Controlling the Direction of the Molecular Axis of Rod‐Shaped Binuclear Ruthenium Complexes on Single‐Walled Carbon Nanotubes

We report the synthesis of a mixed‐valence ruthenium complex, bearing pyrene moieties on one side of the ligands as anchor groups. Composites consisting of mixed‐valence ruthenium complexes and SWNTs were prepared by noncovalent π–π interactions between the SWNT surface and the pyrene anchors of the Ru complex. In these composites, the long axis of the Ru complexes was aligned in parallel to the principal direction of the SWNT. The optimized conformation of these complexes on the SWNT surface was calculated by molecular mechanics. The composites were examined by UV/Vis absorption and FT‐IR spectroscopy, XPS, and SEM analysis. Furthermore, their electrochemical properties were evaluated. Cyclic voltammograms of the composites showed reversible oxidation waves at peak oxidation potentials (Ep_ox) = 0.86 and 1.08 V versus Fc⁺/Fc, which were assigned to the Ru^II‐Ru^II/Ru^II‐Ru^III and the Ru^II‐Ru^III/Ru^III‐Ru^III oxidation events of the dinuclear ruthenium complex, respectively. Based on these observations, we concluded that the electrochemical properties and mixed‐valence state of the dinuclear ruthenium complexes were preserved upon attachment to the SWNT surface.     

Carbon–Carbon Cross‐Coupling Reactions Catalyzed by a Two‐Coordinate Nickel(II)–Bis(amido) Complex via Observable NiI,NiII, and NiIII Intermediates

Recently, the development of more sustainable catalytic systems based on abundant first‐row metals, especially nickel, for cross‐coupling reactions has attracted significant interest. One of the key intermediates invoked in these reactions is a Ni^III–alkyl species, but no such species that is part of a competent catalytic cycle has yet been isolated. Herein, we report a carbon–carbon cross‐coupling system based on a two‐coordinate Ni^II–bis(amido) complex in which a Ni^III–alkyl species can be isolated and fully characterized. This study details compelling experimental evidence of the role played by this Ni^III–alkyl species as well as those of other key Ni^I and Ni^II intermediates. The catalytic cycle described herein is also one of the first examples of a two‐coordinate complex that competently catalyzes an organic transformation, potentially leading to a new class of catalysts based on the unique ability of first‐row transition metals to accommodate two‐coordinate complexes.     

A 1,2,4‐Triazole‐based Polynuclear Mixed‐valence MnIIMnIII Complex: Synthesis,Characterization, and Magnetic Property

A mixed‐valence Mn complex {[Mn^IIMn^III(HL)₂(4,4′‐bpy)(H₂O)₂] · (ClO₄)(DMF)₃(4,4′‐bpy)_0.5}_n ( 1 ) [H₂L = 3‐(2‐phenol)‐5‐(pyridin‐2‐yl)‐1,2,4‐triazole] was synthesized and characterized by X‐ray single‐crystal structure analysis and magnetic susceptibility. Single‐crystal X‐ray analysis revealed that complex 1 has a dinuclear core, in which adjacent central Mn^III atoms are linked by 4,4′‐bipyridine to form an infinite one‐dimensional (1D) molecular configuration. According to the Mn surrounding bond lengths and bond valence sum (BVS) calculations, we demonstrated that the Mn atom coordinated to the pyridine N atoms is in the +2 oxidation state, while another Mn atom coordinated to the phenolic oxygen atoms is in the +3 oxidation state. Magnetic susceptibility data of the complex 1 indicate that the ferromagnetic interaction dominates in this complex.     

Carbon–Carbon Cross‐Coupling Reactions Catalyzed by a Two‐Coordinate Nickel(II)–Bis(amido) Complex via Observable NiI,NiII, and NiIII Intermediates

Recently, the development of more sustainable catalytic systems based on abundant first‐row metals, especially nickel, for cross‐coupling reactions has attracted significant interest. One of the key intermediates invoked in these reactions is a Ni^III–alkyl species, but no such species that is part of a competent catalytic cycle has yet been isolated. Herein, we report a carbon–carbon cross‐coupling system based on a two‐coordinate Ni^II–bis(amido) complex in which a Ni^III–alkyl species can be isolated and fully characterized. This study details compelling experimental evidence of the role played by this Ni^III–alkyl species as well as those of other key Ni^I and Ni^II intermediates. The catalytic cycle described herein is also one of the first examples of a two‐coordinate complex that competently catalyzes an organic transformation, potentially leading to a new class of catalysts based on the unique ability of first‐row transition metals to accommodate two‐coordinate complexes.     

Structural Study of Bromo-Bridged One-Dimensional NiII–NiIV Mixed Valence Complexes by Means of Exafs

Nickel K-edge and Bromine K-edge EXAFS spectra have been measured for Br-bridged one-dimensional Ni^II-Ni^IV mixed valence compounds and their reference Ni^II and Ni^IV complexes. Fourier transforms of the Br K- and Ni K-edge EXAFS data of the mixed valence compounds show one and two sharp peaks, respectively, assigned to the Br-Ni distance, and the Ni-N and Ni-Br distances. By applying least-squares curve-fitting analyses for the Fourier back-transformed first peaks, a mean Ni^IV-Br distance for the mixed valence compounds has been determined to be 2.64 Å, which is comparable to 2.63 Å for the discrete Ni^III complex. This suggests a significant elongation of the Ni^IV-Br bond owing to the charge transfer interaction between the Ni^II and Ni^IV atoms, resulting in the high electrical conductivities of Ni^II–Ni^IV compounds as compared with those of the Pd and Pt analogues. Mean Ni-N distances were accurately determined and were found to increase in the order, octahedral high-spin Ni^II > octahedral Ni^III ? octahedral Ni^IV, and square-planar Ni^II in the mixed valence compound ≥ square-planar low-spin Ni^II in the discrete complex. The Ni^II … Br distance in the mixed valence compound could not be obtained, possibly owing to the essentially weak bonding nature.     

Binuclear,High‐Valent Nickel Complexes: Ni−Ni Bonds in Aryl–Halogen Bond Formation

Metal–metal bonds play a vital role in stabilizing key intermediates in bond‐formation reactions. We report that binuclear benzo[h ]quinoline‐ligated Ni^II complexes, upon oxidation, undergo reductive elimination to form carbon–halogen bonds. A mixed‐valent Ni(2.5+)–Ni(2.5+) intermediate is isolated. Further oxidation to Ni^III, however, is required to trigger reductive elimination. The binuclear Ni^III–Ni^III intermediate lacks a Ni−Ni bond. Each Ni^III undergoes separate, but fast reductive elimination, giving rise to Ni^I species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond‐formation processes.     

Binuclear,High‐Valent Nickel Complexes: Ni−Ni Bonds in Aryl–Halogen Bond Formation

Metal–metal bonds play a vital role in stabilizing key intermediates in bond‐formation reactions. We report that binuclear benzo[h ]quinoline‐ligated Ni^II complexes, upon oxidation, undergo reductive elimination to form carbon–halogen bonds. A mixed‐valent Ni(2.5+)–Ni(2.5+) intermediate is isolated. Further oxidation to Ni^III, however, is required to trigger reductive elimination. The binuclear Ni^III–Ni^III intermediate lacks a Ni−Ni bond. Each Ni^III undergoes separate, but fast reductive elimination, giving rise to Ni^I species. The reactivity of these binuclear Ni complexes highlights the fundamental difference between Ni and Pd in mediating bond‐formation processes.     

N−N Bond Forming Reductive Elimination via a Mixed‐Valent Nickel(II)–Nickel(III) Intermediate

Natural products containing N–N bonds exhibit important biological activity. Current methods for constructing N?N bonds have limited scope. An advanced understanding of the fundamental N?N bond formation/cleavage processes occurring at the transition‐metal center would facilitate the development of catalytic reactions. Herein we present an N?N bond‐forming reductive elimination, which proceeds via a mixed‐valent Ni^II–Ni^III intermediate with a Ni–Ni bond order of zero. The discrete Ni^II–Ni^III oxidation states contrast with the cationic dimeric Ni analogue, in which both Ni centers are equivalent with an oxidation state of 2.5. The electronic structures of these mixed‐valent complexes have implications for the fundamental understanding of metal–metal bonding interactions.     

A novel nickel(II) coordination polymer incorporating 1,4‐phenylene­diacetic acid and 1,10‐phenanthroline

The title nickel(II) coordination polymer, viz. poly[[bis­(1,10‐phenanthroline)tris­(μ₃‐1,4‐phenyl­enediacetato)trinickel(II)] dihydrate], {[Ni₃(C₁₀H₈O₄)₃(C₁₂H₈N₂)₂]·2H₂O}_n, consists of linear trinuclear building blocks with two crystallographically unique Ni atoms. One Ni^II atom and the geometric centre of one 1,4‐phenyl­enediacetate ligand in the trinuclear unit both lie on inversion centres, while the other unique Ni^II atom lies near the inversion centre, together with another 1,4‐phenyl­enediacetate ligand. Each pair of adjacent trinuclear units is bridged by 1,4‐phenyl­enediacetate ligands, forming two kinds of infinite chains along the a and b axes, respectively. These two kinds of chains crosslink to yield a two‐dimensional network in the ab plane. The two‐dimensional sheets further stack along the c axis viaπ–π stacking inter­actions and hydrogen bonds, forming a three‐dimensional supramolecular structure.     

A Mixed‐Valence {Fe13} Cluster Exhibiting Metal‐to‐Metal Charge‐Transfer‐Switched Spin Crossover

It is promising and challenging to manipulate the electronic structures and functions of materials utilizing both metal‐to‐metal charge transfer (MMCT) and spin‐crossover (SCO) to tune the valence and spin states of metal ions. Herein, a metallocyanate building block is used to link with a Fe^II‐triazole moiety and generates a mixed‐valence complex {[(Tp^4‐Me)Fe^III(CN)₃]₉[Fe^II₄(trz‐ph)₆]}?[Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 ; trz‐ph=4‐phenyl‐4H‐1,2,4‐triazole). Moreover, MMCT occurs between Fe^III and one of the Fe^II sites after heat treatment, resulting in the generation of a new phase, {[(Tp^4‐Me)Fe^II(CN)₃][(Tp^4‐Me)Fe^III(CN)₃]₈ [Fe^IIIFe^II₃(trz‐ph)₆]}? [Ph₃PMe]₂?[(Tp^4‐Me)Fe^III(CN)₃] ( 1 a ). Structural and magnetic studies reveal that MMCT can tune the two‐step SCO behavior of 1 into one‐step SCO behavior of 1 a . Our work demonstrates that the integration of MMCT and SCO can provide a new alternative for manipulating functional spin‐transition materials with accessible multi‐electronic states.     

Sunlight‐Driven Formation and Dissociation of a Dynamic Mixed‐Valence Thallium(III)/Thallium(I) Porphyrin Complex

Inspired by a Newton’s cradle device and interested in the development of redox‐controllable bimetallic molecular switches, a mixed‐valence thallium(III)/thallium(I) bis‐strap porphyrin complex, with Tl^III bound out of the plane of the N core and Tl^I hung to a strap on the opposite side, was formed by the addition of TlOAc to the free base and exposure to indirect sunlight. In this process, oxygen photosensitization by the porphyrin allows the oxidation of Tl^I to Tl^III. The bimetallic complex is dynamic as the metals exchange their positions symmetrically to the porphyrin plane with Tl^III funneling through the macrocycle. Further exposure of the complex to direct sunlight leads to thallium dissociation and to total recovery of the free base. Hence, the porphyrin plays a key role at all stages of the cycle of the complex: It hosts two metal ions, and by absorbing light, it allows the formation and dissociation of Tl^III. These results constitute the basis for the further design of innovative light‐driven bimetallic molecular devices.     

Three‐Dimensional Antiferromagnetic Order of Single‐Chain Magnets: A New Approach to Design Molecule‐Based Magnets

Two one‐dimensional compounds composed of a 1:1 ratio of Mn^III salen‐type complex and Ni^II oximato moiety with different counter anions, PF₆^? and BPh₄^?, were synthesized: [Mn(3,5‐Cl₂saltmen)Ni(pao)₂(phen)]PF₆ ( 1 ) and [Mn(5‐Clsaltmen)Ni(pao)₂(phen)]BPh₄ ( 2 ), where 3,5‐Cl₂saltmen^2?=N,N′‐(1,1,2,2‐tetramethylethylene)bis(3,5‐dichlorosalicylideneiminate); 5‐Clsaltmen^2?=N,N′‐(1,1,2,2‐tetramethylethylene)bis(5‐chlorosalicylideneiminate); pao^?=pyridine‐2‐aldoximate; and phen=1,10‐phenanthroline. Single‐crystal X‐ray diffraction study was carried out for both compounds. In 1 and 2 , the chain topology is very similar forming an alternating linear chain with a [‐Mn^III‐ON‐Ni^II‐NO‐] repeating motif (where ‐ON‐ is the oximate bridge). The use of a bulky counteranion, such as BPh₄^?, located between the chains in 2 rather than PF₆^? in 1 , successfully led to the magnetic isolation of the chains in 2 . This minimization of the interchain interactions allows the study of the intrinsic magnetic properties of the chains present in 1 and 2 . While 1 and 2 possess, as expected, very similar paramagnetic properties above 15 K, their ground state is antiferromagnetic below 9.4 K and paramagnetic down to 1.8 K, respectively. Nevertheless, both compounds exhibit a magnet‐type behavior at temperatures below 6 K. While for 2 , the observed magnetism is well explained by a Single‐Chain Magnet (SCM) behavior, the magnet properties for 1 are induced by the presence in the material of SCM building units that order antiferromagnetically. By controlling both intra‐ and interchain magnetic interactions in this new [Mn^IIINi^II] SCM system, a remarkable AF phase with a magnet‐type behavior has been stabilized in relation with the intrinsic SCM properties of the chains present in 1 . This result suggests that the simultaneous enhancement of both intrachain (J) and interchain (J′) magnetic interactions (with keeping J ? J′), independently of the presence of AF phase might be an efficient route to design high temperature SCM‐based magnets.     

An Unusually Delocalized Mixed‐Valence State of a Cyanidometal‐Bridged Compound Induced by Thermal Electron Transfer

The heterometallic complexes trans ‐[Cp(dppe)FeNCRu(o ‐bpy)CNFe(dppe)Cp][PF₆]_n ( 1 [PF₆]_n , n =2, 3, 4; o ‐bpy=1,2‐bis(2,2′‐bipyridyl‐6‐yl)ethane, dppe=1,2‐bis(diphenylphosphino)ethane, Cp=1,3‐cyclopentadiene) in three distinct states have been synthesized and fully characterized. 1 ³⁺[PF₆]₃ and 1 ⁴⁺[PF₆]₄ are the one‐ and two‐electron oxidation products of 1 ²⁺[PF₆]₂, respectively. The investigated results suggest that 1 [PF₆]₃ is a Class II mixed valence compound. 1 [PF₆]₄ after a thermal treatment at 400 K shows an unusually delocalized mixed valence state of [Fe^III‐NC‐Ru^III‐CN‐Fe^II], which is induced by electron transfer from the central Ru^II to the terminal Fe^III in 1 [PF₆]₄, which was confirmed by IR spectroscopy, magnetic data, and EPR and Mössbauer spectroscopy.     

Syntheses,Structures, Photoluminescence,and Magnetism of a Series of Discrete Lanthanide Complexes based on 2,5‐Dichlorobenzoate and 1,10‐Phenanthroline

The syntheses and crystal structures of eight lanthanide complexes with formula [Ln(2,5‐DCB)_x(phen)_y] are reported, which are characterized via single‐crystal, powder X‐ray diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis, photoluminescence measurement, and DC/AC magnetic measurement. These eight complexes are isostructural, and possess a discrete dinuclear structure. The adjacent dinuclear molecules are linked by the hydrogen bonding interactions into a one‐dimensional (1D) supramolecular chain. The neighboring 1D chains are further extended into a two‐dimensional (2D) supramolecular layer by the π–π stacking interactions. The photoluminescent properties of complexes 1 (Nd^III), 2 (Sm^III), 3 (Eu^III), 5 (Tb^III), 6 (Dy^III), and 8 (Yb^III) were investigated. Magnetic investigations also reveal the presence of ferromagnetic interactions in complexes 4 (Gd^III), 6 (Dy^III), and 7 (Er^III). Additionally, complex 6 (Dy^III) demonstrates field‐induced slow magnetic relaxation behavior.     

catena‐Poly­[europium(III)‐tri‐μ‐2,3‐di­methoxy­benzoato]

The title compound, [Eu(C₉H₉O₄)₃]_n or [Eu(2,3‐DMOBA)₃]_n, where 2,3‐DMOBA is 2,3‐di­methoxy­benzoate, is an infinite one‐dimensional non‐centrosymmetric coordination polymer. The unique Eu^III atom is bridged by six carboxyl­ate ligands; it is ennea‐coordinated and has a distorted tricapped trigonal prism geometry. The Eu—O distances are in the range 2.315 (3)–2.959 (5) Å.     

The new one‐dimensional coordination polymer catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐[diaquairon(III)]‐μ‐oxalato]

The oxalate dianion is one of the most studied ligands and is capable of bridging two or more metal centres and creating inorganic polymers based on the assembly of metal polyhedra with a wide variety of one‐, two‐ or three‐dimensional extended structures. Yellow single crystals of a new mixed‐metal oxalate, namely catena‐poly[[diaquasodium(I)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′‐[diaquairon(III)]‐μ‐oxalato‐κ⁴O¹,O²:O^1′,O^2′], [NaFe(C₂O₄)₂(H₂O)₄]_n, have been synthesized and the crystal structure elucidated by X‐ray diffraction analysis. The compound crystallizes in the noncentrosymmetric space group I4₁ (Z = 4). The asymmetric unit contains one Na^I and one Fe^III atom lying on a fourfold symmetry axis, one μ₂‐bridging oxalate ligand and two aqua ligands. Each metal atom is surrounded by two chelating oxalate ligands and two equivalent water molecules. The structure consists of infinite one‐dimensional chains of alternating FeO₄(H₂OW1)₂ and NaO₄(H₂OW2)₂ octahedra, bridged by oxalate ligands, parallel to the [100] and [010] directions, respectively. Because of the cis configuration and the μ₂‐coordination mode of the oxalate ligands, the chains run in a zigzag manner. This arrangement facilitates the formation of hydrogen bonds between neighbouring chains involving the H₂O and oxalate ligands, leading to a two‐dimensional framework. The structure of this new one‐dimensional coordination polymer is shown to be unique among the A^IM^III(C₂O₄)₂(H₂O)_n series. In addition, the absorption bands in the IR and UV–Visible regions and their assignments are in good agreement with the local symmetry of the oxalate ligand and the irregular environment of iron(III). The final product of the thermal decomposition of this precursor is the well‐known ternary oxide NaFeO₂.     

Cycloadducts of 1‐Alkyl‐1,2‐diphospholes with N‐Phenylmaleimide: Synthesis,Structure, Oxidation,and Thionation Reactions

The [4+2] cycloaddition reaction of 1‐alkyl‐1,2‐diphospholes ( 1 ) with N‐phenylmaleimide proceeds at 25°С in toluene to give 1,7‐diphosphanorbornenes ( 2 ) as anti‐endo isomer only. Oxidation of 2 with air at room temperature or thionation with excess of sulfur at 80°С results in the formation of mixed valent P^III, P^V 7‐oxo(thia)‐1,7‐diphosphanorbornenes ( 3 , 4 ) in high yield. The polycyclic compounds 3 and 4 are air stable and have small sums of valence angles at the phosphorus atoms.     

A new heteroleptic oxalate‐based compound: poly[[2‐(aminomethyl)pyridine]di‐μ6‐oxalato‐chromium(III)potassium(I)]

The title compound, [KCr(C₂O₂)₂(C₆H₈N₂)]_n, was obtained from aqueous solution and analyzed with single‐crystal X‐ray diffraction at 100 K. It crystallizes in the monoclinic space group C2/c and displays a three‐dimensional polymeric architecture built up by bimetallic oxalate‐bridged Cr^III–K helical chains linked through centrosymmetric K₂O₂ units to yield a sheet‐like alternating P/M arrangement which looks like that of the previously described two‐dimensional [NaCr(ox)₂(pyim)(H₂O)]·2H₂O [pyim is 2‐(pyridin‐2‐yl)imidazole; Lei et al. (2006). Inorg. Chem. Commun. 9 , 486–488]. The Cr^III ions in each helix have the same chirality. The infinite neutral sheets are eclipsed with respect to each other and are held together by a hydrogen‐bonding network involving 2‐(aminomethyl)pyridine H atoms and oxalate O atoms. Each sheet gives rise to channels of Cr₄K₄ octanuclear rings and each resultant hole is occupied by a pair of 2‐(aminomethyl)pyridine ligands with partial overlap. The shortest Cr...Cr distance [5.593 (4) Å] is shorter than usually observed in the K–M^III–oxalate family.     

Thermally Induced Valence Tautomeric Transition in a Two‐Dimensional Fe‐Tetraoxolene Honeycomb Network

A novel tetraoxolene‐bridged Fe two‐dimensional honeycomb layered compound, (NPr₄)₂[Fe₂(Cl₂An)₃] ?2 (acetone)?H₂O ( 1 ), where Cl₂An^n?=2,5‐dichloro‐3,6‐dihydroxy‐1,4‐benzoquinonate and NPr₄⁺=tetrapropylammonium cation, has been synthesized. 1 revealed a thermally induced valence tautomeric transition at T_1/2=236 K (cooling)/237 K (heating) between Fe^m+ (m=2 or 3) and Cl₂An^n? (n=2 or 3) that induced valence modulations between [Fe^II_HSFe^III_HS(Cl₂An^2?)₂(Cl₂An^.3?)]^2? at T>T_1/2 and [Fe^III_HSFe^III_HS(Cl₂An^2?)(Cl₂An^.3?)₂]^2? at T<T_1/2. Even in a two‐dimensional network structure, the low‐temperature phase [Fe^III_HSFe^III_HS(Cl₂An^2?)(Cl₂An^.3?)₂]^2? valence set can be regarded as a magnetic chain‐knit network, where ferrimagnetic Δ and Λ chains of [Fe^III_HS(Cl₂An^.3?)]_∞ are alternately linked by the diamagnetic Cl₂An^2?. This results in a slow magnetization behavior attributed to the structure acting as a single‐chain magnet at lower temperatures.     

Redox‐Assisted Self‐Assembly of a Water‐Soluble Cyanido‐Bridged Mixed Valence {CoIII/FeII}2 Square

The facile redox‐assisted assembly of a water‐soluble, extremely robust, cyanide‐bridged mixed‐valence [{Co^III{(Me)₂(μ‐ET)cyclen}}₂{(μ‐NC)₂Fe^II(CN)₄}₂]^2? square is reported. The preparation process involved the use of the enhanced lability of inert Co^III synthons triggered by outer‐sphere redox processes. Characterization of the final compounds has been carried out by NMR, UV/Vis, electrochemistry, and ICP analyses. DFT calculations have been conducted to optimize a structure that has the same hydrodynamic radius as that obtained from DOSY experiments. The new compound is extremely robust, surviving in aqueous solution within the 0–12 pH range for months. The species shows a high affinity for both protons and hydroxo ions in aqueous medium.