Structure and optical spectra of bis(pyrrol‐2‐ylmethyleneamine) complexes: A DFT and TDDFT study of the self‐assembly complexes of bis(pyrrol‐2‐ylmethyleneamine) ligands linked by alkyl spacers with Cu(II)

Abstract

ABSTRACT:The UV-Vis absorption spectra of self-assembly Cu (II) complexes for bis(pyrrol-2-ylmethyleneamine) linked by alkylA(CH 2 ) n A(n ¼ 2,3,4,6) spacers were recorded. The ground-state geometries and electronic structures were investigated by density functional theory employing generalized-gradient approximation Perdew-BurkeErnzerhof (PBE) and hybrid B3LYP (20% E x,HF ) and PBE0 (25% E x,HF ) functional, in conjugation with four basis set combinations.[BS1:6-31G(d); BS2:Lanl2dz for Cu and 6-31G(d) for C,H,N; BS3:6-31þG(d); BS4:6-311þG(d,p) for C,H,N and Lanl2dz for Cu]. Compared the optimized geometries with XRD structures, it was found that the choice of methods appeared to have a more pronounced effect on structure than that of the basis set. PBE0/BS4 optimized geometries provide the best agreement with XRD experimental results and the mean absolute errors for bond length is 0.018 Å and for bond angle is 2.1 . Transition excited states of complexes 1-4 in the gas phase and in CH 2 ClCH 2 Cl solution have been studied by the time-dependent density functional theory in conjugated with the Polarizable Continuum Model. Pure PBE and hybrid B3LYP, PBE0 functionals, as well as BS1, BS2,p)] were selected. Calculations indicate that PBE functional provides more accurate descriptions on main UV-vis absorptions than B3LYP and PBE0 functionals. The strongest absorption bands located at 338-356 nm are due to intraligand charge transfer (ILCT) transitions, a mixed-character ILCT þ metal-ligand charge transfer (MLCT) absorptions are calculated at 280-291 nm, the shoulder bands located at 250-257 nm mainly arise from MLCT or ligand-metal charge transfer transitions. Alkyl spacer does not play a crucial role on the main electron transitions.