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-inorga nic structural type. The structure is configured in a manner that iodo formamidinium cation layers terminate the three-dimensional cubic pero vskite 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 M I(5) octahedral chains held together by iodoformamidinium cations. The structural formula can be expressed as [NH2C(I)=NH2](2)[NH2C(I)=NH2]M I(5), which is closely related to the recently discovered series of [1 10]-oriented layered perovskites, [NH2C(I)=NH2](2)(CH3NH3)(m)SnmI3m+2. A close comparison of the title compounds with the [110] series is ca rried out. The distorted tin/lead iodine octahedral geometries observe d in the title compounds indicate that the lone pail electrons of tin( II) and lead(II) are stereochemically active, with the lone pair effec t being stronger in the tin compound. The progressive evolution of the lone pair stereoactivity as well as the transitions of structural dim ensionality and transport properties of these [110]-oriented compounds will be discussed.