Structural Flexibility and Selective Guest Accommodation in Two CuII Metal–Organic Coordination Frameworks

Abstract

AbstractTwo metal–organic coordination frameworks of CuII, [Na2Cu(2,4‐pyrdc)(H2O)(μ‐OH2)2]n (1) and {[Cu(2,5‐pyrdc) (NH3)](2H2O)}n (2) (2,4‐pyrdc = pyridine‐2,4‐dicarboxylate; 2,5‐pyrdc = pyridine‐2,5‐dicarboxylate), were synthesized and structurally characterized. The structure of compound 1 was known and shows that Cu(2,4‐pyrdc)2(H2O) functions as a metalloligand and is linked to two different NaI atoms to form a 3D heterometallic CuII–NaI framework. The single crystals of compound 2 were obtained from aqueous ammoniacal solution and crystallize in the triclinic (P$\bar {1}$) crystal system. Compound 2 is a 2D sheet consisting of two different CuII 1D chains bridged by a 2,5‐pyrdc ligand. Stacking of the 2D sheets results in a 3D supramolecular host with 1D water‐filled channels. Both frameworks are highly thermally stable and exhibit reversible structural transformation upon removal of the metal‐bound water and NH3 molecules for 1 and 2, respectively. Sorption studies reveal that desolvated frameworks 1′ and 2′ both behave nonporous to N2. However, 1′ exhibits structural transformation and hysteretic stepwise sorption of H2O and MeOH molecules, but THF and C6H6 molecules are not adsorbed. Similarly, H2O and MeOH molecules are easily adsorbed in 2′, but THF and C6H6 molecules are not. Such high selectivity in 1′ and 2′ was correlated to the smaller pore aperture and specific host–guest interaction conferred by the unsaturated Lewis acidic sites on the pore surfaces and the Lewis basic adsorbates. Low‐temperature magnetic study of 2 revealed that theCuII atoms are antiferromagnetically coupled, with J = –1.45 cm–1 and g = 2.01.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)