Inverted Ligand Field in a Pentanuclear Bow Tie Au/Fe Carbonyl Cluster.

Gold chemistry has experienced in the last decades exponential attention for a wide spectrum of chemical applications, but the +3 oxidation state, traditionally assigned to gold, remains somewhat questionable. Herein, we present a detailed analysis of the electronic structure of the pentanuclear bow tie Au/Fe carbonyl cluster [Au{η2-Fe2(CO)8}2]- together with its two one-electron reversible reductions. A new interpretation of the bonding pattern is provided with the help of inverted ligand field theory. The classical view of a central gold(III) interacting with two [Fe2(CO)8]2- units is replaced by Au(I), with a d10 gold configuration, with two interacting [Fe2(CO)8]- fragments. A d10 configuration for the gold center in the compound [Au{η2-Fe2(CO)8}2]- is confirmed by the LUMO orbital composition, which is mainly localized on the iron carbonyl fragments rather than on a d gold orbital, as expected for a d8 configuration. Upon one-electron stepwise reduction, the spectroelectrochemical measurements show a progressive red shift in the carbonyl stretching, in agreement with the increased population of the LUMO centered on the iron units. Such a trend is also confirmed by the X-ray structure of the direduced compound [Au{η1-Fe2(CO)8}{η2-Fe2(CO)6(µ-CO)2}]3-, featuring the cleavage of one Au-Fe bond.

Effective mutations in a high redox potential laccase from Pleurotus ostreatus.

Since the first report on a laccase, there has been a notable development in the interest towards this class of enzymes, highlighted from the number of scientific papers and patents about them. At the same time, interest in exploiting laccases-mainly high redox potential-for various functions has been growing exponentially over the last 10 years. Despite decades of work, the molecular determinants of the redox potential are far to be fully understood. For this reason, interest in tuning laccase redox potential to provide more efficient catalysts has been growing since the last years. The work herein described takes advantage of the filamentous fungus Aspergillus niger as host for the heterologous production of the high redox potential laccase POXA1b from Pleurotus ostreatus and of one of its in vitro selected variants (1H6C). The system herein developed allowed to obtain a production level of 35,000 U/L (583.3 µkat/L) for POXA1b and 60,000 U/L (1,000 µkat/L) for 1H6C, corresponding to 13 and 20 mg/L for POXA1b and 1H6C, respectively. The characterised proteins exhibit very similar characteristics, with some exceptions regarding catalytic behaviour, stability and spectro-electrochemical properties. Remarkably, the 1H6C variant shows a higher redox potential with respect to POXA1b. Furthermore, the spectro-electrochemical results obtained for 1H6C make it tempting to claim that we spectro-electrochemically determined the redox potential of the 1H6C T2 site, which has not been studied in any detail by spectro-electrochemistry yet.

Practical applications of copper-based enzymes: synthesis of sulfonated polyaniline through laccase-catalyzed oxidation.

Known for its tunable conductivity and stability, Polyaniline (PANI) is a valuable polymer for electronics and sensing devices. Challenges in solubility have been addressed by creating sulfonated PANI (SPANI), enhancing its practical use. Synthesizing SPANI from sulfonated aniline is intricate, but laccase biocatalysis offers an eco-conscious solution, effective even against high redox potential obstacles. This research monitored the Trametes versicolor laccase-induced oxidation of 3-ABSa via UV-vis spectroscopy, with a notable peak at 565 nm signifying SPANI synthesis, effective even at suboptimal pH. Mediators further boost this process. Moreover, NMR and spectroelectrochemistry confirm the green synthesis of SPANI by laccase, hinting that pH fine-tuning could improve yields, alongside the concurrent creation of azobenzene derivatives.

Unprecedented tris-phosphido-bridged triangular clusters with 42 valence electrons. Chemical, electrochemical and computational studies of their formation and stability.

This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(µ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(µ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(µ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate [Pt3(µ-PBu(t)2)3(CO)2I](+) was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(µ-PBu(t)2)3I3, the transient 44e(-) species [Pt3(µ-PBu(t)2)3(CO)3](+) is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.

Synthesis, structure, and electrochemistry of the Ni-Au carbonyl cluster [Ni12Au(CO)24]3- and its relation to [Ni32Au6(CO)44]6-.

A detailed study of the reaction between [Ni(6)(CO)(12)](2-) and [AuCl(4)](-) afforded the isolation of the new Ni-Au cluster [Ni(12)Au(CO)(24)](3-) as well as identifying an improved synthesis for the previously reported [Ni(32)Au(6)(CO)(44)](6-). The new [Ni(12)Au(CO)(24)](3-) cluster is composed by two [Ni(6)(CO)(12)](2-) moieties coordinated to a central Au(I) ion, as determined by X-ray diffraction. It is noteworthy that the two [Ni(6)(CO)(12)](2-) fragments display different geometries, i.e., trigonal antiprismatic (distorted octahedral) and distorted trigonal prismatic (monocapped square pyramidal). The chemical reactivity of these clusters and their electrochemical behavior have been studied. [Ni(12)Au(CO)(24)](3-) is irreversibly transformed, upon electrochemical reduction, into Au(0) and [Ni(6)(CO)(12)](2-), followed by the reversible reduction of the latter homometallic cluster. Conversely, [Ni(32)Au(6)(CO)(44)](6-) displays five reductions, with apparent features of reversibility, confirming the ability of larger metal carbonyl clusters to reversibly accept and release electrons.

Synthesis, reactivity, electrochemical behavior, and crystal structure of a family of multivalent metal carbido-carbonyl clusters based on the Rh10(C)2Au(4-6) framework.

Six metal carbido-carbonyl clusters have been isolated and recognized as members of a multivalent family based on the dioctahedral Rh(10)(C)(2) frame, with variable numbers of CO ligands, AuPPh(3) moieties, and anionic charge: [Rh(10)(C)(2)(CO)(x)(AuPPh(3))(y)](n-) (x = 18, 20; y = 4, 5, 6; n = 0, 1, 2). Anions [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](-) ([2](-)) and [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)](2-) ([2](2-)) have been obtained by the reduction of [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(4)] (2) under N(2), while [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(5)](-) ([3](-)) was obtained from [Rh(10)(C)(2)(CO)(20)(AuPPh(3))(4)] (1) by reduction under a CO atmosphere. [3](-) can be better obtained by the addition of AuPPh(3)Cl to [2](2-). [Rh(10)(C)(2)(CO)(18)(AuPPh(3))(6)] (4) is obtained from [3](-) and 2 as well by the reduction and subsequent addition of AuPPh(3)Cl. The molecular structures of [2](2-) ([NBu(4)](+) salt), [3](-) ([NMe(4)](+) salt), and 4 have been determined by single-crystal X-ray diffraction. The redox activities of complexes 1, 2 and [3](-) have been investigated by electrochemical and electron paramagnetic resonance (EPR) techniques. The data from EPR spectroscopy have been accounted for by theoretical calculations.

Synthesis, structure, and electrochemistry of the dicluster molecular pincer [Pt(3)(mu-PBu(t)(2))(3)(CO)(2)](2)(mu-1',1'''-diethynylbiferrocene).

The CuI catalyzed dehydro-halogenation of 1',1'''-diethynylbiferrocene and {Pt(3)}Cl [{Pt(3)} = Pt(3)(mu-PBu(t)(2))(3)(CO)(2)] (1:2 molar ratio) in diethylamine gives in high yields the bicluster derivative [{Pt(3)}CC-(eta(5)-C(5)H(4))Fe(eta(5)-C(5)H(4))](2), 3, in which two platinum triangles are connected by a diethynylbiferrocene spacer. In the structure of 3, confirmed by a diffractometric study, the two {Pt(3)} fragments lie, perfectly eclipsed, on the same side of the biferrocenyl moiety; this folded structure is also preferred in solution, as suggested by NMR Diffusion Ordered Spectroscopy (DOSY) and 1D Rotating-frame Overhauser Enhancement (ROE) measurements. Compound 3 exhibits a rich redox behavior, with a crowded sequence of six one-electron oxidation processes, the electrode potentials of which have been evaluated by digital simulations. On the basis of a spectroelectrochemical study, the first two oxidations are assigned to the iron centers of the diferrocenyl unit and the subsequent four electrons are removed from the {Pt(3)} units.

Cyclopentadienyl ruthenium(II) complexes with bridging alkynylphosphine ligands: synthesis and electrochemical studies.

The reaction of [CpRuCl(PPh(3))(2)] (Cp = cyclopentadienyl) and [CpRuCl(dppe)] (dppe = Ph(2)PCH(2)CH(2)PPh(2)) with bis- and tris-phosphine ligands 1,4-(Ph(2)PC[triple bond]C)(2)C(6)H(4) (1) and 1,3,5-(Ph(2)PC[triple bond]C)(3)C(6)H(3) (2), prepared by Ni-catalysed cross-coupling reactions between terminal alkynes and diphenylchlorophosphine, has been investigated. Using metal-directed self-assembly methodologies, two linear bimetallic complexes, [{CpRuCl(PPh(3))}(2)(mu-dppab)] (3) and [{CpRu(dppe)}(2)(mu-dppab)](PF(6))(2) (4), and the mononuclear complex [CpRuCl(PPh(3))(eta(1)-dppab)] (6), which contains a "dangling arm" ligand, were prepared (dppab =1,4-bis[(diphenylphosphino)ethynyl]benzene). Moreover, by using the triphosphine 1,3,5-tris[(diphenylphosphino)ethynyl]benzene (tppab), the trimetallic [{CpRuCl(PPh(3))}(3)(mu(3)-tppab)] (5) species was synthesised, which is the first example of a chiral-at-ruthenium complex containing three different stereogenic centres. Besides these open-chain complexes, the neutral cyclic species [{CpRuCl(mu-dppab)}(2)] (7) was also obtained under different experimental conditions. The coordination chemistry of such systems towards supramolecular assemblies was tested by reaction of the bimetallic precursor 3 with additional equivalents of ligand 2. Two rigid macrocycles based on cis coordination of dppab to [CpRu(PPh(3))] were obtained, that is, the dinuclear complex [{CpRu(PPh(3))(mu-dppab)}(2)](PF(6))(2) (8) and the tetranuclear square [{CpRu(PPh(3))(mu-dppab)}(4)](PF(6))(4) (9). The solid-state structures of 7 and 8 have been determined by X-ray diffraction analysis and show a different arrangement of the two parallel dppab ligands. All compounds were characterised by various methods including ESIMS, electrochemistry and by X-band ESR spectroscopy in the case of the electrogenerated paramagnetic species.

Experimental and TDDFT characterization of the light-induced cluster-to-iron charge transfer in the (ferrocenylethynyl)-substituted trinuclear platinum derivative [Pt3(mu-PBu(t)2)3(CO)2(C[triple bond]C-Fc)]+.

The reaction between Pt(3)(mu-PBu(t)(2))(3)(CO)(2)Cl (2) and ethynylferrocene, in the presence of catalytic amounts of CuI, gives Pt(3)(mu-PBu(t)(2))(3)(CO)(2)C[triple bond]CFc (1), characterized by X-ray crystallography and representing a rare example of the sigma-coordination of an alkynyl moiety to a cluster unit. In a dichloromethane (CH(2)Cl(2)) solution, compound 1 undergoes three consecutive one-electron oxidations, the first of which is assigned to the ferrocene-centered Fe(II)/Fe(III) redox couple. Spectroelectrochemistry, carried out on a solution of 1, shows the presence of a broad band in the near-IR region, growing after the electrochemical oxidation, preliminarily associated with a metal-to-metal charge transfer toward the Fe(III) ion of the ferrocenium unit. Density functional theory (DFT) has been employed to analyze the ground- and excited-state properties of 1 and 1(+), both in the gas phase and in a CH(2)Cl(2) solution. Vertical excitation energies have been computed by the B3LYP hybrid functional in the framework of the time-dependent DFT approach, and the polarizable continuum model has been used to assess the solvent effect. Our results show that taking into account the medium effects together with the choice of an appropriate molecular model is crucial to correctly reproducing the excitation spectra of such compounds. Indeed, the nature of the substituents on P atoms has been revealed to have a key role in the quality of the calculated spectra.

Synthesis and electrochemical characterization of halide, isocyanide, and alkynyl synthons containing the encumbered triangular cluster unit Pt3(mu-P(t)Bu2)3.

Useful synthons containing the tribridged triangular unit {Pt(3)} = [Pt(3)(mu-P(t)Bu(2))(3)](+) were prepared starting from the known tricarbonyl derivative [{Pt(3)}(CO)(3)]Z, [(1(+))Z, Z = CF(3)SO(3)(-)]. This was easily converted into the monohalides {Pt(3)}(CO)(2)X [2, X = Cl; 3, X = Br; 4, X = I], by reaction with the appropriate halide salt. The coupling reaction between 2 and terminal alkynes in the presence of CuI afforded in good yields the sigma-alkynyl derivatives {Pt(3)}(CO)(2)(CC-R) [6, R = SiMe(3); 7, R = CC-SiMe(3); 8, R = C(6)H(5); 9, R = C(6)H(4)-4-Br; 10, R = C(6)H(4)-4-CCH; 11, R = 2-C(4)H(2)S-5-CCH; 12, R = 9-C(14)H(8)-10-CCH], while desilylation of 6 or 7 with TBAF/THF gave, respectively, the derivatives 13 (R = H) and 14 (R = CCH). The stepwise elongation of the arylalkynyl chain was obtained by the Sonogashira coupling of 10 with an excess of 1,4-diiodobenzene, which produced 15 (R = C(6)H(4)-4-CC-C(6)H(4)-4-I), and by coupling the latter with an excess of 1,4-diethynylbenzene, which formed 16 (R = [C(6)H(4)-4-CC](3)H). Branched synthons were obtained by substitution of the carbonyl ligands with functional isocyanides; the reaction of an excess of CN-C(6)H(4)-4-R (R = I, CCH) with {Pt(3)}(CO)(2)H, 5, or with complex (1(+))Z afforded, respectively, {Pt(3)}(CN-C(6)H(4)-4-I)(2)H, 17, or [{Pt(3)}(CN-C(6)H(4)-4-R)(3)]Z [(18(+))Z, R = I; (19(+))Z, R = CCH]. The crystal structures of complexes 2, 8, and 9 were established by X-ray diffraction studies. The electrochemical characterization of representative examples of the clusters prepared in this work shows that all clusters are characterized by the presence of two oxidations; an analysis of ligands' effects on the redox processes is also included.

New Blue Donor-Acceptor Pechmann Dyes: Synthesis, Spectroscopic, Electrochemical, and Computational Studies.

The design, synthesis, and characterization of a new class of blue-colored thiophene-substituted Pechmann dyes are reported. Due to a distinguishing blue coloration and the capability to absorb light in one of the most photon-dense regions of the solar spectrum, such compounds are of great interest for application as photoactive materials in organic optoelectronics, in particular, in dye-sensitized solar cells. To achieve fine tuning of the optical and electrochemical properties, the electron-poor thiophene-bis-lactone moiety has been decorated with donor (D) and acceptor groups (A), targeting fully conjugated D-A-π-A structures. The designed structures have been investigated by means of DFT and time-dependent DFT calculations, and the most promising dyes have been synthesized. These molecules represent the very first preparation of unsymmetrical Pechmann derivatives. Optical and electrochemical properties of the new dyes have been studied by cyclic voltammetry and UV-vis and fluorescence spectroscopy. In two cases, test cells were built proving that a photocurrent can indeed be generated when using electrolytes especially formulated for narrow-band-gap dyes, although with a very low efficiency.

Electrochemical and optoelectronic properties of terthiophene- and bithiophene-based polybenzofulvene derivatives.

The electrochemical behavior of some polybenzofulvene derivatives bearing bithiophene (BT) or terthiophene (TT) side chains was investigated by cyclic voltammetry. Very interestingly, the presence of unsubstituted terminal thiophene moieties allowed poly-6-BT-BF3k and poly-6-TT-BF3k to be cross-linked by electrochemical procedures. Conductive films were obtained by electrodeposition from solutions of these polymers onto electrode surfaces through the formation of covalent cross-linking due to dimerization (i.e. electrochemical oxidation) of the BT or TT side chains. The films showed electrochromic features and switched from yellow-orange (neutral) to green (positively charged) by switching the potential, and were stable to tenths of cycles, without degradation in the wet state in the electrolyte solution. Finally, the thin film obtained by electrodeposition of poly-6-TT-BF3k on a indium tin oxide (ITO) glass substrate showed in the neutral state a significantly red-shifted photoluminescence (PL) emission (∼40 nm red-shifted with respect to that of the corresponding film obtained by casting procedures), which was consistent with the presence of more conjugated moieties produced by the oxidative dimerization of the TT side chains. The innovative architecture and the easy preparation could lead to a broad range of applications in optoelectronics and bioelectronics for these cross-linked hybrid materials based on π-stacked polybenzofulvene backbones bearing oligothiophene side chains.

Synthesis of 13-vertex dimetallacarboranes by electrophilic insertion into 12-vertex ruthenacarboranes.

The electrophilic insertion of organometallic species into metallacarboranes was studied in detail for the model compound - the 12-vertex closo-ruthenacarborane anion [Cp*Ru(C2B9H11)]- (1). Reactions of the anion 1 with the 12-electron cationic species [M(ring)]+ (M(ring) = RuCp, RuCp* and Co(C4Me4)) gave the 13-vertex closo-dimetallacarboranes Cp*Ru(C2B9H11)M(ring). Similar reactions of the neutral ruthenacarborane Cp*Ru(Me2S-C2B9H10) produce the cationic dimetallacarboranes [Cp*Ru(Me2S-C2B9H10)M(ring)]+. The symmetrical 13-vertex diruthenacarboranes (C5R5)Ru(R2C2B9H9)Ru(C5R5) can be prepared by the direct reactions of Tl2[7,8-R2-7,8-C2B9H9] (R = H and Me) with two equivalents of [CpRu(MeCN)3]+ or [Cp*RuCl]4. The insertions of the 14-electron cationic species [M(ring)]+ (M(ring) = NiCp, NiCp* and Co(C6Me6)) into 1 gave the 13-vertex dimetallacarboranes Cp*Ru(C2B9H11)M(ring), which have a distorted framework with one open face. The structures of Cp*Ru(C2B9H11)Co(C4Me4) and Cp*Ru(C2B9H11)NiCp were established by X-ray diffraction. Some of the 13-vertex dimetallacarboranes have two electrons less than required by Wade's rules. This violation is explained by the absence of the appropriate pathway for the distortion of the framework.

How to get the desired reduction voltage in a single framework! Metallacarborane as an optimal probe for sequential voltage tuning.

An appealingly wide set of redox couples ranging from -1.74 to -0.35 V based on a metallabisdicarbollide derivative, [M(C2B9H11-yIy)2](-) (M = Co, Fe), each being distinguished from the former by near 0.15 V and all having the same structure have been demonstrated. The redox active methyl viologen moiety ([MV](2+)) has been used as a benchmark.

Ferrocene-Based Tris(1-pyrazolyl)borates: A New Approach to Heterooligometallic Complexes and Organometallic Polymers Containing Transition Metal Atoms in the Backbone.

Starting from mono- and bifunctional ferrocene-based tris(1-pyrazolyl)borates, a novel route to oligonuclear complexes is presented, which incorporates transition metal centers differing substantially in their chemical nature. Both binuclear organometallics FcB(pz)(3)ML(n)() (Fc: ferrocenyl. pz: 1-pyrazolyl. ML(n)(): Tl, 1-Tl; Mo(CO)(3)Li, 1-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 1-Mo; ZrCl(3), 1-Zr) and trinuclear complexes 1,1'-fc[B(pz)(3)ML(n)()](2) (fc: ferrocenylene. ML(n)(): Tl, 2-Tl; Mo(CO)(3)Li, 2-MoLi; Mo(CO)(2)(eta(3)-methylallyl), 2-Mo) have been prepared. The trinuclear compound [FcB(4-SiMe(3)pz)(3)](2)Fe, 1-FeSi, has been investigated as a model system for organometallic coordination polymers, consisting of the bifunctional linker 1,1'-fc[B(pz)(3)](2)(2)(-) and transition metal ions M(n)()(+). X-ray crystallography shows 1-Tl to establish a polymeric structure in the solid state, while 1-Mo features the usual tridentate coordination mode of the scorpionate ligand (C(25)H(25)BFeMoN(6)O(2); a = 8.756(1) Å, b = 12.154(1) Å, c = 12.927(1) Å, alpha = 105.26(1) degrees, beta = 102.29(1) degrees, gamma = 105.09(1) degrees; triclinic space group P&onemacr;; Z = 2). With the exception of 1,2-Tl, the anodic oxidation of the ferrocene moiety is generally reversible; cyclic voltammetry measurements indicate the two Mo centers in 2-Mo and the two Fc moieties in 1-FeSi to be noncommunicating.

Redox Behavior of [H(6)(-)(n)()Ni(38)Pt(6)(CO)(48)](n)()(-) (n = 4-6) Anions: A Series of Metal Carbonyl Clusters Displaying Electron-Sink Features.

An investigation of the chemical and electrochemical redox behavior of the bimetallic [H(6)(-)(n)()Ni(38)Pt(6) (CO)(48)](n)()(-) (n = 4-6) clusters shows that they display electron-sink features encompassing up to six different oxidation states. As a corollary, these studies provide an indirect proof of the presence of hydride atoms where n = 4 and 5. The difference in the formal electrode potentials of consecutive redox couples of both [HNi(38)Pt(6) (CO)(48)](5)(-) and [Ni(38)Pt(6) (CO)(48)](6)(-) is almost constant and amounts on the average to ca. 0.33 and 0.28 V, respectively. Such constancy of DeltaE within each species points out the absence of a well-defined HOMO-LUMO gap in both clusters. Besides, its value is an indication of their semiconductor rather than metallic nature. A plot of the average DeltaE exhibited by the known carbonyl clusters displaying electrochemically reversible multiple redox changes versus their nuclearity suggests that the transition from semiconductor to metallic behavior might occur upon a ca. 50% increase of the today available cluster nuclearities.

Organic dyes with intense light absorption especially suitable for application in thin-layer dye-sensitized solar cells.

Three new thiazolo[5,4-d]thiazole-based organic dyes have been designed and synthesized for employment as DSSC sensitizers. Alternation of the electron poor thiazolothiazole unit with two propylenedioxythiophene (ProDOT) groups ensured very intense light absorption in the visible region (ε up to 9.41 × 10(4) M(-1) cm(-1) in THF solution). The dyes were particularly suitable for application in transparent and opaque thin-layer DSSCs (TiO2 thickness: 5.5-6.5 µm, efficiencies up to 7.71%), thus being good candidates for production of solar cells under simple fabrication conditions.

Metal Segregation in Bimetallic CoPd Carbide Carbonyl Clusters: Synthesis, Structure, Reactivity and Electrochemistry of [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6).

Nanometric CoPd bimetallic [H6-n Co20 Pd16 C4 (CO)48 ]n- (n=3-6) tetracarbide carbonyl clusters have been prepared by redox condensation of [Co6 C(CO)15 ]2- with [PdCl2 (Et2 S)2 ]. The crystal structures of both the dihydride tetra-anion and monohydride penta-anion have been determined as their [NEt4 ]4 [H2 Co20 Pd16 C4 (CO)48 ]⋅4 CH3 COCH3 and [NMe3 (CH2 Ph)][NMe4 ]4 [HCo20 Pd16 C4 (CO)48 ]⋅5 CH3 COCH3 salts, respectively. The two species are isostructural and their structures display a perfect segregation of the two metals. They are composed of a cubic close-packed (ccp) Pd16 core stabilised on its surface by four {Co5 C(CO)12 } organometallic fragments. Their polyhydride nature has been corroborated by the study of their reactions with acids and bases, and confirmed by electrochemical studies. In addition, the reactions of [H2 Co20 Pd16 C4 (CO)48 ]4- with Na/naphthalene and PPh3 /CO allowed the isolation of other lower nuclearity homoleptic and heteroleptic clusters, that is, [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6), [Co4 Pd2 C(CO)11 (PPh3 )2 ], [Co2 Pd5 C(CO)8 (PPh3 )5 ], and [Co4 Pd4 C2 (PPh3 )4 (CO)10 Cl]- . [H6-n Co16 Pd2 C3 (CO)28 ]n- (n=5, 6) represent the first homoleptic metal-carbonyl clusters containing three interstitial carbide atoms.

Selective synthesis of the [Ni36Co8C8(CO)48]6- octa-carbide carbonyl cluster by thermal decomposition of the [H2Ni22Co6C6(CO)36]4- hexa-carbide.

The thermal decomposition in thf solution of [H2Ni22Co6C6(CO)36](4-) results in the new [HNi36Co8C8(CO)48](5-) bimetallic Ni-Co octa-carbide, which can be converted into the closely related [H6-nNi36Co8C8(CO)48](n-) (n = 3-6) polyhydrides by means of acid-base reactions. The structure of the [Ni36Co8C8(CO)48](6-) hexa-anion has been established via X-ray crystallography, showing that the eight interstitial carbide atoms are lodged within different metal cages. Thus, two C-atoms are enclosed within regular square anti-prismatic Ni8C cages, four within irregular Ni8C square anti-prismatic cages, and the last two within mono-capped trigonal prismatic Ni5Co2C cages. The structure of [Ni36Co8C8(CO)48](6-) is non-compact and closely related to [Ni32C6(CO)38](6-) and [HNi38C6(CO)44](5-). [Ni36Co8C8(CO)48](6-) approaches the nanosize regime and the whole molecular ion has a diameter (measured from the outer oxygen atoms) of ca. 1.61 nm.

Nickel poly-acetylide carbonyl clusters: structural features, bonding and electrochemical behaviour.

The reactions of [NEt(4)](2)[Ni(6)(CO)(12)] with miscellaneous carbon halides (e.g. CCl(4), C(4)Cl(6)) in CH(2)Cl(2) have been extensively investigated particularly focusing on the stoichiometric ratio of the reagents and reaction temperature. This allowed the preparation of the previously known acetylide clusters [Ni(16)(C(2))(2)(CO)(23)](4-), [HNi(25)(C(2))(4)(CO)(32)](3-) and [Ni(22)(C(2))(4)(CO)(28)Cl](3-), as well as isolation and full characterisation of the closely related [Ni(17)(C(2))(2)(CO)(24)](4-) and [Ni(25)(C(2))(4)(CO)(32)](4-) tetraanions. From a structural point of view, all these clusters are based on a Ni(16) square orthobicupola which contain interstitial C(2), Ni(η(2)-C(2))(4) or Ni(2)(µ-η(2)-C(2))(4) moieties, displaying rather short C-C bonds. Electrochemical studies reveal that all these species undergo different redox processes, even if their stability is rather limited. This is corroborated by an extensive analysis of the interaction between interstitial C(2) acetylide units and the metal cluster cage by Extended Huckel Molecular Orbital (EHMO) calculations, which indicates that tightly bonded C-C units are less effective than isolated C-atoms in stabilising the cluster cage.