PH-controlled construction of Cu(I) coordination polymers: In situ transformation of ligand, network topologies, and luminescence and UV-vis-NIR absorption properties

Two new complexes [Cu^I₃(L1)I₃]_n (1, L1 = 2,5-bis(4-pyridyl)-1,3,4-oxadiazole) and [Cu^I ₃(L2)I₂]_n (2, L2 = 2,5-bis(4-pyridyl)-1,2,4- triazolate) are controllably formed by using aqueous ammonia to regulate the pH value of the reaction involving CuI and L1. Interestingly, L2 of 2 is in situ generated from the ring transform of L1 when increase the pH value of the reaction. 1 exhibits 2-D layer, while 2 shows 3-D MOFs with a novel 3-nodal 4,4,5-connected net topology of an unprecedented Point (Schlafli) symbol: (4•5²•6²•7)(5⁴•8 ²)(4³•5•6⁶). Although both 1 and 2 are built of CuI and similar ligands, different arrangements of CuI chains and ligands endow them with different physical properties. 1 displays a strong pure red luminescence emission, while 2 is nonluminescent and shows a broad absorption band covering the whole UV-vis-NIR spectrum range. The emissive excited states of 1 and the charge transitions of the optical absorption for 2 are solved by DFT calculations.