Example of Disulfide Conformational Change in the Solid State: Preparation, Optical Properties, and X‐ray Studies of a Cystamine‐Based Iodoplombate Hybrid

A novel cystamine‐based hybrid, namely, α‐[{NH 3 (CH 2 ) 2 SS(CH 2 ) 2 NH 3 }PbI 6 ] · 2H 3 O ( 1a ), was prepared under solvothermal conditions. Interestingly, 1a , which is built up from isolated PbI 6 octahedra, can be easily changed into its polymorph, namely, β‐[{NH 3 (CH 2 ) 2 S–S(CH 2 ) 2 NH 3 }PbI 6 ] · 2H 3 O ( 1b ) only by heating it up to 45 °C. According to the results of X‐ray diffraction analyses, the polymorphic phenomenon of 1a and 1b results from a conformational change in the helical diprotonated cystamine cation in the solid state. Both 1a and 1b crystallized in the orthorhombic Pna 2 1 space group. The reversibility of this transformation is proved by single‐crystal X‐ray diffraction and second harmonic generation measurements.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)