Metal-organic coordination polymers based on a flexible tetrahydrofuran-2,3,4,5-tetracarboxylate ligand: syntheses, crystal structures, and magnetic/photoluminescent properties

The coordination possibilities of flexible heteroalicyclic ligands with transition metals have been explored. Five Cu-II, Mn-II, and Cd-II coordination polymers with the fully deprotonated tetrahydrofuran-2,3,4,5-tetracarboxylate (L) ligand were synthesized and characterized, sometimes incorporating different auxiliary ligands: {[Cu-2(L)(H2O)](H2O)(1.42)}(infinity) (1), {[Cu-2(L)(2bpy)(H2O)(2)](H2O)(2)}(infinity) (2), {[Cu-2(L)(phen)(H2O)(2)](H2O)(1.5)(CH3OH)(0.25)}(infinity) (3), {[Mn-2(L)(phen)(2)(H2O)](H2O)(2)}(infinity) (4), and {[Cd-2(L)(phen)(2)(H2O)](H2O)(2)}(infinity) (5) (2bpy = 2,2'-bipyridine and phen 1,10-phenanthroline). The structural analysis related to 1-5 reveals that the fully deprotonated L ligand displays versatile coordination modes, which result in the generation of a fairly complicated three dimensional (3D) framework for 1 with a Schlafli symbol of (4(3).6(7))(4(6).6(4)), two isostructural two dimensional (2D) puckered layers for 2 and 3 with the decorated binodal (3,5)-connected (3.5(2))(2)(3(2).5(3).6(4).7) topology, and two isostructural one dimensional (1D) ribbon-like chains for 4 and 5, respectively. The present work indicates that, in comparison with the rigid aromatic multicarboxylate ligands, tetrahydrofuran-2,3,4,5-tetracarboxylate (L), a heteroalicyclic multicarboxylate ligand, has richer coordination modes and a more flexible ring skeleton, which may remain largely unexpected in the process of constructing metal-organic frameworks (MOFs) and make it more difficult to predict and control the final coordination polymers. Magnetic susceptibility measurements demonstrate that complexes 1 and 4 exhibit antiferromagnetic coupling, whereas 2 and 3 show ferromagnetic coupling, with the corresponding J values of -23.62 cm(-1) for 1, 5.18 cm(-1) for 2, 3.90 cm(-1) for 3, and -0.79 cm(-1) for 4. Moreover, complex 5 displays solid blue emission originating from an intraligand pi -> pi* transition of the auxiliary phen ligand.