Shin-ichi Nishikiori’s research while affiliated with The University of Tokyo and other places

A newly synthesized coordination polymer, [(CH3)3NH]2[CuZn(CN)5], was investigated using ¹³C and ⁶³Cu solid‐state NMR techniques and single‐crystal X‐ray diffractometry. It consists of a three‐dimensional (3D) net composed of tetrahedral CuI and ZnII ions and CN– ligands bridging between the two metal ions. (CH3)3NH⁺ ions are trapped in the inner space of the 3D net. Three coordination sites of each metal ion are used for the formation of the 3D net and the remaining site is occupied by a unidentate CN– ligand. The structure of the 3D net is chiral and categorized as srs in the notation of the Reticular Chemistry Structure Resource (RCSR). In water vapor or open air at room temperature under ambient pressure, a powder of [(CH3)3NH]2[CuZn(CN)5] showed a structural transformation to [(CH3)3NH][CuZn(CN)4]·1.5H2O, which is a known compound with a diamond‐like 3D net of [CuZn(CN)4]– composed of tetrahedral CuI and ZnII ions and bridging CN– ligands. ⁶³Cu solid‐state NMR spectroscopy revealed that the Cu‐CN‐Zn orientation of the bridging CN– ligands was conserved after the structural transformation.

The new inclusion compound [(CH3)2NH2][CuZn(CN)4]∗ nH2O, whose host is a 3-D coordination polymer net formed with tetrahedral Cu(I) and Zn(II), as well as bridging cyanido ligands, exhibited a new type of structural transformation upon desorption/absorption of the guest water. This consisted of a reversible reconstruction of the host between a cristobalite-like and tridymite-like net. 63Cu solid-state NMR showed the conservation of the orientation of the cyanido bridges during the structural transformation, which required the breaking and reforming of the coordination bonds.

The title compound, {(C3H10N)2[CdCu2(CN)6]}n, has been synthesized as an alternative to the high-emitting complexes containing more expensive metals. The CN⁻ ligands make linkages between the CuI and CdII ions to form the coordination polymer, [CdCu2(CN)6]n²⁻, which is a three-dimensional framework classified as pyrite net (pyr). The net has a void space for accommodating a tri­methyl­ammonium ion located on a threefold rotation axis. The CdII ion lies on a special position with site symmetry -3 and is octa­hedrally coordinated by six N atoms. The CuI ion is located on a threefold rotation axis and has a trigonal-planar coordination geometry formed by three C atoms. In the three-dimensional net, two CuI ions are arranged closely [Cu⋯Cu = 3.9095 (5) Å], but the distance is not short enough to suggest a CuI–CuI inter­action. The crystal studied was a merohedral twin (twin operation 2[101]), the refined component ratio being 0.9202 (7):0.0798 (7). A powder of the title compound shows strong luminescence with an emission maximum at 509 nm and a quantum yield of 98% at room temperature.

A newly prepared metal complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O, which was estimated to have a structure similar to the Hofmann-type clathrate host, changed its color from orange to deep orange and yellow on exposure to ethanol and acetone vapor, respectively, and the respective samples showed thermally induced two-step and one-step spin transitions.

A new framework structure of the coordination polymer [CuZn(CN)4]– has been discovered in the newly synthesized [Na(H2O)n][CuZn(CN)4] (n = 12.7; 1). X-ray crystal structure analysis revealed a 3D framework comprised of tetrahedral Cu(I) and Zn(II) centres with bridging cyanide ligands containing both octagonal and square channel cavities; these channels contain hydrated Na⁺ ions as guests. In open air, complex 1 is extremely unstable and loses water molecules to form [Na(H2O)n][CuZn(CN)4] (n = 5.2–6.8; 2) within 30 min. Powder X-ray diffraction patterns showed that this change results in the conversion of the framework of complex 1 to the same framework observed in [K(H2O)n][CuZn(CN)4]. The [CuZn(CN)4]– framework of [K(H2O)n][CuZn(CN)4] has a tridymite structure with hexagonal channel cavities occupied by hydrated K⁺ ions. Like 1, 2 is also unstable under atmospheric conditions, yielding [Na(H2O)n][CuZn(CN)4] (n = 3), which has an unknown structure. While the framework of [K(H2O)n][CuZn(CN)4] is structurally flexible and robust, the framework of 2 is unstable and fragile. This contrast comes from the difference between the nature of the hydrated K⁺ and Na⁺ ions present in the frameworks.

The framework host [CuZn(CN)4]-, a coordination polymer composed of tetrahedral Cu(I) and Zn(II) ions and CN- bridges, exhibits a reversible reconstructive transition in the solid-state between a cristobalite-like framework and a tridymite-like one induced by guest exchange between water and acetonitrile molecules.

Bis(-diketonato) Co(II) complex, [Co(dbm)(2)] (dbm = dibenzoylmethanato or 1,3-diphenyl-propane-1,3-dionato), was examined as a linear building block for the construction of coordination polymers in the combination with a potentially tridentate ligand, 2,6-bis(4-pyridyl)-4-(3-pyridyl)pyridine (L1). L1 was expected to work as a conformationally flexible ligand because of the rotation of the terminal 3-pyiridyl moiety. A porous coordination polymer, [Co(dbm)(2)](3/2)(L1) (G) (Co-1, G = guest molecules) with a fourfold interpenetrating -hydroquinone framework was obtained from a methanol-nitrobenzene-benzonitrile mixed solution containing [Co(dbm)(2)(H2O)(2)] and L1. Single crystal X-ray diffraction analysis reveals that Co-1 crystallizes in a trigonal space group R-3 with unit-cell parameters, a = b = 53.8629(12), c = 14.0649(7) angstrom, and V = 35338(3) angstrom(3). Solvent molecules were indicated to be included in the large hexagonal channel from thermogravimetry and elemental analyses, while they could not be determined from X-ray analysis because of the severe disorder. Meanwhile, a 2-D (6. 3) coordination polymer (Co-2) was obtained from the nitrobenzene-methanol mixed solution. In Co-2, [Co(dbm)(2)] and L1 also work as a linear building block and a tridentate ligand, respectively. Moreover, a coordination polymer with a 1-D chain structure (Co-3) was obtained from a hydrothermal synthetic condition. In Co-3 with no guest molecules, [Co(dbm)(2)] works as a linear building block, while L1 behaves as a bidentate ligand. Comparison of the three structures indicates the templating role of solvent molecules in forming the -hydroquinone framework of Co-1.

Two types of bis(β-diketonato) Co(II) complexes, [Co(CNacac)2] (CNacac = 3-cyano-pentane-2,4-dionato), and [Co(dbm)2] (dbm = dibenzoylmethanato or 1,3-diphenyl-propane-1,3-dionato) were examined as linear building blocks for the construction of coordination polymers in combination with two oligopyridines, 1,4-bis(4,2’:6’,4”-terpyridin-4’-yl)benzene (L1) and 1,3-bis(3,2’:6’,3”-terpyridin-4’-yl)benzene) (L2). From combinations of [Co(CNacac)2] with L1 and L2, 2-D coordination polymers, [Co(CNacac)2]2(L1)·(CHCl3)·(CH3OH) (CoCN-1) and [Co(CNacac)2](L2)1/2·(tetrachloroethane)3/2 (CoCN-2), are obtained. Both CoCN-1 and CoCN-2 have 2D (4,4) net structures, in which L1 and L2 are tetradentate. In contrast, combination of [Co(dbm)2] with L2 affords a 1-D coordination polymer, [Co(dbm)2](L2)·4(CH3OH) (Codbm-1), in which L2 is bidentate. L2 as a tetradentate ligand was inhibited by bulky phenyl rings in [Co(dbm)2]. These results indicate that [Co(CNacac)2] with a relatively simplified structure is useful as a linear building block in combinations with bulky oligopyridines.

We previously reported that monomeric and polymeric metal complexes are obtained from solution and mechanochemical reactions of 3-cyano-pentane-2,4-dione (CNacacH) with 3d metal acetates (M=Mn(II) , Fe(II) , Co(II) , Ni(II) , Cu(II) , and Zn(II) ). A common feature found in all complexes was that their structural base is trans-[M(CNacac)(2) ]. Here, we report that the reactions of CNacacH with Cd(II) acetate in the solution and solid states afford different coordination polymers composed of trans-[Cd(CNacac)(2) ] and cis-[Cd(CNacac)(2) ] units, respectively. From a methanol solution containing CNacacH (L) and Cd(OAc)(2) ⋅2 H(2) O (M), a coordination polymer (Cd-1) in which trans-[Cd(CNacac)(2) ] units are three-dimensionally linked was obtained. In contrast, two different coordination polymers, Cd-2 and Cd-3, were obtained from mechanochemical reactions of CNacacH with Cd(OAc)(2) ⋅2 H(2) O at M/L ratios of 1:1 and 1:2, respectively. In Cd-2, cis-[Cd(CNacac)(2) ] units are two-dimensionally linked, whereas the units are linked three-dimensionally in Cd-3. Furthermore, Cd-1 and Cd-2 converted to Cd-3 by applying an annealing treatment and grinding with a small amount of liquid, respectively, in spite of the polymeric structures. These phenomena, 1) different structures are formed from solution and mechanochemical reactions, 2) two polymorphs are formed depending on the M/L ratio, and 3) structural transformation of resulting polymeric structures, indicate the usability of mechanochemical method in the syntheses of coordination polymers as well as the peculiar structural flexibility of cadmium-CNacac polymers.

A residual-host prepared by thermal removal of naphthalene (NA) from the inclusion compound [Ni(SCN)(2)(isonicotinic acid)(2)]·(NA)(0.5) was found to function as an adsorbent for aromatic molecules and exhibit method-dependent selectivity.