Reductive Formation of Straight Linear Metal−Metal Bonded Tetranuclear Complexes X−M−Mo−Mo−M−X from X2M···Mo−Mo···MX2 Supported by Four Tridentate 6-Diphenylphosphino-2-pyridonate Ligands (M = Pd, Pt; X = Cl, Br, I)

Aiming for dynamic behaviours of molecular metal chains

The dynamical functions of molecular metal chains, that could be derived from unique physical and chemical properties coupled with self-assembly of metal chain components, have largely been unexplored, and this review paper focuses on the dynamic behaviours of Pd chains supported by linear tetraphosphines, meso- and rac-Ph₂PCH₂P(Ph)CH₂P(Ph)CH₂PPh₂ recently reported, and the current development on fine-tuning of metal chains by introducing heterometal atoms, i.e. heterometallic molecular metal chains, that are considered as promising dynamical components in the next generation.

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.

Nonanuclear zinc-gold [Zn3Au6] heterobimetallic complexes

Nonanuclear zinc-gold heterobimetallic complexes were synthesized in a two-step process. Commercially available carboxy-functionalized phosphine ligands were used for selective binding to Zn and Au centers. In the first step, bipyridine coordinated Zn-metalloligands with free phosphine moieties were prepared. Reaction of Zn-metalloligands with [AuCl(tht)] (tht = tetrahydrothiophene) resulted in the formation of nonanuclear Zn-Au heterobimetallic complexes. The flexibility of the carboxy-functionalized phosphine ligands was shown to be crucial for the formation of aurophilic interactions. Further, the photoluminescence of the Zn-metalloligands and one Zn-Au complex was investigated at room temperature as well as 77 K. The emission spectra showed clear difference between the Zn-metalloligands and the Zn-Au complex.

A dimolybdenum paddlewheel as a building block for heteromultimetallic structures

A series of heteromultimetallic complexes, containing a Mo₂⁴⁺core unit, were synthesized based on a bifunctional phosphine–carboxylic acid ligand system, leadingi.e.to the formation of supramolecular structuresviaaurophilic interactions.

Nonhelical heterometallic [Mo2M(npo)4(NCS)2] string complexes (M = Fe, Co, Ni) with high single-molecule conductance

Nonhelical metal strings, [MoMoM(npo)₄(NCS)₂], exhibited better overlaps of d_x2−y2 between neighbouring metal centres, stronger MoMo bonds, and superior single-molecule conductance.

Tantallacyclopentadiene as a unique metal-containing diene ligand coordinated to nickel for preparing tantalum–nickel heterobimetallic complexes

The mononuclear tantallacyclopentadiene, TaCl₃(C₄H₂^tBu₂), coordinates to Ni to form heterobimetallic complexes of Cl₃Ta(μ-C₄H₂^tBu₂)Ni(L) (L = COD, phosphines, IPr).

Heterometallic multiple bonding: delocalized three-center σ and π bonding in chains of 4d and 5d transition metals

Heterotrimetallic compounds Mo2Ru(dpa)4Cl2 (1) and W2Ru(dpa)4Cl2 (2) are prepared by reactions of M2(dpa)4 (M = Mo or W; dpa = 2,2'-dipyridylamide) with [Ru(CO)3Cl2]2. Crystallographic studies reveal short Mo-Ru and W-Ru distances, 2.38 Å (1) and 2.39 Å (2), suggestive of delocalized Mo-Mo-Ru and W-W-Ru bonding. In contrast to the σ bonding found in the corresponding iron compounds, density functional theory calculations reveal both a three-center/two-electron σ bond and two three-center/four-electron π bonds in the M-M-Ru compounds.

Crystallographic and structural characterization of heterometallic platinum compounds part IV: heterotetranuclear clusters

This review includes over two hundred heterotetranuclear platinum clusters. The clusters are of the compositions Pt3M, Pt3M2, PtM3, Pt′2MM′, PtM2M′ and PtMM′M”. There are twenty five different M atoms (transition and non-transition) as a partner(s) of platinum. The four metal atoms are found in a tetrahedral, planar-rhombohedral, butterfly, spited-triangular, cubane, eight — and oligo-membered rings and a unique structures. There is wide variety of the ligands from uni to- undecadentate, with the most common P and C donor sites. The shortest Pt-M (transition) versus Pt-M (non-transition) bond distances are 2.4833(8)Å (M=Pd) vs. 2.4365(5)Å (Ge). Several relationships between the various structural parameters were found and are discussed.

Linear Metal−Metal-Bonded Tetranuclear M−Mo−Mo−M Complexes (M = Ir and Rh): Oxidative Metal−Metal Bond Formation in a Tetrametallic System and 1,4-Addition Reaction of Alkyl Halides

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism.

Weak antiferromagnetic coupling for novel linear hexanuclear nickel(II) string complexes (Ni6 12+) and partial metal-metal bonds in their one-electron reduction products (Ni6 11+)

The preparation, crystal structures, magnetic properties and electrochemistry of novel linear hexanuclear nickel string complexes (Ni6(12+)) and their corresponding 1-e(-) reduction products (Ni6(11+)) are reported. In these complexes, the hexanickel chain is in a symmetrical arrangement (approximately D(4) symmetry) and is helically supported by four bpyany(2-) ligands [bpyany(2-) = the dianion of 2,7-bis(alpha-pyridylamino)-1,8-naphthyridine]. The Ni6(12+) complexes show that the two terminal nickel ions have high-spin states (S = 1) and the four inner ones have low-spin states (S = 0). The two terminal nickel ions exhibit weak antiferromagnetic coupling of ca.-5 cm(-1). All of Ni6(12+) complexes display three reversible redox couples at about -0.70, -0.20 and +1.10 V (vs. Ag/AgCl). The first reduction wave at about -0.20 V suggests facility of 1-e(-) reduction for the Ni(6)(12+) compounds. The reaction of Ni(6)(12+) complexes with hydrazine afforded the 1-e(-) reduction products (Ni6(11+)). As far as we are aware, the shortest bond distance of 2.202 A with a partial metal-metal bond was observed in Ni6(11+) compounds. The magnetic results of these Ni6(11+) compounds are in agreement with a localized model, in which the two terminal nickel ions are in a spin state of S = 1 whereas the central Ni3-Ni4 pair in a spin state of S = 1/2. The N6(11+) compounds show relatively strong antiferromagnetic coupling of about 60 cm(-1) between the terminal and the central dinickel ions.

Novel linear hexanuclear cobalt string complexes (Co6(12+)) and one-electron reduction products (Co6(11+)) supported by four bpyany2- ligands

The new ligand, 2,7-bis(alpha-pyridylamino)-1,8-naphthyridine (H2bpyany), was synthesized by the reaction of 2,7-dichloro-1,8-naphthyridine with 2-aminopyridine in the presence of t-BuOK under palladium(0)-catalyzed conditions. The preparation and characterization of novel hexacobalt string complexes, [Co6(mu6-bpyany)4(NCS)2](PF6)n (n=1 (1); n=2 (2)) and [Co6(mu6-bpyany)4(OTf)2](OTf)n (n = 2 (3); n = 1 (4)) are presented. The crystal structures for compounds have been determined by X-ray crystallography. Compounds 1 and 4 have the Co6 11+ configurations and are air-stable. Compounds 2 and 3 with Co6 12+ configurations are structurally similar to 1 and 4, respectively. The electrochemistry of 1 displays four redox couples at E1/2= -0.55, +0.38, +0.91, and +1.18 V (vs. Ag/AgCl). The magnetic data show that compounds 1 and 4 are in a spin state of S = 1/2, and 2 and 3 in a spin state of S = 1. The results of the EHMO calculations on compounds 1 and 2 are in agreement with their magnetic measurements.

An Infinite Zigzag Chain of Alternating Cl−Pd−Pd−Cl and Mo−Mo Units

Treatment of Pd(2)Cl(2)(CNC(6)H(3)Me(2)-2,6)(4) (1) with Mo(2)(O(2)CCF(3))(4) (2) in dichloromethane afforded an infinite zigzag chain [[Pd(2)Cl(2)(CNC(6)H(3)Me(2)-2,6)(4)][Mo(2)(O(2)CCF(3))(4)]](n) (3), where two metal-metal bonded dinuclear Pd-Pd and Mo-Mo units were bridged by chloro atoms. The Mo-Mo distance (2.1312(3) A) of 3 is significantly elongated compared to that of 2 (2.090(4) A) and lies in the range of that of the quadruple Mo-Mo bonded complexes. Such elongation might be attributed to the axial donation of the chloro atoms of the Pd-Pd unit to the Mo-Mo moiety.

Unique Oxidative Metal−Metal Bond Formation of Linearly Aligned Tetranuclear Rh−Mo−Mo−Rh Clusters

Reaction of Mo2(pyphos)4 (1) with [RhCl(CO)2]2 followed by treatment of excess amounts of tBuNC resulted in the clean formation of [Mo2Rh2(tBuNC)4(pyphos)4](X)2 (4a; X = Cl). The X-ray diffraction study as well as spectroscopic analyses of 4c (X = BPh4) implied that there is no direct sigma-bonding interaction between each Rh(I) atom and the Mo2 core. Each Rh(I) atom in 4 can be oxidized concurrently by 2 equiv of [Cp2Fe]PF6 to afford [Mo2Rh2(Cl)2(tBuNC)4(pyphos)4](PF6)2 (5) along with the formation of two Mo-Rh(II) single bonds and the reduction of the bond orders of the Mo-Mo moiety.

Dinuclear and heteropolynuclear complexes containing Mo2(4+) units

The quadruply bonded compound Mo2(DpyF)4 (1), where DpyF- is the anion of N,N'-di(2-pyridyl)formamidine, has been prepared by ligand substitution reactions of Mo2(OOCCF3)4 and either the neutral ligand, HDpyF, at ambient temperature or its lithium salt, LiDpyF, under refluxing conditions. An X-ray structural analysis shows that 1 has a paddlewheel structure with a [symbol: see text] distance of 2.1108(6) A. Reaction of 1 with CoCl2 in methanol produces the paramagnetic compound [Mo2Co(DpyF)4][CoCl4].2MeOH (2). The Co(II) atom in the cation [Mo2Co(DpyF)4]2+ resides on a low-spin hexacoordinate environment (S = 1/2) with a Co...Mo separation of 2.979(6) A, suggesting there is no direct bonding interaction between the Co and Mo atoms. The Mo-Mo distance of 2.1096(5) A is similar to that in 1. Reaction of 1 and CuCl in methanol yields [Mo2Cu4(DpyF)4Cl2][CuCl2]2.2MeOHxEt2O (3). In the cation there are two copper atoms on each side of the Mo2 core. Each is coordinated to two pyridyl nitrogen atoms of the cis DpyF- ligands and loosely bridged to the other by a chloride ion. As a result, the Cu(I) atoms are not aligned with the Mo2 unit. The Cu to Mo separations are in the range 3.003(1)-3.015(1) A, and the Mo-Mo distance of 2.127(1) A is comparable to those in 1 and 2.

Heteronuclear chains of four metal atoms including one quadruply bonded dimetal unit. Dichromium and dimolybdenum compounds with appended copper(I) atoms

It is shown that the M2(DPhIP)4 molecules (M = Cr, Mo; HDPhIP = 2,6-di(phenylimino)piperidine) can each capture two CuI atoms to form molecules with linear Cu...M[symbol: see text] M...Cu chains. In these chains the CuI atoms have only weak interactions with the M atoms (Cr...Cu = 2.628 A; Mo...Cu = 2.615 A) even though their introduction causes marked decreases in the M[symbol: see text]M distances (from 2.265 to 1.906 A for Cr and from 2.114 to 2.078 A for Mo). These seemingly contradictory facts are explained by noting that in the M2(DPhIP)4 molecules there are strong destabilizing (to the M[symbol: see text]M bonds) donor interactions of the dangling nitrogen atoms with the pi* orbitals. When these are eliminated by the introduction of the CuI atoms, the M[symbol: see text]M bonds become stronger and shorter.

Preparation, Spectroscopic Characterization, and Theoretical Study of the [Pd(4)(dmb)(4)(PPh(3))(2)]Cl(2) Complex (dmb = 1,8-Diisocyano-p-menthane) and Its Organometallic Polymer {[Pd(4)(dmb)(5)](CH(3)CO(2))(2)}(n)(): The First Examples of 58-Electron Linear Pd(4) Clusters

The title compounds [Pd(4)(dmb)(4)(PPh(3))(2)]Cl(2) (1) and {[Pd(4)(dmb)(5)](CH(3)CO(2))(2)}(n)() (2) were prepared from the reactions Pd(2)(dba)(3).CHCl(3) + 2dmb + PPh(3) for 1 (dba = dibenzylideneacetone) and Pd(2)(dba)(3).S + excess dmb + Pd(O(2)CCH(3))(2) for 2 (S = benzene or CHCl(3)), in good yields. The stuctures consist of quasi-linear Pd(4)(2+) species (d(PdPd) = 2.524(10), 2.524(10) and 2.534(10) Å for 1 and 2.5973(18), 2.6080(18), and 2.6080(18) Å for 2) where the dmb ligands bridge the Pd atoms, forming a catenate. While the PPh(3) ligands axially coordinate the M(4) structure in 1, a fifth dmb bridges another Pd(4)(dmb)(5)(2+) species, forming an organometallic polymer. From Raman spectroscopy, the two nu(PdPd) active modes (nu(1) and nu(2)) are observed at 165 and 86 cm(-)(1), respectively, for 1 (F(PdPd) = 1.44 mdyn Å(-)(1)). On the basis of EHMO (extended Hückel molecular orbital calculations), we predict that the HOMO and LUMO are the two dsigma orbitals arising from four interacting Pd atoms via the d(x)()()2(-)(y)()()2, d(z)()()2, and p(x)() M atomic orbitals. This assignment is confirmed by the UV-vis spectra, in particular from the second-moment band analysis, which indicates that the two Franck-Condon active modes are modes with frequencies of 165 and 86 cm(-)(1), which are assigned to nu(PdPd). The compounds exhibit luminescence at 77 K with lifetimes in the microsecond regime. During the course of this study, use of TCNQ(0) (tetracyanoquinodimethane) as the oxidizing agent during the reaction (instead of CHCl(3) or Pd(O(2)CCH(3))(2)) leads to 3 ([Pd(2)(dmb)(4)(&mgr;-Cl)](TCNQ)(3)), which is the first encapsulated halide ion "M(2)(dmb)(4)" species that is characterized from X-ray crystallography (d(PdCl) = 2.7143(6) Å). X-ray data for 2.4H(2)O: monoclinic, P2(1)/c, a = 19.433(2) Å, b = 15.312(2) Å, c = 29.156(2) Å, beta = 98.841(10) degrees, V = 8572.7(15) Å(3), Z = 4. X-ray data for 3: triclinic, P&onemacr;, a = 13.314(2) Å, b = 13.490(2) Å, c = 14.645(2) Å, alpha = 108.267(10) degrees, beta = 104.834(10) degrees, gamma = 101.221(10) degrees, V = 2303.8(6) Å(3), Z = 1.

Preparation, Characterization, and Luminescence Properties of a 58-Electron Linear Pt(4) Cluster, [Pt(4)(dmb)(4)(PPh(3))(2)](2+) (dmb = 1,8-Diisocyano-p-menthane), and Its Diphosphine Polymers

The title compounds [Pt(4)(dmb)(4)(PPh(3))(2)]Cl(2) (1) and {[Pt(4)(dmb)(4)(diphos)]Cl(2)}(n)() (diphos = dppb (2), dppp (3), dpph (4)) have been prepared in good yields from the reaction of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 1 equiv of PPh(3) for 1 (dba = dibenzylideneacetone) and from the reactions of Pt(2)(dba)(3).CHCl(3) with 2 equiv of dmb and 0.5 equiv of diphos for 2-4. The structure for 1 consists of a quasi-linear Pt(4)L(2)(2+) species (L = PPh(3); d(PtPt) = 2.666(2), 2.655(2), 2.641(2) Å), where the dmb ligands bridge the Pt atoms forming a catenate. From Raman spectroscopy, the two nu(PtPt) active modes for 1 are observed at 162 and 84 cm(-)(1) (F(PtPt) = 2.36 mdyn Å(-)(1)). For 2-4, the diphos ligands induce the formation of amorphous polymeric materials (X-ray powder diffraction patterns) with MW ranging from 84 000 to 307 000 according to viscometry. EHMO calculations predict that the HOMO and LUMO are the two dsigma orbitals arising from four interacting Pt atoms via the d(x)()()2(-)(y)()()2, d(z)()()2, s, and p(x)() M atomic orbitals. These are mixed with the ddelta and CNR(pi) MO's. From the examination of the position, absorptivity, and fwhm (full width at half maximum) of the strongly allowed low-energy UV-vis band, a dsigma --> dsigma assignment is made (lambda(max) = 405 nm, epsilon = 35 800 M(-)(1) cm(-)(1); EtOH for 1). The four compounds are luminescent at 77 K in EtOH, where lambda(emi) are 750, 736, 750, and 755 nm and tau(e) are 2.71, 4.78, 5.15, and 5.17 ns for 1-4, respectively. On the basis of the Stokes shifts (10 000-12 000 cm(-)(1)) and the long emission lifetimes, a phosphorescence dsigma --> dsigma assignment is made for the observed emissions. Crystal data for 1: crystal system triclinic; space group P1; a = 12.624(4) Å; b = 14.24(2) Å; c = 27.312(3) Å; alpha = 92.35(3) degrees; beta = 91.655(15) degrees; gamma = 90.28(5) degrees; V = 4903(7) Å(3); Z = 2; D(calc) = 1.528 g cm(-)(3); R(1) = 0.0738; wR(2) = 0.2097; S = 1.018.