Nickel, colorful complexes

Nickel also has been used as a dye site in polyolefin polymers, particularly fibers. When a nickel compound, eg, the stearate or bis(p-alkylphenol) monosulfide, is incorporated in the polyolefin melt which is subsequently extmded and processed as a fiber, it complexes with certain dyes upon solution treatment to yield bright fast-colored fibers which are useful in carpeting and other appHcations (189). Nickel stearate complexing of disperse mordant dyes has been studied (190). 

Most four-coordinate nickel(ll) complexes are square planar. They are of red, brown and yellow color and practically aU are diamagnetic. Some examples are red bis(dimethylglyoximato)nickel(II) and the yellow tetracyanonick-elate(ll) ion, [Ni(CN)4]2-... 

The addition of excess ZnBr2 to a Ni(bpy)32+-containing solution (Zn/Ni = 10/1) does not lead to a color change of the solution. The complexes obtained from a mixture of Ni2+ and 2,2/-bipyridine are more stable than those obtained in the presence of zinc9. However, studies by cyclic voltametry of nickel-bpy complexes show several changes in... 

Divalent nickel forms two main types of complexes. The first consists of complexes of the spin-free ( ionic or outer orbital) octahedral type (see also Ligand for their discussion) in which the ligands are principally H2O, NH3, and various amines such as ethylenediamine and its derivates, e.g., Ni(H20>62+. Ni(NH3)e2+, Ni(en)62+. These complexes usually have colors toward the high-frequency side of the spectrum, i.e., violet, blue, and green. The other class consists of tetracovalent square complexes with ligands such as CN, the dioximes and their derivatives, and other chelates, which usually have colors on the low frequency side of the spectrum, i.e., red. orange, and yellow. The structure of the nickel-climethylglyoxime complex is... 

QuinoxaIinedithiolate was first prepared in 1956 by Morrison and Furst (4) who observed that qdt formed colored complexes with metals in aqueous ammonium hydroxide. Nickel was first quantitated using qdt in 1958 by Skoog et al. (26) in liquid ammonia. Silver, copper, cobalt, and manganese were found to interfere with nickel detection. In particular, under the conditions of Skoog et al., the absorbance of [Co(qdt)3]3- (A.max = 475 nm) significantly overlapped with the absorbance of [Ni(qdt)2]2 at 520 nm. 

FIGURE 22 Preparation of supramolecular catalysts for hydrocyanation reactions (82) (A) assembly of heterodimeric chelating ligands (B) structure of the optimal nickel-diphosphine complex for hydrocyanation (other ligands of the metal center are omitted for clarity) and (C) hydrocyanation of functionalized styrenes. (For a color version of this figure, the reader is referred to the Web version of this chapter.)... 

Three-spin allowed transitions are observed for octahedral nickel(II) complexes (see Pre-lab 6.2 for theory on state assignment) with wavelength ranges 769-1428, 500-900, and 370-525 nm, and with s values typically 10 M-1cm-1. Tetrahedral complexes generally show one d—d transition in the visible region at 650 nm (e 100 M-1cm-1). Square planar complexes show a band in the 450-600 nm (e 60-100 M-1 cm-1) range and the absorption responsible for their characteristic color is at 400 nm (e 1000 M-1 cm-1). 

Complex Structure. The violet-colored solution of very stable nickel ammine complexes also confirms, through the described experiments, that practically no free nickel ions exist in the complex solution (see E9.7). The analysis of... 

A.3 Proposed Demonstrations for Lecture 9 Colorful complexes of nickel... 

This demonstration shows the formation of colorful complexes of nickel by adding solutions of different ligands to solutions of nickel sulfate. The ligands bind to the Ni " " ion and form the corresponding complexes. The formation of the complexes is accompanied by color changes. The observed colors are discussed in terms of the strengths of the Ni +-ligand bonds, which also affect the relative stabilities of the complexes. 

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