Two dicyanamido- and azido-bridged Cu(II) coordination polymers with N-(2-pyridylmethyl)-L-alaninato as chiral ligand: Synthesis, structures, luminescence properties, and Hirshfeld surface analysis

Abstract

Two copper(II) coordination polymers bridged by dicyanamido (N(CN)₂⁻)- and azido (N₃⁻) ligands, [CuLN(CN)₂]_n (1) and [{CuLN₃}₂(H₂O)]_n (2) (L⁻ = N-(2-pyridylmethyl)-L-alaninato) have been synthesized and thoroughly studied using structural and spectroscopic methods. Both complexes crystallize in the chiral orthorhombic P2₁2₁2₁ space group. Complex 1 features 1D zigzag chains through the two terminal nitrogen nitrile groups of the μ_1,5-bridging N(CN)₂⁻ ligand. These chains are assembled via intermolecular N–H···O hydrogen bonding interactions, forming a 3D supramolecular network. Complex 2 is a dissymmetric dimer with the Cu1 center being in a distorted square pyramidal geometry environment, while the Cu2 center is in a distorted octahedral geometry. In complex 2, an infinite 3D supramolecular structure is achieved via Cu1-O2ⁱ bonds, O2ⁱ being the oxygen atom of a carboxylate group from the L⁻ ligand of an adjacent dimer. Intermolecular hydrogen bonding interactions of the type N–H···O in 1 and N–H···O and O–H···O in 2 contribute to stabilizing the three-dimensional frameworks. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint (2D-FP) plots reveal that the two structures are dominated by the H┄H and N⋯H/H⋯N contacts. Upon excitation at 315 nm, maximum emissions centered at 498 nm and 805 nm for 1 and at 497 nm and 805 nm for 2 are exhibited. These luminescence behaviors are attributed to charge transition between the L⁻ ligand and the Cu²⁺ ions.