© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim2-R-2H-Tetrazol-5-ylacetic acids (abbreviated as 2-R-taa; R = Me, iPr, tBu) react with K2[PtCl4] in 1 m HCl in H2O at r.t. furnishing trans-platinum(II) complexes trans-[PtCl2(2-R-taa)2] (1–3), whereas cis-isomeric species cis-[PtCl2(2-R-taa)2] (R = iPr, 4; tBu, 5) are isolated at lower temperature (4–6 °C). In the presence of EtOH in the reaction mixture, esterification of the tetrazol-5-ylacetoxy group of 2-tBu-taa leads to trans-[PtCl2(ethyl 2-tert-butyl-2H-tetrazol-5-ylacetate)2] (6). Complexes 1–6 were characterized by elemental analyses (CHN), HRESI+-MS, 1H, 13C{1H}, 195Pt{1H} NMR and IR spectroscopy, differential scanning calorimetry/thermogravimetry (DSC/TG), and X-ray diffraction (for 1·H2O, 2, 3·2H2O, 4, 5·2H2O, and 6). The generation of the tetrazole-based complexes in solution (1 m DCl in D2O, 25 °C) was studied by 1H NMR spectroscopy and HPLC-MS. The obtained data indicate the initial formation of anionic [PtCl3(2-R-taa)]– complexes that are subseq