Solid−Solid Phase Transitions indl-Norvaline Studied by Differential Scanning Calorimetry and Raman Spectroscopy

2010 ◽  
Vol 114 (3) ◽  
pp. 1294-1300 ◽  
Author(s):  
Petros Chatzigeorgiou ◽  
Nikos Papakonstantopoulos ◽  
Nikolitsa Tagaroulia ◽  
Evangelos Pollatos ◽  
Pantelis Xynogalas ◽  
...  
Keyword(s):  
Differential Scanning Calorimetry ◽  
Raman Spectroscopy ◽  
Phase Transitions ◽  
Solid Phase ◽  
Scanning Calorimetry

scholarly journals Formamidinium iodide: crystal structure and phase transitions

2017 ◽  
Vol 73 (4) ◽  
pp. 569-572 ◽  
Author(s):  
Andrey A. Petrov ◽  
Eugene A. Goodilin ◽  
Alexey B. Tarasov ◽  
Vladimir A. Lazarenko ◽  
Pavel V. Dorovatovskii ◽  
...  
Keyword(s):  
Differential Scanning Calorimetry ◽  
Phase Transitions ◽  
Powder Diffraction ◽  
Solid Phase ◽  
Monoclinic Space Group ◽  
Scanning Calorimetry ◽  
Polymorphic Modifications ◽  
Different Temperatures ◽  
Physicochemical Methods ◽  
Hydrogen Bonded

At a temperature of 100 K, CH5N2+·I−(I), crystallizes in the monoclinic space groupP21/c. The formamidinium cation adopts a planar symmetrical structure [the r.m.s. deviation is 0.002 Å, and the C—N bond lengths are 1.301 (7) and 1.309 (8) Å]. The iodide anion does not lie within the cation plane, but deviates from it by 0.643 (10) Å. The cation and anion ofIform a tight ionic pair by a strong N—H...I hydrogen bond. In the crystal ofI, the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1]viastrong N—H...I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour ofIwas studied by different physicochemical methods (thermogravimetry, differential scanning calorimetry and powder diffraction). Differential scanning calorimetry revealed three narrow endothermic peaks at 346, 387 and 525 K, and one broad endothermic peak at ∼605 K. The first and second peaks are related to solid–solid phase transitions, while the third and fourth peaks are attributed to the melting and decomposition ofI. The enthalpies of the phase transitions at 346 and 387 K are estimated as 2.60 and 2.75 kJ mol−1, respectively. The X-ray powder diffraction data collected at different temperatures indicate the existence ofIas the monoclinic (100–346 K), orthorhombic (346–387 K) and cubic (387–525 K) polymorphic modifications.

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