. This can be oxidized to a Ni111 species in which a substitution reaction by sulfate in the NiN6 chromophore is observed.514... 

An spontaneous assembly of 15 components is reported in the synthesis of [Ag9L6](OTf)9 where L is the hexadentate, tris-chelating 6,6-bis[2-(6-methylpyridine)]-3j3 -bipyrazine. The structure consists of a 3x3 grid of Ag-atoms (average Ag" Ag = 3.72(3)A), sandwiched between two almost perpendicular sets of three parallel L ligands (Figure 10).641... 

H NMR studies of the zinc complex formed with the hexadentate aniline functionalized triazacyclononane ligand (70) showed C3 symmetry in solution. It is suggested a six-coordinate complex is formed with all A-donors bound.664 This compares with the benzyl amino derivative,... 

The ligand 6,13-dimethyl-l,4,8,ll-tetra-azacyclotetradecane-6,13-diamine coordinates as a hexadentate ligand to zinc in neutral aqueous solution. Potentiometric titrations were used to determine the stability constant for formation. The pXa values were determined for five of the six possible protonation steps of the hexamine (2.9, 5.5, 6.3, 9.9 and 11.0).697 Studies of the syn and anti isomers of 6,13-dimethyl-1,4,8, ll-tetraazacyclotetradecane-6,13-diamine reveal that they offer different shapes for metal binding, which is reflected in the stability constants for 1 1 zinc ligand ratio complexes. The selectivity of binding to the zinc ion compared to the cadmium(II) ion by both isomers is significant.698... 

A hexadentate N202S2 ligand (116) has been synthesized as a dithiaalkyl-substituted triazene-1-oxide and forms an unusual hexacoordinated zinc complex with thioether donors. Both the phenyl and the methyl derivatives form structurally characterized octahedral complexes.896... 

A number of ligands based on the encapsulating hexadentate edta ligand have been structurally characterized with zinc, including the 3,4-toluenediamine-/V, V, /V",/V" -tetraacetate.897... 

Hexadentate ligands l,12-bis(2-pyridyl)-5,8-dioxa-2,ll-diazadodecane and l,12-bis(2-pyridyl)-5,8-dithia-2,ll-diazadodecane have pyridine, amine, and ether or thioether donors offering an N402 or N4S2 donor set. The X-ray structures of the zinc complexes are distorted octahedral with the zinc center encapsulated by the ligand.898... 

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