Serena Fedi

Magnetic Behavior of Odd- and Even-Electron Metal Carbonyl Clusters: The Case Study of [Co8Pt4C2(CO)24]n− (n = 1, 2) Carbide Cluster

The reaction of [Co(6)C(CO)(15)](2-) with 2 equiv of PtCl(2)(Et(2)S)(2) affords the new heterobimetallic [Co(8)Pt(4)C(2)(CO)(24)](2-), [1](2-), carbonyl cluster. [1](2-) undergoes reversible chemical and electrochemical oxidation and reduction processes disclosing a complete series of [1](n-) (n = 1-4) clusters. The mono- and dianion of [1](n-) have been isolated as their tetra-substituted ammonium salts and fully characterized by means of IR, (13)C NMR, ESI-MS, and X-ray crystallography. Variable-temperature (VT) solid-state EPR studies on pure crystalline samples indicate that both [1](2-) and [1](-*) are paramagnetic, due to a doublet state of the latter and a triplet state of [1](2-). This conclusion is supported by SQUID measurements on the same crystalline sample of [1](2-). The present study indisputably demonstrates that even-electron transition metal carbonyl clusters (TMCC) can be magnetic.

Dinuclear Pt(II)-bisphosphonate complexes: a scaffold for multinuclear or different oxidation state platinum drugs†

Geminal bisphosphonates (BPs), used in the clinic for the treatment of hypercalcaemia and skeletal metastases, have been also exploited for promoting the specific accumulation of platinum antitumor drugs in bone tissue. In this work, the platinum dinuclear complex [{Pt(en)}(2)(μ-AHBP-H(2))](+) (1) (the carbon atom bridging the two phosphorous atoms carrying a 2-ammonioethyl and a hydroxyl group, AHBP-H(2)) has been used as scaffold for the synthesis of a Pt(II) trinuclear complex, [{Pt(en)}(3)(μ-AHBP)](+) (2), and a Pt(IV) adamantane-shaped dinuclear complex featuring an oxo-bridge, [{Pt(IV)(en)Cl}(2)(μ-O)(μ-AHBP-H(2))](+) (3) (X-ray structure). Compound 2 undergoes a reversible, pH dependent, rearrangement with a neat switch point around pH = 5.4. Compound 3 undergoes a one-step electrochemical reduction at E(pc) = -0.84 V affording compound 1. Such a potential is far lower than that of glutathione (-0.24 V), nevertheless compound 3 can undergo chemical reduction to 1 by GSH, most probably through a different (inner-sphere) mechanism. In vitro cytotoxicity of the new compounds, tested against murine glioma (C6) and human cervix (HeLa) and hepatoma (HepG2) cell lines, has shown that, while the Pt(IV) dimer 3 is inactive up to a concentration of 50 μM, the two Pt(II) polynuclear compounds 1 and 2 have a cytotoxicity comparable to that of cisplatin with the trinuclear complex 2 generally more active than the dinuclear complex 1.

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.

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.

Manganese clusters derived from a 2,6-diacetylpyridine dioximato ligand: structure and magnetic study.

Reactions of 2,6-diacetylpyridine dioxime (dapdoH₂) with Mn(NO₃)₂ or Mn(SO₃CF₃)₂ under a variety of conditions or co-ligands yield compounds with the formula [Mn₆O₂(OMe)₂(dapdo)₂(dapdoH)₄](X)₂ in which X = NO₃⁻ (1) or SO₃CF₃⁻ (2), [Mn₈O₂(dapdo)₆(NO₃)₂]·H₂O (3) and [Mn(dapdoH₂)(N₃)₂](n) (4). Compounds 1, 3 and 4 were structurally characterized and equivalent structures for 1 and 2 were inferred from spectroscopic and analytical results. Compounds 1 and 2 consist of hexanuclear Mn₂(II)Mn₄(III) complexes whereas 3 consists of an octanuclear Mn₆(II)Mn₂(III) cluster in which the manganese atoms exhibit a rare bicapped elongated octahedral topology. Compound 4 consists of a 1D system bridged by double end-on azido ligands. Variable temperature magnetic studies were performed between 2-300 K, confirming the ground state S = 5 for 1 and 2, S = 0 for 3 and ferromagnetic response for 4.

Structural variations, electrochemical properties and computational studies on monomeric and dimeric Fe-Cu carbide clusters, forming copper-based staple arrays.

The halide ligands of [Fe(4)C(CO)(12)(CuCl)(2)](2-) (1) and [Fe(5)C(CO)(14)CuCl](2-) (2) can be displaced by N-, P- or S-donors. Beside substitution, the clusters easily undergo structural rearrangements, with loss/gain of metal atoms, and formation of Fe(4)Cu/Fe(4)Cu(3) metallic frameworks. Thus, the reaction of 1 with excess dppe yielded [{Fe(4)C(CO)(12)Cu}(2)(μ-dppe)](2-) (3). [{Fe(4)C(CO)(12)Cu}(2)(μ-pyz)](2-) (4) was obtained by reaction of 2 with Ag(+) and pyrazine. [Fe(4)C(CO)(12)Cu-py](-) (5) was formed more directly from [Fe(4)C(CO)(12)](2-), [Cu(NCMe)(4)](+) and pyridine. [Fe(4)Cu(3)C(CO)(12)(μ-S(2)CNEt(2))(2)](-) (6) and [{Fe(4)Cu(3)C(CO)(12)(μ-pz)(2)}(2)](2-) (7) were prepared by substitution of the halides of 1 with diethyldithiocarbamate and pyrazolate, in the presence of Cu(i) ions. All of these products were characterized by X-ray analysis. 3 and 4 and 5 are square based pyramids, with iron in the apical sites, the bridging ligands connect the two copper atoms in 3 and 4. 6 and 7 are octahedral clusters with an additional copper ion held in place by the two bridging anionic ligands, forming a Cu(3) triangle with Cu-Cu distances ranging 2.63-3.13 Å. In 7, an additional unbridged cuprophilic interaction (2.75 Å) is formed between two such cluster units. DFT calculations were able to reproduce the structural deformations of 3-5, and related their differences to the back-donation from the ligand to Cu. Additionally, DFT found that, in solution, the tight ion pair [NEt(4)](2)7 is almost isoenergetic with the monomeric form. Thus, 3, 4 and 7 are entities of nanometric size, assembled either through conventional metal-ligand bonds or weaker electrostatic interactions. None of them allows electronic communication between the two monomeric units, as shown by electrochemistry and spectroelectrochemical studies. (dppe = PPh(2)CH(2)CH(2)PPh(2), pyz = pyrazine C(4)N(2)H(4), py = pyridine C(5)H(5)N, pz = pyrazolate C(3)N(2)H(3)(-)).

Cooperative Effects of Electron Donors and Acceptors for the Stabilization of Elusive Metal Cluster Frameworks: Synthesis and Solid-State Structures of Pt-19(CO)(24)(mu(4)-AuPPh3)(3)](-) and Pt-19(CO)(24){mu(4)-Au-2(PPh3)(2)}(2)]

The anionic cluster [Pt(19)(CO)(22)](4-) (1), of pentagonal symmetry, reacts with CO and AuPPh(3)(+) fragments. Upon increasing the Au:Pt(19) molar ratio, different species are sequentially formed, but only the last two members of the series could be characterized by X-ray diffraction, namely, [Pt(19)(CO)(24)(μ(4)-AuPPh(3))(3)](-) (2) and [Pt(19)(CO)(24){μ(4)-Au(2)(PPh(3))(2)}(2)] (3). The metallic framework of the starting cluster is completely modified after the addition of CO and AuL(+), and both products display the same platinum core of trigonal symmetry, with closely packed metal atoms. The three AuL(+) units cap three different square faces in 2, whereas four AuL(+) fragments are grouped in two independent bimetallic units in the neutral cluster 3. Electrochemical and spectroelectrochemical studies on 2 showed that its redox ability is comparable with that of the homometallic 1.

Cooperative effects of electron donors and acceptors for the stabilization of elusive metal cluster frameworks: synthesis and solid-state structures of [Pt19(CO)24(μ4-AuPPh3)3]- and [Pt19(CO)24{μ4-Au2(PPh3)2}2].

The anionic cluster [Pt(19)(CO)(22)](4-) (1), of pentagonal symmetry, reacts with CO and AuPPh(3)(+) fragments. Upon increasing the Au:Pt(19) molar ratio, different species are sequentially formed, but only the last two members of the series could be characterized by X-ray diffraction, namely, [Pt(19)(CO)(24)(μ(4)-AuPPh(3))(3)](-) (2) and [Pt(19)(CO)(24){μ(4)-Au(2)(PPh(3))(2)}(2)] (3). The metallic framework of the starting cluster is completely modified after the addition of CO and AuL(+), and both products display the same platinum core of trigonal symmetry, with closely packed metal atoms. The three AuL(+) units cap three different square faces in 2, whereas four AuL(+) fragments are grouped in two independent bimetallic units in the neutral cluster 3. Electrochemical and spectroelectrochemical studies on 2 showed that its redox ability is comparable with that of the homometallic 1.

Synthesis, Reactivity, Electrochemical Behavior, and Crystal Structure of a Family of Multivalent Metal Carbido–Carbonyl Clusters Based on the Rh10(C)2Au4–6 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.