A twofold interpenetrating three-dimensional heterometallic metal-organic framework with pcu topology based on 2-methylbiphenyl-4,4'-dicarboxylic acid.

Abstract

The 2-methylbiphenyl-4,4'-dicarboxylate (mbpdc2-) ligand has versatile coordination modes and can be used to construct multinuclear structures. Despite this, reports of the synthesis of coordination complexes involving this ligand are scarce. The title compound, poly[[triaquadi-μ3-hydroxido-hexakis(μ4-2-methylbiphenyl-4,4'-dicarboxylato)calcium(II)hexazinc(II)] monohydrate], {[CaZn6(C15H10O4)6(OH)2(H2O)3]·H2O}n, has been prepared by the hydrothermal assembly of Zn(NO3)2·6H2O, CaCl2 and 2-methylbiphenyl-4,4'-dicarboxylic acid. Two ZnII atoms adopt a four-coordinated distorted tetrahedral geometry by bonding to three O atoms from three different 2-methylbiphenyl-4,4'-dicarboxylate (mbpdc2-) dianionic ligands and one bridging hydroxide O atom. For the remaining ZnII atom, a five-coordinate environment is completed half the time by one carboxylate O atom, and then the same carboxylate O atom and an aqua O atom are present the other half of the time, giving a six-coordinate environment. The CaII atom is coordinated by six O atoms to give an octahedral coordination geometry. The supramolecular secondary building unit (SBU) is a hamburger-like heptanuclear unit (Zn6CaO30) and these units are interconnected through mbpdc2- carboxylate groups to generate a three-dimensional framework with the pcu topology. The single net leaves voids that are filled by mutual interpenetration of an independent equivalent framework in a twofold interpenetrating architecture. The title compound shows thermal stability up to 673 K. The excitation and luminescence data showed the emission of a bright-blue fluorescence.