Ni(NH3)2(NO3)2—A 3-D Network through Bridging Nitrate Units Isolated from the Thermal Decomposition of Nickel Hexammine Dinitrate

Joachim Breternitz,Agata Godula-Jopek,Duncan Gregory

doi:10.3390/inorganics6020059

Abstract

Nickel nitrate diammine, Ni(NH3)2(NO3)2, can be synthesised from the thermal decomposition of nickel nitrate hexammine, Ni[(NH3)6](NO3)2. The hexammine decomposes in two distinct major stages; the first releases 4 equivalents of ammonia while the second involves the release of NOx, N2, and H2O to yield NiO. The intermediate diammine compound can be isolated following the first deammoniation step or synthesised as a single phase from the hexammine under vacuum. Powder X-ray diffraction (PXD) experiments have allowed the structure of Ni(NH3)2(NO3)2 to be solved for the first time. The compound crystallises in orthorhombic space group Pca21 (a = 11.0628 (5) Å, b = 6.0454 (3) Å, c = 9.3526 (4) Å; Z = 4) and contains 11 non-hydrogen atoms in the asymmetric unit. Fourier transform infrared (FTIR) spectroscopy demonstrates that the bonding in the ammine is consistent with the structure determined by PXD.

Highlights

Ammonia is increasingly being considered as a safe, readily available alternative to hydrogen as an energy vector with an energy density of 13.6 GJ·m−3 [1] and the added advantage of possible storage at high gravimetric and volumetric capacities
We identified nickel salts as a promising group of ammonia storage materials [4]
Nickel hexammine, [Ni(NH3 )6 ](NO3 )2, was prepared using our previously published method, Nickel hexammine, [Ni(NH3)6](NO3)2, was prepared using our previously published method, and its complete characterisation is discussed therein [5]. [Ni(NH3 )6 ](NO3 )2 was studied by and its complete characterisation is discussed therein [5]. [Ni(NH3)6](NO3)2 was studied by simultaneous thermal analysis that combined thermogravimetry (TG), differential thermal analysis simultaneous thermal analysis that combined thermogravimetry (TG), differential thermal analysis (DTA), and evolved gas analysis by mass spectrometry (MS) in the same experiment (Figure 1)

Summary

Introduction

Ammonia is increasingly being considered as a safe, readily available alternative to hydrogen as an energy vector with an energy density of 13.6 GJ·m−3 (at 10 bar) [1] and the added advantage of possible storage at high gravimetric and volumetric capacities. Metal ammine salts are attracting considerable interest as potential ammonia storage materials [2]. Transition metal salts readily form ammoniate complexes (ammines) with variable and controllable ammonia content [3]. The highest capacity (gravimetric density of ammonia) materials—typically hexammines—can be synthesised by the ambient temperature and pressure ammoniation of the respective transition metal salts. We identified nickel salts as a promising group of ammonia storage materials [4]. The thermal decomposition of nickel nitrate hexammine has been discussed previously in the literature [6,7] and the products of the decomposition tentatively identified. We revisit the thermal decomposition of [Ni(NH3 )6 ](NO3 ) and determine the conditions for synthesis of the respective

Methods

Results

Conclusion