A novel oxalato bridged supramolecular ternary complex of Cu(II) involving energetically significant π-hole interaction: Experimental and theoretical studies

A novel oxalate bridged supramolecular ternary complex viz. [Cu-2(mu(2)-C2O4)(phen)(2)(H2O)(2)] [Cu(phen)(male) (NO3)](2) (1) (phen = 1,10-phenanthroline, C2O4 = oxalate, male = maleate) has been synthesized from purely aqueous media and characterized using elemental analysis, spectroscopic (IR, UV-Vis-NIR and ESR) and single crystal X-ray diffraction techniques. The supramolecular assembly in 1 have been built up involving association of O-H center dot center dot center dot O, C-H center dot center dot center dot N, C-H center dot center dot center dot O and pi-pi stacking interactions. Interestingly in compound 1, oxygen atom of the coordinated maleate of anionic complex unit is involved in Tr-hole bonding interaction with the pi-cloud of the oxalate moiety of the cationic complex unit which has not been reported before in oxalic acid or in their derivatives. By means of DFT calculations and the utilization of theoretical models, we also have studied the pi-hole interaction energetically and confirmed its existence using the NCI plot analysis. The thermal stability of the compound has been verified by thermogravimetric (TG) analysis. The microbial activities have been investigated for compound 1.