Octahedral Core Research Articles

Synthesis and coordinating properties of the anionic tridentate ligand, methyl tris(1-pyrazolyl)gallate, [MeGa(N2C3H3)3]−. X-ray crystal structure of [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5)

The anionic tridentate ligand, [MeGa(N2C3H3)3]−, has been characterized and its coordinating properties studied. It acts as a six-electron chelating ligand to divalent transition metal ions giving complexes of the type, [MeGa(N2C3H3)3]2M (M = Mn, Fe, Co, Ni, Cu, Zn), believed to possess an octahedral MN6 core. The ligand also forms numerous carbonyl complexes and its coordinating ability in Mo, W, and Mn carbonyl derivatives is compared with that of similar boron ligands and the η5-C5H5 ligand. From ir measurements and bond length data it appears that the [MeGa(N2C3H3)3]− ligand is superior in creating an electron-rich transition metal centre, and it also affords greater steric protection for the central metal. The expected tridentate chelating nature of the new ligand has been demonstrated through a crystal structure determination of the complex [MeGa(N2C3H3)3]Mo(CO)2(η3-C3H5). Crystals of this complex are tetragonal, a = 26.217(3), c = 10.723(2) Å, Z = 16, space group I41/a. The structure was solved by Patterson and Fourier syntheses and was refined by full-matrix least-squares procedures to a final R of 0.030 and Rw of 0.031 for 2582 reflections with I ≥ 3σ(I).

On the origin of the rounded dodecahedral habit of natural diamond

The morphology of natural rounded rhombic dodecahedral diamonds has been studied optically and by scanning electron microscopy, and their internal structures have been investigated by X-ray topographic techniques. That this rounded habit arises from dissolution of a sharp-edged octahedral growth form is indicated both by theoretical considerations and experimental evidence. The hypothesis that these diamonds grew throughout their history as rounded rhombic dodecahedra is directly refuted by the X-ray topographic studies. The information on dislocation distribution revealed by X-ray topographs also provides strong evidence against a current variant of the growth hypothesis, that the rounded rhombic dodecahedral habit developed upon an octahedral core. The manner by which dissolution of surfaces of rounded dodecahedral diamonds proceeds can be described on an atomic scale by motion of kinks along stable monomolecular steps parallel to 〈110〉 directions. It is shown that this process leads to the development of edges parallel to the minor diagonals of the rhombic surfaces, in accord with observation.

Studies on natural diamonds of the dodecahedral form

Abstract Natural diamonds of the dodecahedral form have been studied. Contrary to the widely held belief that the dodecahedral form is derived from the octahedral form by dissolution, it is shown that the process is one of growth. Setting the crystal so that the (110), (101) and (011) faces become equally inclined to the line of the microscope, the three faces could be simultaneously seen and studied. This has led to the discovery that the striatums of dodecahedral faces previously called ‘ruts’(channels) are the spaces between successive layers in the (111) plane, a finding confirmed by the discovery of trigons in the narrow spacings between them. It is shown with examples how straight-edged triangular layers piling up on an octahedral core would produce an ideal sharp-edged dodecahedron and how curved polygonal layers produce the rounded dodecahedron. Boat-shaped features, usually seen on dodecahedral faces, have been shown to be small strips of layers containing trigons. The experimental observation th...