Heptanuclear Complex Research Articles

Restriction of reaction sites on metal-sulfide cores induced by steric repulsion of bis-N-heterocyclic carbene ligands in trinuclear complexes bearing triply bridging sulfide ligands.

Mixed-ligand and mixed-metal trinuclear complexes bearing two {Pt-bisNHC-C1} moieties, [{Pt(bisNHC-C1)}2(ML)(μ3-S)2] n+ (ML = Pt(bisNHC-C2), n = 2; ML = Pt(bisNHC-C3), n = 2; ML = Rh(cod), n = 1; ML = RhCp*, n = 2), where bisNHC-C1, bisNHC-C2 and bisNHC-C3 represent methylene-, ethylene- and propylene-bridged bis-NHC ligands, respectively, were synthesised and structurally characterised. Reactions of these complexes with a half eq. of Ag(i) ions were examined using 1H and 195Pt NMR spectroscopy. The results exhibit that the trinuclear complexes react with Ag(i) ions accompanied by the formation of Ag-Pt bonds with the {Pt-bisNHC-C1} moieties in the first step affording corresponding heptanuclear complexes except for the RhCp* complex. The RhCp* complex gave a tetranuclear complex bearing the trinuclear unit with an Ag(i) ion. Further addition of Ag(i) ions for the other complexes resulted in disassembling of the heptanuclear clusters affording tetranuclear complexes confirmed by the observation of exchange of the Ag(i) ions in 195Pt NMR measurements, which exhibited signals with no coupling to Ag nuclei.

Structures and magnetic properties of a trinuclear angular [Ni3] and a heptanuclear wheel-like [Ni7] complexes with a Schiff base ligand

The presence of large magnetic anisotropy with nickel(II) ions facilitates the single-molecule magnet (SMM) behavior in multimetallic nickel(II) complexes. Herein syntheses under ambient conditions, characterizations, crystal structures, and experimental magnetic analyses of an angular [NiII3L4] and a wheel-like [NiII7L6] complexes of general formula [Ni3L2(μ-L)2(μ-OH2)2(CF3CO2)2] (1) and [Ni7(μ-L)6(μ-OMe)6]Cl2·6H2O (2) (HL = 2-{(3-ethoxypropylimino)methyl}-6-methoxyphenol) have been reported. The angular core of trimetallic neutral complex 1 is assembled using four L−, two bridging water molecules, and two bound trifluoroacetate anions. In contrast, the heptanuclear complex 2 features a planar wheel-like arrangement with a central NiII enclosed by a {NiII6} hexagon bound to six MeO− and six L−. The isolation of these two aggregates of varying nuclearity and metal ion: ligand anion ratio indicated the importance of reaction conditions and crystallization to follow the bottom-up assembly processes. Experimental magnetic studies showed antiferromagnetic interactions between the central and terminal NiII ions in complex 1 and competing ferro- and antiferromagnetic interactions in the wheel-like complex 2.

Bismut in der Dynamisch Kovalenten Chemie: Makrocyclen und Siebenkernige Komplexkationen mit Ungewöhnlichen Strukturen

AbstractDynamisch kovalente Chemie (DCvC) ist ein wertvolles und breit eingesetztes Werkzeug in der modernen Synthesechemie, das auf dem reversiblen Knüpfen und Brechen kovalenter Bindungen basiert. Eine der inhärenten Stärken dieses Ansatzes ist das Potential, in einfachen Syntheseprotokollen reversibel neue Strukturmotive generieren zu können, die mit anderen Methoden nur schwer oder gar nicht zugänglich sind und eine Vielzahl von Bindungsbrüchen und ‐knüpfungen erfordern. Bislang sind diese fundamentalen synthesechemischen und konzeptionellen Herausforderungen in der DCvC verstärkt mit leichteren p‐Block‐Elementen angegangen worden, obwohl schwerere p‐Block‐Elemente angesichts geringer Bindungsdissoziationsenergien ideal geeignet für den Einsatz in der DCvC erscheinen. Wir zeigen hier, dass eine zweikernige metallorganische Bismutverbindung, bestehend aus zwei Thioxanthen‐verbrückten BiMe2‐Einheiten, bereitwillig selektive und reversible Bi−C Bindungsbrüche vollzieht, wenn sie externen Stimuli ausgesetzt wird. Das Ausnutzen von DCvC in der metallorganischen Chemie schwerer p‐block‐Elemente gewährt Zugang zu präzedenzlosen Makrocyclen und oligonuklearen Komplexen mit Fass‐ähnlicher Struktur.

Bismuth in Dynamic Covalent Chemistry: Access to a Bowl-Type Macrocycle and a Barrel-Type Heptanuclear Complex Cation.

Dynamic covalent chemistry (DCvC) is a powerful and widely applied tool in modern synthetic chemistry, which is based on the reversible cleavage and formation of covalent bonds. One of the inherent strengths of this approach is the perspective to reversibly generate novel structural motifs in an operationally simple approach, which are difficult or impossible to access with more traditional methods and require multiple bond cleaving and bond forming steps. To date, these fundamentally important synthetic and conceptual challenges in the context of DCvC have predominantly been tackled by exploiting compounds of lighter p-block elements, albeit heavier p-block elements show low bond dissociation energies and appear to be ideally suited for this approach. Here we show that a dinuclear organometallic bismuth compound, containing BiMe2 groups that are connected by a thioxanthene linker, readily undergoes selective and reversible cleavage of its Bi-C bonds upon exposure to external stimuli. The exploitation of DCvC in the field of organometallic heavy p-block chemistry grants access to unprecedented macrocyclic and barrel-type oligonuclear compounds.

Synthesis, Structure, and Characterizations of a Heterobimetallic Heptanuclear Complex [Pb2Co5(acac)14

An unusual heterobimetallic volatile compound [Pb2Co5(acac)14] was synthesized by the gas phase/solid-state technique. The preparation can be readily scaled up using the solution approach. X-ray powder diffraction, ICP-OES analysis, and DART mass spectrometry were engaged to confirm the composition and purity of heterobimetallic complex. The composition is unique among the large family of lead(tin): transition metal = 2:1, 1:1, and 1:2 β-diketonates compounds that are mostly represented by coordination polymers. The molecular structure of the complex was elucidated by synchrotron single crystal X-ray diffraction to reveal the unique heptanuclear moiety {Co(acac)2[Pb(acac)2-Co(acac)2-Co(acac)2]2} built upon bridging interactions of acetylacetonate oxygens to neighboring metal centers that bring their coordination numbers to six. The appearance of unique heptanuclear assembly can be attributed to the fact that the [Co(acac)2] units feature both cis- and trans-bis-bridging modes, making the polynuclear moiety rather flexible. This type of octahedral coordination is relatively unique among known lead(tin)-3d transition metal β-diketonates. Due to the high-volatility, [Pb2Co5(acac)14] can be potentially applied as a MOCVD precursor for the low-temperature preparation of lead-containing functional materials.

Homoleptic complexes of isocyano- and diisocyanobiazulenes with a 12-electron, ligand-based redox capacity.

Oligo- and polyazulenes are attractive π-conjugated building blocks in designing advanced functional materials. Herein, we demonstrate that anchoring one or both isocyanide termini of the redox non-innocent 2,2'-diisocyano-6,6'-biazulenic π-linker (1) to the redox-active [Cr(CO)5] moiety provided a convenient intramolecular redox reference for unambiguously establishing that the 6,6'-biazulenic scaffold undergoes a reversible one-step 2e- reduction governed by reduction potential compression/inversion. Treatment of bis(η6-naphthalene)chromium(0) with six equiv. of 2-isocyano-1,1',3,3'-tetraethoxycarbonyl-6,6'-biazulene (6) or [(OC)5Cr(η1-2,2'-diisocyano-1,1',3,3'-tetraethoxycarbonyl-6,6'-biazulene)] (11) afforded homoleptic Cr(0) complexes 13 and 14 with a 12e- (per molecule) ligand-based reduction capacity at mild E1/2 of -1.29 V and -1.15 V vs. Cp2Fe0/+, respectively. The overall reversible redox capacity varies from 15e- for the mononuclear complex 13 to 21e- for the heptanuclear complex 14. The latter "nanocomplex" has a diameter of ca. 5 nm and features seven Cr(0) centers interlinked with six 2,2'-diisocyano-6,6'-biazulenic bridges. The X-ray structure of [(OC)5Cr(2-isocyano-1,1',3,3'-tetraethoxycarbonyl-6,6'-biazulene)] (7) indicated a 43.5° interplanar angle between the two azulenic moieties. Self-assembly of 11 on a Au(111) substrate afforded an organometallic monolayer film of 11 featuring approximately upright orientation of the 2,2'-diisocyano-6,6'-biazulenic linkers, as evidenced by ellipsometric measurements and the RAIR signature of the C4v-symmetric [(-NC)Cr(CO)5] infrared reporter within 11. Remarkably, comparing the FTIR spectrum of 11 in solution with the RAIR spectrum of 11 adsorbed on Au(111) suggested electronic coupling at a ca. 2 nm distance between the Cr(0) and Au atoms linked by the 2,2'-diisocyano-6,6'-biazulene bridge.

Self-association synthesis with ortho-vanillin to promote mono- and heptanuclear complexes and their evaluation as antioxidant agents

This study describes the synthesis, crystal structure, antioxidant activity, and molecular modeling calculations for two CuII complexes obtained from the condensation of ortho-vanillin with furfurylamine. Both complexes catalyzed superoxide dismutation and were evaluated and quantified by nitro blue tetrazolium photoreduction, efficiently demonstrating McCord-Fridovich constant values from 5.50 to 2.87 × 106 (M−1s−1) in the 1.3–1.4 µM range and an aqueous solution of pH 7.8. Despite an unusual arrangement containing seven CuII cations obtained by self-association processes, the heptamer, proportionally speaking, did not show multiplicative activity as initially expected. This situation was also evaluated using molecular docking.

Electronic and steric impact of bis-NHC ligands on reactions of Pt3S2 cores in trinuclear complexes bearing bis-NHC ligands with various lengths of alkylene bridges.

Alkylene-bridged bis-N-heterocyclic carbene ligands working as strong σ-donors enhance the reactivity of the Pt3S2 core in a triplatinum complex. Although an Ag(I) ion possibly reacts with the Pt-Pt bond, one of the sulfide ligands coordinates to an Ag(I) ion due to the steric hindrance of the ligands.

Efficient Convergent Energy Transfer in a Stereoisomerically Pure Heptanuclear Luminescent Terpyridine-Based Ru(II)-Os(II) Dendrimer.

The stereoisomerically pure synthesis of a novel heptanuclear Ru(II)-Os(II) antenna bearing multitopic terpyridine ligands is reported. An unambiguous structural characterization was obtained by 1H NMR spectroscopy and ion mobility spectrometry (IMS-MS). The heptanuclear complex exhibits large molar absorption coefficients (77900 M-1 cm-1 at 497 nm) and undergoes unitary, downhill, convergent energy transfer from the peripheral Ru(II) subunits to the central Os(II) that displays photoluminescence with a lifetime (τ = 161 ns) competent for diffusional excited-state electron transfer reactivity in solution.

Spin-frustration with two quasi-degenerated spin states of a copper(II) heptanuclear complex obtained from an amino acid ligand.

The Cu(ii) heptanuclear complex (Cu7atac) was synthesised using the hydrated amino acid ligand 2-(5-amino-1H-1,2,4-triazol-3-yl)acetic acid (Hatac·H2O). Single crystal X-ray diffraction analysis revealed a μ3-hydroxo bridged Cu(ii) heptanuclear complex, consisting of two triangular subunits and one Cu(ii) ion as a bridge with the formula [Cu7(atac)6(μ3-OH)2(NO3)2(H2O)10](NO3)4. The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu(ii) mediated by N,N bonding and an anti-anti modes of the carboxylate anion of the ligand atac-. The magnetic data were fitted considering a 3J model. To support the model used to fit the magnetic data of the Cu7atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu7atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state.

Metal-metal bond formation of triplatinum cores with a silver(i) ion affording a heptanuclear cluster bearing four Pt-Ag bonds.

An N-heterocyclic carbene triplatinum complex with two triply bridging sulfide ligands reacts with a silver(i) salt and affords a heptanuclear complex. X-ray crystallographic analysis revealed that a silver(i) ion connects two triplatinum complexes with one of the three Pt-Pt bonds of each triplatinum unit.

Rational Improvement of Single-Molecule Magnets by Enforcing Ferromagnetic Interactions.

The anisotropy barrier of polynuclear single-molecule magnets is expected to be higher with less tunneling the better stabilized the spin ground state is so that less MS mixing in the ground state and with excited spin states occur. We have realized this experimentally in two structurally related heptanuclear SMMs: the triplesalen-based [MnIII 6 CrIII ]3+ and the triplesalalen-based *[MnIII 6 CrIII ]3+ . The ligand system triplesalen was developed to enforce ferromagnetic interactions by the spin-polarization mechanism. However, we found weak antiferromagnetic couplings, that we assigned to an inefficient spin-polarization by a heteroradialene formation. To prevent this heteroradialene formation, the triplesalalen ligand H6 talalen was designed. Here, we present the building block [(talalen )MnIII 3 ]3+ and its application for the assembly of [{(talalen )MnIII 3 }2 {CrIII (CN)6 }]3+ (=*[MnIII 6 CrIII ]3+ ). Both the trinuclear and heptanuclear complexes are SMMs. The comparison to the related triplesalen complex [(feld )MnIII 3 ]3+ proves the absence of heteroradialene character and the enforcement of ferromagnetic MnIII -MnIII interactions in the (talalen )6- complexes. This results in an increase of the barrier for spin reversal Ueff from 25 K in the triplesalen-based [MnIII 6 CrIII ]3+ SMMs to 37 K in the triplesalalen-based *[MnIII 6 CrIII ]3+ SMM proving the success of our concept. Based on this study, the next step in the rational improvement of our SMMs is discussed.

Square Planar Coordination of Silver in a η4‐Cyclobutadiene‐(η5‐C5H5)ReBr2 Complex Framework

Halide addition and abstraction experiments with the cationic rhenacyclopentatriene [(η5‐C5H5){ReC4(SBn)4}Br]BF4 and the side‐on cyclobutadiene complexes [(η5‐C5H5)(η4‐C4Ph4)ReX2] (X = Br, I), respectively, are described. Reversible interconversion of both coordination modes of the metal bonded C4R4 moiety depending on the presence or absence of the second bromide ligand is demonstrated for the sulfide derivative. However, formation of the [(η5‐C5H5)(ReC4Ph4)X]+ congener by halide abstraction at [(η5‐C5H5)(η4‐C4Ph4)ReX2] turned out to be impossible. Instead, formation of silver halide complexes with the halide bridging rhenium and silver under retention of the metalorganic scaffold are observed. Governed by the phenyl substituent framework a square‐planar coordination environment about the Ag cation is adopted for X = Br. Changing X = Br by X = I led to the formation of a heptanuclear complex with di‐ and three‐coordinate silver ions.

Phenoxide and alkoxide complexes of Mg, Al and Zn, and their use for the ring-opening polymerization of ℇ-caprolactone with initiators of different natures.

A new packing polymorph of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(tetrahydrofuran-κO)magnesium, [Mg(C15H23O)2(C4H8O)2] or Mg(BHT)2(THF)2, (BHT is the 2,6-di-tert-butyl-4-methylphenoxide anion and THF is tetrahydrofuran), (1), has the same space group (P21) as the previously reported modification [Nifant'ev et al. (2017d). Dalton Trans. 46, 12132-12146], but contains three crystallographically independent molecules instead of one. The structure of (1) exhibits rotational disorder of the tert-butyl groups and positional disorder of a THF ligand. The complex of bis(2,6-di-tert-butyl-4-methylphenolato-κO)bis(μ2-ethyl glycolato-κ2O,O':κO)dimethyldialuminium, [Al2(CH3)2(C4H7O3)2(C15H23O)2] or [(BHT)AlMe(OCH2COOEt)]2, (2), is a dimer located on an inversion centre and has an Al2O2 rhomboid core. The 2-ethoxy-2-oxoethanolate ligand (OCH2COOEt) displays a μ2-κ2O,O':κO semi-bridging coordination mode, forming a five-membered heteronuclear Al-O-C-C-O ring. The same ligand exhibits positional disorder of the terminal methyl group. The redetermined structure of the heptanuclear complex octakis(μ3-benzyloxo-κO:κO:κO)hexaethylheptazinc, [Zn7(C2H5)6(C7H7O)8] or [Zn7(OCH2Ph)8Et6], (3), possesses a bicubic Zn7O8 core located at an inversion centre and demonstrates positional disorder of one crystallographically independent phenyl group. Cambridge Structural Database surveys are given for complexes structurally analogous to (2) and (3). Complexes (2) and (3), as well as derivatives of (1), are of interest as catalysts for the ring-opening polymerization of ℇ-caprolactone, and polymerization results are reported.

Heterometallic lanthanide-centred [NiLnIII] rings.

A [NiII6DyIII] heptanuclear complex featuring a rare six-membered {NiII6} metal ring surrounding the central Dy(iii) ion is reported. Magnetic studies reveal single-molecule magnet behaviour for the complex under zero external dc field, while replacing the DyIII ion with [capital Upsilon]III or GdIII ions allows for a comprehensive understanding of the magnetic behaviour.

Mono, di and heptanuclear metal(II) complexes based on symmetric and asymmetric tetradentate Salamo-type ligands: Syntheses, structures and spectroscopic properties

Mono, di and heptanuclear metal(II) complexes with chemical formulae [Cu(L1)] (1), [Co2(L2)2]·2CH3CN (2) and [Ni7(L3)3(μ3-OEt)2(μ3-OH)6(EtOH)6] (3) have been synthesized by variational tetradentate Salamo-type ligands based on 3,5-dichlorosalicylaldehyde, and characterized by elemental analyses, FT-IR, UV–Vis spectra and X-ray crystallography. The Cu(II) complex 1 is a mononuclear complex with tetracoordinate Cu(II) atom lies in the N2O2 coordination sphere. The Co(II) complex 2 is a dinuclear complex with a central Co2O2 bridged unit via CoO bonds to form a head-to-head dimer, the pentacoordinate Co(II) atoms (Co1 and Co2) have a distorted square pyramidal (τ1=0.454) and trigonal bipyramidal (τ2=0.538) geometries, respectively. Interestingly, the Ni(II) complex 3 is a novel heptanuclear complex with an unprecedented 3:7 ligand to metal stoichiometry. Furthermore, fluorescence properties of the Cu(II) and Ni(II) complexes have been studied.

Bismuth(III)dichalcogenones as highly active catalysts in multiple C-C bond formation reactions.

Thirteen new bismuth(III) dichalcogenone derivatives of triflates and halides were synthesized and structurally characterized. The mono, di, tetra and heptanuclear complexes were isolated with different bismuth(III) coordination environments. These newly isolated bismuth(III)dichalcogenones were characterized by multinuclear NMR, FT-IR, UV-vis, TGA and single crystal X-ray diffraction techniques. These complexes were tested for the synthesis of symmetrical triaryl- or triheteroarylmethanes and the catalysts were found to be highly active. In particular, the selone complexes were relatively more active than thione complexes. Subsequently, the scope of the catalytic reactions was further explored with different substituents.

Synthesis, Structures, and Single-Molecule Magnet Behaviour of High-Nuclearity Nickel(II) Dicubane-Type Complexes with Pyridyl-Alcohol Ligands.

The condensation reaction between two chemically different tetranuclear cubane-like clusters [Ni(μ3 -Cl)(Cl)(HL)]4 (1; HL=2-methyl-1-(pyridin-2-yl)propan-2-ol) and [Ni(μ3 -OH)(Cl)(HL)]4 (2) provides new access to higher nuclearity complexes, as shown with the synthesis of the octanuclear complex [Ni8 (μ3 -Cl)3 (μ3 -OH)5 (μ-Cl)2 Cl6 (HL)7 ] (3). In one instance, we also isolated the heptanuclear complex [Ni7 (μ3 -Cl)2 (μ3 -OH)6 Cl4 (H2 O)2 (HL)6 ]Cl2 (4). Magnetic properties measured by superconducting quantum interference device (SQUID) susceptometry evidenced S=8 and S=5 ground states for complexes 3 and 4, respectively. In particular, alternating current (ac) susceptometry evidenced slow relaxation of the magnetisation for complex 3, and suggests a similar behaviour at sub-kelvin temperatures for complex 4.

A new heptanuclear complex based on hexacyanoferrate with cobalt(II) cations of tridentate ligands

A new heptanuclear compound [{Co(TPA)CN}6Fe][PF6]8 (1) (TPA=tris(2-pyridylmethyl)amine) was constructed by the reaction of [Co(TPA)]2+ cations and K3Fe(CN)6. The cyanometalate core is capped by six mono-nuclear cobalt units via the cyanides. 1 crystallizes in triclinic space group C2 with a=19.5720Å, b=26.2450Å, c=16.3820Å, β=118.500° and Z=2. Variable temperature magnetic measurements have demonstrated that very weak antiferromagnetic interaction between the nearest paramagnetic CoII centers is exhibited. Thus weak antiferromagnetic coupling might be transferred by NCFeCN bridging units.

Disklike hepta- and tridecanuclear cobalt clusters. Synthesis, structures, magnetic properties, and DFT calculations.

The synthesis, structure and magnetic properties are reported of two disklike mixed-valence cobalt clusters [Co(III)Co(II)6(thmp)2(acac)6(ada)3] (1) and [Co(III)2Co(II)11(thmp)4(Me3CCOO)4(acac)6(OH)4(H2O)4](Me3CCOO)2·H2O (2). Heptanuclear complex 1 was prepared by solvothermal reaction of cobalt(II) acetylacetonate (Co(acac)2), 1,1,1-tris(hydroxymethyl)-propane (H3thmp), and adamantane-1-carboxylic acid (Hada), whereas by substituting Hada with Me3CCO2H, tridecanuclear complex 2 was obtained with an unexpected [Co(III)2Co(II)11] core. The core structures of 1 and 2 are related to each other: that of 1 arranges as a centered hexagon of a central Co(III) ion surrounded by a [Co(II)6] hexagon, while that of 2 can be described as a larger oligomer based on two vertex-sharing [Co(III)Co(II)6] clusters. Variable-temperature direct-current magnetic susceptibility measurements demonstrated overall ferromagnetic coupling between the Co(II) ions within both clusters. The magnetic exchange (J) and magnetic anisotropy (D) values were quantified with appropriate spin-Hamiltonian models and were also supported by density functional theory calculations. The presence of frequency-dependent out-of-phase (χM″) alternating current susceptibility signals at temperatures below 3 K suggested that 2 might be a single-molecule magnet.