Hexacoordinate Compounds Research Articles

Co-ordination behaviour of various 2-pyridyl ketones. Part I. Copper(II) halide and perchlorate complexes with di-2-pyridyl ketone and 2-benzoylpyridine

Copper(II) perchlorate yields the following hexaco-ordinate complexes with di-2-pyridyl ketone (pyCOpy) and 2-benzoylpyridine (PhCOpy): Cu(pyCOpy)2(ClO4)2(NN-co-ordination), [Cu(pyCOpy)2(H2O)2], (ClO4)2(NO-co-ordination), and Cu(PhCOpy)2(ClO4)2. The complexes M(PhCOpy)2X2(M = CuII or ZnII; X = Cl or Br) are hexaco-ordinate compounds with weak interaction between the carbonyl group and the metal ion. The nature of the complex Cu(pyCOpy)2Cl2,2H2O is discussed. The compounds Cu(pyCOpy)X2,ROH (X = Cl or Br; R = Et or Prn)(NO-co-ordination) possibly contain pentaco-ordinate copper(II) whereas Cu(PhCOpy)Cl2 and Cu(pyCOpy)Cl2(NN-co-ordination) are considered to be planar complexes. Red-brown Cu(PhCOpy)Br2 is suggested to be a tetrahedral compound.

The Mössbauer spectra, structure, and bonding of some hexaco-ordinate compounds of tin(IV)

The Mossbauer spectra of a large number of hexaco-ordinate tin(IV) compounds have been investigated. No quadrupole interaction is observed even when the six atoms bonded to tin are not all the same, provided that all six have non-bonding pπ electrons. When some of the attached groups have no such pπ electrons (e.g., methyl) then substantial quadrupole splitting is observed. Isomer shifts show the expected trend with electronegativity of the halogen but are somewhat insensitive to the nature of the chelating ligand. The results have been used to draw structural conclusions about several compounds whose detailed structures have not previously been established unambiguously. Among these are the adducts of the tin(IV) halides with 8-hydroxyquinoline, with [Ph2P(O)]2NH, and with dinitrogen tetroxide.

The problem of the composition and structure of potassium cyano-cobaltate (II)

An approach to the problem of the composition and structure of potassium cyanocobaltate (II) has been made. The complex prepared by the interaction of Co(II) and KCN gave, on analysis, a compound with the formula K3Co(CN)4H2O (with about 0·1 M KCN adsorbed per mole). Potentiometric and amperometric titrations carried out between cobalt (II) nitrateand potassium cyanide gave support to the formation of a pentacyanocobaltate (II) but failed to give an insight into the structure of the complex. Polarographic studies, however, were found useful in deciding whether the complex is hexa- or penta-co-ordinated. The freshly prepared complex gave an anodic wave with E1/2−0·35 volt. This is due to pentacyanocobaltate (II), since the anodic wave is suppressed and finally eliminated by oxidising the compound with H2O2. The oxidised product was found to be irreversibly reduced at the dropping mercury electrode (d.m.e.) at a potential of −1·3 volts. That the product is hydroxopentacyano-cobaltate (III) could be seen by getting identical polarograms for the oxidised product and for a sample of the hydroxocompound. From these experiments it has been concluded that the original complex is a hexaco-ordinated compound with the formula K3[Co(CN)4.H2O] and it gets oxidised to K3[Co(CN)5OH] K3[Co(CN)5.OH] and finally to K3[Co(CN)4] on long standing or on boiling. It appears that either five cyanogen radicals are bound to the central atom and the co-ordination number six is maintained by co-ordinating with a water molecule, or a dimer through a water bridge as Open image in new window is formed.