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

Abstract

Three new metal-organic framework polymers [Pb2(btdc)2] (1), [Pb3(ttdc)3(dma)2] (2), and [Pb(ttdc)(dma)] (3) (H2btdc = 2,2′-bithiophene-5,5′-dicarboxylic acid, H2ttdc = 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 π-systems of thiophene groups. The luminescence spectrum of 2 contains two bands corresponding to two types of ttdc2– 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 ttdc2– ion. For the ligands associated in closely packed chains by continuous π-stacking the appearance of a new maximum in the red range is observed, which is due to the delocalization of electron orbitals.