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

The reaction of Ni[CO 3 ] with an aqueous solution of the free acid (H 3 O) 2 [B 12 Cl 12 ] leads to green single crystals with the composition Ni(H 2 O) 6 [B 12 Cl 12 ] · 6 H 2 O. 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 °C. Ni(H 2 O) 6 [B 12 Cl 12 ] was obtained at 30 °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 ¯ c as space group, displaying a CsCl-type arrangement. The six water molecules of hydration, which coordinate each Ni 2+ cation show fourfold disorder. Above 450 °C all remaining water molecules have left the sample and the color shifts to yellow indicating the formation of anhydrous Ni[B 12 Cl 12 ]. This water-free salt crystallizes also in the cubic system ( a = 986.71(9) pm, Z = 2), but with Im 3 ¯ as space group. In the crystal structure the Ni 2+ positions are occupied only by 1 / 4 and each of them is coordinated by two [B 12 Cl 12 ] 2− anions attached via two faces offering six chlorine atoms in an octahedral shape. [ABSTRACT FROM AUTHOR]