Kazuhiro Uemura

Dynamic porous properties of coordination polymers inspired by hydrogen bonds

In a decade, many porous coordination polymers have been synthesized, providing a variety of properties ranging from storage, separation, exchange of guests in their cavities, magnetism, conductivity and catalysis by their frameworks. In this tutorial review, we focus on the hydrogen bonding type arrangements for dynamic porous coordination polymers exhibiting elastic guest accommodations, in contrast to rigid three-dimensional (3-D) frameworks. Such dynamic porous properties induce highly-selective guest accommodation and magnetic modulation, and could now be considered a new class of practical materials.

Temperature- and stoichiometry-controlled dimensionality in a magnesium 4,5-imidazoledicarboxylate system with strong hydrophilic pore surfaces.

1D, 2D, and 3D three metal-organic hybrid frameworks of Mg (II) have been synthesized using 4,5-imidazoledicarboxylic acid (H 3idc) with control of the temperature and stoichiometry in a hydrothermal technique. All of the frameworks show high thermal stability, and frameworks 1D and 3D provide highly hydrophilic pore surfaces, correlated by the selective sorption of water molecules over the organic vapor and other gases like N 2 and CO 2.

Adsorption and Catalytic Properties of the Inner Nanospace of a Gigantic Ring-Shaped Polyoxometalate Cluster**

are of great interestbecause of their unique properties such as adsorption,separation, exchange, and catalysis, which are all associatedwith the presence of a functional nanospace. In this respect,polyoxometalate clusters, which are nanosized metal-oxidemacroanions built from molecular precursors with a range ofunique redox and acidic properties, are ideally suited for thedevelopment of functional nanospaces but have not yet beenthus explored.

Two-Step Adsorption on Jungle-Gym-Type Porous Coordination Polymers: Dependence on Hydrogen-Bonding Capability of Adsorbates, Ligand-Substituent Effect, and Temperature

A preliminary study of isopropanol (IPA) adsorption/desorption isotherms on a jungle-gym-type porous coordination polymer, [Zn(2)(bdc)(2)(dabco)](n) (1, H(2)bdc = 1,4-benzenedicarboxylic acid, dabco =1,4-diazabicyclo[2.2.2]octane), showed unambiguous two-step profiles via a highly shrunk intermediate framework. The results of adsorption measurements on 1, using probing gas molecules of alcohol (MeOH and EtOH) for the size effect and Me(2)CO for the influence of hydrogen bonding, show that alcohol adsorption isotherms are gradual two-step profiles, whereas the Me(2)CO isotherm is a typical type-I isotherm, indicating that a two-step adsorption/desorption is involved with hydrogen bonds. To further clarify these characteristic adsorption/desorption behaviors, selecting nitroterephthalate (bdc-NO(2)), bromoterephthalate (bdc-Br), and 2,5-dichloroterephthalate (bdc-Cl(2)) as substituted dicarboxylate ligands, isomorphous jungle-gym-type porous coordination polymers, {[Zn(2)(bdc-NO(2))(2)(dabco)]·solvents}(n) (2 ⊃ solvents), {[Zn(2)(bdc-Br)(2)(dabco)]·solvents}(n) (3 ⊃ solvents), and {[Zn(2)(bdc-Cl(2))(2)(dabco)]·solvents}(n) (4 ⊃ solvents), were synthesized and characterized by single-crystal X-ray analyses. Thermal gravimetry, X-ray powder diffraction, and N(2) adsorption at 77 K measurements reveal that [Zn(2)(bdc-NO(2))(2)(dabco)](n) (2), [Zn(2)(bdc-Br)(2)(dabco)](n) (3), and [Zn(2)(bdc-Cl(2))(2)(dabco)](n) (4) maintain their frameworks without guest molecules with Brunauer-Emmett-Teller (BET) surface areas of 1568 (2), 1292 (3), and 1216 (4) m(2) g(-1). As found in results of MeOH, EtOH, IPA, and Me(2)CO adsorption/desorption on 2-4, only MeOH adsorption on 2 shows an obvious two-step profile. Considering the substituent effects and adsorbate sizes, the hydrogen bonds, which are triggers for two-step adsorption, are formed between adsorbates and carboxylate groups at the corners in the pores, inducing wide pores to become narrow pores. Interestingly, such a two-step MeOH adsorption on 2 depends on the temperature, attributed to the small free-energy difference (ΔF(host)) between the two guest-free forms, wide and narrow pores.

Zipped‐Up Chain‐Type Coordination Polymers: Unsymmetrical Amide‐Containing Ligands Inducing β‐Sheet or Helical Structures

The crystal structures of thirteen AgI coordination polymers involving py-CONH-(CH2)n-py (py=pyridine; n=0, 1) derivatives were determined by means of single-crystal X-ray analyses. All of the compounds form one-dimensional chains composed of AgI atoms and bridging ligands with formulas [[Ag(py-CONH-(CH2)n-py)][X]]n (X=PF6 -, ClO4 -, BF4 -, and NO3 - with solvent molecules). The unsymmetrical coordination environments around AgI atoms induce direction in the chains, that is, -[NH-(CH2)n-py-Ag-py-CO]-, which resembles the alignment of amino acid chains in proteins. In compounds [[Ag(4-pia)][X]]n (1 supersetX; 4-pia=N-(4-pyridyl)isonicotinamide; X=PF6 -, ClO4 -, BF4 -, and NO3 -), [[Ag(4-pmia)][X]]n (2 supersetX; 4-pmia=N-(pyridin-4-ylmethyl)isonicotinamide; X=PF6 -, ClO4 -H2O, and NO3 -H2O), and [[Ag(3-pmia)][X]]n (3 supersetX; 3-pmia=N-(pyridin-3-ylmethyl)isonicotinamide; X=PF6 -, ClO4 -, BF4 -, and NO3 -H2O), each chain is aligned parallel to neighboring chains, but adjacent chains run in the opposite direction. Particularly in [[Ag(3-pmia)][PF6]]n (3 supersetPF6 -), [[Ag(3-pmia)][ClO4]]n (3 supersetClO4 -), and [[Ag(3-pmia)][BF4]]n (3 supersetBF4 -), amide moieties of 3-pmia ligands are complementarily hydrogen bonded to amide moieties in neighboring chains, as in the beta-sheet motif in proteins. On the other hand, in [[Ag(4-pmna)][PF6]MeOH]n (4-pmna=N-(pyridin-4-ylmethyl)nicotinamide), all chains in the crystal form left-handed (4 a supersetPF6 -MeOH) and right-handed (4 b supersetPF6 -MeOH) helical structures with a helical pitch of 28 A. Heterogeneous anion exchanges proceed reversibly in 2, but not in 3, which provides information about the thermal stabilities of the crystals.

One-dimensionally extended paddlewheel dirhodium complexes from metal-metal bonds with diplatinum complexes.

We have succeeded in obtaining unique one-dimensional (1D) chain complexes (1, 2, and 3) comprised of two types of metal species: rhodium and platinum. These compounds are constructed from a dinuclear rhodium complex (i.e., [Rh(2)]) and a pivalamidate-bridged platinum complex (i.e., [Pt(2)]), forming an attractive quasi-1D infinite chain, expressed as -{[Rh(2)]-[Pt(2)]-[Pt(2)]}(n)-. Interestingly, the bridging ligands of [Rh(2)] can be varied with trifluoroacetate, acetate, and acetamidate groups, indicating the possibility of electronic structure modulation in the 1D chain.

Paramagnetic one-dimensional chains comprised of trinuclear Pt-Cu-Pt and paddlewheel dirhodium complexes with metal-metal bonds.

One-dimensional (1-D) chain complexes constructed by metal-metal bonds containing three types of metal species-platinum, rhodium, and copper-have been rationally synthesized and characterized by single-crystal X-ray analyses and physical measurements. The paddlewheel or lantern type complex, [Rh2(O2CCH3)4] (i.e., [Rh2]), has a vacant σ* orbital which accepts the electrons from the filled dz(2) orbital of cis-[Pt(piam)2(NH3)2]·2H2O (1, i.e. [Pt], where piam = pivalamidate) to afford a tetranuclear complex, [{Rh2(O2CCH3)4}{Pt(piam)2(NH3)2}2]·2H2O (2). Compound 2 forms a linear alignment as [Pt]-[Rh2]-[Pt] with unbridged Rh-Pt bonds, where the oxygen atoms of the piam ligands in the [Pt] are noncoordinated, showing the capability of binding another metal ion. Simply mixing [Rh2] and the heterometallic trinuclear complex [Pt2Cu(piam)4(NH3)4](PF6)2 (3, i.e. [Pt-Cu-Pt]) in a ratio of 1:1 in MeOH, EtOH, or Me2CO affords [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (4), [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (5), or [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n·6nMe2CO (6), respectively. Compounds 4-6 form infinite chains with the repetition of -{[Rh2]-[Pt-Cu-Pt]}n-, which to our knowledge, are the first examples of heterometallic 1-D chains comprised of three types of metal species with direct metal-metal bonds. The CF3CO2(-), ClO4(-), and water molecules influence the crystal packing to form an octanuclear complex of [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}2](CF3CO2)2(ClO4)2·2H2O (7) with [Pt-Cu-Pt]-[Rh2]-[Pt-Cu-Pt] alignment. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 4-7, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)]}n- or [Pt(II)-Cu(II)-Pt(II)]-[Rh2(II,II)]-[Pt(II)-Cu(II)-Pt(II)], which are unchanged from those in the starting compounds. Electron paramagnetic resonance spectra of 4-7 show axially symmetric spectra with g∥ > g⊥, indicating that the HOMO (SOMO) is a Cu d(x(2)-y(2)) orbital. In 7, the hyperfine coupling in the spectrum indicates that the unpaired spin on Cu is perturbed by the Pt atoms.

Synthesis, Crystal Structure, and Characterization of a Heterometallic One-Dimensional Complex with Metal−Metal Bonds

The quasi-one-dimensional chain [{PtRh(TCM)(2)(NH(3))(2)Cl(2.5)}(2){Pt(2)(PVM)(2)(NH(3))(4)}(2)](n)(PF(6))(6n).2nH(2)O (Chain-2; TCM = Cl(3)CCONH(-), PVM = (t)BuCONH(-)), which consists of Pt and Rh atoms, has been obtained from two dinuclear compounds, [Pt(2)(PVM)(2)(NH(3))(4)](PF(6))(2).H(2)O (1) and [PtRh(TCM)(2)(NH(3))(2)Cl(3)] (2). Single-crystal X-ray analysis showed that the dinuclear compounds stack with metal-metal bonds to form octameric units, Pt-Rh-Pt-Pt-Pt-Pt-Rh-Pt (Pt(6)Rh(2)), that are bridged by the Cl(-) ion to be a quasi-one-dimensional chain. Elemental analysis, X-ray photoelectron spectroscopy, electron paramagnetic resonance (EPR), and magnetic susceptibility measurements showed that Chain-2 has a mixed valency and one unpaired electron per octameric Pt(6)Rh(2) unit. Taking into account the small observed g(av) value (g(av) = 2.01 at room temperature) obtained by EPR measurement and B3LYP density functional theory calculations of the model complex, oxidation states of the octameric unit are postulated to be Pt(3+)-Rh(2.5+)-Pt(2+)-Pt(2+)-Pt(2+)-Pt(2+)-Rh(2.5+)-Pt(3+), where the EPR isotropic signal showed that the unpaired electron resides in the Rh d(xy) orbitals (delta* orbitals in Pt-Rh dinuclear parts) and hops from one Rh atom to another.

Two types of heterometallic one-dimensional alignment composed of acetamidate-bridged dirhodium and pivalamidate-bridged diplatinum complexes.

Two types of heterometallic one-dimensional chains, [{Rh2(acam)4}{Pt2(piam)2(NH3)4}2]n(CF3SO3)4n·2nMeOH (2, where acam = acetamidate, piam = pivalamidate) and [{Rh2(acam)4}{Pt2(piam)2(NH3)4}]n(CF3CO2)2n·2nEtOH (3), have been synthesized and characterized by single-crystal X-ray analyses. The chain structures in 2 and 3 are composed of two kinds of dinuclear complexes, [Rh2(acam)4] (i.e., [Rh2]) and [Pt2(piam)2(NH3)4] (i.e., [Pt2]), where Rh and Pt atoms are axially linked by metal-metal bonds. In 2 and 3, each complex is one-dimensionally aligned as -{[Rh2]-[Pt2]-[Pt2]}n- or -{[Rh2]-[Pt2]}n-, respectively, in which different alignments are caused by different isomers of [Pt2] that are HH (head-head) and HT (head-tail) orientation of piam ligands and their hydrogen bonding modes. Considering the crystal structures and X-ray photoelectron spectra (XPS) measurements in 2 and 3, the oxidation states of the metal atoms are -{[Rh2(II,II)]-[Pt2(II,II)]-[Pt2(II,II)]}n- and -{[Rh2(II,II)]-[Pt2(II,II)]}n-, which are unchanged from those in the starting compounds. The diffuse reflectance spectra show that LUMOs are M-M σ-type orbitals. The gap between filled and vacant σ-type orbitals in 3 is narrower than that in 2, and is attributed to the relative higher destabilized filled σ-type orbitals caused by lower numbers of linking platinum atoms.

A paramagnetic quasi-1D chain comprised of Pt/Rh possessing an unpaired electron

Abstract In this manuscript we review the structure of the novel 1-D chain complex, {[PtRh(PVM)2(NH3)2Cl2.5]2[Pt2(PVM)2 (NH3)4]2(PF6)6. 2MeOH. 2H2O}n (4) (PVM = pivalamidate), consisting of mixed-valence dimeric complexes with appreciably extended metal–metal bondings. Compound 4 is made up of octameric segments, each of which consists of two platinum-rhodium dinuclear complexes and a tetrameric platinum unit. The charge of 19+ for the Pt6Rh2 octameric segment in 4 was deduced from the number of the independent PF6 counter ions, and is the supporting evidence for one unpaired electron per one octameric segment The tetrameric platinum unit in 4 is the structural motif that is observed in [Pt2(PVM)2(NH3)4](PF6)2.H2O (2) and [Pt4(PVM)4(NH3)8](PF6)4(ClO4) .2H2O (3 =“platinum blue” with one electron delocalized over the four platinum atoms). On the basis of the EPR, magnetic susceptibility, and electrical conductivity results, the nature of the unpaired electron in 4 is discussed.