Nickel complexes tetrahedral structure

Macrocyclic N-donor ligands. Nickel complexes of macrocyclic ligands have been studied by cyclic voltammetry, and the irreversible or quasi-reversible couples Ni" L Ni L Ni L have been established. The structure of (124) has been reported and the co-ordination is essentially square-planar with a slight tetrahedral distortion. The reaction of [Ni(pn)3] with... 

In summary, it can be seen that the structural chemistry of the zero-valent complexes has to date been dominated by investigations on nickel carbonyl. Preliminary studies on other compounds indicate that the tetrahedral structure may not be the only possibility, and thorough investigation of the unsaturatcd species is likely to develop. Back-donation may be examined by study of force constants, in favorable cases merely of observed frequencies, and it would be interesting to see more cases of competition for back-donation, as in (MeNC)3Ni(CO). 

Bis(salicylaldoximato)nickel(II) is diamagnetic in the solid state, but becomes partially paramagnetic in solution in chloroform157 and aqueous dioxane.151 This is likely to be due to molecular association or solvation,158 rather than to the adoption of a distorted tetrahedral structure in solution.151 The nickel(II) complex readily forms pseudo-octahedral bis-adducts in the presence of large amounts of amines,159 160 although analogous complexes of commercial orffto-hydroxy-oximes have been reported to retain the square-planar structure in hydrocarbon solution in the presence of moderate amounts of ammonia or aliphatic amines.161... 

The organisms Pyricularia oryzae, which causes rice blast, and Helminthosporium oryzae, which causes brown leaf spot, can be controlled with complexes of the ligands 1-phenyl-3-methyl-4-nitroso-2-pyrazolin-5-one (36) and 3-methyl-4-nitroso-2-pyrazolin-5-one (37). The complexes were of the type ML Xj (L = 36, 37 X = C1-, Br, N03 ) or [ML2]Y2 (Y = C104 ). The former were assigned an octahedral or distorted octahedral structure and the latter are tetrahedral. The most active nickel complex was (38).92... 

The nickel chloride complex(VIII) of N P (NHMe)g is paramagnetic (3.2 B.M.). The phosphorus NMR spectrum shows a single line which shifts upfield by 4.0 6 compared to the ligand. A tetrahedral structure is proposed for this complex in whioh the metal is coordinated to two antipodal nitrogen atoms of the ligand (Figure 2). 

In the discussion about the structure of selenosalicylideneiminates 496 [884], it was emphasized that the corresponding nickel complex is cis-planar, while the related cobalt and zinc compounds have a tetrahedral structure. Kinetics of enantioisomery in chelates 496 (M = Zn, Cd, Pb R — <-Pr) have been studied in detail [884b],... 

The tetrahedral [160-163] and cis-planar [100,134,164-167] structures are characteristic for chelates of type 874 with coordination units NiN4 and MN2S2, respectively, as well as chelates 868 discussed above. Original polyhedral forms were discovered by x-ray diffraction for nickel and palladium ICC of the discussed type 874. It is accepted that, in case of a nickel complex, the compound with a carbon-carbon bond 875 is formed [165,166] formation of palladium chelates is accompanied by the cyclometallation reaction leading to tetranuclear clusters 876, where the tridentate ligand behaves as C,N,S-donor [168]. 

In a difference from above, the nickel and copper ICC 874 (X = O) with coordination unit MN202 evidently have tetrahedral structure, which is also characteristic for analogous cobalt and zinc complexes [169], as proved for a zinc complex by x-ray diffraction. In this respect we note a nonstandard behavior of manganese. As a result of the interaction of the ligand 873 (X = 0, R = H, N02 Ar = C6H4R, R =H, OMe, N02) and the acetate of the metal in methanol, together with an expected ICC of type 874 (X = O, M = Mn) [17], tetrameric cluster structures are formed (4.46) [171] ... 

In contrast to the cyanides, other complexes of nickel with a coordination number of four, e,g, [Ni(NH3 J2+S04 , show paramagnetism corresponding to one or two unpaired electrons, which has been regarded as evidence for a tetrahedral structure of the complex ion. This has not been confirmed experimentally. 

Figure 7-47 shows the molecular structure of the diphenylfosphinoferrocene-nickel complex [Fe(fy -C5H4PPh2)2]NiCl2 [150]. The nickel atom assumes an essentially tetrahedral coordination. The cyclopentadienyl rings of the ferrocene group are parallel and nearly eclipsed. 

Experimental evidence supporting the square planar structure of first row transition metal ions was presented in 1931 [Ni(CN)4] complexes were found to be diamagnetic, and K2Ni(CN)4-H20 and K2Pd(CN)4-H20 were found to be isomorphous (75, 74). Pauling s prediction (75) that bivalent nickel complexes could be either square planar dsp hybridization) or tetrahedral sp hybridization) stimulated interest in the square con-... 

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