Schiff bases hexadentate

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 =... 

Iron(II) systems based on hexadentate ligands where all the donor functions are imines will generally be low-spin. One well-known example is the Schiff base ligand obtained by condensing tren with 2-pyridinecarbaldehyde (22). 

Schiff base-type systems are the second most widespread class of ligands which have been used to obtain Fe(III) spin crossover materials. These ligands may be classified according to the number of donor atoms available for coordination to the Fe(III) ion. In Sects. 3.1 to 3.4 attention is drawn to tri-, tetra-, penta- and hexadentate Schiff base-type ligands, severally. Section 3.5 focuses on spin crossover in iron(III) induced by light irradiation, whereas Sect. 3.6 is devoted to recent developments in the field of materials science with the objective of incorporation of Fe(III) spin crossover materials in devices. 

Fig. 18 Hexadentate N402-donating Schiff base ligands...

In a systematic study of the effects of variation of the tetramine involved in formation of the hexadentate N402 donor Schiff base the linear 3,3,3-, 3,2,3-, 2,3,2- or 2,2,2-tetramines, where the numbers refer to the number of carbon atoms between the amine groups (note 2,2,2-tetramine is synonymous with the nomenclature trien used previously) have been condensed with salicylaldehyde, acetophenone or benzophenone [206]. Crystal struc-... 

Activation volumes for aquation of Schiff base complexes [Fe(C5H4NCH=NHR)3]2+ (R = Me, Et, nPr, nBu) are between +11 and +14 cm3 mol-1 (107), and thus within the range established earlier (108) for (substituted) tris-l,10-phenanthroline-iron(II) complexes, viz. +11 to +22 cm3 mol-1. These positive values are consistent with dissociative activation. Kinetic studies of the reaction of a CH2S(CH2)3SCH2 -linked bis(terpy) ligand (L6) with [Fe(terpy)2]2+ showed a very slow two-step process. The suggested mechanism consisted of slow loss of one terpy, rapid formation of [Fe(terpy)(L6)], and finally slow displacement of the second terpy as the partially-bonded L6 becomes hexadentate (109). 

Belokon, Y. N. Chusov, D. Borkin, D. A. Yashkina, L. V. Dmitriev, A. V. Katayeva, D. North, M. (2006) Chiral Ti(lV) complexes of hexadentate Schiff bases as precatalysts for the asymmetric addition of TMSCN to aldehydes and the ring opening of cyclohexane oxide.. Tetrahedron Asymmetry, 17, 2328-2333. 

There are only trinuclear and tetranuclear manganese(III) complexes reported with hexadentate Schiff base ligands. Two such hexadentate ligands, bamen and Saltren (Figure 19), form unique core structures. 

Activation volumes have been determined for base hydrolysis of [Fe(phen)3] ", [Fe(bipy)3] ", [Fe(4MeObsb)3] " ", and [Fe(3Mebsb)3] + (3Mebsb = (107)). The overall pattern of AF and A7/ values for aquation and for base hydrolysis favors dissociative activation for all these reactions. Activation volumes have been also determined for base hydrolysis of several bidentate, and one hexadentate, Schiff base complexes in several binary aqueous solvent mixtures and for... 

Figure 20 Some potentially hexadentate Schiff bases...

The potentially heptadentate Schiff base, obtained from tris(2-aminoethyl)amine and three moles of SAL and shown in Figure 21a, reacts with trivalent metal ions to form neutral 1 1 compounds, and in so doing acts as a hexadentate ligand. An X-ray structural analysis of an Fem complex has shown that the tertiary nitrogen atom of the amine is not bonded to Fe.144... 

As previously observed with hexadentate Schiff bases, potentially heptadentate ligands easily form dinuclear metal complexes. This is the case with trisalicylidenetriethylenetetramine, shown in Figure 21b, which gives methoxo145 and hydroxo146 dinuclear Fe111 complexes. 

Costes, J.R, Clemente-Juan, J.M., Dahan, R et al. (2002) Dinuclear (Re , Gd ) complexes deriving from hexadentate Schiff bases synthesis, structure, and Mossbauer and magnetic properties. Inorganic Chemistry,... 

Fluorinated R groups (C2F5, C6F5, etc.) enhance thermal stabilities and improve volatilization of salicylaldimines, Schiff bases, /3-diketonates, /3-dithiones, and hexadentate macrocyclic complexes of lanthanides, transition metals, and Zn11 for GC separations.45... 

One subset of Schiff base complexes are the hydrazone complexes which have a R—C=N—N functional group instead of the R C=N—C functionality. These compounds have been prepared as models for bromoperoxidase389 and other biological systems.390 In the solid state, the hydrazones have coordination patterns similar to those of the Schiff bases and the majority of the complexes are oxovanadium(V) hexadentate or pentacoordinate complexes with tridentate 02N donor sets (see Table 5). While most structures contain alkoxide donors,390-403 complexes have been reported with diols and catechols,129,404,405 hydroxamic acids,288,391 hydroxy quinolinate,406, 7 and benzoylhydrazine.408 In addition, dioxo,375,409-412 oxo-bridged... 

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