Coordination networks generated from transition metal chlorides and a flexible double betaine

The new flexible double betaine 1,4-bis(2-picolyloxyl)benzene-N,N′-diacetate (L) has been synthesized and used to generate five complexes with divalent metal chlorides: [M(H2O)6]Cl2·L·2H2O (M=Mn (1), Co (2)), [Cu(μ-L)Cl2]∞ (3), {[Zn(μ-L)Cl2]·2H2O}∞ (4), and {[Cd2(μ-Cl)2(μ-L)Cl2(H2O)2]·2H2O}∞ (5). Isomorphous compounds 1 and 2 have a hydrogen-bonded three-dimensional network in which adjacent L ligands overlap through π–π stacking of the pyridine and benzene rings. Compounds 3, 4, and 5 display three different types of one-dimensional polymeric structures. Bridged by L acting in the anti mode, compound 3 exhibits an infinite zigzag chain in which consecutive, approximately planar L ligands are arranged in a crossed manner when viewed along the chain direction, the distance between adjacent copper(II) ions being about 13 A˚. In contrast, compound 4 features a spring-like infinite helical chain with zinc ions lying on the axis and bridged by L acting in the syn fashion, and the Zn(II)⋯Zn(II) separation is approximately 9 A˚. In compound 5, the building unit is a centrosymmetric Cd2Cl2 moiety, and adjacent dimeric units are linked by the centrosymmetric L ligand acting in the anti mode to give an infinite zigzag chain running along the c axis; such chains are further connected through hydrogen bonds to form a three-dimensional network. [Copyright &y& Elsevier]