Evidences of the formation of a tin(IV) complex in citric–citrate buffer solution: A study based on voltammetric, FTIR and ab initio calculations

We studied the Sn(IV)-complex, [Sn(C6H4O7)2]2− formed after anodic dissolution of a tin surface through its passive oxide film in citric–citrate aqueous solution buffer pH 3. Tin-complex was experimentally characterized using infrared spectroscopy while ab initio calculations were made to study its structure and vibrational properties. These calculations gave us a precise knowledge of the normal modes of vibration taking into account that in the complex the molecule comprises a system of two citrate ions that are attached to a central Sn(IV) atom. The coordination about Sn(IV) consists of a distorted octahedral SnO6 where two tridentate citrates are bonding to the central metal. The calculated harmonic vibrational frequencies are consistent with the experimental vibrational spectra. The theoretical calculations of the wavenumbers allowed us to obtain a tentative assignment of the observed spectral features. The nature of the different Sn–O and Sn ← O bonds in the complex and their topological properties were investigated by means of natural bond orbital (NBO) analysis and Bader’s atoms in the molecule (AIM) theory, respectively.