Nickel complex trigonal bipyramidal

Let us now examine the pentacoordinate Ni(II) complexes with the already cited Schiff base bis(salicylideneimmine-3-propyl)amine, [Ni(R-X-saldpt)]. As for the cases of iron(II) and cobalt(II) complexes, this ligand constrains the central nickel(II) ion to assume a trigonal bipyramidal geometry, Figure 105.156... 

Low-spin nickel(II) complexes are numerous and many studies of their spectra have appeared in the literature. The most common stereochemistry is trigonal bipyramidal mainly because of the frequent use of tripod-hke hgands. 

Fig. 36. Energy level diagram for trigonal bipyramidal complexes of nickel(II), d, ...

Relevant structural features of the S02 complexes are collected in Table 16 together with the IR absorption frequency of SO2. In complex (63) the nickel atom is in a distorted trigonal bipyramidal environment,250 with a bent coordinated S02 molecule, while in [Ni(p3)(S02)] (64) S02 is coplanar with nickel which achieves a distorted pseudotetrahedral structure. 

When nickel(II) salts containing a coordinating anion (halide and pseudohalide) are reacted with NaBH4 in the presence of np3, trigonal bipyramidal nickel(I) complexes of the type [NiXnp3], in which the coordinating anion occupies die axial position, 39,340 are obtained. When nickel(II) salts with poorly coordinating anions are used, non-stoichiometric hydrido complexes of nickel(II) are obtained (equations 108 and 109). 

Table 31 Magnetic Moments and Spectral Parameters for some High-spin Five-coordinate Nickel II) Complexes with Nearly Trigonal Bipyramidal... 

The X-ray crystal structure933 of dibromo[l,3-di(6-methyl-2-pyridine)-2-azapropane]-nickel(II) (107) has shown that in this complex the nickel(II) is five-coordinate in an approximate trigonal bipyramidal geometry with the bromine atoms lying in the basal plane (average Ni—N and Ni—Br distances 203 pm and 248 pm, respectively). 

The Ni3S2 fragments in the two complexes (263) and (265) have a trigonal bipyramidal geometry with the two S atoms in the apical positions and the three nickel atoms in the equatorial plane, as found in other organometaUic compounds which contain the same Ni unit.1939 The formation of the enneanuclear complex (264), on the contrary, is exceptional and no other complex of this stoichiometry was isolated with analogous tertiary phosphines, with selenium, or with metals other than nickel. It is not possible to assign any definite oxidation number to nickel in complex (264). The lack of two electrons with respect to the situation of nine nickel(II) ions was reported to be essential for the existence of complex (264) because the oxidation is spontaneous and its reduction invariably leads to the decomposition of the cluster compound.19 ... 

Both nickel(III) and nickel(IV) complexes are usually found in octahedral environments. Less common geometries are the square planar and the trigonal bipyramidal ones. 

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