Methylammonium halide
{{Short description|Group of chemical compounds}}
Methylammonium halides are organic halides with a formula of {{chem2|[CH3NH3]+X-}}, where X is F for methylammonium fluoride, Cl for methylammonium chloride, Br for methylammonium bromide, or I for methylammonium iodide. Generally they are white or light colored powders.
Applications
These salts are components of perovskite solar cells, which are being evaluated for commercialization.{{cite journal|author=Li, Hangqian. |date=2016 |title=A modified sequential deposition method for fabrication of perovskite solar cells |journal=Solar Energy |volume=126 |pages=243–251 |doi=10.1016/j.solener.2015.12.045 |bibcode=2016SoEn..126..243L}} The iodide is the most commonly used. Magneto-optical data storage concepts are also being testing based on various ammonium halides.{{cite journal|last1=Náfrádi|first1=Bálint|title=Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3|journal=Nature Communications|date=24 November 2016|volume=7|page=13406|doi=10.1038/ncomms13406|arxiv=1611.08205|pmid=27882917|pmc=5123013|bibcode=2016NatCo...713406N}}
Production
These compounds are usually prepared by combining equimolar amounts of methylamine with the appropriate halide acid. For instance methylammonium iodide is prepared by combining methylamine and hydrogen iodide at 0 °C for 120 minutes followed by evaporation at 60 °C, yielding crystals of methylammonium iodide.{{Citation|title=All-solid-state hybrid solar cells based on a new organometal halide perovskite sensitizer and one-dimensional TiO2 nanowire arrays|first1=Jianhang|last1=Qiu|first2=Yongcai|last2=Qiu|first3=Keyou|last3=Yan|first4=Min|last4=Zhong|first5=Cheng|last5=Mu|first6=He|last6=Yan|first7=Shihe|last7=Yang|journal=Nanoscale|year=2013|volume=5|issue=8|pages=3245–3248|doi=10.1039/C3NR00218G|pmid=23508213|bibcode=2013Nanos...5.3245Q}}
:{{chem2|CH3NH2 + HI → [CH3NH3]I}}
Crystallography
These compounds' crystallography has been the subject of much investigation. J.S. Hendricks published an early paper on them in 1928.{{Citation|first1=J.S.|last1=Hendricks|year=1928|journal=Z. Kristallogr.|title=The crystal structures of the monomethyl ammonium halides|volume=67|issue=1|pages=106–118|doi=10.1524/zkri.1928.67.1.106|s2cid=101288454}} Methylammonium chloride was investigated again in 1946{{Citation|title=The Crystal Structure of Methylammonium Chloride|first1=Edward W.|last1=Hughes|first2=William N.|last2=Lipscomb|journal=J. Am. Chem. Soc.|year=1946|volume=68|issue=10|pages=1970–1975|doi=10.1021/ja01214a029}} and methylammonium bromide in 1961.{{Citation|title=The crystal structure of methylammonium bromide|journal=Acta Crystallogr.|year=1961|volume=14|issue=12|page=1296|last1=Gabe|first1=E.J.|doi=10.1107/S0365110X6100382X|doi-access=free|bibcode=1961AcCry..14.1296G }}