Partial in Situ Reduction of Copper(II) Resulting in One-Pot Formation of 2D Neutral and 3D Cationic Copper(I) Iodide–Pyrazine Coordination Polymers: Structure and Emissive Properties

On the way to copper(I) iodide coordination polymers with specific luminescent properties, the in situ reduction of Cu(II) in the presence of KI and bidentate N-heteroatomic ligand, either pyrazine (pyz) or 4,4'-bipyridine (bpy), resulted in one two-dimensional and two three-dimensional new coordination networks. Starting from Cu(NO 3 ) 2 ·3H 2 O in the presence of pyz, successive precipitation of known yellow [(Cu I I) 2 (pyz)] n , new orange [Cu I I(pyz)] n , and new dark blue {[Cu I (pyz) 2 ]·I 5 } n polymeric solids was observed. Starting from the same salt in the presence of bpy resulted in the successive precipitation of known yellow [(Cu I I) 2 (bpy)] n and new brown {[Cu II (NO 3 )(bpy) 2 ]·I 3 ·(dmf·H 2 O)} n coordination polymers. By using either Cu(CH 3 COO) 2 ·H 2 O or Cu(BF 4 ) 2 as starting materials, both known forms, yellow [(Cu I I) 2 (bpy)] n and orange [Cu I I(bpy)] n , precipitated successively. The new solids were characterized by IR spectroscopy and X-ray analysis. [Cu I I(pyz)] n represents the missing member in the row of two-dimensional coordination networks with general formula [Cu I X(pyz)] n (X = Cl, Br, I). Its steady state and time-resolved characterization together with DFT and TDDFT calculations revealed that the emission at room temperature is mainly delayed fluorescence originating from mixed singlet metal-to-ligand charge transfer and halide-to-ligand charge transfer states, while that at 77 K is phosphorescence, associated with the small singlet-triplet energy differences (ΔE = 70 meV).