Halogen-bridged Complexes Research Articles

Synthesis, crystal structure and DFT study of a dinuclear CuI complex with (E)-2-benzylidene- N-methylhydrazinecarbothioamide: Role of halogen-hydrogen bonds in copper-copper bridge bonding

An equimolar reaction of copper(I) chloride with the (E)-2-benzylidene-N-methylhydrazinecarbothioamide (btscH-N1HMe) thio-ligand in acetonitrile followed by the addition of one equivalent of triphenylphosphine (Ph3P) gave crystals. The elemental analysis, and infrared and proton NMR spectra of the crystals supported the empirical composition, {CuCl(Ph3P)(btscH-N1HMe)}, and single crystal X-ray crystallography revealed formation of the dinuclear compound, [Cu2(µ-Cl)2(Ph3P)2(κ1S-btscH-N1HMe)2] (1). There is intramolecular H-bonding between the hydrazinic hydrogen atom (N2-H) and chloride ion {NH⋅⋅⋅Cl, 2.29; N⋅⋅⋅Cl, 3.144 Å}. The intermolecular H-bonding between the dimeric units led to the formation of a H-bonded 1 D polymer. DFT calculations on complexes of copper(I) halides with the model thiosemicarbazone, {H2C2=N3-N(H)-C(=S)-N1HMe}, and PH3 as a co-ligand, revealed the formation of halogen-bridged or sulfur-bridged dinuclear complexes, without or with the halogen - solvent/water hydrogen bonding. Some interesting conclusions are inferred from the experimental-theoretical correlations.

Exploration of Boundary between Charge-Density-Wave and Mott–Hubbard States in Quasi-One-Dimensional Halogen-Bridged Metal Complexes

Abstract In spite of a long history of quasi-one-dimensional halogen-bridged complexes (MX-chains), all Pt and Pd complexes form charge-density-wave (CDW) state (–X···M2+···X–M4+–X···), while all Ni complexes form Mott–Hubbard (MH) state (–X–Ni3+–X–Ni3+–X–), without exception. Although an interesting charge dynamics are expected at the boundary between the two states, no compound thus far reported forms both states. Thus, we have sought a phase boundary in bromo-bridged Pd compounds by decreasing Pd···Pd distance. In this article, we introduce the following two methods to decrease Pd···Pd distances: introduction of long alkyl chains which can afford attractive force between them, and partial substitution with smaller Ni ions, [Ni1−xPdx(chxn)2Br]Br2. In both systems, we have succeeded in realizing Pd3+ MH state. It has been revealed that the electronic state of bromo-bridged Pd compounds is determined by the Pd···Pd distances, in other words, CDW and MH states are stabilized when Pd···Pd distances are longer and shorter than 5.26 Å, respectively.

Novel halogen-bridged bisphosphine nickel(II) complexes

Reaction of [NiCl2(dtbpe)] (dtbpe=1,2-bis(di-tert-butylphosphino)ethane) with one equivalent of NaBArF4 (BArF4=tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) gives the dinuclear chloro-bridged nickel complex [Ni2(μ-Cl)2(dtbpe)2](BArF4)2 (1). [Ni(solv)6](BF4)2 reacts with dtbpe to give, depending on the solvent, the fluoro-bridged complex [Ni2(μ-F)2(dtbpe)2](BF4)2 (2) (solv=THF) or the mononuclear chelate complex [Ni(MeCN)2(dtbpe)](BF4)2 (3) (solv=MeCN). In 1–3, nickel cations are coordinated in a square-planar fashion according to X-ray crystallography. No Ni–Ni interaction was observed in dinuclear halogen-bridged complexes 1 and 2.

Versatile Behavior of the Schiff Base Ligand 2,5-Me2C6H3C(H)═N(2,4,6-Me3C6H2) toward Cyclometalation Reactions: C(sp2,phenyl)−H vs C(sp3,methyl)−H Activation

Treatment of the Schiff base ligand a with palladium(II) acetate in toluene gave 1a, with metalation of an aromatic phenyl carbon atom. Reaction at room temperature gave the trinuclear complex 4a. Treatment of a with palladium(II) acetate in refluxing acetic acid gave 1a′. The reaction of complexes 1a and 1a′ with sodium chloride or lithium bromide gave the halogen-bridged complexes 2a, 3a, 2a′, and 3a′. © 2010 American Chemical Society.

Stabilization of Pd(iii) states in nano-wire coordination complexes

In spite of a long history of quasi-one-dimensional halogen-bridged complexes (MX-chains), all Pt and Pd complexes form the charge-density wave (CDW) state (-X...M(II)...X-M(IV)-X...), while all Ni complexes form Mott-Hubbard (MH) states (-X-Ni(III)-X-Ni(III)-X-), without exception. We have succeeded in stabilizing the Pd(iii) MH state for the first time by utilizing the following two methods: partial substitution with Ni(iii) ions, [Ni(1-x)Pd(x)(chxn)(2)Br]Br(2), and chemical pressure via long alkyl chains introduced as counter-anions, [Pd(en)(2)Br](C(n)-Y)(2).H(2)O. In both systems, it has been revealed that the electronic state of bromo-bridged Pd compounds are determined by the PdPd distances, in other words, CDW and MH states are stabilized when PdPd distances are longer and shorter than 5.26 A, respectively.

Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2], ( 1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2]} 2(OCOCH 3) 2], ( 2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC 5H 4C(H) N[2′,4′,6′-(CH 3)C 6H 2], ( 4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(OCOCH 3)] 2, ( 5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Cl)] 2, ( 6) and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Br)] 2, ( 7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(Cl)(PPh 3)], ( 8) and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}-(Br)(PPh 3)], ( 9), as air stable solids. Treatment of 6 and 7 with Ph 2P(CH 2) 2PPh 2 (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(PPh 2(CH 2) 2PPh 2)][Cl], ( 10), and [Pd{4-(O)NC 5H 3C(H) N[2′,4′,6′-(CH 3)C 6H 2]}(PPh 2(CH 2) 2PPh 2)][PF 6], ( 11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.

Dynamical Valence Fluctuation at the Charge−Density−Wave Phase Boundary in Iodide-Bridged Pt Compound [Pt(chxn)2I]I2

We synthesized a novel iodo-bridged linear chain platinum compound, having the quasi-two-dimensional charge-density-wave (CDW) ground state and the smallest band gap. In this compound, we discovered an anomalous valence state in the boundary region at which the CDW phase alternates in the crystal by means of ESR, X-ray diffuse scattering, STM, and electrical resistivity. This anomalous state can be explained by the fast fluctuation between Pt(IV)-I...Pt(II) and Pt(II)...I-Pt(IV) in the double well potential. This is the first observation of the dynamical fluctuation of the CDW phase among the quasi one-dimensional halogen-bridged complexes.

Magnetic excitations in halogen-bridged nickel complex, [Ni(chxn)2Br]Br2

Abstract We performed inelastic neutron scattering experiments on [Ni(chxn) 2 Br]Br 2 . Magnetic excitations peaked at 6 meV were observed at the magnetic zone center at 5 K , also, integrated intensity including quasielastic scattering showed a maximum at 35 K . These properties are consistent with the spin-Peierls state.

Drastic suppression of electron-lattice interaction in a one-dimensional Mott-insulator system – a polaron and a self-trapped exciton

The effects of electron-lattice (e-1) interaction in a halogen-bridged Ni complex chain are discussed. As is already known, these complexes are most suitably described as a one-dimensional Mott insulator driven by a strong on-site Coulombic repulsion on the Ni sites. In fact, we see no lattice displacement in their ground states. In doped or photoexcited states, however, there is a possibility that the e-1 interaction manifests itself as a local deformation such as a polaron or a self-trapped exciton (STE), even if the Coulombic repulsion is extremely strong. We have therefore investigated the lattice relaxations in such cases and found that the interaction is drastically suppressed in a regime of weak and moderate strength.

13C NMR Spectra, 1H NMR Relaxation and ESR Measurements of Br2 Doped {[Pt(en) 2][PtBr2(en) 2]}3(CuBr4)4·12H2O

We measured NMR and ESR in solid state of a Br 2 doped halogen-bridged one-dimensional mixed-valence complex, {[Pt(en) 2 ][PtBr 2 (en) 2 ]} 3 (CuBr 4 ) 4 .12H 2 O, which forms a double chain structure consisting of -Pt(II)-Br-Pt(IV)-Br- and -Cu(I)-Br-Cu(I)-Br-, 13 C NMR measurements gave broad spectra explainable by marked effects from paramagnetic sites assignable to Pt(III) and/ or Cu(II) in the chain oxidized by bromine. Pt(III) sites are considered to form neutral solitons by referring to the electrical conductivity result.

PHOTOEMISSION STUDY OF QUASI-ONE-DIMENSIONAL HALOGEN-BRIDGED COMPOUND [Ni(chxn)2Br]Br2

We report results of the angle-resolved photoemission experiments on a quasi-one-dimensional halogen-bridged complex [Ni(chxn) 2 Br]Br 2 ( chxn = 1R, 2R-cyclohexanediamine), which is a one-dimensional Heisenberg spin chain with S = 1/2 and J ~ 3600 K . The expected two dispersions, originated with spin–charge separations as have been observed in other quasi-one-dimensional electron systems like Sr 2 CuO 3, are not clearly observed in this compound. Instead, only one 'band" having about 0.5 eV energy dispersion is found in the half of the Brillouin zone.

Electronic State of a Halogen-Bridged Mixed-Valence Binuclear Complex, Ni 2 ( dta ) 4 I

The electronic state of a halogen-bridged mixed-valence binuclear nickel complex, Ni 2 ( dta ) 4 I ( dta = CH 3 CS 2 m ), has been investigated by optical and magnetic measurements. The X-ray photoelectron spectrum of Ni 2 P 3/2 region is reasonably fitted with two components. Under the time scale of X-ray photoelectron spectroscopy (10 m 16 s), the charges of nickel ions in Ni 2 ( dta ) 4 I were detected as Ni 2+ and Ni 3+ . The strong absorption band was observed at 0.65 eV, which is attributable to an interdimer ( d * M d * ) transition. This band was clearly split below 100 K, implying a charge ordering in the one-dimensional -Ni-Ni-I- chains, such as Ni 2+ -Ni 3+ -I-Ni 3+ -Ni 2+ INi 2.5+ -Ni 2.5+ I. This distortion is also suggested by the spin concentration ∼1/3, the splitting of (Ni-Ni) mode, and the activation of (Ni-I) mode in Raman spectra at low temperature. 1-D chain compound Mixed-Valence MX chain MMX chain Interdimer transition Raman spectra

Organization of One-Dimensional Mixed-Valence Platinum Complexes at the Air-Water Interface and in Langmuir-Blodgett Films

Surface monolayers consisting of cationic, halogen-bridged linear platinum complex and anionic amphiphiles are formed at the air-water interface. Lipophilic polyion complex prepared from lipid and one-dimensional platinum complex is dispersed in chloroform as an indigo-colored solution, which color is ascribed to charge transfer (CT) absorption of the halogen-bridged complex (PtII→PtIV). Upon heating the solution, the indigo color disappeared due to dissociation of the linear complex into molecular unit complexes. Oriented surface monolayer is formed on water by spreading the colorless chloroform solution. Appearance of the CT band in reflectance spectra of monolayers indicates that the one-dimensional halogen-bridged complex is reformed at the air-water interface. The present technique opens an avenue to dimension-controlled organization of linear halogen-bridged complexes.

Valence Localization and its Ordering in a Mixed-Valence MMX-Chain Complex, Pt2(dta)4I (dta = CH3CS2 −)

The temperature dependencies of UV-VIS-NIR, IR, and Raman spectra of an MMX-type halogen-bridged mixed-valence complex Pt2(dta)4I (dta = CH3CS2 −) and the monovalent dimers Pt2(dta)4 and Pt2(dta)4I2 were investigated. The former undergoes a metal-insulator transition at 300 K, below which a characteristic splitting of C=S stretching mode was observed. The valence localization and its ordering are considered to occur coupled to the metal-insulator transition; -Pt2.5+-Pt2.5+-I-Pt2.5+-Pt2.5+-I- is for the metallic phase, while -Pt2+-Pt3+-I-Pt2+-Pt3+-I- for the insulating one.

Electron spin carriers in halogen-bridged 1-d complexes with nondegenerate cdw ground state

We measured temperature dependences of ESR spectra and 1 H NMR spin-lattice relaxation time T 1 on recently prepared mixedvalence hetero-metal complexes [Pd(en) 2 ][PtX 2 (en) 2 ](ClO 2 ) 4 (en: ethylenediamine; X: Cl, Br) which consist of a 1-D structure of-X-Pd II -X-Pt IV -X-Pd II -X-Pt IV -X-chain giving a non-degenerated electronic ground state. The observed low-concentration of paramagnetic M III sites and also long 1 H NMR T 1 compared with those in homo-metal complexes [M II (en) 2 ][M IV X 2 (en) 2 ](ClO 4 ) 4 (M: Pt, Pd; X: Cl, Br) having the degenerated ground state, can be explained well by the hindrance of the formation of domainwall type spin solitons in the hetero-metal complexes. This result supports our previous conclusion of the neutral soliton formation in the homo-metal halogen-bridged complexes.

Structure and stability of gaseous fluorine-bridged heterodimers and heteropolymers: (AF) n(MF 3) m, A′F 2MF 3 (A = H, Li, Na, K; M = B, Al, Fe; A′ =Be, Mg, Mn; n,m = 1, 2)

Starting from an overview of experimentally identified and quantum chemically calculated gaseous fluoride heterodimers and oligomers, it is the intention of the authors to survey the present knowledge on structures and stabilities of these complexes and to draw some consequences for experimental chemistry. General characteristics of gaseous halogen-bridged complexes are explained in Section 2. The present knowledge on experimentally identified and quantum chemically calculated fluorine-bridged heterocomplexes is summarized in Section 3. Finally, stabilities and structures of fluoroaluminate complexes in the vapour phase are discussed in Section 4. The discussion is focused on fluoroaluminate complexes containing mono-, di-and trivalent cations.

Spin solitons in a halogen-bridged 1-D Pt complex

Temperature and Larmor frequency dependences of 1H NMR relaxation time T 1 were measured in a 1-D halogen-bridged complex [Pt(en) 2][PtX 2(en) 2](ClO 4) 4 in ranges of 90 – 300 K and 15 – 60 MHz, respectively. The observed main and long T 1 component was explainable by the magnetic dipolar relaxation due to electron spins diffusing along the 1-D chain containing paramagnetic Pt III sites with a concentration of 10 −4 in molar ratio. These spins attributed to neutral spin solitons were shown to diffuse more rapidly than those in [Pd(chxn) 2][PdBr 2(chxn) 2]Br 4 forming 2-D H-bond networks

Electroabsorption in poly(paraphenylene vinylene) and PtI: Exciton vs band descriptions

We contrast the electroabsorption (EA) spectra calculated within an exciton model (Pariser-Parr-Pople Hamiltonian) with that in a band description. The former model combined with small lattice relaxation of excited states is found to give a very good EA description for poly(paraphenylene vinylene) (PPV). A band picture gives qualitatively different EA behavior. As an illustration, we consider a two-band charge-density-wave model, for which we find three kinds of linewidth broadening behavior: (1) For weak fields, the broadening decreases with electric field; (2) for intermediate field strength, the broadening is dominated by damping effects and is independent of the field; (3) for strong fields the traditional Franz-Keldysh law holds. The EA spectrum calculated using the two-band model is in very good agreement with experiments on PtI, a halogen-bridged mixed-valence metal linear-chain complex.

Low-Dimensional Magnetic Systems With S=1, 3/2 and 2

Abstract New Haldane gap compounds with S=1 have been characterized by single-crystal X-ray analyses and magnetic measurements. From these results, it has been found that the magnitude of the Haldane gaps can be controlled by substituting the bridging groups and in-plane ligands. The magnetic measurements of quasi-one-dimensional halogen-bridged binuclear Ru complexes with S=3/2. Ru2(CH3COO)4X (X=Cl, Br and 1) have revealed that the Br- and I-bridged compounds show one-dimensional antiferromagnetic interactions but no spin-Pelerls transition over the temperature range measured, while the C1-bridged compound shows no magnetic interaction among binuclear RU2 units through the bridging Cl− ions along the chain but spin-crossover behavior between S=3/2 and 1/2 in the binuclear Ru2 unit. The oxalato-bridged Fe2+ compound with S=2, Fe(ox).2Hz0 has no Haldane gap but shows metamagnetism under the high magnetic field.

Model of electron-proton correlation in quasi-one-dimensional halogen-bridged mixed-valence complexes: Role of proton motion.

The role of interchain hydrogen (H) bonds in one-dimensional electron systems is studied in halogen-bridged mixed-valence transition-metal complexes. A cluster theory is developed to predict the proton-induced ordering among charge-density-wave (CDW) chains in terms of pseudospin formalism for proton motion on H bonds. It is pointed out that the electron-proton coupling can control the CDW state which is produced from the competition between electron-electron and electron-phonon coupling.