Synthesis, structural elucidation, and supramolecular analysis of brominated β-ketoiminato palladium(II) complexes: Insights from X-ray crystallography, Hirshfeld surface, and DFT studies

A new series of brominated β-ketoiminate ligands and their palladium(II) complexes (Pd(CH 3 C(NAr)CHC(O)R) 2 ) 2a – i ( a , R = CH 3 , Ar = 2-Br-C 6 H 4 ; b , R = CH 3 , Ar = 3-Br-C 6 H 4 ; c , R = CH 3 , Ar = 4-Br-C 6 H 4 ; d , R = CH 3 , Ar = 2,4-Br 2 C 6 H 3 ; e , R = CH 3 , Ar = 2,4,6-Br 3 C 6 H 2 ; f , R = Ph, Ar = 2-Br-C 6 H 4 ; g , R = Ph, Ar = 3-Br-C 6 H 4 ; h , R = Ph, Ar = 4-Br-C 6 H 4 ; i , R = Ph, Ar = 2,4-Br 2 C 6 H 3 ) were synthesized and comprehensively characterized. Single-crystal X-ray diffraction of seven representative complexes 2a – d and 2g – i reveals mononuclear square-planar Pd(II) species with N 2 O 2 coordination environments and highly delocalized six-membered chelate rings. Structural analysis demonstrates that crystal packing is governed by a diverse network of noncovalent interactions, including C–H···Br, C–H···O, C–H···π, Br···π, C–H···Pd, and Type II Br···Br contacts, with dispersion forces providing the dominant stabilizing contribution. QTAIM and NCI analyses identify the Br···Br interaction and Pd···H anagostic contact as among the most significant contributors to intermolecular stabilization in complex 2c . Density functional theory calculations reproduce the experimental structural and spectroscopic trends and show that metal coordination increases the HOMO–LUMO energy gap. The electronic transitions are strongly influenced by ligand substitution, with ligand-centered excitations predominating in the methyl-substituted complexes ( 2a − e ) and ligand-to-metal-charge-transfer transitions becoming dominant in the phenyl substituted-analogues ( 2f − i ).