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α,ω-Ditetrazol-5-ylalkanes with 1 to 5 methylene groups in the alkyl fragment display the properties of dibasic heterocyclic NH acids with pK a values lying in the range 3.4-6.1. The pK a values of these compounds are in a linear dependence on the values of the dielectric permeability of the medium, on the chemical shifts of the signals of the endocyclic carbon atom, and of the carbon atom of the α-methylene group in the 13 C NMR spectra.It is known that multibasic carboxylic acids are efficient ligands for binding metal ions into stable complexes [2]. The search for compounds possessing similar or greater complex-forming activity is an urgent problem. The polynuclear heterocyclic systems are extremely promising in this aspect. They are analogs of multibasic carboxylic acids in which the carboxyl groups are replaced by tetrazol-5-yl fragments. The NH-tetrazole ring possesses acidity close to a carboxyl group and is able to form stable complexes with metal ions. Comparison of the complex-forming ability of standard complexones containing carboxyl fragments in their structure, and their tetrazol-5-yl analogs in relation to ions of copper, cobalt, and nickel showed a preference for these heterocyclic derivatives [3]. The complex-forming activity of ligands may also be assessed from their acid-base properties [2].Previously we synthesized polynuclear 2-(tetrazol-5-yl)ethyl compounds and investigated their acidic properties [1,4]. Nonetheless the significant differences in the structure and in the solubility of these compounds does not permit a structure-property or property-property dependence to be reached correctly.In the present work, using 1,3-dipolar cycloaddition of alkylammonium azides to dinitriles of dicarboxylic acids, ditetrazol-5-ylalkanes 1-5 with the number of methylene groups in the aliphatic fragment from 1 to 5 have been synthesized. Their acidic properties have been investigated. The 5,5'-ditetrazole 6 has been considered as a model compound. N N N H N N N N N H 1 n = 1, 2 n = 2, 3 n = 3, 4 n = 4, 5 n = 5, 6 n = 0 1-6 (CH 2 ) n

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