Complexes with nickel compounds

The first Ni Mossbauer spectrum of nickel in a bioinorganic compound with determinable EFG and isomer shift was reported for a nickel complex compound with planar [NiSJ core and considered as a model compound for hydrogenase. This Mossbauer spectrum from the formal Ni compound is presented in Fig. 7.16. The observed quadrupolar interaction can be understood in terms of ligand field theory. In this approach, the b g and levels (d y2 and d ) are not occupied which is expected to cause a large negative EFG contribution [32]. 

Fig. 7.16 Ni Mossbauer spectrum at 4.2 K of a nickel complex compound with planar [NiS4] core known as a model compound for hydrogenase (source Nio.gsCro.is (97% enriched) activated at Mainz Microtron) (from [32])...

Ni3(2,2,2-tet)3(/u-N3)3](PF6)3 and its perchlorate analogue have been suggested as trinuclear complexes with an irregular triangle structure.2117 While a crystal structure is lacking, EXAFS and XANES spectra support the occurrence of azido-bridged trinuclear nickel(II) compounds with Ni- -Ni separations of 5.16 A and 5.12 A, respectively. Two J parameters had to be... 

USE Forms a complex compound with ferrous ions which is used under the name of Terrain as an indicator in oxidation reduction systems, eg., titration of ferrous salts. Also used in determination of nickel, ruthenium, silver and other metals. 

This nickel (IV) complex compound is obtained by oxidation of the corresponding nickel (H) complex compound with O3. 

Synthesis of 8,9-dihydroindenes with nickel complex compounds... 

Substances showing catalytic waves in ammoniacal cobalt or nickel solutions< > must fulfil another condition beside the two conditions mentioned above the substance has to form a complex-compound with cobalt and other components of the solution. Moreover, the acid properties of this complex and its adsorbability also seem to be of importance. The substances showing a catalytic effect of this type usually contain at least an atom of sulphur in their molecule (e.g. cysteine, dithiopyrimidine or proteins). Whether or not the presence of sulphur in the catalytically active molecule is a sufficient condition has yet to be decided. It was shown that e.g. gelatin or casein containing little or no sulphur atoms do not produce any catalytic wave of this type. Similarly, in the series of hydantoin, thiohydantoin and dithiohydantoin as well as pyrimidine, thiopyrimidine, and dithiopyrimidine, the catalytic effect was only observed for the thioderivative and it increased with the number of sulphur atoms in the molecule. 

To the first group belongs the determination of propylene diamine S ) This is based upon the formation of the copper-diamine complex, which is reduced at a potential different from that of the uncomplexed copper ion. Similarly, the determination of 1,2-diaminocyclohexane can be carried out in the presence of excess of hexamethylenediamine. ) It depends upon the fact that 1,2-diaminocyclohexane forms at pH ll-7-12-2 a complex compound with nickel ions which is reduced at —1-05 V. Hexa-methylenediamine at this pH does not form complexes and... 

TC-Cyclopentadienyl Nickel Complexes. Nickel bromide dimethoxyethane [29823-39-9] forms bis(cydopentadienyl)nickel [1271 -28-9] upon reaction with sodium cyclopentadienide (63). This complex, known as nickelocene, 7T-(C3H3)2Ni, is an emerald-green crystalline sandwich compound, mp 173°C, density 1.47 g/cm. It is paramagnetic and slowly oxidi2es in air. A number of derivatives of nickelocene are known, eg, methylnickelocene [1292-95-4], which is green and has mp 37°C, and bis( 7t-indenyl)nickel [52409-46-8], which is red, mp 150°C (87,88). 

Nickel salts form coordination compounds with many ligands. Dibromobis(tri- -butylphosphine)nickel(Il) [15242-92-9], [( -C4H2)3P]2NiBr2, dicyanoammineaquanickel(11), Ni(NH3)(H20)(CN)2, and bromonitrosobis(triphenylphosphine)nickel(Il) [14586-72-2], are complexes used for syntheses in preparative organonickel chemistry. 

Coordination-catalyzed ethylene oligomerization into n-a-olefins. The synthesis of homologous, even-numbered, linear a-olefins can also be performed by oligomerization of ethylene with the aid of homogeneous transition metal complex catalysts [26]. Such a soluble complex catalyst is formed by reaction of, say, a zero-valent nickel compound with a tertiary phosphine ligand. A typical Ni catalyst for the ethylene oligomerization is manufactured from cyclo-octadienyl nickel(O) and diphenylphosphinoacetic ester ... 

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