Assemblies of a New Flexible Multicarboxylate Ligand and d¹⁰ Metal Centers toward the Construction of Homochiral Helical Coordination Polymers: Structures, Luminescence, and NLO-Active Properties

Hydro(solvo)thermal reactions between a new flexible multicarboxylate ligand of 2,2‘,3,3‘-oxydiphthalic acid (2,2‘,3,3‘-H4ODPA) and M(NO3)2·xH2O (M = Zn, x = 6; M = Cd, x = 4) in the presence of 4,4‘-bipyridine (bpy) afford two novel homochiral helical coordination polymers {[Zn2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 1 and [Cd2(2,2‘,3,3‘-ODPA)(bpy)(H2O)3]·(H2O)2 for 2}. Though having almost the same chemical formula, they have different space groups (P212121 for 1 and P21 for 2) and different bridging modes of the 2,2‘,3,3‘-ODPA ligand. Two kinds of homochiral helices (right-handed) are found in both 1 and 2, each of which discriminates only one kind of crystallographical nonequivalent metal atom. 1 has a 2D metal−organic framework and can be seen as the unity of two parallel homochiral Zn1 and Zn2 helices, in which the nodes are etheric oxygen atoms. In contrast, 2 has a 3D metal−organic framework and consists of two partially overlapped homochiral Cd1 and Cd2 helices in the two dimensions. Moreover, metal−ODPA helices give a 2D chiral herringbone structural motif in both 1 and 2 in the two dimensions, which are further strengthened by the second ligand of bpy. Bulk materials for 1 and 2 all have good second-harmonic generation activity, approximately 1 and 0.8 times that of urea.