Bridging nitrate groups in [Mn(4)O(3)(NO(3))(O(2)CMe)(3)(R(2)dbm)(3)] (R = H, Et) and [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)): acidolysis routes to tetranuclear manganese carboxylate complexes

New synthesis procedures are described to tetranuclear manganese carboxylate complexes containing the [Mn(4)O(2)](8+) or [Mn(4)O(3)X](6+) (X(-) = MeCO(2)(-), F(-), Cl(-), Br(-), NO(3)(-)) core. These involve acidolysis reactions of [Mn(4)O(3)(O(2)CMe)(4)(dbm)(3)] (1; dbm is the anion of dibenzoylmethane) or [Mn(4)O(2)(O(2)CEt)(6)(dbm)(2)] (8) with HX (X(-) = F(-), Cl(-), Br(-), NO(3)(-)); high-yield routes to 1 and 8 are also described. The X(-) = NO(3)(-) complexes [Mn(4)O(3)(NO(3))(O(2)CR)(3)(R'(2)dbm)(3)] (R = Me, R' = H (6); R = Me, R' = Et (7); R = Et, R' = H (12)) represent the first synthesis of the [Mn(4)O(3)(NO(3))](6+) core, which contains an unusual eta(1):mu(3)-NO(3)(-) group. Treatment of known [Mn(4)O(2)(O(2)CEt)(7)(bpy)(2)](ClO(4)) with HNO(3) gives [Mn(4)O(2)(NO(3))(O(2)CEt)(6)(bpy)(2)](ClO(4)) (15) containing a eta(1):eta(1):mu-NO(3)(-) group bridging the two body Mn(III) ions of the [Mn(4)O(2)](8+) butterfly core. Complex 7 x 4CH(2)Cl(2) crystallizes in space group P2(1)2(1)2(1) with (at -168 degrees C) a = 21.110(3) A, b = 22.183(3) A, c = 15.958(2) A, Z = 4, and V = 7472.4(3) A(3). Complex 15 x (3)/(2)CH(2)Cl(2) crystallizes in space group P2(1)/c with (at -165 degrees C) a = 26.025(4) A, b = 13.488(2) A, c = 32.102(6) A, beta = 97.27(1) degrees, Z = 8, and V = 11178(5) A(3). Complex 7 contains a [Mn(4)(mu(3)-O)(3)(mu(3)-NO(3))](6+) core (3Mn(III), Mn(IV)) as seen for previous [Mn(4)O(3)X](6+) complexes. Complex 15 contains a butterfly [Mn(4)(mu(3)-O)(2)](8+) core. (1)H NMR spectra have been recorded for all complexes reported in this work and the various resonances assigned. All complexes retain their structural integrity on dissolution in chloroform and dichloromethane. Magnetic susceptibility (chi(M)) data were collected on 12 in the 5-300 K range in a 10.0 kG (1 T) field. Fitting of the data to the theoretical chi(M) vs T expression appropriate for a [Mn(4)O(3)X](6+) complex of C(3)(v)() symmetry gave J(34) = -23.9 cm(-)(1), J(33) = 4.9 cm(-)(1), and g = 1.98, where J(34) and J(33) refer to the Mn(III)Mn(IV) and Mn(III)Mn(III) pairwise exchange interactions, respectively. The ground state of the molecule is S = 9/2, as found previously for other [Mn(4)O(3)X](6+) complexes. This was confirmed by magnetization data collected at various fields and temperatures. Fitting of the data gave S = 9/2, D = -0.45 cm(-1), and g = 1.96, where D is the axial zero-field splitting parameter.     

Synthesis, structure and magnetic properties of a decametallic Ni single-molecule magnet

Ferromagnetic exchange between the ten Ni2+ ions in the complex [Ni10(tmp)2(N3)8(acac)6(MeOH)6] leads to a spin ground state of S = 10; single crystal M vs. H studies reveal the temperature and sweep rate dependent hysteresis loops expected for a single-molecule magnet.     

Guest‐, Light‐ and Thermally‐Modulated Spin Crossover in [FeII2] Supramolecular Helicates

A new bis(pyrazolylpyridine) ligand (H₂L) has been prepared to form functional [Fe₂(H₂L)₃]⁴⁺ metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe₂(H₂L)₃]X(PF₆)₂?xCH₃OH ( 1 , x=5.7 and X=Cl; 2 , x=4 and X=Br), X@[Fe₂(H₂L)₃]X(PF₆)₂?yCH₃OH?H₂O ( 1 a , y=3 and X=Cl; 2 a , y=1 and X=Br) and X@[Fe₂(H₂L)₃](I₃)₂?3 Et₂O ( 1 b , X=Cl; 2 b , X=Br). Their structure and functional properties are described in detail by single‐crystal X‐ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2 , respectively, by a single‐crystal‐to‐single‐crystal mechanism. The three possible magnetic states, [LS–LS], [LS–HS], and [HS–HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe^II centers. The nature of the guest (Cl^? vs. Br^?) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS–HS] or [HS–HS] states are generated through irradiation. All helicates (X@[Fe₂(H₂L)₃])³⁺ persist in solution.     

Structural and Magnetic Diversity in Alkali‐Metal Manganate Chemistry: Evaluating Donor and Alkali‐Metal Effects in Co‐complexation Processes

By exploring co‐complexation reactions between the manganese alkyl Mn(CH₂SiMe₃)₂ and the heavier alkali‐metal alkyls M(CH₂SiMe₃) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4‐dioxane, and 1,4‐diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali‐metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X‐ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA)₂MMn(CH₂SiMe₃)₃] (M=Na, 3 ; M=K, 4 ) to dimers [{KMn(CH₂SiMe₃)₃?C₆H₆}₂] ( 2 ) and [{NaMn(CH₂SiMe₃)₃}₂(dioxane)₇] ( 5 ); and to more complex supramolecular networks [{NaMn(CH₂SiMe₃)₃}_∞] ( 1 ) and [{Na₂Mn₂(CH₂SiMe₃)₆(DABCO)₂}_∞] ( 7 )). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4‐dioxane, as 1 produces coordination adduct 5 , while 2 forms heteroleptic [{(dioxane)₆K₂Mn₂(CH₂SiMe₃)₄(O(CH₂)₂OCH=CH₂)₂}_∞] ( 6 ) containing two alkoxide–vinyl anions resulting from α‐metalation and ring opening of dioxane. Compounds 6 and 7 , containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways.     

Highly enantioselective organocatalytic synthesis of piperidines. Formal synthesis of (−)-Paroxetine

A highly enantioselective organocatalytic synthesis of piperidines is reported. The reaction is catalyzed by simple and commercially available secondary amines, affording the corresponding adducts with high yields and enantioselectivities. Moreover, this reaction is used for the formal synthesis of (−)-Paroxetine, a blockbuster drug, in only three steps.     

Phase mask selection in wavefront coding systems: A design approach

A method for optimizing the strength of a parametric phase mask for a wavefront coding imaging system is presented. The method is based on an optimization process that minimizes a proposed merit function. The goal is to achieve modulation transfer function invariance while quantitatively maintaining final image fidelity. A parametric filter that copes with the noise present in the captured images is used to obtain the final images, and this filter is optimized. The whole process results in optimum phase mask strength and optimal parameters for the restoration filter. The results for a particular optical system are presented and tested experimentally in the laboratory. The experimental results show good agreement with the simulations, indicating that the procedure is useful.     

Local Coordination Geometry and Spin State in Novel Fe(II) Complexes with 2,6-Bis(pyrazol-3-yl)pyridine-Type Ligands as Controlled by Packing Forces: Structural Correlations

A substituted 2,6-bis(pyrazol-3-yl)pyridine (3-bpp) ligand, H(4) L, created to facilitate intermolecular interactions in the solid, has been used to obtain four novel Fe(II) complexes: [Fe(H(4) L)(2) ](ClO(4) )(2) ?2?CH(3) NO(2) ?2?H(2) O, [Fe(H(4) L)(H(2) LBF(2) )](BF(4) )?5?C(3) H(6) O (H(2) LBF(2) is an in situ modified version of H(4) L), [Fe(H(4) L)(2) ](ClO(4) )(2) ?2?C(3) H(7) OH and [Fe(H(4) L)(2) ](ClO(4) )(2) ?4?C(2) H(5) OH. Changing of spin-inactive components (solvents, anions or distant ligand substituents) causes differences to the coordination geometry of the metal that are key to the magnetic proper- ties. Magnetic measurements show that, contrary to the previously published complex [Fe(H(4) L)(2) ](ClO(4) )(2) ?H(2) O?2?CH(3) COCH(3) , the newly synthesised compounds remain in the high-spin (HS) state at all temperatures (5-300?K). A member of the known family of Fe(II) /3-bpp complexes, [Fe(3-bpp)(2) ](ClO(4) )(2) ?1.75?CH(3) COCH(3) ?1.5?Et(2) O, has also been prepared and characterised structurally. In the bulk, this compound exhibits a gradual and incomplete spin transition near 205?K. The single-crystal structure is consistent with it being HS at 250?K and partially low spin at 90?K. Structural analysis of all these compounds reveals that the exact configuration of intermolecular interactions affects dramatically the local geometry at the metal, which ultimately has a strong influence on the magnetic properties. Along this line, the geometry of Fe(II) in all published 3-bpp compounds of known structure has been examined, both by calculating various distortion indices (Σ, Θ, θ and Φ) and by continuous shape measures (CShMs). The results reveal correlations between some of these parameters and indicate that the distortions from octahedral geometry observed on HS systems are mainly due to strains arising from intermolecular interactions. As previously suggested with other related compounds, we observe here that strongly HS-distorted systems have a larger tendency to remain in that state.     

Tetranuclear Cu(II) complex supported by a central mu4-1,1,3,3 azide bridge

The new cluster [Cu4L2(N3)]Cl.16H2O has been synthesized and characterized; it features a unique mu4-1,1,3,3 bridging mode for azide, whose capacity to mediate magnetic coupling has been examined through bulk magnetic measurements and numeric fitting procedures.     

Mobility of a one-dimensional confined file of water molecules as a function of file length

Confinement of water by pore geometry to a one-dimensional file of molecules interacting with the pore alters the diffusion coefficient D(W). Here we report an exponential dependence of D(W) on the number of water positions in the pore. The result is based on measurements of single channel water permeabilities of structurally similar peptidic nanopores of different length. The inconsistency with predictions from continuum or kinetic models indicates that pore occupancy is reduced in single file transport. In longer pores (e.g., in aquaporins) the presence of charged residues increases D(W).     

Application of field portable EDXRF spectrometry to analysis of pigments of Levantine rock art

The results of the analyses of elemental composition of red and black pigments of Levantine rock art from La Saltadora rock shelters (Valltorta gorge, Castellón, Spain) are presented in this paper. Nondestructive analyses were carried out using a portable energy dispersive X‐ray fluorescence (EDXRF) spectrometer developed for in situ analysis. The results revealed the strong presence of calcium in all the analyzed locations due to the contribution of the underlying calcareous bedrock and the overlying crust. Iron is the main element detected in red pigments and manganese in black pigments. Iron and calcium ratios have been found indicative of the degree of preservation of the pictorial layer. Trace elements detected in the pigment composition confirm the use of different raw materials. Therefore, this work illustrates the potential of the portable EDXRF spectrometers for in situ analysis of rock art paintings. Copyright © 2010 John Wiley & Sons, Ltd.