Tetranuclear Assembly Research Articles

A bright tetranuclear iridium(iii) complex

A cyclic tetranuclear cyclometallated iridium(III) complex using cyanide anions as bridging ligands and displaying a tetrahedrally distorted square geometry has been obtained with high yield; photo- and electrochemical characterizations show that most interesting properties of mononuclear cyclometallated iridium complexes are retained in the tetranuclear assembly.

Oligonuclear Homoleptic Copper(I) Pyrazolates with Multinucleating Ligand Scaffolds: High Structural Diversity in Solid-State and Solution

The synthesis of three pyrazole-based, potentially binucleating ligands 3,5-bis(R(1)N(CH(3))CH(2))-4-R(2)pyrazole (L(1)H: R(1) = pyridyl-2-methyl-, R(2) = Ph; L(2)H: R(1) = 8-quinolyl-, R(2) = H; L(3)H: R(1) = 8-quinolyl-, R(2) = Ph) is described. Reaction of L(1-3)H with 1 equiv. of mesitylcopper affords oligonuclear homoleptic complexes of the type [CuL](n) (1-3). The single crystal X-ray structure of 2 shows a tetranuclear assembly of linear coordinated copper(I)-centers bridged by pyrazolato ligands that alternate above and below the Cu(4) plane, with additional weak interactions from some of the ligand side arms. As the single crystal X-ray structure of 3 reveals, phenyl substitution at the 4-position of the pyrazolato framework leads to significant structural modification of the Cu(4) array, giving a rhombical tetranuclear complex with two linear coordinated copper(I) centers that exhibit a short intramolecular Cu...Cu contact (2.8212(10) A) and two peripheral copper(I) centers in a distorted tetrahedral coordination mode. Thus, 3 represents a very rare example of an inorganic pyrazolato cuprate which can also be viewed as a partly rearranged structural isomer of 2. Furthermore, the crystal lattice of 3 shows an extended network of intra- and intermolecular pi-pi stacking interactions between the aromatic rings. In solution, 1-3 each form two types of oligomers a and b that slowly (<1 s(-1)) equilibrate at room temperature. Using Diffusion Ordered Spectroscopy (DOSY) and variable temperature (1)H NMR spectroscopy it can be shown that a and b correspond to a tetrameric and a (planar) trimeric species. Coordination of the pyridyl/quinolyl side arms that is observed in the solid state seems to be only transient in solution.

Synthesis, structure, magnetism and nuclease activity of tetranuclear copper(ii) phosphonates containing ancillary 2,2′-bipyridine or 1,10-phenanthroline ligands

The reaction of cyclohexylphosphonic acid (C(6)H(11)PO(3)H(2)), anhydrous CuCl(2) and 2,2'-bipyridine (bpy) in the presence of triethylamine followed by a metathesis reaction with KNO(3) afforded [Cu(4)(mu-Cl)(2)(mu(3)-C(6)H(11)PO(3))(2)(bpy)(4)](NO(3))(2) (1). In an analogous reaction involving Cu(OAc)(2).H(2)O, the complex [Cu(4)(mu-CH(3)COO)(2)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4)](CH(3)COO)(2) (2) has been isolated. The three-component reaction involving Cu(NO(3))(2).3H(2)O, cyclohexylphosphonic acid and 2,2'-bipyridine in the presence of triethylamine afforded the tetranuclear assembly [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4) (H(2)O)(2)](NO(3))(3) (3). Replacing 2,2'-bipyridine with 1,10-phenanthroline (phen) in the above reaction resulted in [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(phen)(4)(H(2)O)(2)](NO(3))(3) (4). In all the copper(II) phosphonates (1-4) the two phosphonate ions bridge the four copper(II) ions in a capping coordination action. Each phosphonate ion bridges four copper(II) ions in a mu(4), eta(3) coordination mode or 4.211 of the Harris notation. Variable-temperature magnetic studies on reveal that all four complexes exhibit moderately strong intramolecular antiferromagnetic coupling. The DNA cleavage activity of complexes 1-4 is also described. Compounds 1 and 3 were able to completely convert the supercoiled pBR322 DNA form I to nick form II without any co-oxidant. In contrast, 50% conversion occurred with and 40% with 4. In the presence of magnesium monoperoxyphthalate all four compounds achieved rapid conversion of form I to form II.

Acid‐Base Self‐Assembly Chemistry and Hydrogen Bonding Interactions Resulting in the Formation of a Tetranuclear Aggregate Containing Four Crystallographically Non‐Equivalent FeIII Centers

AbstractThe synthesis and characterization of a mononuclear iron(III) complex [Fe(Hphpz)Cl(CH3OH)] (1) and a tetranuclear assembly of a bis(μ‐hydroxo)‐bridged dinuclear iron(III) complex [{Fe(Hphpz)2(OH)}2][Fe(Hphpz)3]2 (2) with the ligand 3(5)‐methyl‐5(3)‐(2‐hydroxyphenyl)pyrazole (H2phpz) is reported. Compound 1 is converted into 2 in a methanol solution and in the presence of a base. The asymmetric unit of 2 consists of two independent [Fe(Hphpz)3] molecules and one dinuclear complex [Fe(Hphpz)2(OH)]2 containing two crystallographically non‐equivalent iron(III) ions; the three units are linked by N−H···O and O−H···O hydrogen bonding and stacking interactions to form a cluster with an approximate C2‐symmetry. The Mössbauer spectra of [{Fe(Hphpz)2(OH)}2][Fe(phpz)3]2 have been measured at 295 and 78 K and indicate the presence of four crystallographically distinct, but chemically similar iron(III) sites. The magnetic properties of this compound originate from the weak antiferromagnetic interaction between the FeIII ions of the [Fe(phpz)2(OH)]2 dimer (J = −2.8 cm−1). (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)

Calixarenes as aryloxides: oligonuclear europium(iii) derivatives

Synthetic and structural studies of europium complexes of calix[8]arene, p-t-Bu-calix[7]arene and p-t-Bu-calix[9]arene are reported. The complex [Eu2(calix[8]arene-6H)(dmso)5] was found to have a similar structure to previously reported p-t-Bu- and p-nitro-calix[8]arene complexes of the lanthanides. Despite being prepared under similar conditions, the complex of p-t-Bu-calix[7]arene was found to be a tetranuclear assembly, formulated as [(HO)2(OCO2)Eu4(p-t-Bu-calix[7]arene-4H)2(dmso)6]. Expanding the ligand to p-t-Bu-calix[9]arene resulted in the isolation of a larger oligonuclear assembly, [(HO)9(H2O)2Eu7(p-t-Bu-calix[9]arene-6H)2(dmso)6]. In contrast to the consistent structural type found with the calix[8]arene system, however, use of a different solvent (acetone) gave rise to a much simpler species, [Eu2(p-t-Bu-calix[9]arene-3H)2(dmso)4].

Synthesis, magnetochemical studies and X-ray molecular structures of some mononuclear copper(II)–1 H-pyrazole adducts and mono(μ-pyrazolate) bridged dicopper(II) complexes derived from N-salicylidenearoylhydrazines

1 H-Pyrazole complexes, [Cu(HL)HPz Cl] nH 2O and [Cu(L)HPz] nH 2O were prepared and characterized, where HL and L, respectively, refer to the mononegative and dinegative N-salicylidenearoylhydrazine anions. The X-ray crystal and molecular structure of [monochloro( N-salicylidenebenzoylhydrazinato)ONO(−1)monopyrazole] copper(II) monohydrate, [Cu(HSBzh)HPz Cl] H 2O, and [( N-salicylidenebenzoylhydrazinato)ONO(−2)monopyrazole] copper(II) hemihydrate, [Cu(SBzh)HPz] 1/2H 2O, were determined. The Cu(II) in [Cu(HSBzh)HPz Cl] H 2O is in a distorted square pyramidal environment and is bound in the equatorial plane with the mononegative tridentate aroylhydrazone anion and pyrazole nitrogen, the axial fifth coordination site is occupied by a chloride ion. On the other hand, the complex [Cu(SBzh)HPz] 1/2H 2O consists of two monomeric crystallographically independent but chemically similar molecules. In each molecule, the Cu(II) is in a distorted square planar geometry and is coordinated to the dinegative tridentate aroylhydrazone via the phenoxy oxygen, azomethine nitrogen and enolimide oxygen, and the fourth coordination site is occupied by the pyrazole nitrogen. The mono(μ-pyrazolate) dicopper(II) complexes, K[Cu 2(L) 2Pz] nH 2O, were also prepared and the X-ray molecular structure of K 2[Cu 4(SBzh) 4(Pz) 2] 2H 2O 1/2CH 3OH was determined. In this complex, two copper(II) atoms are bridged by only one pyrazolate anion forming a dicopper mono(μ-pyrazolate) unit. Each two units are connected together by a five coordinate K + cation forming a tetranuclear assembly. These tetranuclear assemblies are connected together by another K + cation forming a supramolecular structure. Variable temperature magnetic studies on these pyrazolate complexes indicated antiferromagnetic behaviour with −2 J values varying from 25 to 36 cm −1.

Isolation and Characterization of a Biologically Active Chromium Oligopeptide from Bovine Liver

Low-molecular-weight chromium-binding substance (LMWCr), the only known naturally occurring Cr-containing polypeptide from mammals and candidate for the biologically active form of chromium, has been isolated for the first time in yields sufficient for spectroscopic studies capable of providing structural and mechanistic data on a molecular level. The results of paramagnetic1H NMR, electron paramagnetic resonance, and electronic spectroscopic studies indicate that the four chromic ions per polypeptide are probably arranged in an integer-spin tetranuclear assembly, although an alternate possibility, the presence of two dinuclear assemblies, could not be ruled out. This assembly (or assemblies) is bridged by anionic ligands and supported by carboxylates provided by the polypeptide.

Design and Study of Synthetic Chiral Nanoscopic Assemblies. Preparation and Characterization of Optically Active Hybrid, Iodonium−Transition-Metal and All-Transition-Metal Macrocyclic Molecular Squares

The synthesis and characterization of various optically active nanoscale-size tetranuclear assemblies held together by coordination bonds is described. Interaction of bis[4-(4‘-pyridyl)phenyl]iodonium triflate and bistriflates of chiral transition metal (Pd(II) or Pt(II)) bisphosphines resulted in the formation of chiral hybrid iodonium-transition metal molecular squares. Restricted rotation of the coordinated bis[4-(4‘-pyridyl)phenyl]iodonium moiety was detected in these squares and investigated by using variable-temperature NMR. The preparation of chiral hybrid squares which possess the elements of helicity (twist) in the assembly was accomplished using the above bisphosphines and bis(3-pyridyl)iodonium triflate. Interaction between the bistriflates of chiral (R(+)-BINAP or S(−)-BINAP)) transition metal (Pd(II) or Pt(II)) bisphosphines and a diaza ligand with C2h symmetry, 2,6-diazaanthracene (DAA) or 2,6-diazaanthracene-9,10-dione (DAAD), in acetone at ambient temperature results in chirality-directed ...

Isomerization of a Linear Pentamine, 1,4,7,10,13-Pentaazatridecane, to a Branched Form, 4-(Aminoethyl)-1,4,7,10-tetraazadecane, on a Schiff-base Copper Complex Relevant to Multi-copper Enzymes

Abstract The 1:2 Schiff-base of 2,6-diformyl-4-methylphenol and 1,4,7,10,13-pentaazatridecane formed a tetranuclear assembly complex {Cu(II)-Cu2(II,II)-Cu(II)} possessing a dinuclear Cu2 core and two mononuclear Cu auxiliaries. The two-electron reduction of the complex and reoxidation in air resulted in the formation of a dinuclear Cu2(II,II) complex of a macrocycle comprised of 2,6-diformyl-4-methylphenol and branched 4-(2-aminoethyl)-1,4,7,10-tetraazadecane (2:2) instead of the linear pentamine.