Asymmetric heterometal string complexes: stereochemical control of the unique isomer of (4,0)[CuCuPd(npa)4Cl][PF6] and (4,0)[CuCuPt(npa)4Cl][PF6]

Structure and redox behaviour of a paramagnetic Rh-Pt-Cu-Pt-Rh heterometallic-extended metal-atom chain

A paramagnetic, pentanuclear, metal-metal bonded complex comprising three metals is isolated. The Cu dx2-y2 orbital of the Rh-Pt-Cu-Pt-Rh chain contains an unpaired electron. The close energetic levels and symmetric overlap of the Cu dx2-y2 and Rh-Pt δ* induces a charge-transfer reaction to achieve the diamagnetic Rh-Pt-Cu-Pt-Rh complex.

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.

Transition Metal Chain Complexes Supported by Soft Donor Assembling Ligands

The chemistry of discrete molecular chains constituted by metals in low oxidation states, displaying metal-metal proximity and stabilized by suitable metal-bridging, assembling ligands comprising at least one soft donor atom is comprehensively reviewed; complexes with a single (hard or soft) bridging atom (e.g., μ-halide, μ-sulfide, or μ-PR₂ etc.) as well as "closed" metal arrays (that fall in the realm of cluster chemistry) are excluded. The focus is on transition metal-based systems, with few excursions to cases combining transition and post-transition elements. Most relevant supporting ligands have neutral C, P, O, or S donor (mainly, N-heterocyclic carbene, phosphine, ether, thioether) or anionic donor (mainly phenyl, ylide, silyl, phosphide, thiolate) groups. A supporting-ligand-based classification of the metal chains is introduced, using as the classifying parameter the number of "bites" (i.e., ligand bridges) subtending each intermetallic separation. The ligands are further grouped according to the number of donor atoms interacting with the metal chain (called denticity in the following) and the column of the Periodic Table to which the set of donor atoms belongs (in ascending order). A complementary metal-based compilation of the complexes discussed is also provided in a concise tabular form.

A new series of heteronuclear metal strings, MRhRh(dpa)4Cl2 and MRhRhM(dpa)4X2, from the reactions of Rh2(dpa)4 with metal ions of group 7 to group 12

A new series of trinuclear and tetranuclear HMSCs, MRhRh(dpa)₄Cl₂ and MRhRhM(dpa)₄X₂, from the reactions of Rh₂(dpa)₄ and metal ions were synthesized.

Paramagnetic Metal-Metal Bonded Heterometallic Complexes

Significant progress has been made in the past 10-15 years on the design, synthesis, and properties of multimetallic coordination complexes with heterometallic metal-metal bonds that are paramagnetic. Several general classes have been explored including heterobimetallic compounds, heterotrimetallic compounds of either linear or triangular geometry, discrete molecular compounds containing a linear array of more than three metal atoms, and coordination polymers with a heterometallic metal-metal bonded backbone. We focus in this Review on the synthetic methods employed to access these compounds, their structural features, magnetic properties, and electronic structure. Regarding the metal-metal bond distances, we make use of the formal shortness ratio (FSR) for comparison of bond distances between a broad range of metal atoms of different sizes. The magnetic properties of these compounds can be described using an extension of the Goodenough-Kanamori rules to cases where two magnetic ions interact via a third metal atom. In describing the electronic structure, we focus on the ability (or not) of electrons to be delocalized across heterometallic bonds, allowing for rationalizations and predictions of single-molecule conductance measurements in paramagnetic heterometallic molecular wires.

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* (d_z²) 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.

Linear CuI2 Pd0 , CuI Pd02 , and AgI2 Pd0 Metal Chains Supported by Rigid N,N'-Diphosphanyl N-Heterocyclic Carbene Ligands and Metallophilic Interactions

Selective copper(I) to palladium(0) transmetallation of P-donors from the rigid N,N'-diphosphanyl-imidazol-2-ylidene C₃ H₂ [NP(tBu)₂ ]₂ (PC^NHC P) was observed when known [Cu₃ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₃ was reacted with [Pd(PPh₃ )₄ ]. When 1.2 equivalents of [Pd(PPh₃ )₄ ] was used, the product [Cu₂ Pd(μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (2(OTf)₂ ) was obtained, which features a Cu^I -Cu^I -Pd⁰ chain and appears to be the first linear heterotrinuclear complex with d¹⁰ -d¹⁰ interactions between Pd⁰ and Cu^I . When the Cu₃ precursor was reacted with 3.0 equivalents of [Pd(PPh₃ )₄ ], the complex [CuPd₂ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (3(OTf)₂ ) was obtained, which, on the basis of magnetic measurements, DFT calculations, and computed nuclear shieldings, was formulated as containing a Pd⁰ -Cu^I -Pd⁰ chain with an electron hole delocalized over the whole cation, including the metal chain. Similarly, selective transmetallation of the P-donors in [Ag₃ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₃ from silver to palladium (originating from [Pd(PPh₃ )₄ ]) gave the linear chain [Ag₂ Pd(μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (5(OTf)₂ ), which on the basis of NMR spectroscopy comprises an Ag^I -Ag^I -Pd⁰ metal core. However, X-ray diffraction data collected on various samples of 5(OTf)₂ were modeled with 50:50 metal disorder at the terminal positions, corresponding to a (Ag^I /Pd⁰ )-Ag^I -(Ag^I /Pd⁰ ) formulation. Upon standing in solution, 5(OTf)₂ transformed to 6(OTf)₂ , the regioisomer of 5(OTf)₂ in which the Pd center has migrated to the central position of an Ag^I -Pd⁰ -Ag^I chain. Prolonged standing in CH₂ Cl₂ or by reaction with [PtCl₂ (NCMe)₂ ] converts complex 6(OTf)₂ to the Ag^I /Pd^II complex [Ag₂ PdCl₂ (μ₃ -PC^NHC P,κP,κC^NHC ,κP)₂ ](OTf)₂ (7(OTf)₂ ). The structural data of 2(OTf)₂ , 3(OTf)₂ , and 7(OTf)₂ establish significant heterometallophilic interactions.

K3[Mo2(SNO5)4Cl]3[Mo2(SNO5)4]: the first example of a heterometallic extended metal atom node (HEMAN)

We present the synthesis, structure, and electrochemistry of K₃[Mo₂(SNO5)₄Cl]₃[Mo₂(SNO5)₄] (1, HSNO5 = monothiosuccinimide), the first example of a heterometallic extended metal atom node (HEMAN).

Cu(I) and Pb(II) complexes containing new tris(7-naphthyridyl)methane derivatives: synthesis, structures, spectroscopy and geometric conversion

Two novel facial-capping tris-naphthyridyl compounds, 2-chloro-5-methyl-7-((2,4-dimethyl-1,8-naphthyridin-7(1H)-ylidene)(2,4-dimethyl-1,8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L(1)) and 2-chloro-7-((2-methyl-1,8-naphthyridin-7(1H)-ylidene)(2-methyl-1,8-naphthyridin-7-yl))methyl-1,8-naphthyridine (L(2)), as well as their Cu(i) and Pb(ii) complexes, [CuL(a)(PPh(3))]BF(4) (1) (PPh(3) = triphenylphosphine, L(a) = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methane), [CuL(b)(PPh(3))]BF(4) (2) (L(b) = bis(2-methyl-1,8-naphthyridin-7-yl)(2-chloro-1,8-naphthyridin-7-yl)methane), [Pb(OL(a))(NO(3))(2)] (3) (OL(a) = bis(2,4-dimethyl-1,8-naphthyridin-7-yl)(2-chloro-5-methyl-1,8-naphthyridin-7-yl)methanol) and [Pb(L(b))(2)][Pb(CH(3)OH)(NO(3))(4)] (4), have been synthesized and characterized by X-ray diffraction analysis, MS, NMR and elemental analysis. The structural investigations revealed that the transfer of the H-atom at the central carbon to an adjacent naphthyridine-N atom affords L(1) and L(2) possessing large conjugated architectures, and the central carbon atoms adopt the sp(2) hybridized bonding mode. The reversible hydrogen transfer and a geometric configuration conversion from sp(2) to sp(3) of the central carbon atom were observed when Pb(II) and Cu(I) were coordinated to L(1) or L(2). The molecular energy changes accompanying the hydrogen migration and titration of H(+) to different receptor-N at L(1) were calculated by density functional theory (DFT) at the SCRF-B3LYP/6-311++G(d,p) level in a CH(2)Cl(2) solution, and the observed lowest-energy absorption and emission for L(1) and L(2) can be tentatively assigned to an intramolecular charge transfer (ICT) transition in nature.

Group 6 complexes with iron and zinc heterometals: understanding the structural, spectroscopic, and electrochemical properties of a complete series of M≡M···M' compounds

Binuclear quadruply bonded complexes Cr(2)(dpa)(4) (1, dpa = 2,2'-dipyridylamide), Mo(2)(dpa)(4) (2), and W(2)(dpa)(4) (3) react with anhydrous FeCl(2), yielding heterometallic compounds CrCrFe(dpa)(4)Cl(2) (4), MoMoFe(dpa)(4)Cl(2) (5), and WWFe(dpa)(4)Cl(2) (6). These molecules are structurally similar, having a linear M≡M···Fe chain that is axially capped by chloride ions and is equatorially supported by the helically twisted dpa ligands. A structurally related zinc analog, CrCrZn(dpa)(4)Cl(2) (7), can be prepared upon metalation of 1 with ZnCl(2). This reaction also persistently produces a 2:1 adduct of ZnCl(2) with 1, [Cr(2)(dpa)(4)](ZnCl(2))(2) (8), which is in equilibrium with 7 and has the two zinc ions bound externally to the Cr(2) core and axial bridging chloro ligands attached to each Cr ion. The sole isolable product of the addition of ZnCl(2) to 3 is a 1:1 adduct, [W(2)(dpa)(4)]ZnCl(2) (9). The structurally related chain complexes 4, 5, 6, and 7 are characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and (57)Fe Mössbauer spectroscopy for the iron complexes in order to gain insights into the nature of heterometallic interactions, electronic excited states, and redox properties of these compounds, which have implications for all other M≡M···M' molecules. Additionally, NMR spectroscopy has been used to gain insight into the mechanism of the metalation of 1 by Zn(II).

New generation of metal string complexes: strengthening metal-metal interaction via naphthyridyl group modulated oligo-alpha-pyridylamido ligands

To design new metal string complexes, several naphthyridyl group modulated oligo-alpha-pyridylamido ligands have been synthesized in the past five years. Because these ligands are less anionic than pyridylamido ligands, the resulting metal string complexes tend to form reduced mixed-valence [Ni(2)(napy)(4)](3+) dinuclear units which contain a delocalized unpaired electron and thus significantly enhance the conductance of metal string complexes. Furthermore, the asymmetric naphthyridyl group modulated oligo-alpha-pyridylamido ligands can stabilize the central heteronuclear or charge disproportionational metal frameworks, providing a plausible strategy to build inorganic molecular rectifiers.

Clear evidence of electron delocalization: synthesis, structure, magnetism, EPR and DFT calculation of the asymmetric hexanickel string complex containing a single mixed-valence (Ni(2))(3+) unit

This paper describes the physical properties of the (Ni(2))(3+) mixed-valence unit that is an excellent conductivity-enhanced tool for metal string complexes.