Infrared and XAFS study on structure and transition behavior of zinc stearate

Structure and transition behavior of zinc(II) stearate crystal were investigated by infrared and XAFS spectroscopies. Structure of zinc stearate at room temperature was estimated as follows. From XAFS analysis, the coordination number of the carboxylate groups around the zinc atom was evaluated as 4 and the Zn-O distance as 1.95 A. Based on the infrared spectrum and a normal mode analysis, the conformation of the alkyl chain was confirmed as all-trans and the sub-cell packing was considered as parallel type, and also the coordination form of the carboxylate groups was determined as bridging bidentate type. As increasing temperature, zinc stearate has a solid liquid phase transition at 130 degrees C. At the transition, the alkyl chains goes into liquid like state as reported by Mesubi but the coordination structure was confirmed to be maintained.