An unusual 2D → 3D polythreading framework based on a long 1,10-phenanthroline derivative ligand

In the compound [Pb2(L)2(1,4-bdc)2]n (1), each Pb(II) atom is seven-coordinated by two nitrogen atoms from one L ligand, and five carboxylate oxygen atoms from three different 1,4-bdc ligands in a distorted monocapped triangular prismatic coordination geometry (1,4-bdc = 1,4-benzenedicarboxylate and L = dipyrido[7,6-a:6′,7′-c]-3-chloropyrido[2,3-b]quinoxaline). The Pb(II) atoms are connected together by the 1,4-bdc ligands to form a 2D network with large windows. The dangling L ligands of each layer are threaded into the voids of the two adjacent layers above and below, thus every window of each layer is threaded by only two dangling ligands that come from opposite directions. Finally, this unique simultaneous threading fashion of adjacent polymeric motifs gives the novel 2D → 3D polythreading array. In addition, the strong π–π interactions between the L ligands and the 1,4-bdc ligands of neighboring layers make great contribution to the structural stabilization of 1.