Martínez-Casado F J, Ramos-Riesco M, Rodríguez-Cheda J A, Redondo-Yélamos M I, Garrido L, Fernández-Martínez A, García-Barriocanal J, da Silva I, Durán-Olivencia M, Poulain A
MAX IV Laboratory, Lund University, Fotongatan 2, SE-225 94 Lund, Sweden.
Phys Chem Chem Phys. 2017 Jul 5;19(26):17009-17018. doi: 10.1039/c7cp02351k.
The long-chain members of the lead(ii) alkanoate series or soaps, from octanoate to octadecanoate, have been thoroughly characterized by means of XRD, PDF analysis, DSC, FTIR, ssNMR and other techniques, in all their phases and mesophases. The crystal structures at room temperature of all of the members of the series are now solved, showing the existence of two polymorphic forms in the room temperature crystal phase, different to short and long-chain members. Only nonanoate and decanoate present both forms, and this polymorphism is proven to be monotropic. At higher temperature, these compounds present a solid mesophase, defined as rotator, a liquid crystal phase and a liquid phase, all of which have a similar local arrangement. Since some lead(ii) soaps appear as degradation compounds in oil paintings, the solved crystal structures of lead(ii) soaps can now be used as fingerprints for their detection using X-ray diffraction. Pair distribution function analysis on these compounds is very similar in the same phases and mesophases for the different members, showing the same short range order. This observation suggests that this technique could also be used in the detection of these compounds in disordered phases or in the initial stages of formation in paintings.
铅（II）链烷酸酯系列或皂类的长链成员，从辛酸酯到十八烷酸酯，已通过X射线衍射（XRD）、PDF分析、差示扫描量热法（DSC）、傅里叶变换红外光谱法（FTIR）、固体核磁共振（ssNMR）和其他技术，在其所有相和中间相中得到了充分表征。该系列所有成员在室温下的晶体结构现已解析出来，表明在室温晶体相中存在两种多晶型形式，这与短链和长链成员不同。只有壬酸酯和癸酸酯呈现出这两种形式，并且这种多晶型被证明是单向性的。在较高温度下，这些化合物呈现出一种被定义为旋转体的固体中间相、一种液晶相和一种液相，所有这些相都具有相似的局部排列。由于一些铅（II）皂类在油画中表现为降解产物，现已解析出的铅（II）皂类晶体结构现在可以用作通过X射线衍射进行检测的指纹图谱。对于不同成员，在相同相和中间相中对这些化合物进行的对分布函数分析非常相似，显示出相同的短程有序。这一观察结果表明，该技术也可用于检测绘画中无序相或形成初期阶段的这些化合物。
