Regulating the structural dimensionality, gas sorption and magnetic behavior of Co(ii) coordination polymers

Abstract

Ligands play a key role in the regulation of dimentionality and multi-functional properties of coordination polymers. An interesting example of structural modulation based on the chain length of aliphatic dicarboxylic acids is shown here in this work. Three new Co(II) based coordination polymers (CPs) [Co₂(L)(SA)₂]_n (1), [Co₂(L)(AA)₂]_n (2), and [Co₂(L)(STDCA)₂]_n (3) [SA = succinic acid, AA = adipic acid, STDCA = 4,4′-stilbenedicarboxylic acid and L = 4′-(4-methoxyphenyl)-4,2′:6′,4′′-terpyridine] have been synthesized by solvothermal reactions and characterized by single-crystal X-ray diffraction (SCXRD), thermogravimetric analysis (TGA) and IR spectroscopy. Structural analysis reveals that 1 exhibits a two dimensional (2D) sheet type structure with the sql topolgy whereas 2 adopts a three dimensional (3D) framework with the pcu topology due to enhanced flexibility of the AA coligand; 3 also forms a 3D coordination network but crystallizes with new topology. Brunauer–Emmett–Teller (BET) analysis revealed surface areas between 2.092–7.827 m² g⁻¹ and pore volumes between 0.010 and 0.076 cm³ g⁻¹ for the CPs 1–3. Magnetic investigation revealed that CPs 1–3 show strong antiferromagnetic behaviour. PHI fitting of the susceptibilty data show magnetic exchange values of −221 cm⁻¹, −18 cm⁻¹ and −2.2 cm⁻¹ for 1, 2 and 3 respectively. Interestingly, CPs 1 and 2 show a pronounced decrease in the χ_MT values with decreasing temperature likely due to direct Co(II)⋯Co(II) interaction within the dinuclear core of the frameworks of CPs.