A novel ligand ((1E)-(2-(4-fluorobenzylidene)amino)methyl) phenyl)diazenyl)-1,3,7-trimethyl-3,7-dihydro-1H-purine-2,6-dione (4-FADPD) was synthesized via the azotization reaction of 2-aminobenzylamine with caffeine, and the resultant compound was condensed with 4-fluorobenzaldehyde to form a newly azo-Schiff base ligand. Its complexes with Cu(II), Ag(I), and Au(III) were synthesized. The results of multi-identifications, including XRD, elemental analysis (C.H.N), UV-vis spectroscopy, FTIR, and 1H-NMR, were used to propose the suggested structures using molar conductivity measurements. These data were utilized to propose appropriate geometric configurations for all complexes. The azo-Schiff base ligand coordinates toward the Cu(II) ion in octahedral geometry and Ag(I) ion in tetrahedral geometry, whereas the Au(III) ion gives it a square planar structure. Nanoparticle size was determined using scanning microscopy (FE-SEM). Significant antiproliferative activity was observed with the Au(III) nanocomplex against human lung cancer (A549) cells, compared with normal cell lines (HDFn), as indicated by the IC50 values. The purpose of our research is to prepare new nanocomplexes derived from caffeine and to demonstrate the effectiveness of an Au(III) nanocomplex against lung cancer as a future treatment that may benefit pharmaceutical preparations.