Use of Metalloligands [CuL] (H2L = Salen Type Di-Schiff Bases) in the Formation of Heterobimetallic Copper(II)-Uranyl Complexes: Photophysical Investigations, Structural Variations, and Theoretical Calculations

Five heterobimetallic copper­(II)–uranium­(VI) complexes [(CuL1)­UO2(NO3)2] (1), [{CuL1(CH3CN)}­UO2(NO3)2] (2), [{CuL1(CH3COCH3)}­UO2(NO3)2] (3), [{CuL2(CH3CN)}­UO2(NO3)2]­(4), and [{CuL2(CH3COCH3)}­UO2(NO3)2]­[{CuL2}­UO2(NO3)2] (5) have been synthesized by reacting the Cu­(II)-derived metalloligands [CuL1] and [CuL2] (where, H2L1 = N,N′-bis­(α-methylsalicylidene)-1,3-propanediamine and H2L2 = N,N′-bis­(salicylidene)-1,3-propanediamine) with UO2(NO3)2·6H2O in 1:1 ratio by varying the reaction temperature and solvents. Absorption and fluorescence quenching experiments (steady-state and time-resolved) indicate the formation of 1:1 ground-state charge transfer copper­(II)–uranium­(VI) complexes in solution. X-ray single-crystal structure reveals that each complex contains diphenoxido bridged Cu­(II)–U­(VI) dinuclear core with two chelated nitrato coligands. The complexes are solvated (acetonitrile or acetone) in the axial position of the Cu­(II) in different manner or desolvated. The supramolecular interactions that depend upon the co-ordinating metalloligands seem to control the solvation. In complexes 2 and 3 a rare NO3–···NO3– weak interaction plays an important role in forming supramolecular network whereas an uncommon UO···NO3– weak interaction helps to self-assemble heterobinuclear units in complex 5. The significance of the noncovalent interactions in terms of energies and geometries has been analyzed using theoretical calculations.