Attenuation of Conductance in Cobalt Extended Metal Atom Chains

Density functional theory, in conjunction with nonequilibrium Green’s functions, is used to explore the attenuation of the resistance of Co_<i>x</i> wires along the series Co₃(dpa)₄(NCS)₂, Co₅(tpda)₄(NCS)₂, and Co₇(teptra)₄(NCS)₂. At very low bias (0 < <i>V</i> < 25 mV) the conductance, <i>G</i>, decreases in the order <i>G</i>(Co₃) > <i>G</i>(Co₅) > <i>G</i>(Co₇), consistent with experiment and with an anticipated inverse relationship between conductance and chain length. At higher voltages, however, the current–voltage responses of all three are striking nonlinear, and above 50 mV <i>G</i>(Co₅) > <i>G</i>(Co₃) > <i>G</i>(Co₇). The very different behavior of the members of this homologous series can be traced to the different symmetries and multiplicities of their respective ground states, which in turn control the properties of the dominant transport channels

Coupled Electronic and Magnetic Phase Transition in the Infinite-Layer Phase LaSrNiRuO₄

Topochemical reduction of the ordered double perovskite LaSrNiRuO₆ with CaH₂ yields LaSrNiRuO₄, an extended oxide phase containing infinite sheets of apex-linked, square-planar Ni¹⁺O₄ and Ru²⁺O₄ units ordered in a checkerboard arrangement. At room temperature the localized Ni¹⁺ (d⁹, <i>S</i> = ¹/₂) and Ru²⁺ (d⁶, <i>S</i> = 1) centers behave paramagnetically. However, on cooling below 250 K the system undergoes a cooperative phase transition in which the nickel spins align ferromagnetically, while the ruthenium cations appear to undergo a change in spin configuration to a diamagnetic spin state. Features of the low-temperature crystal structure suggest a symmetry lowering Jahn–Teller distortion could be responsible for the observed diamagnetism of the ruthenium centers

Extreme Sensitivity of a Topochemical Reaction to Cation Substitution: SrVO₂H versus SrV_1–<i>x</i>Ti_<i>x</i>O_1.5H_1.5

The anion-ordered oxide–hydride SrVO₂H is an antiferromagnetic insulator due to strong correlations between vanadium d electrons. In an attempt to hole-dope SrVO₂H into a metallic state, a strategy of first preparing SrV_1–<i>x</i>Ti_<i>x</i>O₃ phases and then converting them to the corresponding SrV_1–<i>x</i>Ti_<i>x</i>O₂H phases via reaction with CaH₂ was followed. This revealed that the solid solution between SrVO₃ and SrTiO₃ is only stable at high temperature. In addition, reactions between SrV_0.95Ti_0.05O₃ and CaH₂ were observed to yield SrV_0.95Ti_0.05O_1.5H_1.5 not SrV_0.95Ti_0.05O₂H. This dramatic change in reactivity for a very modest change in initial chemical composition is attributed to an electronic destabilization of SrVO₂H on titanium substitution. Density functional theory calculations indicate that the presence of an anion-ordered, tetragonal SrMO₂H phase is uniquely associated with a d² electron count and that titanium substitution leads to an electronic destabilization of SrV_1–<i>x</i>Ti_<i>x</i>O₂H phases, which, ultimately, drives further reaction of SrV_1–<i>x</i>Ti_<i>x</i>O₂H to SrV_1–<i>x</i>Ti_<i>x</i>O_1.5H_1.5. The observed sensitivity of the reaction products to the chemical composition of initial phases highlights some of the difficulties associated with electronically doping metastable materials prepared by topochemical reactions

Insertion of Allenes into the Pd–C Bond of Ortho-Palladated Primary Arylamines of Biological Relevance: Phenethylamine, Phentermine, (l)‑Phenylalanine Methyl Ester, and (l)‑Tryptophan Methyl Ester. Synthesis of Tetrahydro-3-benzazepines and Their Salts

The previously reported ortho-metalated complexes [Pd­(<i>C</i>,<i>N</i>-ArCH₂CRR'NH₂-2)­(μ-X)]₂ derived from phenethylamine (Ar = C₆H₄, R = R' = H, X = Cl, Br), phentermine (Ar = C₆H₄, R = R' = Me, X = Cl), (l)-phenylalanine methyl ester (Ar = C₆H₄, R = H, R' = CO₂Me, X = Cl, Br)), and (l)-tryptophan methyl ester (Ar = C₈H₅N, R = H, R' = CO₂Me, X = Cl) react with various allenes to give (1) the corresponding η³-allyl complexes derived from the insertion of one molecule of the allene into the Pd–C bond, the formation of which has been studied by DFT using a model complex, or (2) Pd(0) and the tetrahydro-3-benzazepinium salts, resulting from the decomposition of the above mentioned η³-allyl complexes, containing an exocyclic double bond, which, subsequently, react with a base to afford the corresponding benzazepines. The regiochemistry of these decomposition reactions has been studied and compared with that described for similar processes involving five-membered palladacycles. The crystal structures of the salts of some benzazepines and one isoquinoline, derived from a five-membered palladacycle, have been determined by X-ray diffraction studies

Insertion of Allenes into the Pd–C Bond of Ortho-Palladated Primary Arylamines of Biological Relevance: Phenethylamine, Phentermine, (l)‑Phenylalanine Methyl Ester, and (l)‑Tryptophan Methyl Ester. Synthesis of Tetrahydro-3-benzazepines and Their Salts

The previously reported ortho-metalated complexes [Pd­(<i>C</i>,<i>N</i>-ArCH₂CRR'NH₂-2)­(μ-X)]₂ derived from phenethylamine (Ar = C₆H₄, R = R' = H, X = Cl, Br), phentermine (Ar = C₆H₄, R = R' = Me, X = Cl), (l)-phenylalanine methyl ester (Ar = C₆H₄, R = H, R' = CO₂Me, X = Cl, Br)), and (l)-tryptophan methyl ester (Ar = C₈H₅N, R = H, R' = CO₂Me, X = Cl) react with various allenes to give (1) the corresponding η³-allyl complexes derived from the insertion of one molecule of the allene into the Pd–C bond, the formation of which has been studied by DFT using a model complex, or (2) Pd(0) and the tetrahydro-3-benzazepinium salts, resulting from the decomposition of the above mentioned η³-allyl complexes, containing an exocyclic double bond, which, subsequently, react with a base to afford the corresponding benzazepines. The regiochemistry of these decomposition reactions has been studied and compared with that described for similar processes involving five-membered palladacycles. The crystal structures of the salts of some benzazepines and one isoquinoline, derived from a five-membered palladacycle, have been determined by X-ray diffraction studies

Reactivity Studies of [Co@Sn₉]^4– with Transition Metal Reagents: Bottom-Up Synthesis of Ternary Functionalized Zintl Clusters

The binary cluster [Co@Sn₉]^4– (<b>1</b>) was extracted directly from ethylenediamine (en) solutions of an intermetallic precursor with nominal composition “K₅Co₃Sn₉”, and its reactions with various organometallic reagents were explored. Reaction with Ni­(PPh₃)₂(CO)₂ gives [Co@Sn₉Ni­(CO)]^3– (<b>2</b>), a Co-centered <i>closo</i>-Sn₉Ni bicapped square antiprism. Analogous reactions with Ni­(COD)₂, Pt­(PPh₃)₄, and Au­(PPh₃)­Ph led to the isolation of [Co@Sn₉Ni­(C₂H₄)]^3– (<b>3</b>), [Co@Sn₉Pt­(PPh₃)]^3– (<b>4</b>), and [Co@Sn₉AuPh]^3– (<b>5</b>), respectively. <b>3</b> is structurally similar to <b>2</b> but significantly distorted from a <i>closo</i>-cluster with one open square face. The coordination of [CoSn₉]^3– by PtPPh₃ (<b>4</b>) or AuPh (<b>5</b>) induces a structural transformation in the CoSn₉ core, from a monocapped square antiprism (<i>C</i>_4<i>v</i>) to a tricapped trigonal prismatic structure (<i>pseudo</i>-<i>C</i>_3<i>v</i>), with the transition metal fragment capping a triangular face. The four trimetallic anions presented here represent a new family of ternary functionalized Zintl clusters incorporating a d⁹ transition metal center. All clusters were characterized by single-crystal X-ray diffraction and electrospray ionization mass spectrometry (ESI-MS)

A Homologous Series of First-Row Transition-Metal Complexes of 2,2′-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding

The organometallic first-row transition-metal complexes [M­(2,2′-bipy)­(mes)₂] (M = Cr (<b>1</b>), Mn (<b>2</b>), Co (<b>4</b>), Ni (<b>5</b>); 2,2′-bipy = 2,2′-bipyridine; mes = 2,4,6-Me₃C₆H₂) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M­(2,2′-bipy)­(mes)₂]⁻. The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr­(2,2′-bipy)­(mes)₂]·1.5C₆H₆, [Mn­(2,2′-bipy)­(mes)₂], [Co­(2,2′-bipy)­(mes)₂]·THF, [Ni­(2,2′-bipy)­(mes)₂], [K­(dibenzo-18-crown-6)·THF]­[Cr­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·0.67py·0.67tol, [K­(2,2,2-crypt)]­[Co­(2,2′-bipy)­(mes)₂], and [K­(2,2,2-crypt)]­[Ni­(2,2′-bipy)­(mes)₂]. These species, along with the previously reported neutral and anionic iron complexes [Fe­(2,2′-bipy)­(mes)₂]^0/– (<b>3</b>/<b>3</b>^<b>–</b>), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (<b>1</b>^<b>–</b>–<b>5</b>^<b>–</b>) can be best formulated as M­(II) complexes of the 2,2′-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes

A Homologous Series of First-Row Transition-Metal Complexes of 2,2′-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding

The organometallic first-row transition-metal complexes [M­(2,2′-bipy)­(mes)₂] (M = Cr (<b>1</b>), Mn (<b>2</b>), Co (<b>4</b>), Ni (<b>5</b>); 2,2′-bipy = 2,2′-bipyridine; mes = 2,4,6-Me₃C₆H₂) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M­(2,2′-bipy)­(mes)₂]⁻. The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr­(2,2′-bipy)­(mes)₂]·1.5C₆H₆, [Mn­(2,2′-bipy)­(mes)₂], [Co­(2,2′-bipy)­(mes)₂]·THF, [Ni­(2,2′-bipy)­(mes)₂], [K­(dibenzo-18-crown-6)·THF]­[Cr­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·0.67py·0.67tol, [K­(2,2,2-crypt)]­[Co­(2,2′-bipy)­(mes)₂], and [K­(2,2,2-crypt)]­[Ni­(2,2′-bipy)­(mes)₂]. These species, along with the previously reported neutral and anionic iron complexes [Fe­(2,2′-bipy)­(mes)₂]^0/– (<b>3</b>/<b>3</b>^<b>–</b>), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (<b>1</b>^<b>–</b>–<b>5</b>^<b>–</b>) can be best formulated as M­(II) complexes of the 2,2′-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes

SrFe_0.5Ru_0.5O₂: Square-Planar Ru²⁺ in an Extended Oxide

Low-temperature topochemical reduction of the cation disordered perovskite phase SrFe_0.5Ru_0.5O₃ with CaH₂ yields the infinite layer phase SrFe_0.5Ru_0.5O₂. Thermo­gravimetric and X-ray absorption data confirm the transition metal oxidation states as SrFe_0.5²⁺Ru_0.5²⁺O₂; thus, the title phase is the first reported observation of Ru²⁺ centers in an extended oxide phase. DFT calculations reveal that, while the square-planar Fe²⁺ centers adopt a high-spin <i>S</i> = 2 electronic configuration, the square-planar Ru²⁺ cations have an intermediate <i>S</i> = 1 configuration. This combination of <i>S</i> = 2, Fe²⁺ and <i>S</i> = 1, Ru²⁺ is consistent with the observed spin-glass magnetic behavior of SrFe_0.5Ru_0.5O₂

Inhibition of [FeFe]-Hydrogenases by Formaldehyde and Wider Mechanistic Implications for Biohydrogen Activation

Formaldehydea rapid and reversible inhibitor of hydrogen evolution by [FeFe]-hydrogenasesbinds with a strong potential dependence that is almost complementary to that of CO. Whereas exogenous CO binds tightly to the oxidized state known as H_ox but very weakly to a state two electrons more reduced, formaldehyde interacts most strongly with the latter. Formaldehyde thus intercepts increasingly reduced states of the catalytic cycle, and density functional theory calculations support the proposal that it reacts with the H-cluster directly, most likely targeting an otherwise elusive and highly reactive Fe-hydrido (Fe–H) intermediate