Organophosphorus coupling agents bearing permanently charged functional groups (either cationic quaternary ammonium or anionic sulfonates) were synthesized and used for the modification of zirconia nanoparticles with a diameter <10 nm. Surface functionalization was confirmed by FTIR and solid-state NMR spectroscopy. Surface coverages up to 2.3−2.4 molecules/nm 2 were achieved for modification with these charged coupling agents. The pH-dependent charge measurements of homogeneously modified particles showed stable surface charges over a wide range of pH for both ammonium-and sulfonate-functionalized particles. Surface charge measurements of particles cofunctionalized with charged coupling molecules and uncharged methyl phosphonic acid revealed a decreasing charge density with increasing amount of uncharged coupling agent. Thus, an adjustment of charges by co-functionalization was obtained on the particle surface. The thus-formed surface-charged colloids were used in a second step for electrostatic-driven aggregation phenomena necessary for layer-by-layer processes. Sulfonate-modified negatively charged SiO 2 submicrometer particles of 506 nm in diameter were decorated with ammonium-modified ZrO 2 nanoparticles. In addition, a layer-by-layer deposition of alternating charge-modified TiO 2 nanoparticles was proven by optical spectroscopy. Due to the broad applicability of organophosphorus coupling agents for surface modification, particularly for transition-metal oxides, the shown route represents a general method for the creation of almost pH-independent charges on the surface of nanoparticles.

Supramolecular interactions represent versatile, reversible, and intrinsic mechanisms for bond formation after the failure of materials. Ionic interactions excel through high flexibility and binding strength. In this study, ionic interactions...

Liu et al. [Chin. J. Struct. Chem. (1996). 15, 371–373] reported the structure of 6-hydroxy-1,4-diazepane di(hydrogen bromide), C5H12N2O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6-hydroxy-1,4-diazepane-1,4-diium dibromide, C5H14N2O2+·2Br−, measured at 142 K, crystallized in the orthorhombic space group P212121. The structure displays O—H...Br and N—H...Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly-bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br− anions and a protonated substrate such as an amine, is addressed.