Coordination polymers of manganese(II), cobalt(II), nickel(II) and cadmium(II) decorated with rigid pyrazine-2,3-dicarboxylic acid linker: Synthesis, structural diversity, DFT study and magneto-luminescence properties

Abstract

Single crystal diffraction analysis shows the formation of four new coordination polymers (CPs), viz. {[Mn(Pyzdc)(H2O)2]·2H2O}n (1), [Co(Pyzdc)(H2O)2]n (2), [Ni(Pyzdc)(H2O)2]n (3) and [Cd(Pyzdc)]n (4) (where Pyzdc2− stands for the fully-deprotonated pyrazine-2,3-dicarboxylic acid), by the solvothermal self-assembly of the four titled metal(II) nitrates with rigid pyrazine-2,3-dicarboxylic acid. CP 1 crystallizes in the monoclinic P21/c space group, whereas CPs 2, 3 and 4 have orthorhombic Pcca, Pcca and Pnna space groups respectively. CPs 1–4 consist of dinuclear secondary building units (SBUs) [Mn2O10N2 (1), M2O8N4 (where M=Co (2) and Ni (3)) and Cd2O6N4 (4)]. In CPs 1–3 (Mn, Co and Ni), covalent interactions foster into one-dimensional structures, whereas CP 4 (Cd) exhibits a three-dimensional architecture. The Pyzdc linker exhibits three different coordination modes (μ3-κO:κO:κO:κN for CP 1, μ2-κO:κO:κN:κN for CPs 2 and 3, and μ4-κO,O:κO,O:κN:κN for CP 4). DFT calculations reveal that in one compound (CP 1), interesting π-hole interactions exist, which have been evaluated energetically (at the PBE1PBE-D3/def2-TZVP level of theory) and characterized using the quantum theory of “atoms-in-molecules” (QTAIM). Magnetic studies reveal that the Weiss constant, based on the equation χm = C/(T−θ), is negative (θ = −34.37, −50.46 and −37.09 K for CPs 1, 2 and 3 respectively). This suggests weak antiferromagnetic interactions between adjacent M(II) centers. Lastly, the ligand based photoluminescence of CP 4 has been explored.