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, CdSO4 or CuSO4 led to four coordination polymers, {[Zn(AcO)(2)L]center dot H2O center dot CH3OH}(n) (1), {[CdCl2L2]center dot 2DMF}(n) (2), {[CdSO4L(H2O)(3)]center dot 3H(2)O}(n) (3), and {[CuSO4L(H2O)(2)]center dot 2H(2)O}(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.