SYNTHESIS AND CHARACTERIZATION OF [NH2C(I)=NH2](3)MI(5) (M=SN, PB) - STEREOCHEMICAL ACTIVITY IN DIVALENT TIN AND LEAD HALIDES CONTAINING SINGLE [110] PEROVSKITE SHEETS

Isotypic crystals with the composition [NH2C(I)=NH2]MI(5) (M = Sn, Pb) were grown from an aqueous solution. The compounds crystallize in the monoclinic space group P2(1)/c with an unusual layered organic-inorganic structural type. The structure is configured in a manner that iodoformamidinium cation layers terminate the three-dimensional cubic perovskite structure along the [110] direction, resulting in single [110]-oriented [NH2C(I)=NH2]-MI(3) (M = Sn, Pb) perovskite sheets, which are actually characterized by infinite, corner-sharing, one-dimensional MI(5) octahedral chains held together by iodoformamidinium cations. The structural formula can be expressed as [NH2C(I)=NH2](2)[NH2C(I)=NH2]MI(5), which is closely related to the recently discovered series of [110]-oriented layered perovskites, [NH2C(I)=NH2](2)(CH3NH3)(m)SnmI3m+2. A close comparison of the title compounds with the [110] series is carried out. The distorted tin/lead iodine octahedral geometries observed in the title compounds indicate that the lone pail electrons of tin(II) and lead(II) are stereochemically active, with the lone pair effect being stronger in the tin compound. The progressive evolution of the lone pair stereoactivity as well as the transitions of structural dimensionality and transport properties of these [110]-oriented compounds will be discussed.