Nickel complexes, molecular structures

In nickel and palladium dithiobenzoato complexes, four-membered chelate rings are formed (366), whereas, in the corresponding phenyl-dithio acetates [M2(S2CCH2Ph)4], the dithio ligands act as bridging groups between the two metal atoms, with the formation of binuclear units (367). The molecular structure of the latter compounds shows that each metal atom is coordinated to four sulfur atoms and to the other metal atoms in a square-pyramidal geometry. Other evidence for... 

Figure 2.20. Transformation of silica supported dinitrosyl complexes of nickel(II) leading to formation of nitrogen dioxide and its final stabilization on the support. The picture shows the molecular structure and the spin density contours calculated with BP/DNP method of the involved species, and evolution of the X-band EPR spectra of the NiN02 Si02 complex due to spillover of the ligand (adopted from [71]).

In a series of studies of the spectroscopy and photochemistry of nickel(O) -a-diimine complexes, the structural differences among the complexes NiL2 and Ni(CO)2L (L Q-diimine) have been examined by means of molecular orbital calculations and electronic absorption Raman resonance studies.2471, 472 Summing up earlier work, the noninnocence of a-diimine ligands with a flat — N=C—C=N— skeleton in low-valent Ni chemistry and the course of substitution reactions of Ni° complexes with 1,4-diaza-1,3-dienes or a,a -bipyridine have been reviewed.2473... 

From this result it has been concluded that the reactive intermediate is an insertion product with a structure similar to that of the nickel compound 34 and not a silylene complex as postulated in an earlier publication.36 The molecular structures of 34 and 35 are presented in Fig. 6. 

In order to give the usual overview of nickel complexes at increasing coordination numbers we begin with the usual square planar complexes of the Schiff bases salen and saloph.149,150 As an example, Figure 98 shows the molecular structure of [Nin(salen)]. 

Phenylmethylsilanediol, synthesis, 42 155 Phenylsilanetriol, monosodium salts, 42 169 4 -Phenyl-2,2 6, 2 -terpyridine bis nickel complex, 30 74 molecular structure, 30 74 PhjtfluorenyllSiOH, 42 197 (Ph(Me2N)C-=Nli], 37 59-65 orientation of imino ligand, 37 61-63 (PhMe SiljCSiH OH, 42 244-245, 248 (PhMe SiljCsiMeHlOH), 42 191 Phosphaalkenes acyclic, 33 338-353 butadienes, 33 346-349 cumulenes, 33 352... 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

The observation (112-115) that neutral aqueous solutions of [Ni11H 3G4]2 consume molecular oxygen with the appearance of a strongly absorbing transient at 350 nm lead to detailed investigations and discovery of nickel(III)-peptide complexes (113). The oxidized nickel complexes have absorption maxima around 325 and 240 nm (e = 5240 and 11,000 M I cm-1, respectively for [NiM1H 3G4]-). Reduction potentials (116) (Table II), measured by cyclic voltammetry, show a small dependence on ligand structure which can be correlated... 

Unlike metalloporphyrins, the nonporphyrinic metal compounds are poorly characterized with respect to molecular structure and properties. Examining the nature of the nickel and vanadium in these compounds is important from the standpoint that often most of the Ni and V in a petroleum is nonporphyrinic, as shown in Table II. Sugihara et al. (1970) suggested that the nonporphyrin metal compounds comprise a wide variety of coordinated complexes resulting from the reaction of inorganic forms of the metals with polar organic molecules. Larson and Beuther (1966) speculated that the nonporphyrinic metal complexes are simply... 

Figure I. Molecular structure of the nickel complex 3 as determined by x-ray-...

A series of nickel triad complexes ML3(allene) (Table VII) were prepared (122, 123, 139) and studied in solution by means of H NMR spectroscopy. Consistent with a planar molecular structure,... 

A. A. Bennett, M. R. Kopp, E. Wenger, A. C. Willis, Generation of Nickel(0)-Aryne and Nickel(II)-Biphenyldiyl Complexes via in situ Dehydrohalo-genation of Arenas. Molecular Structures of [Ni(2,2 -C6H4C6H4)dcpe)] and C2-Hexabenzotriphenylene, J. Organo-met. Chem. 2003, 667, 8-15. 

The molecular structure of a ditame complex of nickel(II), [(12)Ni(EtOH)]Br2, shows the coordination behavior of this ligand and 1 towards Ni11 to be identical, with similar structural parameters (23). The bond from the metal center to the secondary amine donor in the apical position is shorter at 2.050(5) A than the equatorial Ni-N bonds, whose average is 2.112(7) A, in the same way as in the complexes of the pyN4 ligand (44). The secondary nature of the apical donor atom in [(12)Ni(EtOH)]Br2 gives rise to crystallographic disorder, which has been resolved. 

Some homoleptic unsymmetrical (dmit/mnt, dmit/tdas) dithiolene nickel complex-based D-A compounds with D = TTF and EDT-TTF also exhibit metal-like conductivity (see Table I) (101). Their molecular structure is shown in Scheme 3. The unsymmetrical tetraalkylammonium salts [MLjLJ- (M = Ni, Pd, Pt) have been prepared by ligand exchange reaction between tetraalkylammonium salts of MLj and ML21 (128, 129) and the D-A compounds have been synthesized by electrooxidation. Among these complexes, only the Ni derivatives exhibit metallic-like properties, namely, TTF[Ni(dmit)(mnt)] (metallic down to --30 K), a-EDT-TTF[Ni(dmit)(mnt)] (metallic down to 30 K), TTF[Ni(dmit)(tdas)] (metallic down to 4.2 K), and EDT-TTF[Ni(dmit)(tdas)] (metallic down to --50 K) (see Table I). The complex ot-EDT-TTF-[Ni(dmit)(mnt)J is isostructural (130) to a-EDT-TTF[Ni(dmit)2)] [ambient pressure superconductor, Section II.B.2 (124)]. Under pressure, conductivity measurements up to 18 kbar show a monotonous decrease of the resistivity but do not reveal any superconducting transition (101). 

Fig. 7.10 Schematic representation of the molecular structure of the dinuclear nickel(0) complex Ni2(C sHs)2 (15) the smaller balls represent the CH units of the eight-membered rings...

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