Three one-dimensional chains with bulky backbone carboxylate ligands: Syntheses, crystal structures, and luminescent properties

To explore the influence of bulky backbone on complexes, three Co(II) and Zn(II) complexes with phenanthrene-9-carboxylate (L-1), 9H-fluorene-9-carboxylate (L-2) or biphenyl-4-carboxylate (L-3) together with incorporating auxiliary bridging ligad 4,4'-bipyridine (4Bipy), were synthesized and characterized: [Co(L-1)(2)(4Bipy)(H2O)(2)](a) (I), [Zn(L-2)(2)(4Bipy)(0.5)(4Bipy)(0.5)](a) (II), and [Zn-3(L-3)(4)(4Bipy)(0.5)(4Bipy)(0.5)(4Bipy)(0.5)(OH)(2)](a) (III). X-ray single-crystal diffraction analyses show that complexes I-III both assume one-dimensional (1D) structures by incorporating the bridging 4Bipy (CIF file CCDC nos. 942729 (I), 942727 (II), and 942733 III). In I, mononuclear six-coordinated Co2+ ions are linked into a 1D linear chain by 4Bipy. While in II, mononuclear four-coordinated Zn2+ ions are linked into a 1D zigzag chain by 4Bipy. But in III, because of the existence of OH-, hexanuclear Zn(II) can be regarded as a node, then bridge adjacent hexanuclear Zn(II) nodes by almost parallelled three 4Bipy ligands into a 1D linear chain. Finally the 1D chains of I-III are further assembled into an overall three-dimensional (3D) framework via intermolecular H-bonding, pi aEuro broken vertical bar pi stacking, and/or C-HaEuro broken vertical bar pi supramolecular interactions, respectively. The results indicate that, besides different metal ions Co2+ and Zn2+ or OH- anions, the steric hindrance of backbone ligands play an important role in the formation of I-III. Moreover, the luminescent properties of corresponding ligands and their complexes were briefly investigated.