Eight new complexes based on flexible multicarboxylate ligands: synthesis, structures and properties

Abstract

Eight new coordination complexes, namely [ZnL1(H₂O)₂]_n (1), [CdL1(H₂O)₂]_n (2), [CoL1(H₂O)₃]_n (3), [EuL1(NO₂)(H₂O)]_n (4), [SmL1(NO₂)(H₂O)]_n (5), [CdL2(H₂O)]_n (6), [CoL2(H₂O)₄]_n (7) and [NiL2(H₂O)₄]_n (8) were synthesized under solvothermal conditions based on flexible ligands 2,2′-(naphthalene-2,7-diylbis(oxy)) diacetic acid (H₂L1) and 2,2′-(biphenyl-4,4′-diylbis(oxy)) diacetic acid (H₂L2). X-Ray diffraction analysis revealed that the eight complexes exhibited new frameworks due to diverse coordination conformations of the flexible bicarboxylate ligands. In complexes 1–8, H₂L1 and H₂L2 all acted as bridging ligands to connect the metal ions. Complexes 1 and 2 both exhibited three-demensional (3D) supramolecular structures formed by one-demensional (1D) chains through intermolecular interactions. Complex 3 formed its 3D network by connecting the two-demensional (2D) layers through hydrogen bonds. Complexes 4 and 5 had similar 3D frameworks which are combined by nitroso groups as pillars. Complex 6 represented a 3D framework with pcu α-Po topology by using L2²⁻ ligands as linkers and the [Cd₂O₆] secondary building units (SBUs) as 6-connected nodes. The isostructural complexes 7 and 8 also gave rise to 3D supramolecular networks by joining 1D chains with hydrogen bonds and π–π interactions. The luminescent properties for 1, 2, 4 and 6 are discussed in detail. Complexes 3, 4, 7 and 8 exhibited antiferromagnetic interactions between the magnetic centers.