Synthesis,molecular and crystalline architectures,and magnetic properties of neutral nickel(II)dicyanamide coordination polymers containing a symmetrical/unsymmetrical 1,2-diamine as an end-capping ligand

Two neutral nickel(II) coordination polymers [Ni(en)(dca)₂]_n (1) and [Ni(dmen)(dca)₂]_n (2) (en = ethylenediamine; dmen = N,N-dimethylethylenediamine; dca = dicyanamide) have been synthesized and X-ray crystallographically characterized. Each nickel(II) center in 1/2 adopts a distorted octahedral coordination environment with a NiN₆ chromophore ligated by two amine N atoms of the bidentate amine (en/dmen) and four nitrile N atoms of μ_1,5 bridged dca. The metal(II) centers are connected with each other through single μ_1,5 M–NCNCN–M bridges, resulting in a 2D layer structure with a (4,4) topology in 1 and a 3D network of topology (6,6) in 2. Multiple lateral N–H···N and C–H···N hydrogen bondings promote dimensionality. The magnetic susceptibility results of 1 and 2 at very low temperature support the zero-field splitting effect of the nickel(II) ions.     

Synthesis, characterization, and magnetic properties of self-assembled compounds based on discrete homotrinuclear complexes of Cu(II)

Three new supramolecular entities of Cu(II) were synthesized and characterized: [(Cu(H(2)O)(tmen))(2)(mu-Cu(H(2)O)(opba))](2)[(ClO(4))(2)](2).2H(2)O (1), [(Cu(H(2)O)(tmen))(2) (mu-Cu(H(2)O) (Me(2)pba))](2)[(ClO(4))(2)](2) (2), and [(Cu(H(2)O)(tmen))(Cu(tmen))(mu-Cu(OHpba))](n)() ((ClO(4))(2))(n)().nH(2)O (3), where opba = o-phenylenbis(oxamato), Me(2)pba = 2,2-dimethyl-1,3-propylenbis(oxamato), OHpba = 2-hydroxy-1,3-propylenbis(oxamato), and tmen = N,N,N'N'-tetramethylethylenediamine. The crystal structures of 1, 2, and 3 were solved. Complex 1 crystallizes in the monoclinic system, space group C2/c with a = 20.572(4) A, b = 17.279(6) A, c = 22.023(19) A, beta = 103.13(4) degrees, and Z = 8. Complex 2 crystallizes in the monoclinic system, space group P2(1)/c, with a = 16.7555(7) A, b = 13.5173(5) A, c = 17.1240(7) A, beta = 104.9840(10) degrees, and Z = 4. Complex 3 crystallizes in the orthorhombic system, space group Pca2(1) with a = 21.2859(4) A, b = 12.8286(10) A, c = 12.6456(2) A, and Z = 4. The three complexes are very similar in structure: a trinuclear Cu(II) complex with the two terminal Cu(II) ions blocked by N,N,N',N'-tetramethylethylenediamine, but with a different environment in the Cu(II) central ion. In the case of complex 1, two of these trinuclear entities are packed with a short distance between the central Cu(II) ions of two separate entities forming a hexanuclear-type compound. In the case of 2, two of these trinuclear entities are linked by a hydrogen bond between a water molecule of one terminal Cu(II) and one oxygen atom of the oxamato ligand of the neighboring entity, also forming a hexanuclear complex. In the case of complex 3, the intermolecular linkages give a one-dimensional system where the OH groups of the OHpba entities are linked to the terminal Cu(II) of the neighboring entities. The magnetic properties of the three complexes were studied by susceptibility measurements vs temperature. For complex 1, an intramolecular J value of -312.1 cm(-)(1) and a contact dipolar interaction of -0.44K were found. For complex 2 and 3 the fit was made by the irreducible tensor operator formalism (ITO). The values obtained were as follows: J(1) = -333.9 cm(-)(1) and J(2) = 0.67 cm(-)(1) for 2 and J(1) = -335.9 cm(-)(1) and J(2) = 3.5 cm(-)(1) for 3.     

Electrophilic arene hydroxylation and phenol O-H oxidations performed by an unsymmetric μ-η(1):η(1)-O2-peroxo dicopper(II) complex

Reactions of the unsymmetric dicopper(II) peroxide complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(m-XYL(N3N4))](2+) (1?O(2), where m-XYL is a heptadentate N-based ligand), with phenolates and phenols are described. Complex 1?O(2) reacts with p-X-PhONa (X = MeO, Cl, H, or Me) at -90?°C performing tyrosinase-like ortho-hydroxylation of the aromatic ring to afford the corresponding catechol products. Mechanistic studies demonstrate that reactions occur through initial reversible formation of metastable association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(p-X-PhO)(m-XYL(N3N4))](+) (1?O(2)?X-PhO) that then undergo ortho-hydroxylation of the aromatic ring by the peroxide moiety. Complex 1?O(2) also reacts with 4-X-substituted phenols p-X-PhOH (X = MeO, Me, F, H, or Cl) and with 2,4-di-tert-butylphenol at -90?°C causing rapid decay of 1?O(2) and affording biphenol coupling products, which is indicative that reactions occur through formation of phenoxyl radicals that then undergo radical C-C coupling. Spectroscopic UV/Vis monitoring and kinetic analysis show that reactions take place through reversible formation of ground-state association complexes [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhOH)(m-XYL(N3N4))](2+) (1?O(2)?X-PhOH) that then evolve through an irreversible rate-determining step. Mechanistic studies indicate that 1?O(2) reacts with phenols through initial phenol binding to the Cu(2)O(2) core, followed by a proton-coupled electron transfer (PCET) at the rate-determining step. Results disclosed in this work provide experimental evidence that the unsymmetric 1?O(2) complex can mediate electrophilic arene hydroxylation and PCET reactions commonly associated with electrophilic Cu(2)O(2) cores, and strongly suggest that the ability to form substrate?Cu(2)O(2) association complexes may provide paths to overcome the inherent reactivity of the O(2)-binding mode. This work provides experimental evidence that the presence of a H(+) completely determines the fate of the association complex [Cu(II)(2)(μ-η(1):η(1)-O(2))(X-PhO(H))(m-XYL(N3N4))](n+) between a PCET and an arene hydroxylation reaction, and may provide clues to help understand enzymatic reactions at dicopper sites.     

Redox-controlled molecular flipper based on a chiral Cu complex

A molecular bipaddled flipper based on a tetradentate chiral Cu complex has been designed. The paddling motion of this unprecedented molecular-scale machine can be controlled by reversible oxidation of the metal center. Kinetic and computational (density functional theory) analyses provide a detailed picture of the flipper motion at the molecular scale, rationalize the switching role of the metal-ion oxidation state, and pose the basis for the fine-tuning of the dynamic motion of this new class of molecular-scale devices.     

Recursions for the Individual Risk Model

In the actuarial literature,several exact and approximative recursive methods have been proposedfor calculating the distribution of a sum of mutually independent compound Bernoulli distributed randomvariables.In this paper,we give an overview of these methods.We compare their performance with the straight-forward convolution technique by counting the number of dot operations involved in each method.It turns outthat in many practicle situations,the recursive methods outperform the convolution method.     

Hydrothermal syntheses, crystal structures and magnetic properties of two copper(II) complexes involved in situ ligand synthesis

The hydrothermal reaction of Cu(NO(3))(2), isophthalate (ip) and 2,2'-bipyridine (2,2'-bpy) without or with K(2)Cr(2)O(7) affords different complexes, whose structures are controlled only by the addition of the K(2)Cr(2)O(7). The reaction of Cu(NO(3))(2), isophthalate and 2,2'-bipyridine yields a novel one-dimensional double-chain coordination polymer [Cu(3)(ip)(2)(Hipa)(2)(bpy)(2)](n) (1). However, with the addition of K(2)Cr(2)O(7) in the above reaction at the same hydrothermal conditions, a discrete hexanuclear Cu(II) complex [Cu(6)(ipO)(4)(2,2'-bpy)(2)(H(2)O)(2)].6H(2)O (2) (ipOH = 2-hydroxyisophthalate) was isolated. It is interesting to find that the in situ reaction of isophthalate (ip) oxidized to 2-hydroxyisophthalate (ipOH) occurs. K(2)Cr(2)O(7) acts as an oxidant. The magnetic properties of 1 and 2 have been investigated by variable-temperature magnetic susceptibility and magnetization measurements, and the results reveal that intramolecular ferromagnetic interactions exist with weak intermolecular antiferromagnetic interactions at very low temperature in 1 and weak antiferromagnetic interactions admixture with strong ferromagnetic interactions in 2.     

3D Heterometallic (3d–4f) coordination polymers: A ferromagnetic interaction in a Gd(III)–Cu(II) couple

Four 3d–4f heterometallic coordination polymers, [Cu₃(IDA)₆Ln₂] · n(H₂O) [IDA =  iminodiacetate dianion; Ln = Gd, n = 3 (1); Ln = Nd, n = 6 (2); Ln = Sm, n = 6 (3)] and [Cu(Cl)(NTA)Sm(H₂O)₆] · (ClO₄) · (H₂O) (4) [NTA = nitrilotriacetate trianion], have heen synthesized and characterized by single crystal X-ray diffraction analysis. Complexes 1–3 are isomorphous, showing a 3D coordination framework having tubular channels filled by lattice water molecules running parallel to the c axis. Whereas complex 4 is a 1D polymer of alternating copper and samarium ions connected by NTA, and the chains get involved in H-bonding interactions resulting in a 3D network. A low temperature magnetic study reveals ferromagnetic interactions for complex 1. Thermogravimetric and X-ray powder diffraction analyses of 1, 2 and 3 show that the covalently bonded 3D network remains almost unaffected after deaquation.     

NMR spectroscopic analysis of new spiro-piperidylrifamycins

New spiro-piperidylrifamycin derivatives are presented. These compounds were synthesized from the reaction of 3-amino-4-iminorifamycin S and enantiomerically pure 4-piperidones, which generate diasteroisomeric rifabutin analogues with a new stereocentre at the spiranic carbon. The (1)H and (13)C NMR spectra of these new compounds, and also the configuration of the new stereogenic centres, were assigned using 2D NMR spectroscopic techniques. A preliminary study of the (1)H and (13)C NMR spectra of the starting compounds rifamycin S, 3-amino-4-iminorifamycin S and the related rifabutin was also carried out and as a result, their previously published (13)C NMR data were corrected.