Traditional techniques for the growth of crystals are typically lengthy and are based on the slow over saturation of either solutions or melts. By contrast, the reactions of solids at moderate temperatures and pressures normally lead to the formation of powders of small crystallites. In this paper, we present a new and effective method to grow crystals of surprisingly large sizes (up to ca. 0.05 mm in the largest dimension). We use the reaction of [Ni(H2O)(6)](NO3)(2) with NH3(g) at room temperature to create macro crystals of [Ni(NH3)(6)](NO3)(2). The synthesis proceeds via simple ligand exchange and crystal growth is facilitated in situ via the solvent effect of the released water. The nitrate ammine product was characterised by powder X-ray diffraction (PXD) and Scanning Electron Microscopy (SEM). This reaction is important since it demonstrates that aquo complexes can undergo facile ligand exchange with gaseous ammonia under realistic conditions for ammonia storage. The single crystal structure of [Ni(H2O)(6)] (NO3)(2) was determined for the first time below ambient temperature (at 100 K). The latter result offers 110 evidence to support a previously postulated low temperature phase-transformation at 100 <= T/K <= 295. (C) 2014 Elsevier B.V. All rights reserved.