Supramolecular association in Cu(II) coordination complexes involving energetically significant NO•••NO π-hole interaction and cooperative π-stacked ternary assembly: Experimental and theoretical studies

Two new copper (II) coordination solids involving 1,10-phenanthroline (phen) and benzoate (bz) viz., [Cu(phen) (H2O)(2) (eta(2)-NO3)]center dot NO3 (1) and [Cu(phen)(2)(eta(2)-bz)]center dot 2bzH center dot NO3 (2) [bzH = benzoic acid] have been synthesized and characterized by X-ray crystal structure analysis, FT-IR, electronic spectra, ESR and TGA. Theoretical calculations have been performed to analyse some unconventional non-covalent interactions observed in the solid state structures of compounds 1 and 2. In compound 1, 1D supramolecular chain is formed between the cationic moieties through the anti-parallel NO center dot center dot center dot NO pi-hole interactions involving the coordinated nitrato co-ligands which have been scarcely describe in the literature. The NCI plot analysis reveals the existence of the anti-parallel NO center dot center dot center dot NO pi-hole interaction for the supramolecular dimer of compound 1. The binding energy of the NO center dot center dot center dot NO pi-hole interaction in the supramolecular dimer is -18.2 kcal/mol, thus, indicating a moderately strong interaction. In compound 2, a remarkable cooperative (pi-pi)(2)/(pi-pi)(1)/(pi-pi)(2) type network for self-assembly progression of the ternary Tr-stacked assembly has been studied. The computation of the energetic features reveals that (pi-pi)(1) is reinforced by the presence of (pi-pi)(2) in compound 2. The microbial activities have been investigated for both the compounds.