Toschitake Iwamoto

Past, present and future of the clathrate inclusion compounds built of cyanometallate hosts

One-, two- and three-dimensional CN-bridged metal complex structures made up of building blocks such as linear [Ag(CN)2]−, square planar [Ni(CN)4]2− or tetrahedral [Cd(CN)4]2−, and of the complementary ligands such as ammonia, water, unidentate amine, bidentate a,w- diaminoalkane, etc., are reviewed with an emphasis on their behaviour as hosts to afford clathrate inclusion compounds with guest molecules and as self-assemblies to form supramolecular structures with or without guests. The historical background is explained for Prussian blue and Hofmanns benzene clathrate based on their single crystal structure determinations. The strategies the author and coworkers have been applying to develop varieties of clathrate inclusion compounds from the Hofmann-type are demonstrated with the features observed for the developed structures determined by single crystal X-ray diffraction methods.

The Hofman-type clathrate: M(NH3)2M′(CN)4 . 2G

Abstract A series of clathrates with the general formula M(NH3)2M′(CN)4.2G were prepared. Their structures have been ascertained by powder X-ray diffractometry to be similar to that of Hofmanns clathrate Ni(NH3)2Ni(CN)4.2C6H6. The variation in the lattice constants of the tetragonal unit cells can be correlated with the change in the bond length between the metal, M, at the octahedral site and the nitrogen of the cyanide and in that between the metal, M′, at the square-planar site and the carbon of the cyanide, and with the change of the size of the guest molecules. Their infrared spectra have been interpreted in terms of the weak host-guest interaction depending on the M′, and as being almost independent of the change in the M.

The structure of catena-μ-ethylenediaminecadmium(II) tetracyanoniccolate(II) dibenzene clathrate: Cd(en)Ni(CN)4.2C6H6

Abstract The crystal structure of Cd(en)Ni(CN) 4 · 2C 6 H 6 was determined by the single crystal X-ray diffraction method. The crystal belongs to the tetragonal system with space group of P4/m, a = 7.675±0.003 A, c = 8.056±0.010 A, and Z = 1 (D m = 1.69, D c = 1.72). The structure was solved by the Fourier method and refined by the block-diagonal least-squares method to an R -value of 0.089 for 619 reflection data. The cadmium atoms and the nickel atoms are linked cross-wise with the cyanide anions on the (001) plane to form the layers of the polymeric metal cyanide complex [CdNi(CN) 4 ] ∞ , and the layers are stacked along the c-axis. Each ethylenediamine molecule bridges between the cadmium atoms in the layers to make a three-dimensional host lattice. The benzene molecules are enclathrated in the cavities formed by the host lattice. The electron density for each nitrogen atom of the ethylenediamine molecule was found to be distributed over a torus about the CdCd axis. This fact and the 1 H-NMR data support the rotation of the ethylenediamine molecule about the axis at room temperature.

The crystal structure and ESR studies of diamminecopper(II) tetracyanoniccolate(II) dibenzene clathrate: Cu(NH3)2Ni(CN)4.2C6H6

Abstract The crystal structure of Cu(NH 3 ) 2 Ni(CN) 4 .2C 6 H 6 was determined by three-dimensional X-ray methods. The crystal is tetragonal with the dimensions of a = 7.345 A and c = 16.519 A, and the space group is P4/mcc ( Z = 2). Reflection data were collected with an automatic four circle diffractometer and monochromatized Mo Kα radiation. The structure was solved by the heavy-method and was refined by the block-diagonal least-squares method for 690 independent reflections to a final R-index of 0.068. The copper ions and the nickel ions are linked crosswise with the cyanide anions to form a polymeric two-dimensional metal complex network, and the benzene molecules are trapped among the layers of the networks. This host lattice structure is similar to those of the other Hoffmann-type clathrates, Ni(NH 3 ) 2 Ni(CN) 4 . 2C 6 H 6 and Cd(NH 3 ) 2 Ni(CN) 4 . 2C 6 H 6 , but the c -axis of the cell is doubled due to different orientation of the benzene molecules in alternate guest layers. The copper(II) ion takes a compressed tetragonal coordination with the four nitrogen atoms of the cyanide anions in the (001) plane (the Cu-N distance, 2.20 A) and with the two nitrogen atoms of the ammonia molecules of the [001] axis at the compressed apical positions (the Cu-N distance, 2.05 A). The ESR spectra of the magnetically dilute single crystal of (Cd, Cu)(NH 3 ) 2 Ni(CN) 4 . 2C 6 H 6 can be interpreted in terms of A 1g symmetry of the electronic ground state of the copper(II) ion in the compressed tetragonal environment which was previously concluded from the spectra of the polycrystalline samples.

Crystal structures of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2) and ethylenediaminecadmium(II) tetracyanocadmate(II)

The crystal structure of ethylenediaminecadmium(II) tetracyanocadmate(II)-benzene(1/2),I, has been redetermined based on 1632 reflections collected anew for the crystal coated with epoxy resin, with a final conventionalR=0.038;I crystallizes in space groupP4222, witha=b=8.265(1) andc=15.512(3) Å, andZ=2. Ethylenediaminecadmium(II) tetracyanocadmate(II),II, is concluded to be identical with the residual metal complex host ofI, remaining after the liberation of the guest benzene molecules;II crystallizes from an aqueous solution containing bis- or tris-ethylenediaminecadmium(II) tetracyanocadmate(II) in space groupI41/acd, witha=b=14.366(1) andc=23.771(4) Å, andZ=16; refinement led to a conventionalR=0.043 for 1181 reflections. The bridging ethylenediamine ligand inI turns to a chelating one inII; dissociation and recombination should occur in the coordination sphere of the six-coordinate cadmium atom, whenII is derived fromI by the liberation of the guest molecules.

Crystal structures ofcatena-[diligatocadmium(II) tetra-μ-cyanocadmate(II)] host clathrates: Diamminecadmium(II) tetracyanocadmate(II)-benzene(1/2), diamminecadmium(II) tetracyanocadmate(II)-aniline(1/2), ethylenediaminecadmium(II) tetracyanocadmate(II)-aniline(1/2), and a novel type bis(aniline)cadmium(II) tetracyanocadmate(II)-aniline(2/1)

The crystal structures of the four title clathrate compounds Cd(NH3)2Cd(CN)4 · 2C6H6,I, Cd(NH3)2Cd(CN)4 · 2C6H5NH2,II, Cd(NH2CH2CH2NH2)Cd(CN)4 · 2 C6H5NH2,III, and Cd(C6H5NH2)2Cd(CN)4 · 0.5C6H5NH2,IV, have been analyzed by single crystal X-ray diffraction methods. CompoundI crystallizes in the monoclinic space groupC2/c,a = 12.063(2),b = 12.174(2),c = 14.621(1) Å,β = 90.976(9)°,Z = 4,R = 0.042 for 2388 reflections;II: monoclinic C2/c,a = 12.1951(9),b = 12.078(1),c = 14.6921(7) Å,β = 93.436(5)°,Z = 4,R = 0.039 for 2374 reflections;III: monoclinicCc,a = 11.027(1),b = 12.0767(9),c = 15.837(1) Å,β = 92.059(9)°,Z = 4,R = 0.041 for 2883 reflections; andIV: monoclinicP21/n,a = 15.169(2),b = 16.019(2),c = 8.866(1) Å,β = 95.73(1)°,Z = 4,R = 0.052 for 3612 reflections. The three-dimensionalcatena-[diamminecadmium(II) tetra-μ-cyanocadmate(II)] hosts ofI andII are substantially isostructural to that of the already known Hofmann-Td-type Cd(NH3)2Hg(CN)4 · 2C6H6. The three-dimensional en-Td-typecatena-[catena-μ-ethylenediaminecadmium(II) tetra-μ-cyanocadmate(II)] host ofIII, reinforced by the catena-μ-en linking between the octahedral Cd atoms, accommodates the aniline as the guest with a monoclinic distortion from the tetragonal symmetry of the previously reported en-Td-type benzene clathrate. InIV dual behavior of aniline, one as the unidentate ligand in the three-dimensional host and the other as the guest in the cage-like cavity, has been demonstrated.

Cd(NH2CH2CH2NH2)M′(CN)4. 2C6H6(M′ = Ni, Pd): A new-type of the clathrates with an etylenediamine-bridged host lattice of three dimensions

Abstract A new-type of the clathrates, (Cd(en)M′(CN)4.2C6H6 (M′ = Ni, Pd; en = ethylenediamine), with a host lattice of three dimensions was prepared. The host lattice was developed from the Hofmann-type clathrate M(NH3)2 M′(CN)4. 2G by bridging the two-dimensional metal-complex networks with ethylenediamine. The new clathrates belong to the tetragonal system, as does the Hofmann-type clathrate. The lattice constant a is almost identical with that of the corresponding Hofmann-type clathrate, Cd(NH3)2M′ (CN)4.2C6H6, but the lattice constant c is shortened by the en-bridge the cadmium atoms in the adjacent cyano-metal complex networks. The formation of the en-bridge was ascertained from the infrared spectroscopic and X-ray diffractometric data.

Different co-ordination behaviour of 1,2-diaminoethane (en) and tetracyanonickelate(II) upon accommodation of polar guest molecules in their metal complex hosts: crystal structures of [M(en)2Ni(CN)4]·2PhNH2(M = Ni, Cu, Zn or Cd) and [{Cd(en)}2(en){Ni(CN)4}2]·4PhOH

The single-crystal structures have been determined for aniline and phenol clathrates. Aniline clathrates [M(en)2Ni(CN)4]·2PhNH2(M = Ni, Cu, Zn or Cd; en = 1,2-diaminoethane) are isomorphous, having monoclinic space group P21/c(Z= 2). The unit cell parameters a, b, c and β, and R index for the reflections used are: M = Ni, 9.452(3), 10.125(3), 13.440(3)A and 107.27(2)°, 0.0443 for 1806; for M = Cu, 9.547(4), 10.621(5), 12.746(3)A and 107.89(2)°, 0.0635 for 1861; for M = Zn, 9.550(3), 10.407(2), 13.026(2)A and 107.50(1)°, 0.0513 for 1758; and for M = Cd, 9.924(2), 10.545(3), 12.510(1)A and 107.63(1)° 0.0456 for 1829. The guest PhNH2 molecules are accommodated among [–M(en)2–NC–Ni(CN)2–CN–]n chains extending along the b axis. The bis(en)-chelated M atoms are linked with trans-di-µ-cyano-dicyanonickelate(II) moieties alternately, and adopt an elongated octahedral configuration along the chain. The phenol clathrate [{Cd(en)}2(en){Ni(CN)4}2]·4PhOH belongs to the triclinic system, space group P, with a= 11.868(1), b= 13.030(1), c= 7.7113(6)A, α= 105.956(7), β= 94.951(8), γ= 91.584(9)°, Z= 1 and R= 0.0410 for 4095 reflections. Three kinds of crystallographically independent PhOH molecules are enclathrated in the three-dimensional host framework in which the en-chelated Cd atoms are linked with infinite [〉Ni〈(CN–Cd–NC–)2]n chains and Cd–NC–Ni(CN)2–CN–Cd and Cd–en–Cd bridges. Interhost, interguest and host–guest hydrogen-bond formation stabilize the whole crystal structures, which are compared with those of [M(en)2Ni(CN)4] complexes and the [Cd(en)Ni(CN)4]·2C6H6 clathrate.

Adsorption properties of montmorillonite and synthetic saponite as packing materials in liquid-column chromatography

The adsorption of tris(1,10-phenanthroline)-ruthenium(II) (Ru(phen)32+) by two kinds of colloidally dispersed clays, sodium montmorillonite and synthetic saponite, was studied by spectrophotometric and electron-optical methods. Montmorillonite adsorbed this complex stronger than saponite. The electronic spectrum measurements suggested that the electronic states of the complex were more perturbed on adsorption by montmorillonite than by saponite. High-performance liquid chromatography was attempted on an ion-exchanged adduct of optically active Ru(phen)32+ and these clays. 1,1′-Binaphthol was eluted with a t: 1 (v/v) water-methanol mixture as an eluent. The compound was resolved with a separation factor of 15 and 1.4 on the saponite and montmorillonite columns, respectively. If tris(acetylacetonato)-chromium(III) was eluted with water, the compound was resolved with separation factors of 1.9 and 11 on the saponite and montmorillonite columns, respectively. These separation tendencies were probably due to the difference in the external surface area and the density of the bound chelates.

Silica-mimetic polymorphism of the Cd(CN)2 host lattice depending on the guest G in Cd(CN)2·xG clathrates

The single-crystal structures have been determined for the Cd(CN)2 host clathrates Cd(CN)2·xBun2O·yH2O (x, y≈ 0.5)1, Cd(CN)2·0.5Bui2O 2a, Cd(CN)2·0.5(PriCH2CH2)2O 2b, Cd(CN)2·PriCl 2o, Cd(CN)2·CHCl2CH2Cl 3a, Cd(CN)2·PriBr 3b and Cd(CN)2·PriCN 4, prepared in order to mimic the polymorphism of SiO2 by Cd(CN)2. The hexagonal P63/mmc host lattice of 1 is isostructural with the high-temperature form of tridymite, Accommodating the dibutyl ether guest in the channel cavity extending along the c axis and the water molecule is hydrogen bonded to the ether in the cage neighbouring the channel. The cubic Fdmm host lattice of 2 in the high-temperature cristobalite structure provides two neighbouring tetrahedral cavities for the respective alkyl ether guests in 2a and 2b; the structure of 2o is the same. The cubic Fd3m lattice is transformed into the tetragonal P41212 one in 3 and 4, similar to the deformation from high-to low-temperature cristobalite, the lattice of 4(Z= 8) being more distorted than those of 3a and 3b(Z= 4). The polymorphic behaviour of these Cd(CN)2 lattices is discussed in terms of the geometry and function of the guest molecules.