Metallosupramolecular Crystals Created from an Anionic AuI3CoIII2 Pentanuclear Complex with Penicillaminate

概要

Metallosupramolecular crystals have attracted much attention due to their potential applications in molecular sorption and separation, catalysis, sensor, ion exchange, and optoelectronic. Diverse metallosupramolecular crystals have been created by solvothermal reactions at high temperature or self-assembly at room temperature by using metal ions and ligands as building blocks. Among the important reaction conditions for the creation of desired metallosupramolecular crystals, the combination of molecular building blocks is the most effective factor. Recently in my research group, three-dimensional (3D) metallosupramolecular crystals with a porosity of 80% were created by the combination of the anionic AuI3CoIII2 pentanuclear complex ([Au3Co2(ᴅ-pen)6]3-, ᴅ-H2pen = ᴅ- penicillamine) with aqua transition metal cations (CoII, NiII, and MnII). In contrast, the use of the related CuI3CoIII2 pentanuclear complex ([Cu3Co2(ᴅ-pen)6]3-) instead of [Au3Co2(ᴅ-pen)6]3- resulted in the formation of less porous metallosupramolecular crystals (porosity = 60%). While the different complexes have been used for the reactions in the previous works, the combination of the AuI3CoIII2 pentanuclear complex with different cations, other than transition metal ions, has not been investigated.

In this study, the creation of metallosupramolecular crystals from the anionic AuI3CoIII2 pentanuclear complex with penicillaminate and diverse cationic species was studied. As the cationic species, cationic phenanthroline complexes, [M(phen)n]2+ (M = MnII, CoII, NiII, and ZnII; phen = 1,10- phenanthroline), Na+ cation, and cationic 2-aminoethanethiolato complexes, [Co3(aet)6]3+, [Ag3Co2(aet)6]3+, and [{Co(aet)3}4Zn4O]6+ (aet = 2-aminoethanethiolate), were used in the reactions with the anionic AuI3CoIII2 pentanuclear complex. Furthermore, vapor sorption properties toward H2O and ethanol, molecular inclusion, and chiralselective inclusion were investigated for the obtained crystals. This study clarified the effect of cationic species on the structures and functions of metallosupramolecular crystals that are obtained in combination with the anionic AuI3CoIII2 pentanuclear complex.

Firstly, the construction of a heterochiral metallosupramolecular framework and its transformation to a homochiral framework were demonstrated by the combination of the anionic AuI3CoIII2 complex ([Au3Co2(ᴅ-pen)6]3-) with cationic phenanthroline complexes, [M(phen)n]2+ (M = MnII, CoII, NiII, and ZnII). The combination led to the formation of ionic crystals, [M(phen)2(H2O)2][Na(H2O)6][{M(phen)2(H2O)}Au3Co2(ᴅ-pen)6]3 (1-M). In 1-M, [Au3Co2(ᴅ-pen)6]3- anions and [M(phen)2(H2O)]2+ cations are linked by COO-M coordination bonds, forming an anionic hexanuclear complex, [{M(phen)2(H2O)}Au3Co2(ᴅ-pen)6]3. The octahedral M ions in 1-M have both Δ and Λ configurations, giving heterochiral crystals. Due to the inherent labile nature of MnII ion, compared with CoII, NiII, and ZnII, only 1-Mn showed the structural transformation to the homochiral metallosupramolecular crystal, [Mn(phen)3]3[Au3Co2(ᴅ-pen)6]2·phen (2-Mn), in the mother liquor. In 2-Mn, a hydrogen-bonding framework composed of [Au3Co2(ᴅ-pen)6]3- anions accommodated [Mn(phen)3]2+ cations and phen ligands in its cavities by CH…π and π…π interactions. It was found that the chirality around the MnII centers changed to Λ during the reaction, giving the homochiral crystals.

Moreover, the porous metallosupramolecular frameworks were constructed by combining Na+ cations and the AuI3CoIII2 pentanuclear complex-anions in a sodium acetate buffer solution. The metallosupramolecular crystals, Na3[Au3Co2(ᴅ-pen)6]・0.33NaOAc (3-D), Na3[Au3Co2(ʟ- pen)6]・0.33NaOAc (3-L), and Na3[Au3Co2(ᴅ-pen)6]0.5[Au3Co2(ʟ-pen)6]0.5・0.33NaOAc (4), were produced. Employing the anionic AuI3CoIII2 pentanuclear complex with ᴅ- or ʟ-pen gave an enantiomeric pair of 3D metallosupramolecular crystals of 3-D or 3-L with a porosity of 78%. In 3, three AuI3CoIII2 complex-anions are linked to each other via COO-M coordination bonds with {Na4(H2O)15}4+ and COO…H2O hydrogen bonds with [Na(H2O)6]+ to form 3-connected nodes. In contrast, the racemic mixture of the AuI3CoIII2 complex gave a racemic metallosupramolecular framework (4) with a lower porosity. In 4, ᴅ- and ʟ-configurational frameworks are interpenetrated to each other. Both of 3 and 4 have the cationic sodium clusters ({Nan(H2O)m}n+) as nodes, which are formed due to the high concentration of sodium acetate in the reaction solution. The chiral metallosupramolecular 3 revealed the accommodation of α- and γ-CDs (CD = cyclodextrin) in the crystals. The obtained crystals,