Flexible Coordination Polymers Composed of Luminescent Ruthenium(II) Metalloligands: Importance of the Position of the Coordination Site in Metalloligands

Coordination polymerization reactions between ruthenium­(II) metalloligands [Ru­(<i>n</i>,<i>n</i>′-dcbpy)]^4– (<b>[</b><i><b>n</b></i><b>Ru]</b>; <i>n</i> = 4, 5; <i>n</i>,<i>n</i>′-dcbpy = <i>n</i>,<i>n</i>′-dicarboxy-2,2′-bipyridine) and several divalent metal salts in basic aqueous solutions afforded porous luminescent complexes formulated as [Mg­(H₂O)₆]­{[Mg­(H₂O)₃]­[4Ru]·4H₂O} (<b>Mg</b>_<b>2</b><b>[4Ru]·13H</b>_<b>2</b><b>O</b>), [Mg₂(H₂O)₉]­[5Ru]·10H₂O (<b>Mg</b>_<b>2</b><b>[5Ru]·19H</b>_<b>2</b><b>O</b>), {[Sr₄(H₂O)₉]­[4Ru]₂·9H₂O} (<b>Sr</b>_<b>2</b><b>[4Ru]·9H</b>_<b>2</b><b>O</b>)₂, {[Sr₂(H₂O)₈]­[5Ru]·6H₂O} (<b>Sr</b>_<b>2</b><b>[5Ru]·14H</b>_<b>2</b><b>O</b>), and {[Cd₂(H₂O)₂]­[5Ru]·10H₂O} (<b>Cd</b>_<b>2</b><b>[5Ru]·12H</b>_<b>2</b><b>O</b>). Single-crystal X-ray structural analyses revealed that the divalent metal ions were commonly coordinated by the carboxyl groups of the <b>[</b><i><b>n</b></i><b>Ru]</b> metalloligand, forming porous frameworks with a void fraction varying from 11.4% <b>Mg</b>_<b>2</b><b>[4Ru]·13H</b>_<b>2</b><b>O</b> to 43.9% <b>Cd</b>_<b>2</b><b>[5Ru]·12H</b>_<b>2</b><b>O</b>. <b>M</b>_<b>2</b><b>[4Ru]·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b> showed a reversible structural transition accompanied by water and methanol vapor adsorption/desorption, while the porous structures of <b>M</b>_<b>2</b><b>[5Ru]·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b> were irreversibly collapsed by the removal of crystal water. The triplet metal-to-ligand charge-transfer emission energies of <b>M</b>_<b>2</b><b>[4Ru]·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b> were lower than those of <b>[4Ru]</b> in aqueous solution, whereas those of <b>M</b>_<b>2</b><b>[5Ru]·</b><i><b>n</b></i><b>H</b>_<b>2</b><b>O</b> were close to those of <b>[5Ru]</b> in aqueous solution. These results suggested that the position of the coordination site in the metalloligand played an important role not only on the structure of the porous framework but also on the structural flexibility involving the guest adsorption/desorption properties

Systematic Syntheses and Metalloligand Doping of Flexible Porous Coordination Polymers Composed of a Co(III)–Metalloligand

A series of flexible porous coordination polymers (PCPs) <b>RE–Co</b>, composed of a Co­(III)–metalloligand [Co­(dcbpy)₃]^3– (<b>Co</b>; H₂dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) and lanthanide cations (RE³⁺ = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Er³⁺), was systematically synthesized. X-ray crystallographic analysis revealed that the six carboxylates at the top of each coordination octahedron of Co­(III)–metalloligand were commonly bound to RE³⁺ cations to form a rock-salt-type porous coordination framework. When <b>RE–Co</b> contains a smaller and heavier RE³⁺ cation than Nd³⁺, the <b>RE–Co</b> crystallized in the cubic <i><i>Fm</i>-3<i>m</i></i> space group, whereas the other three <b>RE–Co</b> with larger RE³⁺ crystallized in the lower symmetrical orthorhombic <i>Fddd</i> space group, owing to the asymmetric 10-coordinated bicapped square antiprism structure of the larger RE³⁺ cation. Powder X-ray diffraction and vapor-adsorption isotherm measurements revealed that all synthesized <b>RE–Co</b> PCPs show reversible amorphous–crystalline transitions, triggered by water-vapor-adsorption/desorption. This transition behavior strongly depends on the kind of RE³⁺; the transition of orthorhombic <b>RE–Co</b> was hardly observed under exposure to CH₃OH vapor, but the <b>RE–Co</b> with smaller cations such as Gd³⁺ showed the transition under exposure to CH₃OH vapors. Further tuning of vapor-adsorption property was examined by doping of Ru­(II)–metalloligands, [Ru­(dcbpy)₃]^4–, [Ru­(dcbpy)₂Cl₂]^4–, [Ru­(dcbpy)­(tpy)­Cl]⁻, and [Ru­(dcbpy)­(dctpy)]^3– (abbreviated as <i><b>Ru</b></i><b>A</b>, <i><b>Ru</b></i><b>B</b>, <i><b>Ru</b></i><b>C</b>, and <i><b>Ru</b></i><b>D</b>, respectively; tpy = 2,2′:6′,2″-terpyridine, H₂dctpy = 4,4″-dicarboxy-2,2′:6′,2″-terpyridine), into the Co­(III)–metalloligand site of <b>Gd–Co</b> to form the Ru­(II)-doped PCP <i><b>Ru</b></i><b>X@Gd–Co</b> (X = A, B, C, or D). Three Ru­(II)–metalloligands, <i><b>Ru</b></i><b>A</b>, <i><b>Ru</b></i><b>B</b>, and <i><b>Ru</b></i><b>D</b> dopants, were found to be uniformly incorporated into the <b>Gd–Co</b> framework by replacing the original Co­(III)–metalloligand, whereas the doping of <i><b>Ru</b></i><b>C</b> failed probably because of the less number of coordination sites. In addition, we found that the <i><b>Ru</b></i><b>A</b> doping into the <b>Gd–Co</b> PCP had a large effect on vapor-adsorption due to the electrostatic interaction originating from the negatively charged <i><b>Ru</b></i><b>A</b> sites in the framework and the charge-compensating Li⁺ cations in the porous channel