The Al13 polycation is the predominant hydroxy-Al species in partially neutralized solutions. However, the existence of the Al13 species and the factors governing its formation in terrestrial environments still remain obscure. The objective of this study was to investigate the influence of pyrogallol, a common polyphenol in soils, on the formation of Al13 tridecamer. Hydroxy-Al solutions with an OH/Al molar ratio of 2.2 (pH 4.53) at pyrogallol/Al molar ratios of 0, 0.01, 0.05, 0.1 and 0.5 were prepared and mixed with 0.5 M sodium sulfate to form aluminum sulfate precipitation products. The solid-state 27Al nuclear magnetic resonance (NMR) spectra of the precipitates show that the pyrogallol perturbed the formation of Al13 tridecamer species as indicated by the decrease in the intensity of resonance peak, observed at 62.5 ppm, with increase in the pyrogallol/Al molar ratio. The crystallization of the precipitated Al sulfates was also hampered by pyrogallol, resulting in the formation of X-ray non-crystalline products at a pyrogallol/Al molar ratio of 0.50. The absorbance at 465 and 650 nm of the hydroxy-Al-pyrogallol solutions, the C coprecipitated, the electron spin resonance and 13C CPMAS-NMR spectra of the precipitates indicate the concomitant enhanced abiotic humification of pyrogallol by the X-ray amorphous Al species.

Lattice parameters and crystal structures of the synthetic spinels Co3O4, CoCr2O4, and solid solutions in the binary join Co3O4-CoCr2O4, have been determined by powder X-ray diffraction structural refinements. In all these spinels the cation distribution is completely normal at room temperature, and the tetrahedrally coordinated cation site is occupied only by Co2+. The ionic radius of Co2+(tet) increases from 0.556(3) in Co3O4 to 0.599(4) in CoCr2O4. In the spinel structure, the interatomic distance between the tetrahedral cations and oxygen are geometrically independent of those between the octahedral cations and oxygen; thus the variation in effective ionic radii is ascribed to next-nearest neighbour effects, induced by covalent tendencies in the low-spin Co3+-O bond. The results demonstrate that the assumption of constant ionic radii even within an isomorphic group such as the oxide spinels needs to be made with caution.

The structure of K3H(SO4)2 is found to be monoclinic with space group C2/c based on analogy of the powder X-ray diffraction pattern with that of the Rb3H(SO4)2. The lattice parameters are a=14.6984(7), b=5.6840(2), c=9.7834(5) Å, and β=103.004(5)°, Vol=796.39(5); Dx=2.589 gcm−3, Z=4, and I/Icor=1.30.