*2.6. Supramolecular Arrangements*

The strategic use of supramolecular synthons to control crystal structure allows the design of new solids with interesting physicochemical properties. However, to achieve this objective, it is necessary to understand the intermolecular interactions in the context of crystal packing. In the current systems, common structural and compositional characteristics allow a deeper study of this aspect. In this sense, chloride ligands have shown through crystallographic data analysis that the weak C–H··· Cl–M interactions exhibit the characteristics of conventional hydrogen bonds and hence are very significant in molecular recognition and crystal engineering. Another interesting feature in these structures is the presence of coordinatively unsaturated metal centers (UMCs), which can interact at longer distances with other atoms. Besides, it should be noted in these compounds that not all of the nitrogen atoms of each tetrazole take part in coordination, so free N-atoms are still available to act as hydrogen acceptors in different interactions, thus playing a significant role in the final supramolecular arrangements. Moreover, the flexible organosulfur chains between the tetrazole groups offer the possibility of establishing noncovalent interactions involving the sulfur atom as an acceptor or the organic fragment as a donor. In addition, the methyl substituent in the tetrazole moiety increases the hydrophobicity and the stability of the molecules, but the most remarkable feature observed in these structures is its role as a donor in multiple interactions.

In this way, chains of **1** are organized into a supramolecular 2D network along the *ab* plane by means of O–H··· Cl hydrogen bonds that involve coordinated water molecules and chloride atoms of neighboring chains. Nonpolar hydrophobic methyl groups are oriented out of the layers and establish C–H··· Cl interactions with other chains to give the final 3D supramolecular array, as shown in Figure 4. An interchain Cl··· π interaction [Cl2··· centroid of N1/N2/N3/N4/C1; d(Cl··· centroid = 3.355 Å; 1 − x, 2 − y, 1 − z)] and CHMe··· N and CHMe··· S interactions, as shown in Table 4, also participate in the formation of the crystal network, which has a Kitaigorodskii packing index [27] of 75%.

**Figure 4.** Supramolecular arrangemen<sup>t</sup> in the crystal structure of **1**.

The supramolecular arrangemen<sup>t</sup> in **1**·**solv** is mainly due to C–H··· X interactions (X = Cl and N) but, as observed in similar compounds [28], solvent molecules are involved in different C–H···X (X = Cl, O, N; Table 4) interactions with the metal–organic framework, so the polymeric chains are extended along the *b* axis and arranged in a sinusoidal manner, with solvent molecules hosted between them, as shown in Figure 5. These hydrogen-bonding interactions are established between the methyl groups of tetrazole or acetonitrile as donors with the available nitrogen atoms of both fragments as acceptors. The metallorganic chains are linked through solvent molecules that act as a bridge in the *ac* plane, as shown in Figure 5 (top, left), to give a shifted parallel arrangement. Furthermore, several weak intra- and inter-molecular C–H··· S interactions reinforce the zig-zag disposition of the chains. The solvent volume makes up 30% of the unit cell volume, as calculated using Mercury [29], and the Kitaigorodskii packing index [27] of 75% is slightly lower than that in **1**.

In the crystal packing of **2**, the nonpolar methyl –CH3 and methylene –CH2– spacer groups, which are oriented outwards from the tetrameric molecule to define a hydrophobic contour, as shown in Figure 2, play an important role as H-donors towards the chloride atoms to establish several intermolecular C–H··· Cl interactions with C··· Cl distances in the range 3.32–3.47 Å, as shown in Table 4 and Figure 6. This kind of interaction is also established with the nitrogen atoms of tetrazole units. Furthermore, a π··· π interaction between the tetrazole groups N1/N2/N3/N4/C1 and N5/N6/N7/N8/C4 (intermolecular centroid–centroid distance of 3.6976 Å and interplanar dihedral angle of 33.40◦; symmetry code: 1 − x, 1 − y, 1 − z) contributes to the crystal packing, with a Kitaigorodskii index [27] of 70%.

The metallorganic layer of **3** has a stair-step disposition along the *ab* plane, as shown in Figure 3, and each layer stacks with adjacent ones through CHmethylene··· Cl interactions, as shown in Table 4, to give a 3D supramolecular array reinforced by the contribution of an S··· π interaction with the tetrazole ring (S··· centroid distance = 3.357 Å; symmetry: 1 − x, y, 1.5 − z). The resulting Kitaigorodskii packing index [27] is 77%.

**Figure 5.** Supramolecular arrangemen<sup>t</sup> in the crystal structure of **1**·**solv.**


**Table 4.** Main hydrogen bonds (Å,◦).

Symmetry code: (**1**) #1 x −1, y, z; #2 −x + 1/2, y + 1/2, −z + 1/2; #3 −x + 3/2, y + 1/2, −z + 1/2; #4 x − 1/2, −y + 3/2, z − 1/2; (**1**·**solv**) #1 −x + 1, −y + 1, −z + 2; #2 −x + 1, −y + 2, −z + 2; #3 x + 1, y, z; #4 x, y − 1, z + 1; #5 −x + 2, −y + 1, −z + 2; #6 −x, −y + 2, −z + 2; #7 1 − x, 1 − y, 3 − z; (**2**) #1 x + 1/2, −y + 3/2, z + 1/2; #2 −x + 3/2, y − 1/2, −z + 3/2; #3 x − 1/2, −y + 3/2, z + 1/2; #4 1 + x, y, z; (**3**) #1 −x + 1, y, −z + 3/2.

**Figure 6.** Supramolecular organization in the crystal structure of **2**.
