Metal borohydrides are potential materials for solid state hydrogen due to their high gravimetric and volumetric hydrogen densities. Among them, Ca(BH₄)₂ is particularly interesting because of the predicted suitable thermodynamic properties. In this work, we investigate a new synthesis route using high pressure reactive ball milling. Starting from CaH₂ and CaB₆ with a TiCl₃ or TiF₃ as additive, a reaction yield of 19% is obtained after 24 h milling at room temperature and 140 bar H₂. The presence of Ca(BH₄)₂ is confirmed by the presence of the stretching mode of the [BH₄]^- group in the infrared spectra of the as-milled samples. Using in-situ XRD, we observe the recrystallisation of a poorly crystallised Ca(BH₄)₂ phase present after milling. The reversible decomposition/formation of Ca(BH₄)₂ is obtained with higher yield (57%) using higher temperature and TiF₃ as additive but not with TiCl₃ despite its similar electronic structure. The differences observed using different additives and the influence of the anion are discussed.

We describe the preparation of a helicate containing four closely spaced, linearly arrayed copper(I) ions. This product may be prepared either directly by mixing copper(I) with a set of precursor amine and aldehyde subcomponents, or indirectly through the dimerization of a dicopper(I) helicate upon addition of 1,2-phenylenediamine. A notable feature of this helicate is that its length is not limited by the lengths of its precursor subcomponents: each of the two ligands wrapped around the four copper(I) centers contains one diamine, two dialdehyde, and two monoamine residues. This work thus paves the way for the preparation of longer oligo- and polymeric structures. DFT calculations and electrochemical measurements indicate a high degree of electronic delocalization among the metal ions forming the cores of the structures described herein, which may therefore be described as "molecular wires".