Phase Polymorphism of [Ni(DMSO)₆](ClO₄)₂ Studied by Differential Scanning Calorimetry

Abstract

Six solid phases of [Ni(DMSO) 6 ](ClO 4 ) 2 have been detected by differential scanning calorimetry (DSC). The five phase transitions were detected between the following solid phases: metastable KIII ↔ undercooled K0 at T C5 = 326 K, stable KIb → stable KIa at T C4 = 350 K, metastable KII ↔ undercooled KI at T C3 = 353 K, stable KIa → stable KI at T C2 = 365 K and stable KI → stable K0 at T C1 = 380 K. At T m2 = 459 K the title compound partially dissolves in DMSO, which arises from the decomposition of [Ni(DMSO) 6 ](ClO 4 ) 2 to [Ni(DMSO) 5 ](ClO 4 ) 2 , and at T m1 = 526 K created in this way a substance which completely melts. From the entropy changes at the melting point and at phase transitions it can be concluded that the phases K0 and undercooled K0 are orientationally dynamically disordered crystals. The stable phases KI, KIa, KIb and the metastable phases KII and KIII are more or less ordered solids.

Thermal analysis, phase transitions and molecular reorientations in [Fe(OS(CH3)2)6](ClO4)2

“…Preparation procedure of a polycrystalline sample was analogical to the synthesis of the analogous compounds with DMSO ligands [1][2][3][4][5][6][7]. Chemical composition of the synthesized sample was analysed by determination of percentage content of carbon, hydrogen and sulphur using an EURO EA 3000 elemental analyser with the accuracy of ±0.3%.…”

“…The results have not shown any significant changes in the character of the DSC curves, so we will present here only the results obtained for sample A. The measurements were performed with different scanning rate and also with initial and final heating and cooling conditions, in order to check whether synthesized compound can create such metastable phases like did other previously studied compounds of [M(OS(CH 3 ) 2 ) 6 ](ClO 4 ) 2 type [1][2][3][4][5][6][7]. Figure 3 presents the temperature dependences of the heat flow (DSC curves) obtained on heating (upper curve) and on cooling (lower curve) of the sample A in the temperature range 100-385 K. One distinct anomaly was registered on each of these two DSC curves at: Table 1.…”

“…The rich and diverse polymorphism of compounds of the type: [M(DMSO) 6 ](ClO 4 ) 2 (where M = Cd, Co, Mn, Zn, Ni, Mg, Sr and DMSO = (CH 3 ) 2 SO) was the subject of our interest since 2003 [1][2][3][4][5][6][7]. We have found that these substances possess both orientationally ordered and highly disordered crystal phases.…”