Cobalt complexes trigonal bipyramidal

Ethanol-dimethoxypropane solutions of either 1-formylisoquinoline or 2-formylquinoline thiosemicarbazone and cobalt(II) salts yield [Co(L)A2] complexes where A = Cl, Br, I, NO3, NCS, or NCSe [147]. All are non-electrolytes, have magnetic moments of 4.30-4.70 B.M. and are five coordinate with approximate trigonal bipyramidal stereochemistry involving NNS coordination based on electronic and infrared spectra. [Co(21-H)2] 2H2O was isolated from a cold methanolic solution of cobalt(II) chloride and 1-formylisoquinoline thiosemicarbazone [187]. Infrared spectral studies show NNS coordination the electronic spectral bands fit a distorted octahedral symmetry, and the magnetic moment is 4.48 B.M. 

Methyl-5-amino-l-formylisoquinoline thiosemicarbazone, 22, also yields cobalt(II) complexes from unheated methanol solution [202]. However, due to this ligand s added steric requirements, a complex, [Co(22)Cl2], with one ligand per metal ion center is formed. This brown solid has a magnetic moment of 4.42 B.M., is a non-electrolyte, has coordination of a neutral NNS ligand, and the electronic spectrum indicates approximate trigonal bipyramidal stereochemistry. 

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... 

Large numbers of low-spin cobalt II) complexes are known, both with essentially trigonal bipyramidal structures and with square pyramidal structures. 

The stereochemistry of the pentakisisocyanidecobalt(I) and (II) complexes is apparently a function of crystallization procedures. To date, four isomeric structures have been identified for isocyanide complexes of co-balt(l) (121) and three for those of cobalt(II) (284). Crystal structure determinations of [Co(CNPh)5]C104 CHCl3 (285) and [Co(CNPh)5]-(CI04)2 C1CH2CH2C1 (284) have shown the coordination around the cobalt to be square pyramidal, whereas with [Co(CNC6H4Me-p)5][Co(NM A)3] (NMA = nitromalonaldehyde) a trigonal bipyramidal structure was found for the cation (286). 

In order to analyze the relation between the observed g values and the electronic structure of the cobalt(II) ion, it is convenient to consider separately the octahedral and square pyramidal complexes which have (quasi) degenerate ground states and the trigonal bipyramidal and tetrahedral complexes. Also it is convenient to resort to approximate models which will be useful for learning which g values are expected in the various coordination environments. It is understood that only a more detailed analysis similar to the one outlined above allows one to fully understand the spin hamiltonian parameters. 

Table 3. Spectral parameters for five coordinate cobalt(II) complexes. The energies of the electronic transitions are labelled according to the symmetry labels of the excited states in D3h symmetry for trigonal bipyramidal, and in C4v symmetry for square pyramidal complexes. F and P refer to the free ion terms which contribute mostly to the indicated state. Don.Set is the donor set of the... 

Rana and Teotia 116) have reported the synthesis of a novel tridentate macrocycle 136 by the reaction of 2,6-dipicolinic acid hydrazide and acetylacetone in the presence of cobalt(II), nickel(II), and copper(II) salts. As is frequently the case, water occupies the axial positions of these trigonal bipyramidal complexes and the chelating nitrogen atoms are essentially coplanar. 

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