Two bicyclic dinuclear complexes generated from 3,3′‐[1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoic acid (L) and dimethylformamide (DMF): [Cu(L)(DMF)]2 and [Zn(L)(DMF)]2

A new 1,3,4‐thiadiazole bridging ligand, namely 3,3′‐1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoic acid (L), has been used to create the novel isomorphous complexes bis{μ‐3,3′‐1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoato}bis(N,N‐dimethylformamide)copper(II)], Cu₂(C₁₈H₁₂N₂O₄S₃)₂(C₃H₇NO)₂], (I), and bis{μ‐3,3′‐1,3,4‐thiadiazole‐2,5‐diyldi(thiomethylene)]dibenzoato}bis(N,N‐dimethylformamide)zinc(II)], Zn₂(C₁₈H₁₂N₂O₄S₃)₂(C₃H₇NO)₂], (II). Both exist as centrosymmetric bicyclic dimers constructed through the syn–syn bidentate bridging mode of the carboxylate groups. The two rings share a metal–metal bond and each of the metal atoms possesses a square‐pyramidal geometry capped by the dimethylformamide molecule. The 1,3,4‐thiadiazole rings play a critical role in the formation of a π–π stacking system that expands the dimensionality of the structure from zero to one. The thermogravimetric analysis of (I) indicates decomposition of the coordinated ligands on heating. Compared with the fluorescence of L in the solid state, the fluorescence intensity of (II) is relatively enhanced with a slight redshift, while that of (I) is quenched.