Tuning of Adsorption and Magnetic Properties in a Series of Self-Templated Isostructural Ni(II) Metal−Organic Frameworks

Abstract

An isomorphous series of five metal–organic frameworks of formula [Ni4(O2CR)(OH)2(4-pyc)5] [4-pyc = 4-pyridinecarboxylate or isonicotinate; R = C6H5 (1), 4-OMe-C6H4 (2), 2,6-(OMe)2-C6H3 (3), 3,5-(OMe)2-C6H3 (4), 3,4,5-(OMe)3-C6H2 (5)] were obtained by solvothermal reactions. These compounds display a three-dimensional framework where the nickel atoms are coordinated to the hydroxyde anions and two different organic ligands: isonicotinate and phenylcarboxylate. Both hydroxyde (μ3-OH) and phenylcarboxylate (μ3-1κO,2κO,3κO′) ligands are coordinated to nickel atoms of the same secondary building unit (SBU). The SBU consists of four edge-sharing NiA6 octahedra (A = O, N). The isonicotinate ligands, however, act as linkers between SBUs displaying three different coordination modes: μ-1κN,2κO; μ3-1κN,2κO,3κO′; and μ4-1κN,2:3κ2O,4κO′. Nitrogen adsorption measurements were done to obtain textural parameters of these microporous networks. Micropore size distributions indicate cylindrical pores with diameters of approximately 0.80 nm. The values of Brunauer–Emmett–Teller surface areas (SBET) obtained are in the range of 382–488 m2/g, and the micropore volumes are between 0.13 cm3/g and 0.19 cm3/g. Both parameters are influenced by the substitution grade and position of the methoxy groups of the phenylcarboxylate ligand. The magnetic properties, which also depend on the arylcarboxylate ligands, vary from compound 1 (with only antiferromagnetic interactions) to compound 5, which shows a spin glass behavior (Tg = 15 K).