Tetrazolecalix[4]arenes as new ligands for palladium(II)

The synthesis of new calix[4]arenes bearing two or four tetrazole liganting groups at the upper rim is decribed. The structures of tetrakis-tetrazolecalix[4]arene and its palladium dichloride (2:2) complex are examined by X-ray crystallography.     

Acetate and acetamide complexes of [Ni(Me4[12]aneN4)]PF6: a tale of two ligands

Although there are many examples of acetate complexes, acetamide complexes are virtually unknown. A side‐by‐side comparison in (acetato‐κ²O,O′)(1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane‐κ⁴N)nickel(II) hexafluoridophosphate, [Ni(C₂H₃O₂)(C₁₂H₂₈N₄)]PF₆, (1), and (acetamidato‐κ²O,O′)(1,4,7,10‐tetramethyl‐1,4,7,10‐tetraazacyclododecane‐κ⁴N)nickel(II) hexafluoridophosphate, [Ni(C₂H₄NO)(C₁₂H₂₈N₄)]PF₆, (2), shows the steric equivalence between these two ligands, suggesting that acetamide could be considered as a viable acetate replacement for electronic tuning.     

A triangle-square equilibrium of metallosupramolecular assemblies based on pd(II) and pt(II) corners and diazadibenzoperylene bridging ligands

Tetraaryloxy-substituted diazadibenzoperylene bridging ligands 1a,b were employed in transition metal-directed self-assembly with Pd(II) and Pt(II) phosphane triflates 2a,b which resulted in complex dynamic equilibria between molecular triangles 3a-d and molecular squares 4a-d in solution. Characterization of the equilibria and assignment of the metallacycles was accomplished by (1)H and (31)P[(1)H] NMR spectroscopy in combination with electrospray ionization Fourier transform ion cyclotron mass spectrometry (ESI-FTICR-MS). It was found that the equilibria depend on several factors, such as the metal ion (Pd(2+) or Pt(2+)), the solvent, and the steric demand of the phenoxy substituents of the diazadibenzoperylene ligands 1a,b. Introduction of bulky tert-butyl groups in 1b shifts the equilibrium significantly in the direction of the molecular squares. Molecular dynamics simulations of the triangle and square structures revealed critical steric effects and restricted conformational flexibilities of the phosphane and diazadibenzoperylene ligands that help explain the distinct dynamic behavior observed in variable-temperature NMR studies. Concentration-dependent UV/vis and fluorescence spectroscopy revealed the limited stability of the assemblies and confirmed the reversible nature of the dynamic equilibria.     

Synthesis and synchrotron X-ray characterization of two 2D Hoffman related compounds [Ni(p-Xylylenediamine)nNi(CN)4] and [Ni(p-tetrafluoroxylylenediamine)nNi(CN)4]

Synchrotron X-ray single crystal structure determination of two 2D Hofmann-related compounds, [Ni(p-Xylyenediamine)_n-tetracyanonickelate] (abbreviated as Ni-pXdam) and [Ni(tetrafluoro-p-Xylyenediamine)_n-tetracyanonickelate] (abbreviated as Ni-pXdamF4), have been conducted. Both the pXdam and pXdamF4 ligands contain two short chains of -CH₂NH₂ at the para-positions of a phenyl ring. These flexible chains link the 6-fold coordinated Ni2 sites throughout the network. In Ni-pXdam, the closed-2D network of [Ni-(CN-Ni_1/4-)₄]_∞ is broken into 1D chains, leaving the C≡N groups at the trans-positions of the Ni(CN)₄ moiety unbridged. The resulting 1D chains [(trans-)-NC-Ni(CN)₂-CN-Ni-]_∞ runs along the [010] direction of the unit cell. The pXdam ligands bridge in pair between the Ni atoms of the adjacent chains. The catenation structure of [Ni{(pXdam)}]_∞ could be referred to as double -1D. In Ni-pXdamF4, the -CH₂NH₂ ligands connect the neighboring chains via the 6-fold Ni2 site. Surrounding the 4-fold Ni1 site, the two trans terminal C≡N groups were replaced by the Lewis base NH₃ during the synthesis process, therefore preventing the propagation of the 2D net to form a 3D network. Computed pore volume of both compounds indicated that there is not sufficient space in the structure to accommodate gas molecules. In both compounds, hydrogen bonds were found, and solvent of crystallization was absent due to the limited free space in the structure.     

Reactivity of 17 e- complex [Re(II)Br4(CO)2]2- with bridging aromatic ligands. Characterization and CO-releasing properties

Carbon monoxide releasing molecules (CO-RMs) are a newly emerging class of compounds of pharmacological interest. Among the transition metal-based CO-RMs, 17-electron complexes of general formula cis-trans-[Re(II)(CO)(2)Br(2)L(2)] are promising candidates but their poor hydrophilicity hampers future applications. In an effort to increase water solubility of d(5) dicarbonyl rhenium CO-RMs, the reaction of the cis-[Re(II)(CO)(2)Br(4)](2-) anion with bridging aromatic ligands of the pyridine and diazine type was investigated. Mononuclear and binuclear complexes are presented and it is shown that the nature of the bridging ligand critically dictates the formation of either species. Most complexes retained their fundamental CO-releasing properties. The synthesis of the molecules together with structural, spectroscopic and theoretical details are discussed.     

Molecular assembly of two [Co(II)4] linear arrays

Molecular chains of four Co(II) ions stabilized by a bis-β-diketone/pyridyl ligand may be isolated or linked into molecular pairs of two semi-independent such units.     

The liquid-crystalline properties of bis[N-[[4-[4-(alkoxy)benzoyloxy]2-hydroxyphenyl]methylene]alkanamino] complexes of Cu(II), Pd(II) and Ni(II). A general view

The thermotropic liquid-crystalline phase behaviour of a homologous set of bis[N-[[4-[4-(alkoxy)benzoyloxy]2-hydroxyphenyl]methylene]alkanamino] copper(II) complexes is examined. New data are reported and taken into account in addition to those previously reported in this Journal. The influence of alkoxy and alkanamine groups on the nature and stability of the mesophase is underlined. As a general trend, with some notable exception, smectic (C type) mesomorphism is favoured by longer alkoxy and alkanamine chains. Data concerning some Pd(II) and Ni(II) homologous complexes are also reported. The mesophase stability (nematic phase) is higher for palladium and nickel complexes than for the copper containing homologues.     

NaCu(II)4] cluster from alkali template assembly of two asymmetric end-on azido-bridged [Cu(II)2] units

The cluster [NaCu4L2(N3)2](ClO4) [1; H3L is 2-(2'-hydroxyphenyl)-1,3-bis[3'-aza-4'-(2'-hydroxyphenyl)prop-4'-en-1'-yl]-1,3-imidazolidine] has been synthesized and structurally characterized. Complex 1 is formed by the template assembly of two [Cu2L(N3)] neutral fragments through their weak oxophilic interactions with a central Na+ cation as observed in metallacrowns. The cluster exhibits a combination of ferro- and antiferromagnetic interactions. End-on N3- bridging of copper ions within the [Cu(II)2] units facilitates stabilization of S = 1 magnetic subunits that mutually cancel via antiferromagnetic coupling as mediated by the O...Na+...O bridges.     

Monomeric and polymeric dinuclear complexes of Co(II) or Ni(II) with calix[4]arene-tetraphosphineoxide

Monomeric and polymeric 1:2 complexes of a novel calix[4]arene-tetraphosphineoxide with Co(II) or Ni(II) nitrates were synthesized and analyzed by the X-ray method. In the monomeric complexes each metal cation is coordinated by two bidentate NO₃-ligands as well as by two proximal P=O groups at the calixarene skeleton. In the nickel metallopolymer one sort of the cations is bound by the two proximal P=O-groups but other cations link neighboring calixarene molecules through Р=О···Ni···O=P chains. The complexes possess molecular cavities or channels filled by solvent molecules. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Exchange coupling through diamagnetic [Fe(CO)4]2- bridging ligands in a xenophilic cluster

The electronic structure of so-called 'xenophilic' clusters, which contain both organometallic fragments and Werner-type paramagnetic transition metal centres, presents a challenge to simple theories of bonding. Density functional theory shows clearly that the cluster Mn(2)(thf)(4)(Fe(CO)(4))(2) is best described as an exchange-coupled Mn(II)(2) dimer, the closed-shell organometallic [Fe(CO)(4)](2-) fragments acting simply as bridging ligands. The high-spin configuration of the Mn(II) ions leads to single occupation of the Mn-Fe σ* orbitals and therefore substantially weaker metal-metal bonding than in conventional low-valent organometallic clusters. The transition metal fragments are effective mediators of superexchange (J(calc) = -44 cm(-1)), leading to the measured effective magnetic moment of ~5 μ(B) at 300 K, considerably lower than the limiting value of 8.37 μ(B) for two uncoupled S = 5/2 Mn(II) centres.     

Two new [Ni(tren)2]2+ complexes: [Ni(tren)2]Cl2 and [Ni(tren)2]WS4

Both title compounds, bis­[tris(2‐amino­ethyl)­amine]­nickel(II) dichloride, [Ni(tren)₂]Cl₂, (I), and bis­[tris(2‐amino­ethyl)­amine]­nickel(II) tetra­thio­tungstate, [Ni(tren)₂]WS₄, (II), contain the [Ni(tren)₂]²⁺ cation [tren is tris(2‐amino­ethyl)­amine, C₆H₁₈N₄]. The tren mol­ecule acts as a tridentate ligand around the central Ni atom, with the remaining primary amine group not bound to the central atom. In (I), Ni²⁺ is located on a centre of inversion surrounded by one crystallographically independent tren mol­ecule. In the [Ni(tren)₂]²⁺ cation of (II), the Ni atom is bound to two crystallographically independent tren mol­ecules. The Ni atoms in the [Ni(tren)₂]²⁺ complexes are in a distorted octahedral environment consisting of six N atoms from the chelating tren mol­ecules. The counter‐ions are chloride anions in (I) and the tetrahedral [WS₄]^2? anion in (II). Hydro­gen bonding is observed in both compounds.     

Counterdisproportionation between cationic Ni(II) and phosphine Ni(0) complexes

The interaction of Ni(II) bis-tetrafluoroborate complexes [Ni(Dppe)₂](BF₄)₂ and [Ni(CH₃CN)₆](BF₄)₂ (where Dppe = 1,2-bis(diphenylphosphino)ethane)) with Ni(0) phosphine complexes Ni(Dppe)₂ and Ni(PPh₃)₄ in 1 : 1 mixture of toluene-acetonitrile was studied by the EPR method. The counter-disproportionation was shown to occur in a solution between the cationic Ni(II) complexes and the Ni(0) complexes to give Ni(I) complexes almost in quantitative amounts. The structures of the cationic Ni(I) complexes obtained were found to depend on both the solvent nature and the presence of a free phosphine in a solution.     

Hexanuclear [Ni6L12] metallacrown framework consisting of NiS4 square-planar and NiS5 square-pyramidal building blocks

The hexanuclear [Ni(6)L(12)] (2) wheel-type cluster adopts an unusual structural motif whereby four NiS(4) square-planar and two NiS(5) square-pyramidal units are conjoined by edge sharing; the NiS(5) units resemble the Ni centre of the inactive state in the [NiFe] hydrogenase.     

Probing the role of the bridging C509 between the [Fe4S4] cubane and the [Ni(p)Ni(d)] centre in the A-cluster of acetyl-coenzyme A synthase

The A-cluster of acetyl-coenzyme A synthase consists of an [Fe(4)S(4)] cubane bridged to a [Ni(p)Ni(d)] centre via C509 cysteinate. The bridging cysteinate, which could be substituted by histidine imidazole, mediates "communication" between the [Fe(4)S(4)] cubane and the [Ni(p)Ni(d)] centre during the synthesis of acetyl-coenzyme A.     

Synthesis and Crystal Structure of Dichlorobis[N-（4-hydroxylsalicylidene）-3-dimethylaminopropylamine]Ni（II）

1 INTRODUCTION The chemistry of nickel complex with multi- dentate Schiff base ligands has attracted particular attention because this metal can exhibit several oxi- dation states[1]. Such complexes with different oxi- dation states play an important role in bioinorganic chemistry and redox enzyme systems[2], and many of them can provide the basis of models for active sites of biological systems or act as catalysts[3]. Nickel complexes with tetradentate N2O2 and tri- dentate N2O Schi…     

A two-dimensional cationic lattice built from [Zn6(HPO4)2(PO4)2]2+ clusters

A unique cationic zinc phosphate cluster linked by neutral bifunctional rigid ligands to form a two dimensional framework was synthesized and structurally characterized.     

A dinuclear Ni(II) complex with two types of intramolecular magnetic couplings: Ni(II)-Ni(II) and Ni(II)-TTF*+

A dinuclear Ni(II) complex involving tetrathiafulvalene (TTF) radicals as ligands has been prepared and characterized, [Ni2(mu-Cl)2(L*+)2(I3)4(I2)3.(H2O)2.(C4H8O)3 (1), L = 4,5-bis(2-pyridylmethylsulfanyl)-4',5'-ethylenedithiotetrathiafulvalene. There are two types of intramolecular magnetic exchange interactions, namely one ferromagnetic Ni(II)-Ni(II) and one antiferromagnetic Ni(II)-TTF*+. This study is new in the respect of revealing a magnetic exchange interaction between a TTF*+ radical and a paramagnetic transition metal ion. This is due to the fact of a direct binding of the transition metal ion to the skeleton of the TTF*+ radical.     

Calix[4]arene-based ditopic receptors for simultaneous recognition of fluoride and cobalt(II) ions

A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co²⁺and F^? ions through non-covalent interactions. Significant bathochromic shifts in the UV–visible spectrum with a profound colour change promise their use to engineer novel applications.