STRUCTURE AND LUMINESCENT PROPERTIES OF COORDINATION POLYMERS CONTAINING LEAD(II) AND THIOPHENE LIGANDS

Three new metal-organic framework polymers [Pb-2(btdc)(2)] (1), [Pb-3(ttdc)(3)(dma)(2)] (2), and [Pb(ttdc)(dma)] (3) (H(2)btdc = 2,2 '-bithiophene-5,5 '-dicarboxylic acid, H(2)ttdc = thieno[3,2-b]thiophene-2,5-dicarboxylic acid, dma = N,N-dimethylacetamide) are synthesized under solvatothermal conditions. The compounds are characterized by single crystal and powder X-ray diffraction, elemental, thermogravimetric, and IR spectroscopic analyses. All three compounds are three-dimensional coordination polymers with layered (1) or chain (2, 3) motifs. The study of luminescent properties reveals the intraligand nature of radiative transitions. For 1 luminescence quenching is observed because of the strengthening of vibrational states and long-range interactions between pi-systems of thiophene groups. The luminescence spectrum of 2 contains two bands corresponding to two types of ttdc(2-) ligands with principally different structural environments. For the ligands isolated from each other the position of the luminescence maximum corresponds to that of the free ttdc(2-) ion. For the ligands associated in closely packed chains by continuous pi-stacking the appearance of a new maximum in the red range is observed, which is due to the delocalization of electron orbitals.