Spectral, structural and theoretical study of novel helical and linear structures of PbI2 and PbBr2 complexes with a triazine ligand

Two coordination polymers of lead(II), 1D-{Pb(DFPT)(μ-Br)2}n (1) and 1D-helical-{Pb(DFPT)(μ-I)2}n (2), with 5,6-di(furan-2-yl)-3-(pyridin-2-yl)-1,2,4-triazine (DFPT) were prepared and identified by elemental analysis, FT-IR, 1H NMR spectroscopy and single-crystal X-ray diffraction. In the 1D-double chain-coordination polymers of 1 and 2, the lead atom has a PbNpyNtz(μ-X)4 (X: Br (1), I (2)) environment with distorted octahedral geometry and hemidirected coordination sphere. The type of the polymeric chain in both complexes is different; 1 has a linear expansion while 2 shows a helix structure with a racemic mixture of the P and M chains. In the crystal network of the complexes, in addition to hydrogen bonds, there are triazine···furyl and furyl···furyl ring π–π stacking interactions. The thermodynamic stability of the compounds, the polymer stability slope for pentameric chains (PSS5) and also the energy variation of the free DFPT ligand for 360° rotation of the pyridine ring were studied by DFT calculations.