High Nuclearity Assemblies and One-Dimensional (1D) Coordination Polymers Based on Lanthanide-Copper 15-Metallacrown-5 Complexes (LnIII = Pr, Nd, Sm, Eu).

Complexes {[LnCu5(GlyHA)5(m-bdc)(H2O)4-x]2[LnCu5(GlyHA)5(SO4)(m-bdc)(H2O)4]2}·(30 + 2x)H2O (where GlyHA2- = glycinehydroxamate, m-bdc2- = m-phthalate; Ln = Pr and x = 0.21 for compound 1, or Ln = Sm and x = 0.24 for 3) and one-dimensional (1D) coordination polymers {[NdCu5(GlyHA)5(H2O)5(m-bdc)]nn[NdCu5(GlyHA)5(H2O)4(µ-CO3)(m-bdc)]}·13nH2O (2) and {[EuCu5(GlyHA)5(H2O)3](m-bdc)2[EuCu5(GlyHA)5(m-bdc)(H2O)3]}n·17nH2O (4) were obtained starting from the 15-metallacrown-5 complexes {[LnCu5(GlyHA)5(SO4)(H2O)6.5]}2(SO4)·6H2O (Ln = Pr, Nd, Sm, Eu) by the partial or complete metathesis of sulfate anions with m-phthalate. Compounds 1 and 3 contain unprecedented quadruple-decker neutral metallacrown assemblies, where the [LnCu5(GlyHA)5]3+ cations are linked by m-phthalate dianions. In contrast, in complexes 2 and 4, these components assemble into 1D chains of coordination polymers, the adjacent {[NdCu5(GlyHA)5(H2O)5(m-bdc)]+}n 1D chains in 2 being separated by discrete [NdCu5(GlyHA)5(H2O)4(µ-CO3)(m-bdc)]}- complex anions. The crystal lattices of 2 and 4 contain voids filled by solvent molecules. Desolvated 4 is able to absorb up to 0.12 cm3/g of methanol vapor or 0.04 cm3/g of ethanol at 293 K. The isotherm for methanol absorption by compound 4 is consistent with a possible "gate opening" mechanism upon interaction with this substrate. The χMT vs T data for complexes 1-4 and their simpler starting materials {[LnCu5(GlyHA)5(SO4)(H2O)6.5]}2(SO4)·6H2O (Ln(III) = Pr, Nd, Sm, Eu) were fitted using an additive model, which takes into account exchange interactions between lanthanide(III) and copper(II) ions in the metallamacrocycles via a molecular field model. The exchange interactions between adjacent Cu(II) ions in metallacrown fragments were found to fall in the range of -47 < JCu-Cu < -63 cm-1. These complexes are the first examples of a Ln(III)-Cu(II) 15-metallacrowns-5 (Ln(III) = Pr, Nd, Sm, Eu), for which values of exchange parameters have now been reported.

Manifestation of π-π stacking interactions in luminescence properties and energy transfer in aromatically-derived Tb, Eu and Gd tris(pyrazolyl)borate complexes.

The three new complexes Tp(Py)Ln(CH3CO2)2(H2O) (Ln = Eu (1), Gd(2), or Tb (3)) were prepared and characterized crystallographically. In the crystal lattices of these complexes, separate molecules are connected in infinite chains by π-stacking interactions. Complexes 1 and 3 display intense photoluminescence and triboluminescence (red and green respectively), while compound 3 exhibits electroluminescence commencing at 9 V in an ITO/PVK/3/Al device (ITO = indium-tin oxide, PVK = poly(N-vinylcarbazole)). A series of Eu/Tb-doped Gd compounds was prepared by cocrystallization from mixtures of 1 and 2 or 2 and 3, respectively. It was shown that π-stacking interactions are involved in increasing the efficiency of energy transfer from the gadolinium complex to emitting [Tp(Py)Eu](2+) or [Tp(Py)Tb](2+) centers, and this energy transfer occurs through hundreds of molecules, resembling the process of energy harvesting in chloroplast stacks.

Formation of coordination polymers or discrete adducts via reactions of gadolinium(III)-copper(II) 15-metallacrown-5 complexes with polycarboxylates: synthesis, structures and magnetic properties.

Reactions of the copper(II)-gadolinium(III) 15-metallacrown-5 complex [GdCu5(Glyha)5(NO3)2(H2O)6](NO3) (Glyha(2-) = dianion of glycinehydroxamic acid) with different di/tricarboxylates (1,3-phthalate, 1,4-phthalate, biphenyl-4,4'-dicarboxylate, citrate) resulted in formation of different types of products: {[(GdCu5(Glyha)5(H2O)2)(GdCu5(Glyha)5(H2O)3)(1,3-bdc)3]·16H2O}n (1), {[(GdCu5(Glyha)5(H2O)3)2(1,4-bdc)2](1,4-bdc)·8H2O}n (2), {[(GdCu5(Glyha)5(H2O)4)2(1,4-bdc)3]·8H2O}n (3), [GdCu5(Glyha)5(Citr)(H2O)4]·7H2O (4), {[GdCu5(Glyha)5(H2O)5](µ2-CO3)[Cu(Fgg)]}·7H2O (5) and [Cu(Gly)2(H2O)]n (6) (where bdc(2-) is the corresponding phthalate (benzenedicarboxylate), Citr(3-) is citrate, Fgg(3-) is the trianion of [(N-formylaminoacetyl)amino]acetic acid and Gly(-) is glycinate). Complexes 1-5 contain the [GdCu5(Glyha)5](3+) cation. Complexes 2 and 3 possess the same composition but differ by the mode of p-phthalate coordination to the [GdCu5(Glyha)5](3+) unit. In compounds 1-3, metallacrown cations are linked by the corresponding phthalates in 1D, 1D and 2D polymers, respectively, whereas 4 and 5 are discrete molecules. Compound 5 is the product of a multistep reaction, which finally involves atmospheric CO2 capture. Hydrolysis of hydroxamate in this reaction is confirmed by isolation of a mononuclear copper glycine complex 6. The χMT vs T data for 1 were fitted using a model based on the Hamiltonian H (GdCu5) = -2J1(S1 × SGd + S2 × SGd + S3 × SGd + S4 × SGd + S5 × SGd) - 2J2(S1 × S2 + S2 × S3 + S3 × S4 + S4 × S1 + S5 × S1. The best fit corresponded to J1 = +0.60(2) cm(-1), J2 = -61.0(5) cm(-1) and zJ' = -0.035(4) cm(-1). Complex 1 is the first example of a 15-metallacrown-5 system, for which numerical values of exchange parameters have been reported. The isotherm for methanol absorption by compound 1 at 293 K was typical for microporous sorbents, whereas ethanol sorption was negligibly small.

Magnetocaloric effect in 1D-polymers bearing 15-metallacrown-5 {GdCu5}3+ units and anionic oxalate complexes.

Two complexes {[GdCu5(GlyHA)5(H2O)7Cr(C2O4)3]·11.02H2O}n (1) and {{[GdCu5(GlyHA)5(H2O)6]µ2-[Cu(C2O4)2(H2O)]}2µ4-[Cu(C2O4)2]·15.8H2O}n (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu5(GlyHA)5}3+ 15-metallacrown-5 complex (where GlyHA2- = glycinehydroxamate) and the anionic oxalate complexes K3[Cr(C2O4)3] or K2[Cu(C2O4)2]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C2O4)3]3-, the Cu5 mean planes of neighboring 15-metallacrown-5 units {GdCu5(GlyHA)5}3+ are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions µ2-[Cu(C2O4)2(H2O)]2-, for one of which, coordination to two adjacent {GdCu5(GlyHA)5}3+ units leads to formation of linear 1D-chains in 2, while the second type, µ4-[Cu(C2O4)2]2-, is coordinated to four {GdCu5(GlyHA)5}3+ units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of χMT vs. T data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental χMT vs. T data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu5(GlyHA)5}3+ units and additionally Gd-Cr exchange interactions. Fitting of the χMT vs. T data for 2 was not possible, since coordination of µ4-[Cu(C2O4)2]2- to {GdCu5(GlyHA)5}3+ led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-ΔSM at 13 T reaches 24.26 J K-1 kg-1 at 5 K and 19.14 J K-1 kg-1 at 4 K for 1 and 2, respectively).

Iridium dihydroxybipyridine complexes show that ligand deprotonation dramatically speeds rates of catalytic water oxidation.

We report highly active iridium precatalysts, [Cp*Ir(N,N)Cl]Cl (1-4), for water oxidation that are supported by recently designed dihydroxybipyridine (dhbp) ligands. These ligands can readily be deprotonated in situ to alter the electronic properties at the metal; thus, these catalyst precursors have switchable properties that are pH-dependent. The pKa values in water of the iridium complexes are 4.6(1) and 4.4(2) with (N,N) = 6,6'-dhbp and 4,4'-dhbp, respectively, as measured by UV-vis spectroscopy. For homogeneous water oxidation catalysis, the sacrificial oxidant NaIO4 was found to be superior (relative to CAN) and allowed for catalysis to occur at higher pH values. With NaIO4 as the oxidant at pH 5.6, water oxidation occurred most rapidly with (N,N) = 4,4'-dhbp, and activity decreased in the order 4,4'-dhbp (3) > 6,6'-dhbp (2) ≫ 4,4'-dimethoxybipyridine (4) > bipy (1). Furthermore, initial rate studies at pH 3-6 showed that the rate enhancement with dhbp complexes at high pH is due to ligand deprotonation rather than the pH alone accelerating water oxidation. Thus, the protic groups in dhbp improve the catalytic activity by tuning the complexes' electronic properties upon deprotonation. Mechanistic studies show that the rate law is first-order in an iridium precatalyst, and dynamic light scattering studies indicate that catalysis appears to be homogeneous. It appears that a higher pH facilitates oxidation of precatalysts 2 and 3 and their [B(Ar(F))4](-) salt analogues 5 and 6. Both 2 and 5 were crystallographically characterized.

Bis[3-(anthracen-9-yl)pentane-2,4-dionato-κ2 O,O'](N,N-di-methyl-formamide-κO)[tris-(pyrazol-1-yl-κN 2)hydroborato]europium(III).

The title compound, [Eu(C9H10BN6)(C19H15O2)2(C3H7NO)] or [TpEu(Anthracac)2(DMF)], was synthesized by reaction of a tris-(pyrazol-yl)borate (Tp-) Eu3+ complex with 3-(anthracen-9-yl)pentane-2,4-dione (HAnthracac) in the presence of tri-ethyl-amine. In the title compound, Eu3+ is located in an octa-vertex square-pyramidal coordination environment. In the two Anthracac- ligands, the anthracene and nearly planar acetyl-acetonate fragments are almost orthogonal. Neighboring mol-ecules of TpEu(Anthracac)2(DMF) are connected in the crystal by inter-molecular van der Waals inter-actions, while π-stacking inter-actions are limited to the edges of two anthracene rings.

Chloro-cobalt complexes with pyridyl-ethyl-derived di-aza-cyclo-alkanes.

Syntheses are described for the blue/purple complexes of cobalt(II) chloride with the tetra-dentate ligands 1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine (Ppz), 1,4-bis-[2-(pyridin-2-yl)eth-yl]homopiperazine (Phpz), trans-2,5-dimethyl-1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine (Pdmpz) and tridentate 4-methyl-1-[2-(pyridin-2-yl)eth-yl]homopiperazine (Pmhpz). The CoCl2 complexes with Ppz, namely, {µ-1,4-bis-[2-(pyridin-2-yl)eth-yl]piperazine}bis-[di-chlorido-cobalt(II)], [Co2Cl4(C18H24N4)] or Co2(Ppz)Cl4, and Pdmpz (structure not reported as X-ray quality crystals were not obtained), are shown to be dinuclear, with the ligands bridging the two tetra-hedrally coordinated CoCl2 units. Co2(Ppz)Cl4 and {di-chlorido-{4-methyl-1-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}cobalt(II) [CoCl2(C13H21N3)] or Co(Pmhpz)Cl2, crystallize in the monoclinic space group P21/n, while crystals of the penta-coordinate mono-chloro chelate 1,4-bis-[2-(pyr-id-in-2-yl)eth-yl]piperazine}chlorido-cobalt(II) perchlorate, [CoCl(C18H24N4)]ClO4 or [Co(Ppz)Cl]ClO4, are also monoclinic (P21). The complex {1,4-bis-[2-(pyridin-2-yl)eth-yl]-1,4-di-aza-cyclo-hepta-ne}di-chlorido-cobalt(II) [CoCl2(C19H26N4)] or Co(Phpz)Cl2 (P ) is mononuclear, with a penta-coordinated CoII ion, and entails a Phpz ligand acting in a tridentate fashion, with one of the pyridyl moieties dangling and non-coordinated; its displacement by Cl- is attributed to the solvophobicity of Cl- toward MeOH. The penta-coordinate Co atoms in Co(Phpz)Cl2, [Co(Ppz)Cl]+ and Co(Pmhpz)Cl2 have substantial trigonal-bipyramidal character in their stereochemistry. Visible- and near-infrared-region electronic spectra are used to differentiate the two types of coordination spheres. TDDFT calculations suggest that the visible/NIR region transitions contain contributions from MLCT and LMCT character, as well as their expected d-d nature. For Co(Pmhpz)Cl2 and Co(Phpz)Cl2, variable-temperature magnetic susceptibility data were obtained, and the observed decreases in moment with decreasing temperature were modelled with a zero-field-splitting approach, the D values being +28 and +39 cm-1, respectively, with the S = 1/2 state at lower energy.

Structural trends in a series of isostructural lanthanide-copper metallacrown sulfates (Ln(III) = Pr, Nd, Sm, Eu, Gd, Dy and Ho): hexaaquapentakis[µ3-glycinehydroxamato(2-)]sulfatopentacopper(II)lanthanide(III) heptaaquapentakis[µ3-glycinehydroxamato(2-)]sulfatopentacopper(II)lanthanide(III) sulfate hexahydrate.

The seven isostructural complexes, [Cu(5)Ln(C(2)H(4)N(2)O(2))(5)(SO(4))(H(2)O)(6.5)](2)(SO(4))·6H(2)O, where Ln(III) = Pr, Nd, Sm, Eu, Gd, Dy and Ho, are representatives of the 15-metallacrown-5 family. Each dianion of glycinehydroxamic acid (GlyHA) links two Cu(II) cations forming a cyclic [CuGlyHA](5) frame. The Ln(III) cations are located at the centre of the [CuGlyHA](5) rings and are bound by the five hydroxamate O atoms in the equatorial plane. Five water molecules are coordinated to Cu(II) cations, and one further water molecule, located close to an inversion centre between two adjacent [Cu(5)Ln(GlyHA)(5)](2+) cations, is disordered around this inversion centre and coordinated to a Cu(II) cation of either the first or second metallacrown ether. Another water molecule and one of the two crystallographically independent sulfate anions are coordinated, the latter in a bidentate fashion, to the Ln(III) cation in the axial positions. The second sulfate anion is not coordinated to the cation, but is located in an interstitial position on a crystallographic inversion centre, thus leading to disorder of the O atoms around the centre of inversion. The Ln-O bond distances follow the trend of the lanthanide contraction. The apical Ln-O bond distances are very close to the sums of the ionic radii. However, the Ln-O distances within the metallacrown units are slightly compressed and the Ln(III) cations protrude significantly from the plane of the otherwise flat metallacrown ligand, thus indicating that the cavity is somewhat too small to accommodate the Ln(III) ions comfortably. This effect decreases with the size of the lanthanide cation from complex (I) (Ln(III) = Pr; 0.459) to complex (VII) (Ln(III) = Ho; 0.422), which indicates that the smaller lanthanide cations fit the cavity of the pentacopper metallacrown ring better than the larger ones. The diminished contraction of Ln-O distances within the metallacrown planes leads to an aniostropic contraction of the unit-cell parameters, with a, c and V following the trend of the lanthanide contraction. The b axes, which are mostly aligned with the rigid planes of the metallacrown units, show only a little variation between the seven compounds.

Crystal structure of a TbIII-CuII glycine-hydroxamate 15-metallacrown-5 sulfate complex.

The core of the title complex, bis-[hexa-aqua-hemi-aqua-penta-kis-(µ3-glycine-hydroxamato)sulfato-penta-copper(II)terbium(III)] sulfate hexa-hydrate, [TbCu5(SO4)(GlyHA)5(H2O)6.5]2(SO4)·6H2O (1), which belongs to the 15-metalla-crown-5 family, consists of five glycine-hydroxamate dianions (GlyHA2-; C2H4N2O2) and five copper(II) ions linked together forming a metallamacrocyclic moiety. The terbium(III) ion is connected to the centre of the metallamacrocycle through five hydroxamate oxygen atoms. The coordination environment of the Tb3+ ion is completed to an octa-coordination level by oxygen atoms of a bidentate sulfate and an apically coordinated water mol-ecule, while the copper(II) atoms are square-planar, penta- or hexa-coordinate due to the apical coordination of water mol-ecules. Continuous shape calculations indicate that the coordination polyhedron of the Tb3+ ion in 1 is best described as square anti-prismatic. The positive charge of each pair of [TbCu5(GlyHA)5(H2O)6.5(SO4)]2 2+ fragments is compensated by a non-coordinated sulfate anion, which is located on an inversion center with 1:1 disordered oxygen atoms. Complex 1 is isomorphous with the previously reported compounds [LnCu5(GlyHA)5(SO4)(H2O)6.5]2(SO4), where Ln III = Pr, Nd, Sm, Eu, Gd, Dy and Ho.

The metamorphosis of heterometallic trinuclear antiferromagnetic complexes into nano-sized superparamagnetic spinels.

Thermal decomposition of the trinuclear heterometallic oxoacetates [Fe(2)M(µ(3)-O)(CH(3)COO)(6)(H(2)O)(3)] has been used as a single-precursor method for synthesis of the spinel-structured ternary oxides MFe(2)O(4) (M = Mn(II), Co(II), and Ni(II)). This facile process occurring at 320 °C results in the formation of nanocrystalline, (7-20 nm) highly pure stoichiometric ferrites in quantitative yield. The magnetic properties of these nanoparticulate ferrites were studied in the 10-300 K temperature range, revealing superparamagnetic behaviour for the Ni and Mn particles and ferromagnetic behavior for the Co ones at room temperature. Their blocking temperatures follow the order: CoFe(2)O(4) > MnFe(2)O(4) > NiFe(2)O(4).

Combination of single-molecule magnet behaviour and luminescence properties in a new series of lanthanide complexes with tris(pyrazolyl)borate and oligo(ß-diketonate) ligands.

A series of tris(pyrazolyl)borate mono-, di- and trinuclear complexes, [Tp2Ln]nX (Ln = Eu, Tb, Gd, Dy, Xn- = various mono-, bis- and tris(ß-diketonates) has been prepared. The Tb3+ and Dy3+ complexes are luminescent single molecular magnets (SMM) and exhibit luminescence quantum efficiencies up to 73% for the Tb3+ and 4.4% for the Dy3+ compounds. Similar Eu3+ complexes display bright emission only at lower temperatures. The Dy3+ and Tb3+ complexes possess SMM behavior in a non-zero dc field at low temperatures, while the polynuclear Dy3+ complexes also show slow magnetic relaxation even in zero dc field up to 8 K. Ueff-values determined from dynamic magnetic measurements were up to 31 and 6 cm-1 for the Dy3+ and Tb3+ complexes, respectively. It was found that within a series of Dy3+ and Tb3+ compounds, Ueff and luminescence quantum yields decreased with increasing nuclearity of the compounds and a shortening of the intramolecular Ln-Ln distance. ΔOrbach-values estimated from low-temperature luminescence spectra were significantly higher than those obtained from ac magnetic data, which may be due to involvement of additional processes in the relaxation mechanism (quantum tunneling, Raman, direct) reducing the energy barrier. Some of the Tb3+-compounds also display metal-centred electroluminescence, giving them potential as emitting layers in LEDs.

The crystal structures of {LnCu5}3+ (Ln = Gd, Dy and Ho) 15-metallacrown-5 complexes and a reevaluation of the isotypic EuIII analogue.

Three new isotypic heteropolynuclear complexes, namely penta-aqua-carbonato-penta-kis-(glycinehydroxamato)nitrato-penta-copper(II)lanthanide(III) x-hydrate, [LnCu5(GlyHA)5(CO3)(NO3)(H2O)5]·xH2O (GlyHA2- is glycine-hydrox-amate, N-hy-droxy-glycinamidate or amino-aceto-hydroxamate, C2H4N2O2 2-), with lanthanide(III) (Ln III) = gadolinium (Gd, 1, x = 3.5), dysprosium (Dy, 2, x = 3.28) and holmium (Ho, 3, x = 3.445), within a 15-metallacrown-5 class were obtained on reaction of lanthanide(III) nitrate, copper(II) acetate and sodium glycinehydroxamate. Complexes 1-3 contain five copper(II) ions and five bridging GlyHA2- anions, forming a [CuGlyHA]5 metallamacrocyclic core. The Ln III ions are coordinated to the metallamacrocycle through five O-donor hydroxamates. The electroneutrality of complexes 1-3 is achieved by a bidentate carbonate anion coordinated to the Ln III ion and a monodentate nitrate anion coordinated apically to one of the copper(II) ions of the metallamacrocycle. The lattice parameters of complexes 1-3 are similar to those previously reported for an EuIII-CuII 15-metallacrown-5 complex with glycine-hydroxamate of proposed composition [EuCu5(GlyHA)5(OH)(NO3)2(H2O)4]·3.5H2O [Stemmler et al. (1999 ▸). Inorg. Chem. 38, 2807-2817]. High-quality X-ray data obtained for 1-3 have allowed a re-evaluation of the X-ray data solution proposed earlier for the EuCu5 complex and suggest that the formula is actually [EuCu5(GlyHA)5(CO3)(NO3)(H2O)5]·3.5H2O.

Absorption- and Excitation-Modulated Luminescence of Pr3+, Nd3+, and Lu3+ Compounds with Dianions of Tetrafluoroterephthalic and Camphoric Acids.

The luminescence of coordination polymers of Pr3+, Nd3+, and Lu3+ with tetrafluoroterephthalate and camphorate, [Ln2(Fbdc)3(DMF)2(H2O)]2 (Ln = Pr, Nd, Lu) and [Ln2(Camph)2(NO3)2(MeOH)]4 (Ln = Pr, Nd, Lu), was studied. Ligand-centered and/or metal-centered emissions appear, which depend on the excitation wavelength, ultimately allowing the emitted light color to be adjusted. Low-efficiency ligand-to-metal energy transfer leads to a difference between the excitation spectra of the tetrafluoroterephthalate- and camphorate-Pr3+ compounds, arising from a primary filtering effect on the ligand-centered excitation, by Pr3+ absorption. A secondary inner filter effect significantly changes the shape of the luminescence band, allowing a wide variation in the emission color, producing, for instance, a purple color, which is not the normal spectral emission. The low-efficiency energy transfer renders tetrafluoroterephthalate and camphorate ineffective as traditional "antenna" ligands for Pr3+ and Nd3+.

Crystal structure of bis-(pivaloyl-hydroxamato-κ2O,O')copper(II).

Reaction of copper(II) nitrate with pivaloyl-hydroxamic acid yielded the title compound, [Cu(pivHA)2] (where pivHA- is pivaloyl hydroxamate, C5H10NO2). The centrosymmetric mononuclear complex consists of a CuII ion, which is located on a center of inversion, with two coordinated pivaloyl hydroxamate monoanions. The CuII ion has a square-planar coordination environment consisting of four O atoms - two carbonyl O atoms and two hydroxamate O atoms from two hydroxamate pivHA- ligands. The pivHA- anions are coordinated to copper(II) in a trans-mode, forming two five-membered O,O'-chelate rings.

Crystal structure of (2,2'-bipyrid-yl)[2,6-bis-(1-butyl-1H-benzimidazol-2-yl)pyridine]-chlorido-iridium(III) tri-fluoro-methane-sulfonate.

The title complex compound, [Ir(C27H29N5)Cl(C10H8N2)](CF3SO3)2, was synthesized for a study of iridium(III)/periodate redox systems in water. The coordination geometry of the complex can be best described as distorted octa-hedral, with an r.m.s. deviation of 8.8 (8)% from ideal octa-hedral rectangular geometry. In the crystal, C-H⋯O and C-H⋯F inter-actions between the complex cation and the tri-fluoro-methane-sulfonate anions are observed, as well as a C-H⋯Cl inter-molecular inter-action between neighboring complex cations. In addition, the benzimidazole ring systems display parallel-displaced π-π stacking with centroid-centroid distances of 3.585 (3)-3.907 (3) Å. One of the two tri-fluoro-methane-sulfonate anions is disordered over two orientations with an occupancy ratio of 0.582 (6):0.418 (6). The title complex was characterized using FT-IR, cyclic voltammetry/rotating disc electrode polarography, fluorescence spectrometry, high resolution mass spectrometry, CHN elemental analysis and 1H NMR spectroscopy.

Crystal structures and intense luminescence of tris(3-(2'-pyridyl)-pyrazolyl)borate Tb3+ and Eu3+ complexes with carboxylate co-ligands.

A series of brightly luminescent new mononuclear TpPyLn(An)2(H2O) (where An- = carboxylate anion, Ln = Eu or Tb and TpPy- = tris(3-(2'-pyridyl)pyrazolyl)borate) and dinuclear (TpPyLn)2pma(MeOH)2 (Ln = Eu, Tb, pma4- = tetraanion of pyromellitic acid) complexes were prepared and characterized by X-ray crystallography. Within each series the compounds possess similar molecular structures, which differ only by the nature of the carboxylate anions. The quantum efficiencies for metal-centered emission of the complexes were up to 29(3)% for Eu3+ and 53(5)% for the Tb3+ compounds and significantly depend on the electronic structure of the additional ligand (i.e. the carboxylate). The aliphatic carboxylate compounds' luminescence quantum yields were all similar, but different from those for the aromatic ones. The complexes with trifluoroacetate and pentafluorobenzoate unexpectedly displayed lower quantum efficiencies compared to those with the corresponding non-fluorinated analogues. Energy transfer from Tb3+ to Eu3+ occurs in a mixture of (TpPyEu)(pma)(TbTpPy)(MeOH)2, (TpPyEu)2(pma)(MeOH)2 and (TpPyTb)2(pma)(MeOH)2 but is not very efficient. The Tb3+-compounds displayed green electroluminescence, and both the Eu3+ and Tb3+ complexes exhibited bright metal-centered red (Eu3+) or green (Tb3+) triboluminescence.

New homodinuclear tris(3-alkylpyrazolyl)borate complexes of CoII and NiII with a tetraacetylethane dianion as a bridging ligand.

Polynuclear complexes and coordination polymers of 3d metals have attracted significant interest evoked by a number of their unique properties. One of the most common approaches to the directed synthesis of coordination polymers is the linking of pre-prepared discrete coordination units by polydentate ligands. The formation of polynuclear complexes is usually a spontaneous process and precise prediction of the products of such reactions is virtually impossible in most cases. Tris(pyrazolyl)borates (Tp) act as tripodal `capping' ligands which form stable complexes with 3d metal ions. In such 1:1 compounds, three metal-ion coordination sites are occupied by N atoms from a Tp anion. This limits the number of remaining coordination sites, and thus the number of additional ligands which may coordinate, and opens an attractive approach for the directed design of desirable structures by exploiting ligands with appropriate composition and topology. In the present study, Tp anions with neopentyl [TpNp, tris(3-neopentylpyrazolyl)borate] and cyclohexyl [TpCy, tris(3-cyclohexylpyrazolyl)borate] substituents were used as `capping' ligands and the dianion of tetraacetylethane (3,4-diacetylhexa-2,4-diene-2,5-diolate, tae2-) was employed as a bridge. The dinuclear complexes (µ-3,4-diacetylhexa-2,4-diene-2,5-diolato-κ4O2,O3:O4,O5)bis{[tris(3-cyclohexyl-1H-pyrazol-1-yl-κN2)borato]cobalt(II)} acetonitrile disolvate, [Co2(C27H40BN6)2(C10H12O4)]·2CH3CN, (I)·2CH3CN, and (µ-3,4-diacetylhexa-2,4-diene-2,5-diolato-κ4O2,O3:O4,O5)bis{[tris(3-neopentyl-1H-pyrazol-1-yl-κN2)borato]nickel(II)}, [Ni2(C24H40BN6)2(C10H12O4)], (II), were synthesized by the reaction of the mononuclear complexes TpCyCoCl or TpNpNiCl with H2tae (3,4-diacetylhexane-2,5-dione or tetraacetylethane) in the presence of NEt3 as base. Compounds (I) and (II) were characterized by mass spectrometry, elemental analysis, and X-ray crystallography. They possess similar molecular structures, X-ray diffraction revealing them to be dinuclear in nature and composed of discrete Tp-M units in which two metal ions are linked by a tae2- dianion. Each metal ion possesses a five-coordinate square-pyramidal environment. The interplanar angles between the acetylacetonate fragments are significantly smaller than the near-90° values commonly observed.

Autoxidation of Reduced Horse Heart Cytochrome c Catalyzed by Cardiolipin-Containing Membranes.

Visible circular dichroism, absorption, and fluorescence spectroscopy were used to probe the binding of horse heart ferrocytochrome c to anionic cardiolipin (CL) head groups on the surface of 1,1',2,2'-tetraoleoyl cardiolipin (TOCL)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) (20%:80%) liposomes in an aerobic environment. We found that ferrocytochrome c undergoes a conformational transition upon binding that leads to complete oxidation of the protein at intermediate and high CL concentrations. At low lipid concentrations, the protein maintains a structure that is only slightly different from its native one, whereas an ensemble of misligated predominantly hexacoordinated low-spin states become increasingly populated at high lipid concentrations. A minor fraction of conformations with either high- or quantum-mixed-spin states were detected at a CL to protein ratio of 200 (the largest one investigated). The population of the non-native state is less pronounced than that found for cytochrome c-CL interactions initiated with oxidized cytochrome c. Under anaerobic conditions, the protein maintains its reduced state but still undergoes some conformational change upon binding to CL head groups on the liposome surface. Our data suggest that CL-containing liposomes function as catalysts by reducing the activation barrier for a Fe2+ → O2 electron transfer. Adding NaCl to the existing cytochrome-liposome mixtures under aerobic conditions inhibits protein autoxidation of ferrocytochrome c and stabilizes the reduced state of the membrane-bound protein.

Crystal structure of 5,7,12,14-tetra-hydro-5,14:7,12-bis-([1,2]benzeno)-penta-cene-6,13-dione.

The lattice of 5,7,12,14-tetra-hydro-5,14:7,12-bis-([1,2]benzeno)-penta-cene-6,13-dione, C34H20O2, at 173 K has triclinic (P-1) symmetry and crystallizes with four independent half-mol-ecules in the asymmetric unit. Each mol-ecule is generated from a C17H10O substructure through an inversion center at the centroid of the central quinone ring, generating a wide H-shaped mol-ecule, with a dihedral angle between the mean planes of the terminal benzene rings in each of the two symmetry-related pairs over the four mol-ecules of 68.6 (1) (A), 65.5 (4) (B), 62.3 (9) (C), and 65.8 (8)° (D), an average of 65.6 (1)°. This compound has applications in gas-separation membranes constructed from polymers of intrinsic microporosity (PIM). The title compound is a product of a double Diels-Alder reaction between anthracene and p-benzo-quinone followed by de-hydrogenation. It has also been characterized by cyclic voltammetry and rotating disc electrode polarography, FT-IR, high resolution mass spectrometry, elemental analysis, and 1H NMR.

A new class of macrocyclic complexes formed via nickel-promoted macrocyclisation of dioxime with dinitrile.

o-Phthalonitrile couples with chelating dioxime on nickel(II), with formation of a dinuclear nickel(II) macrocyclic complex--the first representative of a new class of imine-appended macrocycles.