The thermal decomposition of Ni(H2O)6[B12Cl12] • 6 H2O under X-ray and TG monitoring

The reaction of Ni[CO3] with an aqueous solution of the free acidNi(H2O)(6)[B12Cl12]leads to green single crystals with the compositionNi(H2O)(6)[B12Cl12]center dot 6 H2O . This compound crystallizes in the orthorhombic space group Pnnm with a = 1798.86(9), b = 1312.49(7), c = 1373.63(7) pm for Z = 4. Thermal decomposition studies revealed the possibility for a multi-step dehydration process with the loss of all interstitial and cation-hydrating crystal water molecules. Temperature-dependent X-ray powder diffraction (XRPD) measurements show two characterizable degradation products between 30 and 450 degrees C. Ni(H2O)(6)[B12Cl12]center dot 6 H2O was obtained at 30 degrees C after the loss of all interstitial water molecules as pale green powder with a cubic crystal structure (a = 1700.02(5) pm, Z = 8) and Fm (3) over bar c as space group, displaying a CsCl-type arrangement. The six water molecules of hydration, which coordinate each Ni2+ cation show fourfold disorder. Above 450 degrees C all remaining water molecules have left the sample and the color shifts to yellow indicating the formation of anhydrous Ni[B12Cl12]. This water-free salt crystallizes also in the cubic system (a = 986.71(9) pm, Z = 2), but with Im (3) over bar as space group. In the crystal structure the Ni2+ positions are occupied only by 1/4 and each of them is coordinated by two [B12Cl12](2) anions attached via two faces offering six chlorine atoms in an octahedral shape. (C) 2017 Elsevier B.V. All rights reserved.