Nickel macrocyclic complexes structure

The dissociation kinetics of the nickel chloride complex of the 15-mem-bered, S2N2-macrocycle of type (279) has also been investigated in the presence of hydrochloric acid (Lindoy Smith, 1981). This complex has a similar trans-octahedral structure to that of the 02N2-donor systems just discussed. For the sulfur-containing complex, two consecutive (acid-independent) first-order steps were observed, with the second being slower than the first. The data are in accordance with the scheme ... 

Many new Ni(II) complexes of aza-type macrocycles have been synthesized, and their redox chemistries have been explored. In particular, complexes of macropolycyclic ligands and bismacrocyclic ligands have been prepared. Complexes with uncommon oxidation states of nickel (Nim and Ni1 complexes) have also been synthesized by employing a specially designed macrocycle, and their characteristic spectroscopic properties and X-ray structures reported. These nickel(II) complexes... 

The structures determined by X-ray analysis of the complexes [Ni(Me3[12]eneN3)2](NCS)2 (Me3[12]eneN3 = 2,4,4-trimethyl-l,5,9-triazacyclododec-l-ene) and [Ni(TRI)(H20)N03]N03 (TRI = tribenzo[b,/,/][l,5,9]triazacyclododecane) show that the two triaza macrocycles coordinate facially in both square pyramidal2721 and octahedral complexes.2724 Other complexes with triaza macrocycles have been prepared and are assumed to be either live- or six-coordinate.2721-2725 Selected examples of nickel(II) complexes with unsaturated macrocydes are reported in Table 106. 

The situation with pendant phenol groups is much less ambiguous. The crystal structure of the nickel(II) complex [Ni H 1[14]ane-N4C6H5OH]+ (Fig. 5) shows it to be a square-pyramidal, high-spin species and the reduction potential of the nickel(III) complex is 0.15 V lower than that of the parent saturated 14-membered macrocyclic complex (100). Strong coordination by phenolate oxygen is even more... 

Metal template syntheses of complexes incorporating the p-amino imine fragment have been introduced by Curtis as a result of his discovery that tris(l,2-diaminoethane)nickel(II) perchlorate reacted slowly with acetone to yield the macrocyclic complexes (40) and (41) (equation 8).81-83 In this macrocyclic structure the bridging group is diacetone amine imine, arising from the aldol condensation of two acetone molecules. This reaction is widely general, in the same way that the aldol reaction is, and can be applied to many types of amine complexes. The subject has been reviewed in detail with respect to macrocyclic complexes by Curtis.84... 

The nickel(II) complexes of the closely related macrocycle, tetra-TV-methyl-14-ane-N4 (tmc), can adopt the same set of isomers. It has been noted that the isomer observed depends on whether nickel(II) is four-, five- or six-coordinate[13]. Molecular mechanics modeling of this system and prediction of each of the structures allowed an analysis of the specific interactions between axial ligands and the macrocycle to be carried out 141. In this way a possible explanation for the experimental observations was arrived at. Specifically, it was concluded that the interactions between the methyl substituents on the ring and any axial ligands control the stabilities of the different isomerstl4]. 

Nickel(I) complexes of N4 macrocycles can be prepared by reduction of the corresponding Ni11 complexes with sodium amalgam. They possess more or less distorted square-planar structures.19 By contrast, the one-electron reduction of Ni porphyrin complexes may result in Ni1 porphyrins or Nin jr-anion radicals, depending on the reaction conditions.20 Complexes of this kind are useful models for the Ni sites in certain metalloenzymes (see below). 

The electrocatalytic activity of various nickel macrocycles in aqueous solution was studied. Cyclic voltammograms indicate that 7 / S -NiHTIM2+, NiMTC2+ and NiDMC + are better catalysts than Ni(cyclam)2+ in terms of more positive potentials and/or their larger catalytic currents [26], Bulk electrolyses with 0.5 mM Ni complexes confirm that these complexes are excellent catalysts for the selective and efficient CO2 reduction to CO. The macrocycles with equatorial substituents showed increased catalytic activity over those with axial substituents. These structural factors may be important in determining their electrode adsorption and CO2 binding properties. 

We have reported the synthesis of functionalized calixarene 60. The crystal structure of the nickel azide complex of this dinuclear host indicates two nickel ions bound (one centered in each of the appended lower rim macrocycles), with three unique azide 1,1 end on bridging ligands cascaded in between (Fig. 6) (152). 

A systematic structural study of the DPX Pacman framework has been provided by a homologous series of dinuclear zinc, copper, and nickel derivatives. The molecular structures of the homobimetallic zincfll), copper(II), and nickel(II) complexes of the DPX construct (5-7) are shown in Fig. 3. Trends in bond lengths and angles of macrocyclic core structures and side chains agree well with those observed in related systems including H4(DPA), H4(DPB), and l,2-bis[5-(2,3,7,8-12,13,17,18-octaethyIporphyrinato)]-cw-ethene porphyrins (80-83). 

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