Structural Analysis of Tanning Metallic Heterocomplexes and Testing their Tanning Properties

Knowing the structure of tanning metallic heterocomplexes is closely linked to their chemical properties in relation to stability in various environments specific for natural leather tanning and to their ionic nature which influences their penetration in the dermis of natural leathers. This chapter deals with specific analyses for coordination complexes, for the purpose of anticipating the behaviour of tanning metallic heterocomplexes upon the interaction with natural leather. IR and electron spectroscopy have enabled to identify organic ligands, the polynuclearity of complexes by means of sulphate or hydroxyl anions, the metal-oxygen-metal interactions and have eliminated the hypothesis of direct metal-metal interactions. Electron spin resonance spectroscopy allowed identification of structures in predominantly octahedral environments with rare insertions of tetrahedral environments, which provides steric stability to heterocomplex structures. SEM-EDAX analysis determines the existence of tanning metals used and morphological particularities at microscopic level. Analysis of ionic components explains the more pregnant anionic nature compared to that of the best known tanning agent, basic chromium salt, and therefore, the improved efficiency of using tanning metallic heterocomplexes in natural leather tanning.

Keywords: IR spectroscopy, Electron spectroscopy, Electron spin resonance spectroscopy, SEM-EDAX, Ion exchange chromatography, Tanning properties.