Coordination polymers derived from a flexible bis(pyridylurea) ligand: Conformational change of the ligand and structural diversity of the complexes

The assembly of a bis(pyridylurea) ligand, N,N′-ethane-1,2-diylbis(3- pyridin-4-ylurea) (L), with Zn(AcO)₂, CdCl₂, CdSO ₄ or CuSO₄ led to four coordination polymers, {[Zn(AcO)₂L]·H₂O·CH₃OH} _n (1), {[CdCl₂L₂]·2DMF}_n (2), {[CdSO₄L(H₂O)₃]·3H₂O} _n (3), and {[CuSO₄L(H₂O)₂] ·2H₂O}_n (4). Compound 1 is an infinite 1D zigzag chain with alternate Zn(AcO)₂ units and L molecules. The cadmium(ii) dichloro complex 2 features a corrugated sheet structure with a (4,4) net topology, while the sulfato complex 3 shows a unique 1O/2U interwoven 3D structure assembled from zigzag chains. The copper(ii) complex 4 is an exceptional diamondoid network with an unusual 12-fold [6 + 6] interpenetration mode. Interestingly, the ligand shows the expected flexibility in the formation of the coordination polymers. In 1, 3 and 4, the central ethylene spacer adopts the anti conformations and is roughly linear, whereas in 2 it assumes a gauche form and exists as a V-shaped linker. The structural variation of these coordination polymers as well as the conformational change of the ligand in the presence of different counter anions and metal ions is discussed.