Designing Multifunctional 5-Cyanoisophthalate-Based Coordination Polymers as Single-Molecule Magnets, Adsorbents, and Luminescent Materials.

Abstract

Detailed structural, magnetic, and photoluminescence characterization of a family of new compounds based on 5-cyanoisophthalate (CNip) ligand and several transition metal or lanthanide ions, namely, [Cu3(μ3-CNip)2(μ-H2O)2(μ3-OH)2]n (1), {[Co3(μ4-CNip)3(DMF)4]·∼2DMF}n (2), [Cd(μ4-CNip) (DMF)]n (3), {[Ln2(μ4-CNip)(μ3-CNip)2(DMF)4]·∼DMF·H2O}n (4-Ln) (with LnIII = Tb, Dy, and Er), {[Gd6(μ3-CNip)5(μ4-CNip)3(μ-form)2(H2O) (DMF)10]·∼3DMF·3H2O}n (5), {[Zn32(μ4-CNip)12(μ-CNip)12(μ4-O)8(H2O)24]·∼12DMF}n (6) (where DMF = dimethylformamide, form = formate), is reported. The large structural diversity found in the system may be explained mainly in terms of the coordination characteristics that are inherent to the employed metal ions, the coordination versatility of the dicarboxylic ligand and the synthetic conditions. Interestingly, some crystal structures (three-dimensional (3D) frameworks of 4-Ln and 5 and 3D network of 6) exhibit open architectures containing large solvent-occupied void systems, among which 5 reveals permanent porosity as confirmed by N2 adsorption measurements at 77 K. Magnetic direct current (dc) susceptibility data on compounds 1, 2, and 5 were measured. Moreover, compounds 2, 4-Dy, 4-Er, and 5 show slow magnetic relaxation, from which it is worth highlighting the effective energy barrier of 44 K at zero dc field for the dysprosium counterpart. Compound 5 also deserves to be mentioned given the few 3D Gd-organic frameworks reported examples. Photophysical properties were also accomplished at different temperatures, confirming both the fluorescent emission of 5-cyanoisophthalate ligands when coordinated to cadmium ions in 3 and their capacity to sensitize the long-lived fluorescence of the selected lanthanide ions in 4-Ln. Broken symmetry and time-dependent density functional theory computational calculations support the experimental luminescence and magnetic properties.