Cu(I) and Pb(II) complexes containing new tris(7-naphthyridyl)methane derivatives: synthesis, structures, spectroscopy and geometric conversion.

Two novel facial-capping tris-naphthyridyl compounds, 2-chloro-5-methyl-7-((2,4-dimethyl-1,8-naphthyridin-7(1H)-ylidene)(2,4-dimethyl-1,8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L-1) and 2-chloro-7-((2-methyl-1,8-naphthyridin-7(1H)-ylidene)(2-methyl-1,8-naphthyridin-7-yl)) methyl-1,8-naphthyridine (L-2), as well as their Cu(I) and Pb(II) complexes, [CuLa(PPh3)]BF4 (1) (PPh3 = triphenylphosphine, L-a = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methane), [CuLb(PPh3)]BF4 (2) (L-b = bis(2-methyl-1,8-naphthyridin-7-yl)(2-chloro-1,8-naphthyridin-7-yl)methane), [Pb(OLa)(NO3)(2)] (3) (OLa = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methanol) and [Pb(L-b)(2)][Pb(CH3OH)(NO3)(4)] (4), have been synthesized and characterized by X-ray diffraction analysis, MS, NMR and elemental analysis. The structural investigations revealed that the transfer of the H-atom at the central carbon to an adjacent naphthyridine-N atom affords L-1 and L-2 possessing large conjugated architectures, and the central carbon atoms adopt the sp(2) hybridized bonding mode. The reversible hydrogen transfer and a geometric configuration conversion from sp(2) to sp(3) of the central carbon atom were observed when Pb(II) and Cu(I) were coordinated to L-1 or L-2. The molecular energy changes accompanying the hydrogen migration and titration of H+ to different receptor-N at L-1 were calculated by density functional theory (DFT) at the SCRF-B3LYP/6-311++G(d,p) level in a CH2Cl2 solution, and the observed lowest-energy absorption and emission for L-1 and L-2 can be tentatively assigned to an intramolecular charge transfer (ICT) transition in nature.