Alkali- and alkaline-earth metal–organic networks based on a tetra(4-carboxyphenyl)bimesitylene-linker

Abstract

Four new 3D-metal–organic and supramolecular frameworks based on the 3,3′,5,5′-tetrakis(4-carboxyphenyl)-2,2′,4,4′,6,6′-hexamethyl-1,1′-biphenyl ligand (H4L) namely: [Na2(H4L)(H2L)(DMF)2(H2O)2]n (1), 2[Mg(H2O)6]·2H3L·H2L (2), [Mg2L(DMF)2(H2O)]·2.5DMF (3), and 2[Ca(H2L)(H2O)4.5(DMF)0.5]·[Ca(H2L)(H2O)5]n·2H2O (4) were obtained and fully characterized. The sodium ion in compound 1 is coordinated by six oxygen atoms in a distorted octahedral geometry, with the oxygen atoms provided by four monodentate carboxylate groups, one water and one DMF molecule. The polycarboxylate ligand acts as a bridge between four Na ions to form an extended 3D coordination network with (4,4) topology. In compound 2 two crystallographically independent [Mg(H2O)6]2+ complex cations and three non-coordinated mono- and doubly deprotonated tetracarboxylic acid molecules form a 3D supramolecular network consolidated by a multiple system of OH⋯O hydrogen bonds. Compound 3 consists of two Mg2+ cations, one L4− tetra-anion, two coordinated DMF molecules and one aqua ligand to form a 3D coordination polymer. The crystal structure of compound 4 includes three crystallographically independent and chemically non-equivalent molecular entities: two molecular complexes [Ca(H2L)(H2O)4.5(DMF)0.5] and a coordination-polymeric helical strand of repeating formula unit [Ca(H2L)(H2O)5]n. The crystal structure of compound 4 is described as a supramolecular architecture where 1D coordination polymers [Ca(H2L)(H2O)5]n and two molecular units [Ca(H2L)(H2O)4.5(DMF)0.5] are linked through numerous intermolecular H-bonds.