Phase Transitions and Water Dynamics of [Co(H₂O)₆](ClO₄)₂ and [Mn(H₂O)₆](BF₄)₂ Studied by Neutron Scattering Methods

Abstract

Inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) patterns, registered for [Co(H20 ) 6](C104)2 at 18 -270 K and for [Mn(H20 ) 6](BF4)2 at 18 -230 K, provided evidence that these crystals possess three solid phases in these ranges of temperatures. In both compounds the phase transition occurring at T C3 is connected with a change of the crystal structure, and that occurring at T C2 with a change in the rate of the reorientational motions of H20 ligands.

Raman light scattering, infrared absorption and DSC studies of the phase transition and vibrational and reorientational dynamics of H2O ligands and ClO4– anions in [Ba(H2O)3](ClO4)2

“…It should be pointed out that the phase polymorphism of [Ba(H 2 O) 3 ](ClO 4 ) 2 is quite different than those observed in the case we investigated earlier: [Ca(H 2 O) 4 ](ClO 4 ) 2 , [Mg(H 2 O) 6 ](ClO 4 ) 2 , and [Ni(H 2 O) 6 ](ClO 4 ) 2 compounds . All of these aquametal(II) perchlorates, with different coordination number (3,4,6), posses several solid–solid phase transitions.…”

“…In addition, we would like to compare the results obtained for [Ba(H 2 O) 3 ](ClO 4 ) 2 with those for previously studied by us, compounds: [Ca(H 2 O) 4 ](ClO 4 ) 2 , [Mg(H 2 O) 6 ](ClO 4 ) 2 , and [Ni(H 2 O) 6 ](ClO 4 ) 2 . It was thought interesting to see whether a compound of the same type, but with different central cation (Ba 2+ ), different coordination number (3) and different crystal structure, posses a phase polymorphism and molecular dynamics similar to those for the compounds mentioned above.…”

“…Compounds of the type: [M(H 2 O) x ](ClO 4 ) 2 (where x = 4–6) are particularly interesting molecular materials because of the occurrence of different reorientational motions of the complex cations, H 2 O ligands and ClO 4 – anions. Rich phase polymorphism of several compounds of this type (with M = Ni, Mg, Mn, Co, Fe, Cr, and Ca) have been investigated . It is quite interesting to extend similar investigations also for the coordination compound with central metal cation from the second group of the periodic table of elements.…”

13 Manganese, technetium and rhenium

“…39 The value of inelastic incoherent nuclear scattering studies is shown by their use with neutron powder diffraction in detecting two phase changes in [Mn(H 2 O) 6 ][BF 4 ] 2 over the 18-230 K temperature range, these changes being associated with a crystal structure change and the reorientation of water ligands. 40 Crystal structure studies of six tetrahedral Mn() complexes that exhibit triboluminescence, such as [MnI 2 (AsPh 3 ) 2 ], confirm that this property is correlated with the crystals being noncentrosymmetric. 41 A new class of layered Mn() phosphites, [C n H 2nϩ6 N 2 ][Mn 3 (HPO 3 ) 4 ] (n = 3 to 8) has been prepared by the hydrothermal reactions of the alkyldiamines with H 3 PO 3 and [MnCl 2 (H 2 O) 4 ].…”