Antiferromagnetic Interactions through the Thirteen Å Metal-Metal Distances in Heterometallic One-Dimensional Chains.

A heterometallic and paramagnetic one-dimensional aligned chain in -Rh(+2)-Rh(+2)- Pt(+2)-Ni(+2)-Pt(+2)- with direct metal-metal bonds was obtained via HOMO-LUMO interactions at the σ* (dz2) orbital between [Rh2(O2CCH3)4] and [Pt2Ni(piam)4(NH3)4] (piam=pivalamidate). The one-dimensional chains had straight backbones attributed to face-to-face stacking of each complex, and the Ni atoms were separated by approximately 13 Šfrom four different metals. Each Ni atom had two unpaired electrons in the d-orbitals, which strongly exchanged with J=-37.9 cm-1 through the diamagnetic -Pt-Rh-Rh-Pt- bonds.

Enhanced Electrical Conductivity of Polyoxometalates by Bridging with Mixed-valent Multinuclear Platinum Complexes.

Polyoxometalates (POMs) are nanosized molecular metal oxide anion clusters with tuneable structures and functionalities, and they exhibit a redox chemistry and catalytic activity in multielectron redox processes. These are typically poor electrical conductors (< 10-10 Scm-1), which is attributed to negligible electronic interactions among anions in the solid state. Since the reduced electrons on the d0 metals in POMs are delocalized, electrical conductivity was improved when judicious pathways for the electrons were created by bridging the POMs. Utilized with the electronic interactions between bridging oxygen atoms with the highest occupied molecular orbital in the POMs and the metal dz2 orbitals in the multinuclear platinum complexes, and three mixed-valent assemblies were synthesized and characterized. Simply mixing Keggin-type or Dawson-type POMs with tetranuclear or trinuclear platinum complexes in solution afforded three single crystals, and all three compounds were paramagnetic with mixed oxidation states and better conductivities at room temperature than the parent compounds.

Promotion of ABCG2 gene expression by neolignans from Piper longum L.

We focused on Piper longum L., a herbal drug produced in Myanmar, which has a renoprotective effect. Thus, we attempted to isolate and identify compounds that enhance the expression of the ABCG2 gene from the aerial parts of the plant except for the fruit. Among the various P. longum extracts, we isolated and identified the components. Using Caco-2 cells, the hABCG2 mRNA expression-enhancing effects of the isolated compounds were compared with the positive reference compound (3-methylcholanthrene [3MC]) using real-time polymerase chain reaction. Six compounds were isolated and identified from the methanol extract of P. longum. Among the isolated compounds, licarin A and neopomatene had lower toxicity and higher hABCG2 mRNA expression-enhancing effects in Caco-2 cells. Suppression of hAhR expression by siRNA reduced the activity of licarin A and neopomatene, as well as the hAhR agonist 3MC, suggesting that these 2 compounds may act as hAhR agonists to promote hABCG2 expression.

Asymmetrical Platinum and Rhodium Dinuclear Complex Strongly Bound to Filled d z 2 ${{_{{\rm z}{

Heterometallic extended metal atom chains (EMACs) aligned with three types of metal were rationally synthesized by forming unbridged metal-metal bonds based on the interactions between highest occupied and lowest unoccupied molecular orbitals at the d z 2 ${{_{{\rm z}{^{2}}}}}$ orbital. These chains form pentanuclear structures aligned as Rh-Pt-M-Pt-Rh with relatively large formation constants of 5.0×1013  M-2 for M=Pt and 6.3×1011  M-2 for M=Pd, while retaining their backbones in solution. In the case of M=Cu, the original Cu(+2) atoms were reduced to Cu(+1) during the synthetic process. Cu(+1) has an unprecedented trigonal bipyramidal coordination geometry. The reported synthesis based on asymmetrical dinuclear complexes provides a guideline for the synthesis of hetero-EMACs to allow several analogs through judicious combinations realized by tuning the number of metal nuclei and metal species.

Dimerization of Paramagnetic Trinuclear Complexes by Coordination Geometry Changes Showing Mixed Valency and Significant Antiferromagnetic Coupling through -Pt···Pt- Bonds.

Paramagnetic trinuclear complexes, trans-[Pt2M(piam)4(NH3)4](ClO4)x (t-M; piam = pivalamidate, M = Mn, Fe, Co, Ni, and Cu, x = 2 or 3), aligned as Pt-M-Pt were successfully synthesized and characterized. The dihedral angles between the Pt and M coordination planes in t-M are approximately parallel, showing straight metal-metal bonds with distances of approximately 2.6 Å. Except for t-Fe, the trinuclear complexes are dimerized with close contact (approximately 3.9 Å) between the end Pt atoms to form Pt-M-Pt···Pt-M-Pt alignments with high-spin M(+2) containing five (t-Mn), three (t-Co), two (t-Ni), and one (t-Cu) unpaired electrons localized on M atoms. Several physical measurements and calculations revealed that the dimerized structures were maintained in MeCN, where cyclic voltammograms for t-M exhibited two-step oxidation and reduction attributed to Pt-M(+2)-Pt···Pt-M(+2)-Pt ↔ Pt-M(+3)-Pt···Pt-M(+2)-Pt ↔ Pt-M(+3)-Pt···Pt-M(+3)-Pt via mixed-valent states. Magnetic susceptibility measurements for t-M showed antiferromagnetic interaction, t-Mn: J = -0.9 cm-1, t-Co: J = -3.5 cm-1, t-Ni: J = -7.3 cm-1, and t-Cu: J = 0.0 cm-1, between the two M centers with distances of 9.0 Å through Pt···Pt bonds.

Paramagnetic one-dimensional chains containing high-spin manganese atoms showing antiferromagnetic interaction through -Pt-Rh-Rh-Pt- bonds.

To exploit the magnetic interactions of multiple metals, a heterometallic one-dimensional (1D) chain containing three kinds of metals, Rh, Pt, and Mn, where [Rh2(O2CCH3)4] and [Pt2Mn(piam)4(NH3)4]2+ (piam = pivalamidate) are connected through unbridged Rh-Pt bonds to form -Rh-Rh-Pt-Mn-Pt- alignments was successfully synthesized. The Mn atoms are tetrahedrally coordinated by four oxygen atoms of the piam ligands, where the coordination geometries form a zigzag 1D chain. Each Mn atom is linked by -Pt-Rh-Rh-Pt-, with a Mn-Mn separation of 13.9 Å. In parent [Pt2Mn(piam)4(NH3)4](PF6)2, Mn adopts two coordination environments, octahedral and tetrahedral, both of which are Mn(+2) high-spin states. In EtOH, [Rh2(O2CCH3)4] selectively binds tetrahedral Mn to afford a 1D chain. Physical analysis of the 1D chain using electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) revealed that all metals are divalent, indicating five unpaired spin-localized electrons on the Mn atoms. Magnetic susceptibility measurements indicated antiferromagnetic intra-chain interactions between the Mn atoms in the 1D chain, where χT at 300 K was 5.33 cm3 K mol-1 and gradually decreased to 1.65 cm3 K mol-1 at 2 K. Theoretical fitting of the magnetic behavior showed weak exchange coupling (zJ = -0.43 cm-1) between two high-spin Mn(+2) ions through diamagnetic Pt-Rh-Rh-Pt.

Improving the Solubility of Hexanuclear Heterometallic Extended Metal Atom Chain Compounds in Nonpolar Solvents by Introducing Alkyl Amine Moieties.

The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) interaction at the d z 2 orbital between two kinds of metal complex is useful for obtaining heterometallic one-dimensional (1D) chains as well as heterometallic metal string compounds (HMSCs). Platinum dinuclear complexes, [Pt2(piam)2(NH2R)4]X2 (piam = pivalamidate, R = CH3, C2H5, C3H7, or C4H9, X = anion), comprising σ* as HOMO were mixed with [Rh2(O2CCH3)4] comprising σ* as LUMO in solvents to afford single crystals of [{Rh2(O2CCH3)4}{Pt2(piam)2(NH2R)4}2]X4 (2-5). Single-crystal X-ray analyses revealed that 2-5 are hexanuclear complexes that are one-dimensionally aligned as Pt-Pt-Rh-Rh-Pt-Pt with metal-metal bonds, where the alkyl moieties at end Pt atoms obstruct further 1D extension. Complexes 2-5 appear as if they are cut off from an infinite chain [{Rh2(O2CCH3)4}{Pt2(piam)2(NH3)4}2] n (PF6)4n ·6nH2O (1) aligned as -{Pt-Pt-Rh-Rh-Pt-Pt} n -. The diffuse reflectance spectrum of 1 depicts broad shoulder bands, which are not present in the spectra of 2-5, proving that the infinite chain 1 forms a band structure. Compounds 4 and 5 with propyl or butyl moieties at amine ligands, respectively, are soluble in nonpolar solvents, such as CH2Cl2, without the dissociation of their hexanuclear structures. Taking advantage of their solubility, measurement of cyclic voltammetry in CH2Cl2 become possible, which shows the quasi-reversible oxidation and reduction waves at 4: E ox = 0.86 V and E red = 0.69 V and 5: E ox = 0.87 V and E red = 0.53 V.

Modulation of Band Gaps toward Varying Conductivities in Heterometallic One-Dimensional Chains by Ligand Alteration and Third Metal Insertion.

A heterometallic one-dimensional (1-D) chain consisting of multiple kinds of metals, Rh, Pt, and Pd, with direct metal-metal bonds was successfully obtained by mixing a Rh dinuclear complex and Pt-Pd-Pt trinuclear complex. The Pt-Pd-Pt trinuclear complex can be reversibly one-electron-oxidized or -reduced, where the electron paramagnetic resonance spectrum of the one-electron-oxidized one shows an axially symmetric signal with hyperfine splitting by two Pt and Pd, indicating that an unpaired electron is delocalized to the d z 2 orbital of Pt-Pd-Pt. Utilized with the highest occupied molecular orbital and lowest unoccupied molecular orbital interaction at the d z 2 orbital, simple mixing of the Pt-Pd-Pt trinuclear complex and Rh dinuclear complex in adequate solvents afforded heterometallic 1-D chains, which are aligned as -Rh-Rh-Pt-Pd-Pt-. Several physical measurements revealed that the metal oxidation state is +2. Diffuse reflectance spectra and theoretical calculations show that heterometallic 1-D chains have σ-type conduction and valence bands where π*(Rh2) are lying between them, whose gaps become narrower than the prototype chains aligned as -Rh-Rh-Pt-Pt-Pt-Pt-. The narrower band gaps are induced by destabilization of the σ-type valence bands and accompanied by insertion of Pd ions because the d-orbital energy level of Pd is closer in value to Rh compared with Pt. Flash-photolysis time-resolved microwave conductivity measurements exhibited an increase in the product of charge carrier mobility and its generation efficiency (8.1 × 10-5 to 4.6 × 10-4 cm2 V-1 s-1) with narrowing the band gaps, suggesting that the better conductivity is attributed to shorter metal-metal distances in 1-D chains. These results imply the possibilities of controlling band gap with ligand modification and third metal insertion in heterometallic 1-D chains to show various conductivities.

Paramagnetic One-Dimensional Chain Complex Consisting of Three Kinds of Metallic Species Showing Magnetic Interaction through Metal-Metal Bonds.

A heterometallic and paramagnetic one-dimensional (1-D) chain (3) aligned as -Rh(+2)-Rh(+2)-Pt(+2)-Co(+2)-Pt(+2)- with direct metal-metal bonds was obtained by HOMO-LUMO interactions at the σ* (dz2) orbital between two kinds of complexes. The 1-D chains in 3 have relatively straight backbones because the raw material complexes, [Rh2(O2CCH3)4] and [Pt2Co(piam)4(NH3)4], are connected and stacked in a face-to-face fashion, where Co---Co are separated by about 13.3 Å with four different metals. Physical measurements revealed that 3 has a band gap between the σ-type conduction and valence bands, where d-orbitals of the Co ion with three unpaired electrons are laid among them. The magnetic behavior of 3 was investigated and found to be consistent with a complex interaction involving both zero-field splitting and Pauli paramagnetism attributed to band formation superimposed on relatively strong exchange coupling (zJ = -22.2 cm-1) between two high-spin Co(+2) ions separated by the diamagnetic Pt-Rh-Rh-Pt.

Isolation and characterization of a tetranuclear Pt-FeFe-Pt intermediate en route to the trinuclear Pt-Fe-Pt cluster.

An intermediate compound, [{PtFe(piam)2(NH3)2(OCH3)}2(µ-OCH3)2](ClO4)2 (1, piam = pivalamidate), in the synthetic process to form [Pt2Fe(piam)4(NH3)4](ClO4)3 (2) by mixing cis-[Pt(piam)2(NH3)2]·2H2O and iron sources was successfully isolated and characterized by single-crystal X-ray analysis. In 1, the platinum and iron atoms are bridged by two piam ligands to afford a dinuclear Pt-Fe structure and are further linked to each other by methoxide bridges at the equatorial positions of iron atoms to form a tetranuclear Pt-FeFe-Pt complex. The Pt-Fe distances in 1 are 3.0010(16) and 2.9883(17) Å, which are significantly longer than those in 2 (2.5566(15) and 2.5718(15) Å). X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and magnetic susceptibility measurements revealed that the oxidation states are Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) (1) and Pt(+2)-Fe(+3)-Pt(+2) (2) with high-spin (S = 5/2) configurations in iron atoms. The magnetic susceptibility of 1 has a χT value of 5.83 cm3 mol-1 K per Pt(+2)-Fe(+3)Fe(+3)-Pt(+2) unit at 300 K, which decreases down to 0.04 cm3 mol-1 K at 7 K due to antiferromagnetic coupling (J = -28 cm-1) of the two Fe(+3) centers. Compound 2 maintains its trinuclear structure in MeCN, exhibiting reversible one-electron reduction and oxidation, Pt(+2)-Fe(+2)-Pt(+2) ↔ Pt(+2)-Fe(+3)-Pt(+2), at E1/2 = -0.19 V (vs. Fc/Fc+). However, in MeOH, compound 2 is decomposed into a dinuclear structure of Pt-Fe involving an equilibrium between 1 and 2.

One-dimensional complexes extended by unbridged metal-metal bonds based on a HOMO-LUMO interaction at the dz2 orbital between platinum and heterometal atoms.

In this review, the crystal structures of seventeen heterometallic one-dimensional compounds 1-17 are shown, and their electronic structures are discussed based on the diffuse reflectance spectra and other physical measurements. Compounds 1-17 comprise two kinds of complexes with HOMO-LUMO interactions at σ-type (dz2) orbitals between platinum and heterometal atoms, where two or three kinds of metal are regularly aligned through metal-metal bonds. In [{PtRh(piam)2(NH3)2Cl2.5}2{Pt2(piam)2(NH3)4}2]n(PF6)6n·2nMeOH·2nH2O (3, piam = pivalamidate), the platinum and rhodium atoms are aligned as -Pt-Rh-Pt-Pt-Pt-Pt-Rh-Pt-Cl- with a mixed valence, where an unpaired electron hops from one Rh atom to another. [{Rh2(O2CCF3)4}{Pt2(piam)2(NH3)4}2]n(CF3CO2)4n·2nEtOH·2nH2O (6) with -Pt-Pt-Rh-Rh-Pt-Pt- alignment has a conduction band (CB) and a valence band (VB) attributed to σ-type orbitals, exhibiting narrower gaps between CB and VB than other analogues. [{Ru2(O2CCH3)4}{Pt2(piam)2(NH3)4}2]n(PF6)4n·4nH2O (14) with -Pt-Pt-Ru-Ru-Pt-Pt- and [{Rh2(O2CCH3)4}{Pt2Cu(piam)4(NH3)4}]n(PF6)2n (15) with -Rh-Rh-Pt-Cu-Pt- are paramagnetic chains, where one or two unpaired electrons reside at each metal per repeating unit. Thus, this system is diverse in modulating the electronic structures, band structures and the expected physical properties based on the unique oxidation states and redox properties attributed to the metal-metal interaction.

Heterometallic one-dimensional chain with tetradeca metal repetition constructed by amidate bridged dirhodium and pivalate bridged diplatinum complexes influenced by hydrogen bonding.

A novel heterometallic one-dimensional (1-D) chain complex, [{Rh2(acam)4}3{Pt2(OPiv)2(NH3)4}4](ClO4)8 (4, acam = acetamidate, OPiv = pivalate), has been synthesized and characterized by single-crystal X-ray analysis and diffuse reflectance spectroscopy. Complex 4 comprises [Rh2(acam)4] (i.e. [Rh2]) and [Pt2(OPiv)2(NH3)4](ClO4)2 (i.e. [Pt2]), where Rh and Pt atoms are axially linked by metal-metal bonds with a repetition of -{[Rh2]-[Pt2]-[Rh2]-[Pt2]-[Rh2]-[Pt2]-[Pt2]}n-. All metal oxidation states in 4, determined by structural and X-ray photoelectron spectral analyses, are +2. The unbridged Rh-Pt and Pt-Pt bonds in 4 are supported by multiple hydrogen bonds; the distances of Rh-Pt bonds are relatively longer than those in previously reported 1-D chains despite smaller torsion angles between the Rh and Pt coordination planes. Diffuse reflectance spectra revealed that the electronic structure of 4 has a larger gap between filled and vacant σ-type orbitals and a smaller gap between a filled π*(Rh2) and a vacant σ-type orbital.

Integration of Paramagnetic Diruthenium Complexes into an Extended Chain by Heterometallic Metal-Metal Bonds with Diplatinum Complexes.

We successfully obtained a paramagnetic one-dimensional (1D) chain complex [{Ru2(O2CCH3)4}{Pt2(piam)2(NH3)4}2]n(PF6)4n·4nH2O (2; piam = pivalamidate) extended by metal-metal bonds. Compound 2 comprises two types of metal species, ruthenium and platinum, where an acetate-bridged dinuclear ruthenium complex (i.e., [Ru2]) and a pivalamidate-bridged platinum complex (i.e., [Pt2]) are connected by axial metal-metal bonds, forming an attractive quasi-1D infinite chain that can be expressed as -{[Pt2]-[Ru2]-[Pt2]}n-. Such axial metal-metal bonds are attributed to the interaction between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) along the z axis, where both the HOMO in [Pt2(II,II)] and the LUMO in [Ru2(II,II)] are σ* orbitals associated with metal cores. The crystal structure and X-ray photoelectron spectrum for 2 reveal that metal oxidation states are -{[Pt2(II,II)]-[Ru2(II,II)]-[Pt2(II,II)]}n-, where [Ru2(II,II)] can have an electronic configuration of σ(2)π(4)δ(2)δ*(2)π*(2) or σ(2)π(4)δ(2)π*(4). The magnetic susceptibility of 2 has a µeff [∝(χT)(1/2)] value of 2.77 µB per [Pt2(II,II)]-[Ru2(II,II)]-[Pt2(II,II)] unit at 300 K, showing that two unpaired electrons lie on π*(Ru2). Magnetic measurements performed at temperatures of 2-300 K indicate that S = 1 Ru2(II,II) units are weakly antiferromagnetically coupled (zJ = -1.4 cm(-1)) with a large zero-field splitting (D = 221 cm(-1)).

(113)Cd Nuclear Magnetic Resonance as a Probe of Structural Dynamics in a Flexible Porous Framework Showing Selective O2/N2 and CO2/N2 Adsorption.

Two new isomorphous three-dimensional porous coordination polymers, {[Cd(bpe)0.5(bdc)(H2O)]·EtOH}n (1) and {[Cd(bpe)0.5(bdc)(H2O)]·2H2O}n (2) [bpe = 1,2-bis(4-pyridyl)ethane, and H2bdc = 1,4-benzenedicarboxylic acid], have been synthesized by altering the solvent media. Both structures contain one-dimensional channels filled with metal-bound water and guest solvent molecules, and desolvated frameworks show significant changes in structure. However, exposure to the solvent vapors (water and methanol) reverts the structure back to the as-synthesized structure, and thus, the reversible flexible nature of the structure was elucidated. The flexibility and permanent porosity were further reinforced from the CO2 adsorption profiles (195 and 273 K) that show stepwise uptake. Moreover, a high selectivity for O2 over N2 at 77 K was realized. The framework exhibits interesting solvent vapor adsorption behavior with dynamic structural transformation depending upon the size, polarity, and coordination ability of the solvent molecules. Further investigation was conducted by solid state (113)Cd nuclear magnetic resonance (NMR) spectroscopy that unambiguously advocates the reversible transformation "pentagonal-bipyramidal CdO6N → octahedral CdO5N" geometry in the desolvated state. For the first time, (113)Cd NMR has been used as a probe of structural flexibility in a porous coordination polymer system.

Mixed valency in quadruple hydrogen-bonded dimers of bis(biimidazolate)dirhodium complexes.

Dirhodium complexes with biimidazole (H2bim) ligands [Rh2(O2CR)2(H2bim)2Cl2] (R = Bu ([1Cl2]), Pr ([2Cl2])), [Rh2(O2CBu)2(H2bim)2](PF6)2 ([1](PF6)2), [Rh2(O2CBu)2(H2bim)2(PPh3)2](PF6)2 ([1(PPh3)2](PF6)2), and [Rh2(O2CPr)2(H2bim)2(PPh3)2]Cl2 ([2(PPh3)2]Cl2) have been synthesized. Deprotonation of the biimidazole complexes afforded the quadruply hydrogen-bonded dimers of the biimidazolate complexes [Rh2(O2CR)2(Hbim)2(PPh3)2]2 (R = Bu ([1'(PPh3)2]2) and Pr ([2'(PPh3)2]2)). Complementary hydrogen bonds between the Hbim(-) ligands are not coplanar because the Hbim(-) ions in one dirhodium complex are not parallel (the dihedral angle between them is ca. 15°). A cyclic voltammogram of [1'(PPh3)2]2 shows two sets of two consecutive oxidation waves in CH2Cl2. The one-electron-oxidized species of [1'(PPh3)2]2 showed no intervalence charge-transfer band in the electronic spectrum and an axially symmetrical ESR spectrum with hyperfine structure because of two phosphorus atoms. These observations show that the odd electron is localized in a σ(Rh-Rh) orbital on one dirhodium unit. Theoretical calculations indicate that an oxidized complex [Rh2(O2CMe)2(bim)2(PMe3)2](-) hydrogen bonded with a biimidazole complex [Rh2(O2CMe)2(H2bim)2(PMe3)2](2+) was a stable mixed-valence complex.

Assembled structures of tetrakis(biimidazole)dirhodium complexes hydrogen-bonded with common inorganic anions.

Eight new structures of dirhodium complexes, each with four biimidazole (H2bim) ligands, were obtained: [Rh2(H2bim)4(H2O)2](NO3)4·4H2O (I), [Rh2(H2bim)4(H2O)2](ClO4)4·5H2O (II), [Rh2(H2bim)4(MeOH)2](ClO4)4 (III), [Rh2(H2bim)4(DMF)2](BF4)4 (IV), [Rh2(H2bim)4(Mepy)2](SiF6)2·8H2O (V), [{Rh2(H2bim)4(pz)}2(µ-pz)](SiF6)(ClO4)6·12.7H2O (VI), [{Rh2(H2bim)4(pz)}2(µ-pz)](ClO4)8·11.4H2O (VII) and [Rh2(H2bim)4(µ-pz)](SiF6)2·6H2O (VIII). The unbridged Rh-Rh bond distances range between 2.6313 (8) and 2.7052 (5) Å. The dirhodium units adopt a staggered conformation with torsion angles N-Rh-Rh-N of 37.6 (4)-48.98 (8)°. Various assembled structures were constructed by hydrogen bonding between the complexes and the anions: a discrete structure in (IV), one-dimensional structure in (II), two-dimensional structures in (I), (III), (VI), (VII) and (VIII) and a three-dimensional structure in (V).

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.

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.

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.

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.