Synthesis, Crystal Structure, and Optical Properties of (CH3NH3)2CoX4 (X = Cl, Br, I, Cl0.5Br0.5, Cl0.5I0.5, Br0.5I0.5)

Abstract

AbstractThe reaction of methylammonium halides and cobalt halides yielded the organic‐inorganic hybrid compounds of general formula (CH3NH3)2CoX4. By varying the different halides, we were able to synthesize the whole row from Cl to I as well as some mixed halides compounds and to determinate the crystal structures. (CH3NH3)2CoX4 (X = Cl, Br, Cl0.5Br0.5, Br0.5I0.5) crystallize isotypic to (CH3NH3)2HgCl4 in space group P21/c with Z = 4 [X = Cl: a = 7.6483(9), b = 12.6885(18), c = 10.8752(12) Å, β = 96.639(9)°; X = Cl0.5Br0.5: a = 7.8271(9), b = 12.9543(9), c = 11.1007(11) Å, β = 96.320(8)°; X = Br: a = 7.9782(2), b = 13.1673(2), c = 11.2602(2) Å, β = 96.3260(10)° and X = Br0.5I0.5: a = 8.2435(12), b = 13.645(2), c = 11.5856(18) Å, β = 95.54(2)°]. The mixed halides show a statistic distribution in both cases. In (CH3NH3)2CoCl2I2 an ordered variant is realized representing a new structure type [C2/m, Z = 4, a = 18.808(4), b = 7.3604(7), c = 10.4109(17) Å, β = 120.364(13)°]. (CH3NH3)2CoI4 crystallizes again isotypic to the respective mercury compound [(CH3NH3)2HgCl4] [Pbca, Z = 8, a = 10.9265(5), b = 12.1552(5), c = 20.9588(9) Å]. All structures are build up by inorganic tetrahedral [CoX4]2– anions and organic (CH3NH4)+ cations. Additionally the Raman spectra as well as the optical reflectance spectra are discussed.