We describe the syntheses of a series of sodium aminodiboranate salts, Na(H 3 B−NR 2 −BH 3 ), with different substituents on nitrogen, including sodium salts of the unsubstituted aminodiboranate, H 3 B−NH 2 −BH 3 − , and of the N-substituted anions H 3 B−NRR′−BH 3 − , where NRR′ = NHMe, NHEt, NH(SiMe 3 ), NEt 2 , N(i-Pr) 2 , N(SiMe 3 ) 2 , NMe(i-Pr), NMe(t-Bu), NMe-(SiMe 3 ), and the pyrrolidide and piperidide derivatives NC 4 H 8 , NC 5 H 10 , and NC 5 H 8 -cis-2,6-Me 2 . The compounds have been characterized by 1 H and 11 B NMR spectroscopy and IR spectroscopy; crystallographic studies have been carried out for the unsolvated N,N-dimethylaminodiboranate salt Na-(H 3 B−NMe 2 −BH 3 ) and several sodium aminodiboranate salts in which the sodium ions are solvated with ethers (dioxane, diglyme, tetrahydrofuran, and 12-crown-4) or amines (N,N,N′,N′tetramethylethylenediamine). One of the structures contains a rare example of an ether ligand in which one oxygen atom bridges between two metal ions. General structural and spectroscopic trends as a function of the substituents on nitrogen are discussed.

Several dialkyltriazenide complexes of the lanthanide elements neodymium, europium, and erbium have been prepared; these include the homoleptic complex Er(Bu t N 3 Bu t ) 3 , the tetrahydrofuran monoadducts Ln(Bu t N 3 Bu t ) 3 (THF) where Ln = Nd or Eu, and the lithium salts [Li(THF)][Ln(MeN 3 Bu t ) 4 ] where Ln = Eu or Er. Crystal structures, nuclear magnetic resonance data, and infrared data are reported for all complexes. The di-tert-butyltriazenide complexes are thermally stable, sublime at reasonably low temperatures, and show smooth volatilization without decomposition, which make them potentially useful in lanthanide separation processes and as chemical vapor deposition precursors for lanthanide nitrides and other phases.

The magnesium N,N-dimethylaminodiboranate compound Mg[(BH3)2NMe2]2, the most volatile compound of magnesium known, serves as an excellent chemical vapor deposition (CVD) precursor for the growth of thin films such as the dielectric material MgO. To explore how the thermal stability and physical properties of magnesium aminodiboranates depend on the steric and electronic properties of the nitrogen-bound substituents, we have made a series of analogues of Mg[(BH3)2NMe2]2, in which one of the two methyl substituents on nitrogen is replaced with an ethyl, iso-propyl, or tert-butyl group. In the crystal structure of Mg[(BH3)2NMe(t-Bu)]2, the magnesium center is coordinated to two chelating (BH3)2NMe(t-Bu) ligands, each of which binds in a κ2,κ2 fashion so that the magnesium center forms eight Mg–H contacts. Unlike Mg[(BH3)2NMe2]2, however, which has a linear N···Mg···N angle and is an isolated molecule in the solid state, the N···Mg···N angle in Mg[(BH3)2NMe(t-Bu)]2 is distinctly nonlinear (149.9°) because hydrogen atoms of BH3 groups of nearby molecules form two additional Mg–H contacts with the magnesium center. When the complexes are heated in toluene solution, the (BH3)2NMeR– groups reversibly undergo B–N bond cleavage (with concomitant migration of a hydrogen atom) to release the aminoborane BH2NMeR and form magnesium borohydride, Mg(BH4)2. For the methyl, ethyl, and iso-propyl derivatives, the equilibrium strongly favors Mg[(BH3)2NMeR]2. In contrast, for the tert-butyl derivative, the equilibrium strongly favors BH2NMe(t-Bu) and Mg(BH4)2. The results suggest that more strongly electron-donating groups slightly strengthen the B–N bonds and disfavor B–N bond cleavage, provided that the groups are not too large. In contrast, sterically bulky ligands disfavor B–N bond reformation, thus promoting the dissociative equilibrium that involves B–N bond cleavage. Interestingly, the rates at which the complexes approach equilibrium depend only weakly on the nature of the R group, at least within the series studied. These findings are relevant to the potential use of magnesium aminodiboranates as CVD precursors to the superconducting phase MgB2.

This paper demonstrates the fabrication of nanometer-scale metal contacts on individual graphene nanoribbons (GNRs) and the use of these contacts to control the electronic character of the GNRs. We demonstrate the use of a low-voltage direct-write STM-based process to pattern sub-5 nm metallic hafnium diboride (HfB2) contacts directly on top of single GNRs in an ultrahigh-vacuum scanning tunneling microscope (UHV-STM), with all the fabrication performed on a technologically relevant semiconductor silicon substrate. Scanning tunneling spectroscopy (STS) data not only verify the expected metallic and semiconducting character of the contacts and GNR, respectively, but also show induced band bending and p–n junction formation in the GNR due to the metal–GNR work function difference. Contact engineering with different work function metals obviates the need to create GNRs with different characteristics by complex chemical doping. This is a demonstration of the successful fabrication of precise metal contacts and local p–n junction formation on single GNRs.