D/L-mandelic acid-based three new Pb(II) coordination polymers: Influence of temperature and 5,5 '-dimethyl-2,2 '-dipyridyl ancillary ligand on constructuring enantiomeric coordination polymers

摘要

Three new Pb(II) coordination polymers, namely [Pb-2(mand)(2)](n) (1), {[Pb(L-Hmand)(NO3)(5,5'-DM-2,2'-bipy)]center dot 2H(2)O}(n) (2-L), {[Pb(D-Hmand)(NO3)(5,5'-DM-2,2'-bipy)]center dot 2H(2)O} n (2-D) (H(2)mand = D/L-mandelic acid, 5,5'-DM-2,2'-bipy = 5,5'-dimethyl-2,2'-bipyridyl), have been prepared. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, powder X-ray diffraction and thermogravimetric analyses. Complex 1 crystallizes in the triclinic system with space group P-1, and displays a 2D layer structure. Complexes 2-L and 2-D are pairs of enantiomers. They crystallize in the same chiral space group P2(1)2(1)2(1) and feature a 1D chain structure. The influence of the temperature and steric-hinerance of 5,5'-dimethyl-2,2'-dipyridyl molecules on constructing enantiomeric Pb(H) coordination polymers based on chiral mandelic acid ligands have been demonstrated. In addition, the circular dichroism (CD) spectroscopy of 2-L and 2-D exhibit obvious positive or negative Cotton effects indicating their homochirality. The luminescent properties of 1, 2-L and 2-D in the solid state have also been investigated.