The reaction of CH₃NH₂with SnX₂, CH₃NH₃SnX₃(X=Cl, Br, I), and BiI₃– The first Sn(II)‐Ammine complexes as intermediates

Abstract

Abstract In order to understand the “molten salt approach” for CH 3 NH 3 PbI 3 , we have investigated the interaction of gaseous CH 3 NH 2 with Pb X 2 ( X =Cl, Br, I) and MAPb X 3 (MA=CH 3 NH 3 + ; X =Cl, Br, I) and characterised the first ammine complexes of Pb(II). In continuation, we have extended our work to the corresponding Sn(II) halides, i. e. Sn X 2 ( X =Cl, Br, I) and MASn X 3 ( X =Cl, Br, I). With X =iodine we have obtained cubic [Sn(CH 3 NH 2 ) 6 ]I 2 , which is isotypic to the lead compounds with X =I and Br showing a close similarity to the K 2 PtCl 6 type due to the octahedra [Sn(CH 3 NH 2 ) 6 ] 2+ . Release of CH 3 NH 2 yields [Sn(CH 3 NH 2 ) 4 I]I. Here, Sn 2+ is fivefold coordinated by 4 CH 3 NH 2 ligands and one I − as a square pyramid with the I − in an equatorial position. Charge neutrality is achieved by a second I − anion with a significant longer distance of 4.29 Å, completing the square pyramid to a distorted octahedron. With X =Br and Cl, only one compound forms, Sn(CH 3 NH 2 ) 5 Br 2 and Sn(CH 3 NH 2 ) 5 Cl 2 , respectively. Both structures are isotypic and crystallize in an orthorhombic structure with square‐pyramidal [Sn(CH 3 NH 2 ) 5 ] 2+ units. For all representatives with mixed ligands, the interaction with X − is significantly weaker than with CH 3 NH 2 . H‐bridges N−H⋅⋅⋅ X contribute to the interaction between the Sn(CH 3 NH 2 ) 4 X 2 units. All compounds show high sensitivity to moisture and limited thermal stability. They decompose in air to CH 3 NH 3 X and a white amorphous residue, probably Sn(OH) X . The reaction of CH 3 NH 2 with BiI 3 results in (CH 3 NH 3 ) 4 (CH 3 NH 2 )BiI 7 according to traces of moisture.