Halloysite has fascinated investigators ever since it was first discovered that, in obvious contrast to the other kaolin subgroup minerals, namely kaolinite, dickite and nacrite which occur primarily in planar platy or blocky forms, many halloysites adopt an unusual tubular morphology. Spheroidal halloysite is also very well documented especially from soils, but here our focus will be entirely on the tubular form of halloysite, increasingly referred to as halloysite nanotubes or HNTs due to a rapidly expanding range of applications in a wide variety of technologies. Aside from its unusual morphologies, halloysite is also distinct amongst the other kaolin polytypes in that it is hydrated with H2O molecules positioned in the interlayer space between the fundamental 1:1 layer combination of tetrahedral and octahedral sheets that form the basic kaolin structure.Indeed, according to Churchman & Carr (1975) the single most important characteristic that identifies, defines, and distinguishes halloysite as a distinct kaolin mineral is the presence, or evidence of the former presence, of molecules of H2O in the interlayer space. Interlayer H2O in halloysite is exceedingly labile and in response to changing environmental conditions, both naturally in the field or subsequently in the laboratory, it is readily and irreversibly lost. In its fully hydrated state halloysite contains two interlayer H2O molecules accounting for 12.25 wt. % of the molecular formula unit which can be written as Al2Si2O5(OH)4·2H2O. With this full complement of interlayer H2O halloysite has a primary basal spacing, as observed in X-ray diffraction (XRD) patterns, of approximately 10Å. Because the loss of the interlayer H2O is generally not a 3 Published in Clay Minerals V 51,

Thirteen mononuclear, homobinuclear and heterobinuclear transition metal complexes of 4,6-di(2- pyridyl)pyrimidine have been prepared. Assignments of the 1H n.m.r. spectra of the molybdenum(0) and ruthenium(II) complexes were achieved by a combination of one- and two-dimensional n.m.r. techniques, especially 1D-TOCSY. For the ruthenium complexes, electronic absorption spectroscopy and cyclic voltammetry were used to probe the nature of the metal{ligand and, for the binuclear complexes, metal-metal interactions. The complexes have low HOMO−LUMO energy gaps. Meta-metal interactions are shown to be of similar magnitude to those in complexes of the better-studied ligands 2,2′-bipyrimidine and 2,3-di(2-pyridyl)pyrazine.

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ChemInform Abstract Diphosphines, in part for the first time, are prepared in yields between 55 and 67% by an improved procedure heating (CF3)2P-P(CF3)2 and the corresponding diiodoalkane at 130 rc C. These highly π-acidic ligands react with PtCl2(PhCN)2 or cis-Mo(CO)4(piperidine)2 in CHCl3 at 70 or 80 rc C, respectively, to give the complexes (I) or (II). On heating (Ic) in the solid state in vac. the dimer (III) is formed, as confirmed by X-ray crystallography ( P21/n, Z=2).

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