Ni5, Ni8, and Ni10 clusters with 2,6-diacetylpyridine-dioxime as a ligand

In the present work, novel coordination possibilities for the system dapdoH(2)/Ni(II) (dapdoH(2) = 2,6-diacetylpyridine-dioxime) have been explored. Depending on the starting reagents and solution conditions, several clusters with nuclearities ranging from Ni(5) to Ni(10) were achieved and structurally characterized, namely, [Ni(5)(R-COO)(2)(dapdo)(2)(dapdoH)(2)(N(CN)(2))(2)(MeOH)(2)] in which R-COO(-) = benzoate (1) or 3-chlorobenzoate (2), [Ni(8)(dapdo)(4)(NO(3))(4)(OH)(4)(MeOH)(4)] (3), and [Ni(10)(dapdo)(8)(N(CN)(2))(2)(MeO)(MeOH)](NO(3)) (4). For the first time, pentadentate coordination for the dapdo(2-) ligand has been established. All compounds show a combination of square-planar and octahedrally coordinated nickel atoms. According to the Ni(2)(sp)Ni(3)(Oh) (1 and 2), Ni(4)(sp)Ni(4)(Oh) (3), and Ni(4)(sp)Ni(6)(Oh) (4) environments, these systems magnetically behave as trimer, tetramer, and hexanuclear clusters, respectively. dc magnetic measurements in the 2-300 K range of temperature reveal antiferromagnetic coupling for all compounds, and the correlation of the superexchange interaction with the torsion angles involving the oximato bridges is experimentally confirmed.     

Synthesis and magnetism of oxygen-bridged tetranuclear defect dicubane Co(II) and Ni(II) clusters

Reaction of aqueous/ethanolic solutions of CoCl2.6H2O and nitrilotripropionic acid (H3ntp=N(CH2CH2COOH)3) in the presence of potassium hydroxide affords the hydroxy-bridged tetranuclear cluster [Co4mu3-OH)2(H2O)6(ntp)2].2H2O (1). The Ni(II) analogue [Ni4(mu3-OH)2(H2O)6(ntp)2].2H2O (2) can also be isolated using aqueous solutions and Ni(SO4).7H2O as metal salt. With small changes in reaction conditions the methoxy-bridged analogue, [Ni4(mu3-OMe)2(H2O)6(ntp)2](3), can also be isolated. In these tetramers the M(II) ions are oxygen-bridged and exhibit a defect dicubane-like core with two missing vertices. The magnetic properties have been studied for all three clusters and reveal competing antiferromagnetic and ferromagnetic interactions between the four Co(II) ions in 1 and ferromagnetic coupling between the four Ni(II) ions in 2 and 3. In all three compounds the individual clusters order antiferromagnetically at Neel temperatures below 1 K.     

Hole-type mixed-valence tetrahedral cluster: Exchange-tunnel states and magnetic properties

The paper deals with the exchange-tunnel states of a tetrahedral tetrameric hole-type cluster d¹-d²-d²-d² used as a model of metal core of vrious protiens. A new method for group-theoretic classification ofthe quantum states of mixed-valence clusters is suggested. The nature ofthe ground spin state of the above systems has been investigated. The effect of partial spin alignment depending on the double exchange parameter value is discussed.Moldova State University. Translated fromZhumal Strukturnoi Khimii, Vol. 34, No. 3, pp. 14–25, May–June 1993.Translated by L. Smolina     

Cyano-bridged complexes based on re tetrahedral cluster anions, Ni2+ cations, and polydentate amines

Interaction of the tetrahedral chalcocyanide cluster anionic complexes of Re, K₄[Re₄Q₄(CN)₁₂] (Q=S, Se, Te), with Ni²⁺ cationic complexes with polydentate amines, such as ethylenediamine (En), diethylenetriamine (Dien), or triethylenetetraamine (Trien) was used to synthesize six novel complexes: [Ni(NH₃)₄(En)][{Ni(NH₃)(En)₂}Re₄Te₄(CN)₁₂] · 2H₂O, [{Ni(En)₂}₂Re₄Se₄(CN)₁₂] · 3.5H₂O, [Ni(NH₃)₃(Dien)]₂[Re₄Se₄(CN)₁₂] · 5.5H₂O, [{Ni(NH₃)₂(Dien)}₂Re₄Te₄(CN)₁₂] · 2.5H₂O. [Ni(NH₃)₂(Trien)][{Ni(NH₃)(Trien)}Re₄Se₄(CN)₁₂] · 2.5H₂O, [{Ni(Trien)}₂Re₄S₄(CN)₁₂] · 3H₂O. The complexes were studied by single-crystal X-ray diffraction analysis.     

A dimeric high-spin nickel(II) compound with a transition to monomeric tetrahedral nickel(II)

Summary The synthesis and characterisation of dichloro[bis(3,5-dimethylpyrazolyl)methane]nickel(II) s described. At ambient temperature the compound is dimeric with chloro-bridged high-spin five-coordinate Ni^II     

A high-nuclearity 3d/4f metal oxime cluster: an unusual Ni(8)Dy(8) "core-shell" complex from the use of 2-pyridinealdoxime

The initial employment of 2-pyridinealdoxime in 3d/4f chemistry has led to a Ni(II)(8)Dy(III)(8) cluster with an unprecedented metal topology; the compound has an unusual structure, is the highest-nuclearity metal oxime cluster to date, and exhibits slow magnetization relaxation.     

High-nuclearity homometallic iron and nickel clusters: Fe22 and Ni24 complexes from the use of N-methyldiethanolamine

The use of N-methyldiethanolamine (mdaH2) in reactions with Fe(III) and Ni(II) sources has led to Fe22 and Ni24 products; the clusters are the highest and second-highest, respectively, homometallic clusters for these metals to date, and possess S = 0 and S = 6 ground states, respectively.     

A novel trinuclear zinc(II) cluster with a tetrahedral ZnO4 core

The reaction of 0.67 molar equivalents of the O,N,O′‐tridentate zwitterionic Schiff base (2Z,4E)‐4‐[(2‐hydroxyphenyl)iminio]pent‐2‐en‐2‐olate (H₂L) with one equivalent of zinc(II) acetate in methanol affords a novel trinuclear Zn^II cluster, di‐μ‐acetato‐1:2κ²O:O′;2:3κ²O:O′‐dimethanol‐1κO,3κO‐bis{μ‐2‐[(2E,3Z)‐4‐oxidopent‐3‐en‐2‐ylideneamino]phenolato}‐1:2κ⁴O²,N,O⁴:O⁴;2:3κ⁴O⁴:O²,N,O⁴‐trizinc(II), [Zn₃(C₁₁H₁₁NO₂)₂(C₂H₃O₂)₂(CH₄O)₂], (I), in which two bridging acetate ligands link the terminal square‐based pyramidal Zn^II ions to the approximately tetrahedral Zn^II ion at the core of the cluster. The ZnO₄ coordination group of the central Zn^II ion is established by two bridging phenolate and two bridging acetate O atoms. The remaining four coordination sites of each terminal Zn^II ion are occupied by methanol and deprotonated H₂L. Furthermore, the Zn‐bound methanol hydroxyl groups are involved in complementary hydrogen bonding with the Zn‐bound enolate O atom of a neighbouring molecule, about an inversion centre in each case. The structure of (I) is therefore best described as an extended one‐dimensional hydrogen‐bonded chain of trinuclear Zn^II clusters.     

Protonation of cluster molecules: Bridging hydrogen sites in tetrahedral,octahedral and capped square pyramidal clusters: Be4H8, Be4H8

Main group structural models for tetrahedral and octahedral transition metal clusters containing bridging hydrogens are developed using the MNDO quantu     

The electronic and molecular structure of carbon clusters: C8 and C10

Summary The equilibrium geometries of C₈ and C₁₀ have been determined from electronic structure calculations, using a variety of correlated methods and large basis sets of atomic natural orbitals. For C₈, a cyclic form withC _4h symmetry (¹ A _g) and a linear, cumulene-like form (³ _g ^– ) are isoenergetic candidates for the electronic ground state. For C₁₀, the ground-state equilibrium structure is definitely monocyclic. Three different cyclic structures have been considered here, i.e. cumulenicD _10h , distorted-cumulenicD _5h and acetylenicD _5h . These are all essentially isoenergetic, and are about 50 kcal/mol below the linear³ _g ^– state. The choice of basis sets and methods used has a strong impact on the predicted ground-state structures.Dedicated to Prof. Klaus Ruedenberg     

One-pot synthesis of Schiff-base-containing Ni8 clusters: solvothermal synthesis, structure, and magnetic properties

Solvothermal in situ generation of a Schiff-base ligand (L) in the presence NiCl(2) and trimesic acid (H(3)BTC) in ethanol resulted in clusters, Ni(8)(L)(4)Cl(8).(H(2)O)(0.5), consisting of three different coordination geometries, four paramagnetic and four diamagnetic Ni(II), exhibiting both ferromagnetic and antiferromagnetic exchange interactions.     

Synthesis and characterisation of a [Ni8] single molecule magnet and another octanuclear nickel cage

Two new octanuclear nickel(II) cage complexes are reported; the second is a new single molecule magnet.     

Initial structure modification of tetrahedral to planar nickel(II) in a nickel-iron-sulfur cluster related to the C-cluster of carbon monoxide dehydrogenase

A method has been devised that creates a planar Ni(II) site from a tetrahedral site in a NiFe(3)S(4) cubane-type cluster. Reaction of [(Ph(3)P)NiFe(3)S(4)(LS(3))](2)(-) (2) with 1,2-bis(dimethylphosphino)ethane affords [(dmpe)NiFe(3)S(4)(LS(3))](2)(-) (3), isolated in ca. 45% yield as (Et(4)N)(2)[3a].2.5MeCN and (Et(4)N)(2)[3b].0.25MeCN, both of which occur in triclinic space group P. Each crystalline form contains two crystallographically inequivalent clusters with the same overall structure but slightly different dimensions. The cluster is bound by three thiolate terminal ligands to semirigid cavitand ligand LS(3). The NiFe(3)S(4) core contains three tetrahedral sites, one Fe(micro(3)-S)(3)(SR) and two Fe(micro(3)-S)(2)(micro(2)-S)(SR) with normal metric features, and one distorted square planar Ni(micro(3)-S)(2)P(2) site in a Ni(micro(3)-S)(2)Fe face with mean bond lengths Ni-P = 2.147(9) A and Ni-S = 2.29(2) A. The opposite Fe(2)(micro(3)-S)(micro(2)-S) face places the micro(2)-S atom at nonbonding and variable distances (2.60-2.90 A) above the nickel atom. Binding of the strong-field ligand dmpe results in a planar Ni(II) site and deconstruction of the full cubane geometry. The structure approximates that established crystallographically in the C-cluster of C. hydrogenoformans carbon monoxide dehydrogenase whose NiFe(4)S(4) core contains a planar NiS(4) site and three tetrahedral FeS(4) sites in a fragment that is bridged by sulfide atoms to an exo iron atom. M?ssbauer studies of polycrystalline samples containing both clusters 3a and 3b reveal the presence of at least two cluster types. The spectroscopically best defined cluster accounts for ca. 54% of total iron and exhibits hyperfine interactions quite similar to those reported for the S = (5)/(2) state of the protein-bound cubane-type cluster [ZnFe(3)S(4)](1+), whose M?ssbauer spectrum revealed the presence of a high-spin Fe(2+) site and a delocalized Fe(2.5+)Fe(2.5+) pair. Development of reactions leading to a planar nickel and a sulfide-bridged iron atom is requisite to attainment of a synthetic analogue of this complex protein-bound cluster. This work demonstrates a tetrahedral (2) --> planar (3) Ni(II) stereochemical conversion can be effected by binding of ligands that generate a sufficiently strong in-plane ligand field (dmpe = 1,2-bis(dimethylphosphino)ethane, LS(3) = 1,3,5-tris((4,6-dimethyl-3-mercaptophenyl)thio)-2,4,6-tris(p-tolylthio)benzene(3-)).     

Synthesis of Ge2NiS4 clusters and the thermal transformation to a Ge4Ni6S12 cluster

The reaction of Ni(dppe)Cl2 and syn-[DmpGe(SLi)(mu-S)2Ge(SLi)Dmp] prepared in situ from syn-[DmpGe(SH)(mu-S)2Ge(SH)Dmp] (1) and n-BuLi (2 equiv) afforded the Ge2NiS4 cluster, [DmpGe(mu-S)]2(mu-S)2Ni(dppe) (2) (Dmp = 2,6-dimesitylphenyl). The nickel in 2 assumes a slightly distorted square planar geometry. However, another Ge2NiS4 cluster, [DmpGe(mu-S)]2(mu-S)2Ni(PPh3)2 (3) obtained from a similar reaction with Ni(PPh3)2Cl2, contains the nickel in a tetrahedron. When 3 was heated to 120 degrees C in toluene, a novel Ge4Ni6S12 cluster [DmpGe(mu-S)3]4Ni6 (5) was obtained. In cluster 5, six nickels form an octahedron with the nickels occupying its vertexes, and four DmpGeS3 units cap half of the trigonal faces.     

Structure and bonding in the omnicapped truncated tetrahedral Au20 cluster: analogies between gold and carbon cluster chemistry

The proposed omnicapped truncated tetrahedral structure of the recently reported Au20 cluster can be generated from a regular dodecahedron by forming two transannular Au-Au bonds across each face while preserving T symmetry. An electron-precise chemical bonding scheme accounts for the large band gap (1.77 eV) of Au20 and relates its structure to that of titanacarbohedrene Ti8C12 and Os20(CO)40(2)-.