N,N'-bis(3-dithiocarbamatopropyl) piperazine bridged metallomacrocyclic complexes of Ni(II), Cu(II) and Zn(II): Synthesis, characterization, photophysical, in-silico study and their potential utility in heavy metal ion sensing

Two secondary diamines viz. N,N'-bis{3-( p-methoxybenzylamino)propyl}piperazine (H2L1) 2 L 1 ) and N,N'-bis{3-(p- chlorobenzylamino)propyl}piperazine (H2L2) 2 L 2 ) holding N,N'-bispropylpiperazine linkers have been prepared and subsequently used to derive a new series of N,N'-bis(3-dithiocarbamatopropyl) piperazine bridged metallomacrocyclic complexes [M(II)2-mu 2-bis-{(kappa 2S,S-S2CN(R)C3H6)2piperazine}] 2- mu 2-bis-{( kappa 2 S,S-S 2 CN(R)C 3 H 6 ) 2 piperazine}] wherein R = p-methoxybenzyl, M = Ni(II) 1, Cu(II) 2, Zn(II) 3; R = p-chlorobenzyl, M = Ni(II) 4, Cu(II) 5, Zn(II) 6. The formation and purity of all the metallomacrocyclic dithiocarbamate complexes were verified by microanalysis and standard methods such as HRMS, NMR, IR and UV-Visible absorption spectroscopy and corroborated by density functional theory calculations. The experimental (magnetic susceptibility and UV-Visible) and theoretical calculations suggest a square planar/distorted square planar environment around nickel(II)/copper(II) and tetrahedral/distorted tetrahedral environment around zinc(II) centres in 1-6. Thermogravimetric study was carried out on 1-6 to study their thermal stability and degradation behaviour. Notably, TG curves of compounds 2, 3 and 5 gave a stable residual mass corresponding to corresponding metal sulphides (MS). Notably, the calculated HOMO-LUMO gaps (1.19-1.33 eV) for Cu(II)-dithiocarbamate 2 and 5 indicates their semiconducting nature. The potentials of these metallomacrocycles as a molecular probe for optical sensing of environmentally hazardous heavy metal ions ca Pb(II), Cd(II) and Hg(II) were further examined by using UV-Visible and fluorescence spectroscopies.