A new anion sensor [Ru(bpy)2(H2biim)](PF6)2 (1) (bpy = 2,2'-bipyridine and H2biim = 2,2'-biimidazole) has been developed, in which the Ru(II)-bpy moiety acts as a chromophore and the H2biim ligand as an anion receptor via hydrogen bonding. A systematic investigation shows that 1 is an eligible sensor for various anions. It donates protons for hydrogen bonding to Cl-, Br-, I-, NO3-, HSO4-, H2PO4-, and OAc- anions and further actualizes monoproton transfer to the OAc- anion, changing color from yellow to orange brown. The fluoride ion has a high affinity toward the N-H group of the H2biim ligand for proton transfer, rather than hydrogen bonding, because of the formation of the highly stable HF2- anion, resulting in stepwise deprotonation of the two N-H fragments. These processes are signaled by vivid color changes from yellow to orange brown and then to violet because of second-sphere donor-acceptor interactions between Ru(II)-H2biim and the anions. The significant color changes can be distinguished visually. The processes are not only determined by the basicity of anion but also by the strength of hydrogen bonding and the stability of the anion-receptor complexes. The design strategy and remarkable photophysical properties of sensor 1 help to extend the development of anion sensors.

A new copper(II) fluorescent sensor 5,10,15,20-tetra((p-N,N-bis(2-pyridyl)amino)phenyl)porphyrin zinc (1) has been designed and synthesized by the Ullmann-type condensation of bromoporphyrin zinc with 2,2'-dipyridylamine (dpa) under copper powder as a catalyst as well as with K2CO3 as the base in a DMF solution. It consists of two separately functional moieties: the zinc porphyrin performs as a fluorophore, and the dpa-linked-to-zinc porphyrin acts as a selected binding site for metal ions. It displays a high selectivity and antidisturbance for the Cu2+ ion among the metal ions examined (Na+, Mg2+, Cr3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+, and Fe3+) and exhibits fluorescence quenching upon the binding of the Cu2+ ion with an "on-off"-type fluoroionophoric switching property. The detection limit is found to be 3.3 x 10(-7) M (3s blank) for Cu2+ ion in methanol solution, and its fluorescence can be revived by the addition of EDTA disodium solution. The design strategy and remarkable photophysical properties of sensor 1 help to extend the development of fluorescent sensors for metal ions.

A ruthenium(II) complex [Ru(bpy) 2(H 2bbim)](PF 6) 2 ( 1) as anions receptor has been exploited, where Ru(II)-bpy moiety acts as a chromophore and the H 2bbim ligand as an anion binding site. A systematic study suggests that 1 interacts with the Cl (-), Br (-), I (-), NO 3 (-), HSO 4 (-), and H 2PO 4 (-) anions via the formation of hydrogen bonds. Whereas 1 undergoes a stepwise process with the addition of F (-) and OAc (-) anions: formation of the monodeprotonated complex [Ru(bpy) 2(Hbbim)] with a low anion concentration, followed by the double-deprotonated complex [Ru(bpy) 2(bbim)], in the presence of a high anion concentration. These stepwise processes concomitant with the changes of vivid colors from yellow to orange brown and then to violet can be used for probing the F (-) and OAc (-) anions by naked eye. The deprotonation processes are not only determined by the basicity of the anion but also related to the strength of hydrogen bonding, as well as the stability of the formed compounds. Moreover, a double-deprotonated complex [Ru(bpy) 2(bbim)].CH 3OH.H 2O ( 3) has been synthesized, and the structural changes induced by the deprotonation has also been investigated. In addition, complexes [Ru(bpy) 2(Hbbim)] 2(HOAc) 3Cl 2.12H 2O ( 2), [Ru(bpy) 2(Hbbim)](HCCl 3CO 2)(CCl 3CO 2).2H 2O ( 4), and [Ru(bpy) 2(H 2bbim)](CF 3CO 2) 2.4H 2O ( 5) have been synthesized to observe the second sphere coordination between the Ru(II)-H 2bbim moiety and carboxylate groups via hydrogen bonds in the solid state.

Six complexes containing the 2,2′-biimidazole-like ligand and chloride, namely, trans-[Ni(H 2 biim) 2 (H 2 O) 2 ]Cl 2 (1), trans-[Co 1.5 (H 2 biim) 3 (Hand [Zn 2 (Hbbim) 2 (bbim) 0.5 Cl] (6) (where H 2 biim ) 2,2′-biimidazole, H 2 bbim ) 2,2′-bibenzimidazole) have been synthesized by the reactions of the H 2 biim or H 2 bbim ligand with the metal chloride salts. The structures of the complexes were determined by singlecrystal X-ray diffraction analyses, and the results revealed that the distances of N • • • Cl varied from 3.10 to 3.29 Å and the angles of N-H • • • Cl varied from 148 to 169°, O • • • Cl varied from 3.09 to 3.16 Å, O-H • • • Cl varied from 151 to 178°, C • • • Cl varied from 3.49 to 3.69 Å, and C-H • • • Cl varied from 122 to 167°.The chloride may act as a multi hydrogen bonded acceptor varying from 3 to 6, resulting in an important collective contribution to cohesion. The data observed in this study seem to suggest that a variety of X-H • • • Cl (X ) N, O, and C) synthons identified here play a crucial role in the formation and further stabilization of supramolecular architecture, for instance, to link the discrete (0D) or low-dimensional (1D) entities into high-dimensional frameworks. In particular, the coplanar [(H 2 O) 2 Cl 2 ] 2guests are encapsulated in the cavities formed by four [Co(H 2 bbim) 3 ] 2+ cations and stabilized via accepting 6-fold hydrogen bonds from three H 2 bbim ligands in 5. The distance between the chloride anion and the imidazolyl ring (Cl • • • centroid, 3.30 Å and 80°) demonstrates the possible existence of Cl • • • π (imidazolyl) charge-assisted interactions because the coordination of a positively charged Co(II) ion greatly enhances the electron-deficient character of the imidazolyl ring and provides sufficient polarization to produce an anion-π charge-assisted interaction.

Five different cobalt complexes were synthesized by the combination of the multidentate ligand 2,2′-bibenzimidazole (H 2 bbim) and the coordination plasticity of cobalt ion in the presence of 4-cyanopyridine under hydrothermal conditions using temperature as the only independent variable. The structural features of theses complexes, which ranged from zero-dimensional (0D) in [Co(Hbbim) ] n (4), were extremely dependent on the reaction temperature. At 130 °C, discrete 1 was the unique product. However, 4 was the main product when the reaction temperatures were set in the range of 160-200 °C. 2 and 3 yielded at 140 °C as main products. In spite of the structural diversity of this system, crystallographic studies reveal that the H 2 bbim ligand typically displays tridentate (Hbbim -) and/or tetradentate (bbim 2-) coordination modes at high temperature, however, a chelating mode at low temperature. The ligands Hbbimand bbim 2offering donor atoms and charge balance may have both advantages of bipyrimidine and oxalate in the assembly of high-dimensional structures. Indeed, 2 is the first instance of 2D honeycomb (6,3), neutral coordination polymer constructed by only one type of ligand and one type of metal ion. Magnetic properties of 3 and 4 have been studied in the temperature range of 2-300 K. Both compounds exhibit antiferromagnetic interactions between metal ions through the bridging ligand.

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