No abstract

A simple and efficient way to synthesize unsolvated sodium octahydrotriborate has been developed. This method avoids the use of dangerous starting materials and significantly simplifies the reaction setup, thus enabling convenient large-scale synthesis. The structure of the unsolvated compound has been determined through powder X-ray diffraction.

MgB12H12 is an intermediate in the hydrogen desorption and sorption processes of magnesium borohydride, which is an important candidate material for hydrogen storage. It is thus highly desirable to synthesize anhydrous MgB12H12 in order to study its properties and its role in the hydrogenation and dehydrogenation of magnesium borohydride. Contrary to the literature claim, we find that anhydrous MgB12H12 cannot be obtained from simple thermal decomposition of Mg(H2O)6B12H12·6H2O (1) which has different thermal decomposition behavior from that of most hydrated alkali and alkaline earth salts of dodecahydrododecaborates. Thermal decomposition of 1 involves both dehydration and dehydrogenation processes in three steps, resulting in the formation of complexes Mg(H2O)6B12H12 (2), Mg(H2O)3B12H12 (3), and Mg(μ-OH) x B12H12−x (4) that were characterized by XRD, IR, and 11B NMR. Dehydrogenation was also confirmed by both the generation of hydrogen observed in TPD-MS spectra and the formation of polyhydroxylated complexes.

The dinucleating ligand, 2,6-bis{[(2-(2-pyridyl)ethyl)(2-pyridylmethyl)-amino]-methyl}-4-methylphenol) (L1OH) reacts with Mn(ClO4)2.6H2O to form the dinuclear complex [Mn2(II,II)(L1O)(mu-OOCCH3)2]ClO4 (1). The electrolytic oxidation of 1 at 0.7 V (vs Ag/AgCl) produces the mixed valent complex [Mn2(II,III)(L1O)(mu-OOCCH3)2](ClO4)2 (1ox) quantitatively, while electrolysis at 0.20 V converts 1ox back to 1. X-ray crystallographic structures show that both 1 and 1ox are dinuclear complexes in which the two manganese ions are each in distorted octahedral coordination environments bridged by the phenoxo oxygen and two acetate ions. The structural changes that occur upon the oxidation 1 to 1ox suggest an extended pi-bonding system involving the phenoxo ring C-O(phenoxo)-Mn(II)-N(pyridyl) chain. In addition, as 1 is oxidized to 1ox, the rearrangements in the coordination sphere resulting from the oxidation of one Mn(II) ion to Mn(III) are transmitted via the bridging Mn-O(phenoxo) bonds and cause structural changes that render the site of the second manganese ion unfit for the +3 state and hence unstable to reduction. Thus the electrolytic oxidation of 1ox in acetonitrile at 1.20 V takes up slightly greater than 1 F of charge/mol of 1ox, but the starting complex, 1ox, is recovered, showing the instability of the Mn2(III,III) state that is formed with respect to reduction to 1ox. Variable-temperature magnetic susceptibility measurements of 1 and 1ox over the temperature range from 1.8 to 300 K can be modeled with magnetic coupling constants J = -4.3 and -4.1 cm(-1), respectively showing the weak antiferromagnetic coupling between the two manganese ions in each dinuclear complex, which is commonly observed among similar phenoxo- and bis-1,3-carboxylato-bridged dinuclear Mn2(II,II) and Mn2(II,III) complexes.