Coordination polymers of zinc(II) and manganese(II) made by complexation of calix[4]arene functionalized with carboxylates afford alveolar materials

Abstract

25,27-bis(methoxycarboxylic acid)-26,28-dihydroxycalix[4]arene (calixH2), so call here calix[4]arene dimethoxycarboxylic acid, was investigated for its ability to build metal–organic frameworks. When reacted with zinc or manganese chloride in DMF and deprotonated with trimethylamine it gives Zn (1) and Mn (2) coordination compounds. These crystallize in the triclinic P-1 space group and are isostructural as shown by X-ray diffraction on single crystals. The crystal structures evidence the coordination of calix[4]arenedimethoxycarboxylic acid through the carboxylate groups. This makes a 1D coordination polymer running along the c axis direction in which [MII2(calix)2(H2O)3(DMF)2] (M = Zn or Mn) neutral units are connected. Last step refinements of the crystal structure reveal a lot of residual electron density which was ascribed to uncoordinated disordered water and DMF molecules. This was treated with the SQUEEZE routine of the program PLATON from which the solvent accessible voids per unit cell volume was calculated to be 24.5% for compound 1 (Zn) and 24.9% for compound 2 (Mn). Complementary differential thermal analyses (DTA) combined with thermogravimety analysis (TGA) and mass spectrometry (MS) are in agreement with large amount of incorporated and non-coordinated water and DMF molecules. Adsorption isotherms of N2 measured for compound 1 do not show any significant porosity. The temperature dependence of the magnetic susceptibility (χ) of compound 2 evidences antiferromagnetic interactions and was best fitted with a weak antiferromagnetic exchange coupling between the manganese(II) ions J = − 1.5 cm−1 and small antiferromagnetic inter-dinuclear interactions zJ = − 1.2 cm−1 (g = 2.02).