The new ligands Na[(p-IC6H4)B(3-Rpz)3] (R = H, Me) have been prepared by converting I2C6H4 to IC6H4SiMe3 with Li(t)Bu and SiMe3Cl, and then to IC6H4BBr2 with BBr3 and subsequent reaction with 3 equiv of (un)substituted pyrazole and 1 equiv of NaO(t)Bu. These new ligands react with FeBr2 to give either purple, low-spin Fe[(p-IC6H4)B(pz)3]2 or colorless, high-spin Fe[(p-IC6H4)B(3-Mepz)3]2. Depending upon the crystallization conditions, Fe[(p-IC6H4)B(3-Mepz)3]2 can exist both as two polymorphs and as a methylene chloride solvate. An examination of these polymorphs by variable-temperature X-ray crystallography, magnetic susceptibility, and Mossbauer spectroscopy has revealed different electronic spin-state crossover properties for each polymorph and yields insight into the influence of crystal packing, independent of other electronic perturbations, on the spin-state crossover. The first polymorph of Fe[(p-IC6H4)B(3-Mepz)3]2 has a highly organized three-dimensional supramolecular structure and does not undergo a spin-state crossover upon cooling to 4 K. The second polymorph of Fe[(p-IC6H4)B(3-Mepz)3]2 has a stacked two-dimensional supramolecular structure, a structure that is clearly less well organized than that of the first polymorph, and undergoes an abrupt iron(II) spin-state crossover from high spin to low spin upon cooling below ca. 130 K. The crystal structure of the methylene chloride solvate of Fe[(p-IC6H4)B(3-Mepz)3]2 has a similar stacked two-dimensional supramolecular structure, but the crystals readily lose the solvate. The resulting desolvate undergoes a gradual spin-state crossover to the low-spin state upon cooling below ca. 235 K. It is clear from a comparison of the structures that the long-range solid-state organization of the molecules, which is controlled by noncovalent supramolecular interactions, has a strong impact upon the spin-state crossover, with the more highly organized structures having lower spin-crossover temperatures and more abrupt spin-crossover behavior.

Cerium oxide solid samples were prepared via precipitation from aqueous solution of hydrous cerium-(III) nitrate in the presence of different percentages of hydrogen peroxide (H 2 O 2 ) as model corrosion inhibiting coatings materials for aluminum alloys. X-ray absorption spectroscopy at the Ce L III -edge was applied for the characterization of crystalline anhydrous CeO 2 , nanocrystalline hydrous CeO 2 , nanocrystalline CeO 2 sample I precipitated in the presence of H 2 O 2 , and an amorphous CeO 2 sample II precipitated at a higher H 2 O 2 concentration. An analysis by X-ray absorption near-edge structure (XANES) for cerium oxides did not indicate a broad variation in cerium valence state in the precipitated samples as compared to anhydrous CeO 2 . Furthermore, XANES analysis revealed a decrease in the intensity of the white line peaks for the precipitated samples relative to those in anhydrous CeO 2 . The EXAFS spectra of the oxides showed that H 2 O 2 reduced the precipitate's particle diameter and bulk crystallinity. Growth in the coordination number of the first, Ce-O, shell was observed with an increased bond distance R Ce-O in hydrous and precipitated CeO 2 samples. However, the coordination numbers of the second, Ce-Ce, and third, Ce-O, shells were reduced in comparison with anhydrous CeO 2 . Increasing concentration of H 2 O 2 during alkaline precipitation of cerium oxides caused increased hydration, corresponding to a reduced outer-shell coordination number and reduced bulk crystallinity but no corresponding change in the cerium valence state.