**1. Introduction**

Structurally well-defined supramolecular architectures produced by the formation of ordered crystalline materials have attracted considerable attention in recent years due to their different novel chemical properties and their possible new applications. Coordination chemistry has played a central role in the blossoming of this fast-evolving field. In this way, metallosupramolecular chemistry, which concerns non-covalent interactions between discrete or polymeric coordination compounds, has become an interdisciplinary research area that has provided insights into and spurred developments across biology, chemistry, nanotechnology, materials science and physics [1].

Amongst the metallosupramolecular compounds, supramolecular metal–organic frameworks (SMOFs) are materials that can be considered as analogs to metal–organic frameworks (MOFs) in the sense that some coordination bonds are replaced by hydrogen bonds as directional interactions to build the final crystal. In SMOFs, the coordination bonds are released from guiding the crystal structure and supramolecular interactions play this role instead. The strategy for the preparation of SMOFs is based on the synthesis of coordination compounds, with the choice of metal center made on the basis of its coordinative preferences and the ligand or a combination of ligands with the ability to coordinate the metal cation and also facilitate several weak interactions between the diverse rigid molecular units [2].

The final goal of supramolecular chemistry is to understand the inherent complexities of the association mechanisms of molecular and ionic building blocks organized through multiple noncovalent interactions [3,4]. The relatively greater strength of ligand–metal coordination bonds when compared

with other noncovalent interactions allows the stabilization of a range of different structures, whereas the weak and reversible forces are key to understanding these self-assembling systems. In terms of the weak intermolecular noncovalent interactions, the analysis of C–H··· X (X = Cl, S, N) hydrogen bonds in metallosupramolecular systems has received less attention despite its proven participation in several biological systems [5,6]. In this way, the hydrogen bond acceptor capability of halogens has attracted attention on a number of fronts. In the context of metallosupramolecular chemistry, halide ligands (M–X) have been used to drive the self-assembly of coordination compounds due to their directionality and versatility [7,8].

In order to facilitate the hydrogen bond acceptor role of a halide, such as chloride in a SMOF, copper(II) chloride is used as the metal source and, although the Cu(II) cation is stable under ambient conditions, Cu(II)-to-Cu(I) transformations at room temperature can be produced by reaction conditions such as temperature, pH value, solvents and pressure due to the low standard electrode potential between Cu(II) and Cu(I).

The tetrazole organosulfur derivatives and their transition metal complexes are important in medicinal chemistry and drug design [9] and also as industrial materials [10]. In the field of metallosupramolecular chemistry, these compounds are particularly interesting since the tetrazole moiety contains several nitrogen atoms that can facilitate simultaneously the coordination to one or more metal centers and the formation of hydrogen bonds acting as acceptors.

With the aim of studying the role of C–H···X (X = Cl, S, N) hydrogen bonds in the crystalline supramolecular networks based on copper(II/I) chloride/bis-tetrazole organosulfur systems, we report here the crystal structures of four compounds resulting from reactions under different synthetic conditions between the ligands bis(1-methyl-1H-tetrazole-5-ylthio)methane (BMTTM) and 1,2-bis(1-methyl-1H-tetrazole-5-ylthio)ethane (BMTTE) and copper(II) chloride. These ligands have attractive features, such as the multiple heteroatomic potential coordination sites, six N donors and two S atoms, which also contribute to the flexibility of the ligands. In both ligands, there are three adjacent N donors in each methyl-tetrazole group, and these may promote the construction of multinuclear clusters.

In the literature there is structural information on several compounds based on copper(II/I) polyoxometalates (POMs = H2Mo8O26<sup>2</sup><sup>−</sup>, PMo12O40<sup>3</sup><sup>−</sup>, SiW12O40<sup>3</sup><sup>−</sup>, PW12O40<sup>3</sup><sup>−</sup>, SiMo12O40<sup>4</sup><sup>−</sup>, SiW12O40<sup>4</sup><sup>−</sup>, HSiMo12O40<sup>3</sup>−) and these two ligands [11–14]. These compounds are 1D, 2D or 3D coordination polymers in which the ligands are able to coordinate two, three or four copper cations by chelating and/or bridging coordination modes. However, a study of the weak interactions responsible for the supramolecular organization has not been undertaken for any of these compounds.
