Karl S. Hagen

Iron coordination chemistry with tetra-, penta- and hexadentate bispidine-type ligands

Described is the synthesis of tetra-, penta- and hexadentate bispidine ligands with two tertiary amine and two, three or four additional donors (pyridine, phenolate or alcoholate; bispidine/3,7-diazabicyclo[3.3.1]nonanone, coordinating substituents at positions 2,4; 2,4,7; 2,3,4; 2,3,4,7) and of their hexa-coordinate iron(II) complexes. Crystal structural analyses reveal that all complexes are six-coordinate, with one or two co-ligands, and all structures with the tetradentate bispidine ligand are asymmetrical with respect to the two tertiary amine donors, with short Fe� /N 1 and long Fe� /N 2 bonds (N 1 : position 3, N 2 : position 7). This is the same structural type as found for the Jahn/Teller labile copper(II) compounds, the manganese(II) and chromium(III) complexes but different from copper(I), zinc(II) and some cobalt(II) complexes with M � /N 1 ]/M � /N 2 . Additional donors at N 2 modify the structures, but do not lead to a change to the other structural type; additional donors at N 1 lead to structures with M� /N 1 � /M� /N 2 . Solution studies (NMR, UV/Vis, electrochemistry, magnetism) indicate that the co-ligands may be substituted by solvent, with the donors trans to N 2 being more labile than those trans to N 1 , but the over-all structural properties in solution are similar to those in the solid state. The complexes are stable towards oxidation, all except one have high spin electronic configuration. The oxidation potentials strongly depend on the two co-ligands. # 2002 Elsevier Science B.V. All rights reserved.

Intensely Colored Mixed-Valence Iron(II) Iron(III) Formate Analogue of Prussian Blue Exhibits Néel N-Type Ferrimagnetism

The reaction of colorless iron(II) formate or the mixed-valence cluster Fe(3)O(MeCOO)(6)(H(2)O)(3) with formic acid in dimethylformamide exposed to air at 110 degrees C affords black crystals of the mixed-valence (Me(2)NH(2))[Fe(II)Fe(III)(HCOO)(6)] three-dimensional (3D) structure in which the cations occupy half of the channels. The structure consists of alternating layers of Fe(II)O(6) [Fe(1)-O(1), 2.119(1) A] and Fe(III)O(6) [Fe(2)-O(2), 2.0049(9) A] octahedra bridged by anti-anti-bonded formates to afford an open-framework 3D structure. The structure is very similar to those of (Me(2)NH(2))[Fe(II)(HCOO)(3)] and [Fe(III)(HCOO)(3)].HCOOH, both of which are colorless. The black crystals appear dark-purple (lambda(max) approximately 520 nm) when powdered. The room-temperature Mössbauer spectrum confirms the 1:1 ratio of Fe(II) (delta = 1.03 mm/s, DeltaE(Q) = 1.16 mm/s) and Fe(III) (delta = 0.62 mm/s, DeltaE (Q) = 0.49 mm/s). Magnetic ordering that includes negative magnetization at low fields occurs at low temperature. The only molecular-based magnetic materials in which this phenomenon has been observed are the 2D polyiron(II,III) oxalates A[Fe(II)Fe(III)(C(2)O(4))(3)] (A = R(4)N(+) cation).

Pentadecavanadate, V15O429–, a new highly condensed fully oxidized isopolyvanadate with kinetic stability in water

The X-ray structure of the new fully oxidized isopolyvanadate, (TMA)3H6VV15O42·2.5H2O 1(TMA = tetramethyl-ammonium), prepared by reaction of H2O2 with VOSO4·4H2O shows a bicapped Keggin structure with four-, five- and six-coordinate vanadium atoms; 51V NMR indicates that the same structure has considerable kinetic stability in water at ca. pH 3.5 but is thermodynamically unstable with respect to the conventional VV10O286– structure.

In situ probe of photocarrier dynamics in water-splitting hematite (α-Fe2O3) electrodes

The spectra and dynamics of photogenerated electrons and holes in excited hematite (α-Fe2O3) electrodes are investigated by transient absorption (from visible to infrared and from femto- to micro-seconds), bias-dependent differential absorption and Stark spectroscopy. Comparison of results from these techniques enables the assignment of the spectral signatures of photogenerated electrons and holes. Under the pulse illumination conditions of transient absorption (TA) measurement, the absorbed photon to electron conversion efficiency (APCE) of the films at 1.43 V (vs. reversible hydrogen electrode, RHE) is 0.69%, significantly lower than that at AM 1.5. TA kinetics shows that under these conditions, >98% of the photogenerated electrons and holes have recombined by 6 μs. Although APCE increases with more positive bias (from 0.90 to 1.43 V vs. RHE), the kinetics of holes up to 6 μs show negligible change, suggesting that the catalytic activity of the films is determined by holes with longer lifetimes.

A copper(I) oxygenation precursor in the entatic state: two isomers of a copper(I) compound of a rigid tetradentate ligand

Oxygenation of [CuI(L1)(NC-CH3)]+ (L1 = dimethyl 2,4-bis(2-pyridinyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate) leads to a relatively stable mu-peroxo-dicopper(II) product. The stability of this type of oxygenation product has been shown before to be the result of the square pyramidal geometry of L1; preorganization by a dinucleating ligand has been shown to increase the stability of the mu-peroxo-dicopper(II) compound. The structural data presented here indicate that destabilization of the copper(I) precursor is another important factor. There are two isomers of [CuI(L1)(NCCH3)]+; one is yellow, and the other is red. X-ray crystallography indicates that one pyridinyl donor is not coordinated in the yellow compound and that the red compound is 5-coordinate. In the light of the X-ray structure of the metal-free ligand and that of the corresponding copper(II) compound, it emerges that the ligand cavity is well suited for copper(II), whereas the copper(I) compounds are highly strained. This is supported by 1H NMR spectra of the copper(I) species where a fast dynamic process leads to line broadening and by electrochemical data, which indicate that the copper(II) products are exceptionally stable. Also presented are structural (copper(II)), electrochemical, and spectroscopic data (1H NMR, copper(I)) of the derivative [Cu(L2)(X)]n+ with a methyl substituent at the alpha-carbon atom of the two coordinated pyridinyl groups (L2 = dimethyl 2,4-bis(2-pyridinyl-6-methyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate). There are two structural forms of [CuII(L2)(X)]n+ (X = NCCH3, Cl), which depend on the steric demand of the fifth donor X. For both, van der Waals repulsion leads to a destabilization of the copper(II) products, and this is also evident from an increase in the reduction potential (-110 mV vs. -477 mV, Ag/AgNO3).

Site-specific ligand variation in manganese–oxide cubane complexes, and unusual magnetic relaxation effects in [Mn4O4X(OAc)3(dbm)3](X = N3–, OCN– Hdbm = dibenzoylmethane)

Treatment of [Mr4O2(OAc)6(py)2(dbm)2]1(py = pyridine, Hdbm = dibenzoylmethane) in hot MeCN with Me3SiX (X = N3–, OCN –) yields [Mn4O3X(OAc)3(dbm)3] containing extremely rare η1, µ3-N3– or -OCN– groups; alternating-current magnetic susceptibility studies reveal unusual magnetic relaxation effects and indicate these species to be the newest and smallest examples yet of truly molecular magnets.

Synthesis and characterization of a polyvanadate polyester involving a monodentate alcohol, [(n-C4H9)4N][V6O12(OCH3)7]

Abstract Polyvanadates are of interest in conjunction with new materials and catalysis, sensor technology, and enzymology. We report here the preparation, X-ray structure and other properties of the new compound, heptamethoxyhexavanadate, [V6O12(OCH3)7]− (1). Crystalline (n-Bu4N)[V6O12(OCH3)7] (a=10.184(4), b=12.742(4), c=17.148(5) A, α=72.62(3), β=73.42(3), γ=70.92(3)°, Z=2, space group=P 1 ) contains a total of seven μ2-(OCH3) groups with one of the OCH3 groups having two-fold disorder in the solid state. NMR on three nuclei (1H, 13C and 51V) confirm that 1 retains the solid state structure in anhydrous acetonitrile solution at 25 °C. 1 has a quite positive potential: Ef=Epc+Epa/2=−0.344 V versus Fc+/Fc (Epc−Epa=78 mV; n=1 electron).

Analogues of the [Fe4S4]+ sites of reduced ferredoxins: single-step synthesis of the clusters [Fe4S4(SR)4]3− and examples of compressed tetragonal core structures

Determination des structures cristallines des complexes (Et 4 N) 3 [Fe 4 S 4 (S-t-Bu) 4 ].MeCN et (Me 4 N) 3 [Fe 4 S 4 (SEt) 4 ]. Les deux composes presentent des geometries similaires de leur cœur central [Fe 4 S 4 ] +

Combining microarray-based genomic selection (MGS) with the Illumina Genome Analyzer platform to sequence diploid target regions.

Novel methods of targeted sequencing of unique regions from complex eukaryotic genomes have generated a great deal of excitement, but critical demonstrations of these methods efficacy with respect to diploid genotype calling and experimental variation are lacking. To address this issue, we optimized microarray‐based genomic selection (MGS) for use with the Illumina Genome Analyzer (IGA). A set of 202 fragments (304 kb total) contained within a 1.7 Mb genomic region on human chromosome X were MGS/IGA sequenced in ten female HapMap samples generating a total of 2.4 GB of DNA sequence. At a minimum coverage threshold of 5X, 93.9% of all bases and 94.9% of segregating sites were called, while 57.7% of bases (57.4% of segregating sites) were called at a 50X threshold. Data accuracy at known segregating sites was 98.9% at 5X coverage, rising to 99.6% at 50X coverage. Accuracy at homozygous sites was 98.7% at 5X sequence coverage and 99.5% at 50X coverage. Although accuracy at heterozygous sites was modestly lower, it was still over 92% at 5X coverage and increased to nearly 97% at 50X coverage. These data provide the first demonstration that MGS/IGA sequencing can generate the very high quality sequence data necessary for human genetics research.

Spectroscopic Properties and Molecular Structure of 1,3-Dimethyl-2-(Se, Se-dibromoseleno)-2(3H)-imidazolylidene

Oxidative addition of Br2 to 1,3-dimethyl-2(3H)-imidazoleselone results in a compound that can be viewed as a Se(II) bromide complex with a stabilized imidazolylidene ring as verified by X-ray crystallography. The structure consists of dimeric pairs containing nearly linear Br-Se-Br units bonded through carbon to planar imidazolyidene rings at torsion angles of 91.4° for N1-C1-Se1-Br1 and 76.8° for N3-C6-Se2-Br4. Significant intermolecular contacts between dimeric units are seen through short Se–Se [3.494(1) A] and Se1–Br4 bridging [3.509(1) A]. Solution state Raman data show the characteristic peaks for a linear Br-Se-Br moiety with a strong polarized peak at 158 cm−1 and a weak shoulder at 181 cm−1 corresponding to the symmetric and asymmetric Br-Se-Br stretching modes respectively. In the absence of X-ray data, correlation of structure to vibrational data provides further support for structural speculations in other compounds with the linear SeBr2 grouping. Crystal structure data for C5H8N2Br2Se. Cell ...