New Data on the Structures of Sc(III) and Fe(III) Dipivaloylmethanates and Their Solid Solutions in the Range of 90-300 K

The X-ray diffraction analysis of Sc(thd)3 single crystals (thd is 2,2,6,6-tetramethylheptane-2,4-dionate) and Sc(thd)3 and Fe(thd)3 solid solutions is performed in the temperature range of 90-300 K. The new crystalline modification of Sc(thd)3 is found in the range of 90-170 K (space group $P\bar{1}$ ) and a phase transition is detected at 170 K. The DSC analysis of the Sc(thd)3 samples reveals that a smeared thermal anomaly with the signal maximum at Tmax = 176.4 K corresponds to the phase transition with a change in the space group. It is demonstrated that in comparison with Fe(thd)3, the phase transition occurs in Sc(thd)3 at a lower temperature, and the second phase transition is not observed up to 90 K. In the study of the crystals of Sc(thd)3:Fe(thd)3 solid solutions with component ratios of 1:7, 1:3, 1:1, and 3:1 at different temperatures it is established that the phase transition temperature increases with an increase in the Fe fraction in the crystal.