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Formamidinium iodide: crystal structure and phase transitions

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ABSTRACT

Iiiiii: At a temperature of 100 K, CH5N2+·I− (), crystallizes in the monoclinic space group P21/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 of form a tight ionic pair by a strong N—H⋯I hydrogen bond. In the crystal of , the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1] via strong N—H⋯I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour of was 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 of . 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 of as the monoclinic (100–346 K), ortho­rhom­bic (346–387 K) and cubic (387–525 K) polymorphic modifications.

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X-ray powder diffraction data for I at different temperatures.
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fig3: X-ray powder diffraction data for I at different temperatures.

Mentions: The X-ray powder diffraction data collected at different temperatures confirm the existence of different phases (Fig. 3 ▸). At low temperatures, salt I exists in a monoclinic phase and exhibits a significant change of the parameters with a rise in temperature (100 → 195 → 293 K, Fig. 3 ▸). A phase existing at 358 K is indexed in an ortho­rhom­bic crystal system [a = 7.3915 (8) Å, b = 6.3358 (8) Å, c = 5.2391 (9) Å; M(20) = 25, F(20) = 45]. Another high-temperature phase is cubic, exhibiting only a few reflections at 400 K [a = 5.0571 (5) Å; M(13) = 126, F(13) = 109]. It seems to be a plastic phase similar to a plastic phase for methyl­ammonium iodide (Ishida et al., 1995 ▸; Yamamuro et al., 1992 ▸).


Formamidinium iodide: crystal structure and phase transitions
X-ray powder diffraction data for I at different temperatures.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382624&req=5

fig3: X-ray powder diffraction data for I at different temperatures.
Mentions: The X-ray powder diffraction data collected at different temperatures confirm the existence of different phases (Fig. 3 ▸). At low temperatures, salt I exists in a monoclinic phase and exhibits a significant change of the parameters with a rise in temperature (100 → 195 → 293 K, Fig. 3 ▸). A phase existing at 358 K is indexed in an ortho­rhom­bic crystal system [a = 7.3915 (8) Å, b = 6.3358 (8) Å, c = 5.2391 (9) Å; M(20) = 25, F(20) = 45]. Another high-temperature phase is cubic, exhibiting only a few reflections at 400 K [a = 5.0571 (5) Å; M(13) = 126, F(13) = 109]. It seems to be a plastic phase similar to a plastic phase for methyl­ammonium iodide (Ishida et al., 1995 ▸; Yamamuro et al., 1992 ▸).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Iiiiii: At a temperature of 100 K, CH5N2+·I− (), crystallizes in the monoclinic space group P21/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 of form a tight ionic pair by a strong N—H⋯I hydrogen bond. In the crystal of , the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1] via strong N—H⋯I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour of was 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 of . 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 of as the monoclinic (100–346 K), ortho­rhom­bic (346–387 K) and cubic (387–525 K) polymorphic modifications.

No MeSH data available.