Highly reduced, polyoxo(alkoxo)vanadium(III/IV) clusters

A family of high nuclearity oxo(alkoxo)vanadium clusters in unprecedentedly low oxidation states is reported, synthesised from simple vanadium diketonate precursors in alcohols under solvothermal conditions. Crystal structures of [V18(O)12(OH)2(H2O)4(EtO)22(O2CPh)6(acac)2] (1), [V16Na2(O)18(EtO)16(EtOH)2(O2CPh)6(HO2CPh)2]infinity (2), [V13(O)13(EtO)15(EtOH)(RCO2)3] in which R=adamantyl (3) or Ph3C (4), and [V11(O)12(EtO)13(EtOH)(Ph3CCO2)2(MePO3)] (5) are reported, revealing these to be {VIII 16VIV 2} (1), {VIII 9VIV 3VV} (3 and 4) and {VIII 3VIV 8} (5) clusters, while 2 consists of isolated {VIII 8VIV 8} clusters bridged into polymeric chains by {Na2(OEt)2} fragments. Solvothermal conditions are essential to the formation of these species, and the level of oxidation of the isolated clusters is in part controlled by the crystallisation time, with the lowest mean-oxidation-state species being isolated by direct crystallisation on controlled cooling of the reaction solutions.     

A family of ferro- and antiferromagnetically coupled decametallic chromium(III) wheels

The synthesis and crystal structures of a family of decametallic Cr(III) "molecular wheels" are reported, namely [Cr10(OR)20(O2CR')10] [R' = Me, R = Me (1), Et (2); R' = Et, R = Me (3), Et (4); R' = CMe3, R = Me (5), Et (6)]. Magnetic studies on 1-6 reveal a remarkable dependence of the magnetic behaviour on the nature of R. In each pair of complexes with a common carboxylate (R') the nearest neighbour CrCr magnetic exchange coupling is more antiferromagnetic for the ethoxide-bridged (R = Et) cluster than for the methoxide analogue. In complexes 2, 4 and 6 the overall coupling is weakly antiferromagnetic resulting in diamagnetic (S = 0) ground states for the cluster, whilst in 1 and 5 it is weakly ferromagnetic thus resulting in very high-spin ground states. This ground state has been probed directly in the perdeuterated version of 1 ([D]1) by inelastic neutron scattering experiments, and these support the S = 15 ground state expected for ferromagnetic coupling of ten Cr(III) ions, and they also indicate that a single J-value model is inadequate. The ground state of 5 is large but not well defined. The trends in J on changing R are further supported by density functional calculations on 1-6, which are in excellent agreement with experiment. The very large changes in the nature of the ground state between 1 and 2, and 5 and 6 are the result of relatively small changes in J that happen to cross J = 0, hence changing the sign of J.     

Rational synthesis of supramolecular assemblies based on tetraplatinum units: synthesis, characterization, and selective substitution reactions of four different Pt4 clusters

Four different types of square‐planar Pt₄ clusters, trans‐[Pt₄(μ‐OCOCH₃)₆(μ‐ArNCHNAr)₂] ( 2 : ArNCHNAr=N,N′‐diarylformamidinate), [Pt₄(μ‐OCOCH₃)₇(μ‐ArNCHNAr)] ( 8 ), cis‐[Pt₄(μ‐OCOCH₃)₆(κ⁴‐N₄‐DArBp)] ( 9 : DArBp=1,3‐bis(arylbenzamidinate)propane), and [Pt₄Cl₂(μ‐OCOCH₃)₅(κ⁴‐N₂,P₂‐dpfam)] ( 13 : dpfam=N,N′‐bis[(2‐diphenylphosphino)phenyl]formamidinate), were successfully prepared by using selective substitution reactions of in‐plane acetate ligands of [Pt₄(μ‐OCOCH₃)₈] ( 1 ), which has four in‐plane and four out‐plane acetate ligands, with appropriate capping ligands. Fundamental substitution reactions of the remaining in‐plane acetates with benzoic acid derivatives were also investigated. All newly prepared complexes were characterized from spectral and physical data and combustion analysis. X‐ray crystallographic studies of some of the clusters were also performed. Electrochemical measurements of amidinate‐modified Pt₄ clusters revealed stepwise oxidation processes of the Pt₄ core due to Pt₄⁹⁺/Pt₄⁸⁺ and Pt₄¹⁰⁺/Pt₄⁹⁺. Based on the lability of the in‐plane acetate ligands of the modified Pt₄ clusters, reactions of cis‐[Pt₄(μ‐OCOCH₃)₆(κ⁴‐N₄‐DArBp)] ( 9 c : Ar=C₆H₄tBu‐4) with ferrocenedicarboxylic acid and p‐phenylenedipropionic acid resulted in the selective formation of cyclic dimers 17 and 18 and the reaction of 13 with 4,4′‐biphenyldicarboxylic acid afforded a linear dimer 20 . The dimers were characterized by spectral data, as well as X‐ray analyses for 17 and 18 . The finding of two Fe³⁺/Fe²⁺ redox couples in the electrochemical measurement of dimer 17 indicated that two ferrocenyl units in dimer 17 communicated electronically.     

A second metalloid Ga18 cluster and its topological similarity to the high-pressure Ga-II modification

The topology of many modifications of elemental gallium is reflected in the large variety of metalloid Ga clusters that have been isolated as intermediates on the way from the metastable molecular GaX species (X=Cl, Br, I) by means of disproportionation to the bulk metal. Herein, we report the synthesis and characterization of the first metalloid cluster anion [Ga(18)(PtBu(2))(10)](3-) with the singular core topology that resembles the gallium high-pressure modification Ga-II. The stabilization of the cluster anion through ion-pair contacts with a chainlike "Li(4)Br(2) backbone" is discussed. Furthermore, the compound is discussed in context of the other metalloid clusters Ga(18)R(8) and Ga(22)R(8) (R=SitBu(3)) and their structural relation to the elemental modifications Ga-III and beta-Ga, respectively.     

Synthesis of a large functional cage compound based on four Ga-Ga single bonds and its application as an oligoacceptor: on the way to bio-organogallium hybrid molecules

The digallium compound R(2)Ga-GaR(2) (1; R=CH(SiMe(3))(2)) reacts with citracinic acid by the release of two equivalents of bis(trimethylsilyl)methane and the formation of a unique oligofunctional cage compound (2). Four Ga-Ga bonds in a tetrahedral arrangement are bridged by four spacer ligands that are located on the faces of the tetrahedron and bridge the gallium atoms of three different Ga-Ga bonds. Four pyridinium groups result from the shift of one of the three acidic protons of four citracinic acid molecules to the nitrogen atoms of the aromatic rings. The N-H groups are arranged in pairs and are capable of acting as chelating acceptors for the coordination of THF molecules (2(THF)(2)) or the nitrogen atoms of 1-deazapurine (3(OEt(2))(4)). In particular, the last reaction verifies the potential applicability of this relatively water- and air-resistant acceptor compound for the generation of bioorganometallic hybrid molecules.     

Homo- and heteropolynuclear platinum complexes stabilized by dimethylpyrazolato and alkynyl bridging ligands: synthesis, structures, and luminescence

This work describes the synthesis of cis-[Pt(C[triple bond]CPh)2(Hdmpz)2] (1) and its use as a precursor for the preparation of homo- and heteropolynuclear complexes. Double deprotonation of compound 1 with readily available M(I) (M = Cu, Ag, Au) or M(II) (M = Pd, Pt) species affords the discrete hexanuclear clusters [{PtM2(mu-C[triple bond]CPh)2(mu-dmpz)(2)}(2)] [M = Cu (2), Ag (3), Au (4)], in which both "Pt(C[triple bond]CPh)2(dmpz)(2)" fragments are connected by four d(10) metal centers, and are stabilized by alkynyl and dimethylpyrazolate bridging ligands, or the trinuclear complexes [Pt(mu-C[triple bond]CPh)2(mu-dmpz)(2){M(C/\P)}2] (M = Pd (5), Pt (6); C/\P = CH(2)-C(6)H(4)-P(o-tolyl)2-kappaC,P), respectively. The X-ray structures of complexes 1-4 and 6 are reported. The X-ray structure of the platinum-copper derivative 2 shows that all copper centers exhibit similar local geometry being linearly coordinated to a nitrogen atom and eta(2) to one alkynyl fragment. However in the related platinum-silver (3) and platinum-gold (4) derivatives the silver and gold atoms present three different coordination environments. The complexes have been studied by absorption and emission spectroscopy. The hexanuclear complexes exhibit bright luminescence in the solid state and in fluid solution (except 4 in the solid state at 298 K). Dual long-lived emission is observed, being clearly resolved in low-temperature rigid media. The low-energy emission is ascribed to MLM'CT Pt(d)/pi(C[triple bond]CPh)-->Pt(p(z))/M'(sp)/pi*(C[triple bond]CPh) modified by metal-metal interactions whereas the high-energy emission is tentatively attributed to an emissive state derived from dimethylpyrazolate-to-metal (d(10)) LM'CT transitions pi(dmpz)-->M'(d(10)).     

Cuprophilic interactions in luminescent copper(I) clusters with bridging bis(dicyclohexylphosphino)methane and iodide ligands: spectroscopic and structural investigations

Polynuclear copper(I) complexes with bridging bis(dicyclohexylphosphino)methane (dcpm) and iodide ligands, [Cu(2)(dcpm)(2)(CH(3)CN)(2)](BF(4))(2) (1), [Cu(2)(dcpm)(2)](BF(4))(2) (2), [(CuI)(3)(dcpm)(2)] (3), [(CuI)(4)(dcpm)(2)] (4), and [(CuI)(2)(dcpm)(2)] (5) were prepared and their structures determined by X-ray crystal analysis. The shortest Cu--Cu distance found in these complexes is 2.475(1) A for 3. Powdered samples of 1, 3, 4, and 5 display intense and long-lived phosphorescence with lambda(max) at 460, 626, 590, and 456 nm and emission quantum yields of 0.26, 0.11, 0.12, and 0.56 at room temperature, respectively. In the solid state, 2 displays both a weak emission at 377 and an intense one at 474 nm with an overall emission yield 0.42. The difference in emission properties among complexes 1-5 suggests that both Cu--Cu interaction and coordination around the copper(I) center affect the excited state properties. A degassed solution of 2 in acetone gives a bright red emission with lambda(max) at 625 nm at room temperature. The difference absorption spectra of the triplet excited states of 1-5 in acetonitrile show broad absorption peaks at 340-410 and 850-870 nm.     

Experimental and theoretical evidence of aromatic behavior in heterobenzene-like molecules with metal-metal multiple bonds

Binding two quadruply bonded dimolybdenum units [Mo₂(DAniF)₃]⁺ (DAniF=N,N′‐di‐p‐anisylformamidinate) with two chalcogen atoms generated two molecules with a central core composed of a cyclic six‐membered [Mo₂]₂(μ‐EH)₂ species (E=S in 1 and O in 3 , and [Mo₂] is a quadruple‐bonded [Mo₂(formamidinate)₃] unit). Aerobic oxidation of 1 and 3 followed by concomitant deprotonation gave rise to the corresponding [Mo₂]₂(μ‐E)₂ compounds 2 and 4 . The latter show a striking coplanarity and near‐bond equalization of the Mo/E cluster. The oxidized species 2 and 4 are diamagnetic in the measured temperature range of 5 to 300 K, which is somewhat unexpected for molecules that have dimetal units with a σ²π⁴δ¹ electronic configuration. This suggests there are strong interactions between the dimolybdenum units through the E atoms. The large electronic delocalization of the δ electrons over the entire Mo/E core is supported by the exceptionally large potential separation for the two successive one‐electron reductions of the linked Mo₂⁵⁺ units from the oxidized species (ΔE_1/2=1.7 V for the sulfur analogue). This large electronic delocalization has an important effect on the NMR spectroscopic signals for the two sets of methine (N‐(CH)‐N) protons from the DAniF ligands. Those essentially parallel to the core, H_∥, and those essentially perpendicular to the core, H_⊥, exhibit downfield and upfield chemical shifts, respectively, that are separated by δ=1.32 ppm. The structural, electronic, magnetic, and chemical behaviors for 2 and 4 are consistent with aromaticity, with the [Mo₂E₂Mo₂] cores that resemble the prototypical benzene molecule. Theoretical studies, including DFT calculations, natural bond orbital (NBO) analyses, and gauge‐independent atomic orbital (GIAO) NMR spectroscopic calculations, are also consistent with the aromaticity of the [Mo₂]₂(μ‐E)₂ units being promoted by d_δ(Mo₂)–p_π(E) π conjugation. The cyclic π conjugation of the central moiety in 2 and 4 involves a total of six electrons with 2e from δ(Mo₂) and 4e from p_π(E) orbitals, thereby conforming to Hückel’s rule when electrons in the MOs with δ character are considered part of the delocalized system.     

Discussion on the formation and bonding in three [Ga8R10] compounds: the diversity in classical Ga-Ga bonds

Herein we describe three Ga(8) compounds that feature gallium atoms in an oxidation state of 1.25 with normal valent 2e-2c bonding. Their structures and the influence of their ligands (phosphorus and nitrogen atoms directly bonded to the Ga(8) moieties) are discussed on the basis of DFT calculations, providing an insight into a probable mechanism for insertion reactions between GaX and GaX(3) species that lead to a reaction cascade via halides like Ga(2)X(4) and Ga(5)X(7) to Ga(8)X(10) and Ga(8)X(12) (2-), respectively. Finally, the Ga(8) cores of the three title compounds were compared with the topology of carbon atoms in C(8) alkanes.