Diaquabis(ethylenediamine)copper(II) vs. monoaquabis(ethylenediamine)copper(II): Synthesis, characterization, single crystal X-ray structure determination, theoretical calculations and antimicrobial activities of [Cu(en)2(H2O)2](2-phenoxybenzoate)2·H2O and [Cu(en)2(H2O)](diphenylacetate)2·3H2O

Abstract Two new copper(II) complexes of composition [Cu( en ) 2 (H 2 O) 2 ](2-phenoxybenzoate) 2 ·H 2 O, 1 and [Cu( en ) 2 (H 2 O)](diphenylacetate) 2 ·3H 2 O, 2 (where en  = ethylenediamine) have been synthesized, characterized by elemental analyses, spectroscopic techniques (UV–vis and FT-IR), magnetic moment determination and conductance measurements and their structures have been unequivocally confirmed by single crystal X-ray analysis. Both complexes crystallize in the monoclinic crystal system with space groups C 2/ c , for 1 and P 2 1 / n , for 2 . Complex 1 exhibits a distorted octahedral geometry with four nitrogen atoms of chelating en ligands and two oxygen atoms of water molecules coordinated to central Cu(II) ion, whereas complex 2 shows a square pyramidal geometry around copper(II) with four nitrogen atoms of chelating en ligands and one oxygen atom of water molecule. Crystal structures of both complexes are stabilized by collective interplay of various non-covalent interactions such as O–H⋯O, N–H⋯O and C–H⋯π interactions, besides electrostatic attraction. DFT optimization studies clearly showed that complex 2 is quite stable with square pyramidal geometry than expected octahedral geometry. Both complexes show potential antibacterial activities against gram positive and gram negative bacteria.