Metal-containing monomers. Part 1. Spatial and electronic structures of cobalt(II) and nickel(II) complexes with acrylamide and of their polymers

Summary The spatial and electronic structures of the complexes [Co(AAm)₄(H₂O)₂](NO₃)₂ (1), Co(AAm)₄Cl₂ (2), [Ni(AAm)₄(H₂O)₂](NO₃)₂ (3) and Ni(AAm)₄Cl₂ (4), where AAm is acrylamide, and the products of their radical, frontal and post-grafting polymerization have been studied by electronic spectroscopy. The complexes (1), (3) and (4) were found to have pseudooctahedral structures in both the solid and solution phases. A change in the spatial structure of complex (2) was established in going from the crystal (tetragonally distorted octahedral) to solution (tetrahedral). The coordination environment of the metal centre does not change markedly during polymerization of the metal-containing monomers.     

Models of the low-spin iron(III) hydroperoxide intermediate of heme oxygenase: magnetic resonance evidence for thermodynamic stabilization of the d(xy) electronic state at ambient temperatures

The (13)C pulsed ENDOR and NMR study of [meso-(13)C-TPPFe(OCH(3))(OO(t)Bu)](-) performed in this work shows that although the unpaired electron in low-spin ferrihemes containing a ROO(-) ligand resides in a d(pi) orbital at 8 K, the d(xy) electron configuration is favored at physiological temperatures. The variable temperature NMR spectra indicate a dynamic situation in which a heme with a d(pi) electron configuration and planar porphyrinate ring is in equilibrium with a d(xy) electron configuration that has a ruffled porphyrin ring. Because of the similarity in the EPR spectra of the hydroperoxide complexes of heme oxygenase, cytochrome P450, and the model heme complex reported herein, it is possible that these two electron configurations and ring conformations may also exist in equilibrium in the enzymatic systems. The ruffled porphyrinate ring would aid the attack of the terminal oxygen of the hydroperoxide intermediate of heme oxygenase (HO) on the meso-carbon, and the large spin density at the meso-carbons of a d(xy) electron configuration heme suggests the possibility of a radical mechanism for HO. The dynamic equilibrium between the ruffled (d(xy)) and planar (d(pi)) conformers observed in the model complexes also suggests that a flexible heme binding cavity may be an important structural motif for heme oxygenase activity.     

A practical, fast, and high-yielding aziridination procedure using simple Cu(II) complexes containing N-donor pyridine-based ligands

Four-coordinate dichlorocopper(II) complexes derived from di(2-pyridyl)methanes or pyridine itself exhibit high catalytic activity in aziridination of regular olefins with PhINTs in weakly coordinating chloroform in the presence of 1-2 equiv of NaBArF4 (BArF4- = tetra[3,5-di(trifluoromethyl)phenyl]borate). High yields of aziridines exceeding 90% can be obtained with a 1:1 olefin/PhINTs ratio and 1-5 mol % catalyst loading for such reactive olefins as styrene, tri- and tetramethylethylene. For cis-cyclooctene, indene, methyl acrylate, methyl methacrylate, vinyl methyl ketone, tert-butylethylene, and neopentylethylene, as well as for 1-hexene and cyclopentene, yields of corresponding aziridines vary from 44% to 83%. The catalytic activity and efficiency of the reported copper complexes decrease moderately in the absence of NaBArF4.     

über eine Klasse Riemannscher Mannigfaltigkeiten mit raumartigen pkf-ZusammenhÄngen

One considers m-dimensional Riemannian manifoldsM with tangent spaces T_p(M), p M that are a direct sum of a spacelike m-2 planeR _p and a 2-planeH _p. It is supposed that onM there exists a connection whose space-like components are parallel conformal flat (pkf). These components are generated by a vector field X. Assuming that X belongs to a pair X,Y of reciprocal quasi-cocircular vector fields and that the Pfaffian of this pair is the 1-form associated with the connection, the following results are derived: 1. X and Y are of equal constant length (This is true for all Riemannian manifolds). 2. The immersion of the integral manifold ofH _p intoM is cylindrical and the normal connection is flat. 3. The immersion of any space-like submanifold intoM is cylindrical with respect to the sections inH _p and umbilical with respect to all spacelike sections. 4. If m 4, the integral manifoldP _p is flat.

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Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca     

Angular ligand constraint yields an improved olefin aziridination catalyst

[reaction: see text] The use of a pyridinophane, a macrocycle composed of three pyridines linked, via all ortho positions through CH(2) or CH(2)CH(2) groups, bound to copper, gives good performance (rate and yield) catalyzing the conversion of substituted aliphatic olefins and PhINTs to aziridines. Advantages also derive from using CH(2)Cl(2) solvent and the weakly coordinating anions BAr(4)(-) (Ar = C(6)H(5) or 3,5-C(6)H(3)(CF(3))(2)). Reactions are complete in minutes at 20 degrees C, and yields are almost quantitative for olefins not bearing secondary allylic CH bonds; however, cis-cyclooctene gives only the aziridine despite the allylic hydrogens.     

Influences of changes in multitopic tris(pyrazolyl)methane ligand topology on silver(I) supramolecular structures

The reactions between silver tetrafluoroborate and the ligands 1,2,4,5-C(6)H(2)[CH(2)OCH(2)C(pz)(3)](4) (L1, pz = pyrazolyl ring), o-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L2), and m-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (L3) yield coordination polymers of the formula (C(6)H(6)(-)(n)[CH(2)OCH(2)C(pz)(3)](n)(AgBF4)(m))( infinity ) (n = 4, m = 2, 1; n = 2, ortho substitution, m = 1, 2; meta substitution, m = 2, 3). In the solid state, L2 molecules dimerize by a pair of C-H.pi interactions, forming an arrangement that resembles the tetratopic ligand L1. In the solid-state structure of 1, each silver atom is kappa(2)-bonded to two tris(pyrazolyl)methane units from different ligands with the overall structure a polymer made up from 32-atom macrocyclic rings formed by bonding tris(pyrazolyl)methane groups from nonadjacent positions on the central arene rings to the same two silver atoms. In 2, each silver is bonded to two tris(pyrazolyl)methane units in the same kappa(2)-kappa(2) fashion as with 1, forming a polymer chain. The chains are organized into dimeric units by strong face-to-face pi-pi stacking between the central arene rings making bitopic L2 act as half of tetratopic L1. The chains in both structures are organized by weak C-H.F hydrogen bonds and pi-pi stacking interactions into very similar 3D supramolecular architectures. The structure of 3 contains three types of silvers with the overall 3D supramolecular sinusoidal structure comprised of 32-atom macrocycles. Infrared studies confirm the importance of the noncovalent interactions. Calculations at the DFT (B3LYP/6-31G) level of theory have been carried out on L2 and also support C-H.pi interactions. Electrospray mass spectral data collected from acetone or acetonitrile show the presence of aggregated species such as [(L)Ag(2)(BF(4))](+) and [(L)Ag(2)](2+), despite the fact that (1)H NMR spectra of all compounds show that acetonitrile completely displaces the ligand whereas acetone does not.     

Dynamical scaling of single chains on adsorbing substrates: diffusion processes

We study the dynamics of tethered chains of length N on adsorbing surfaces, considering the dilute case; for this we use the bond fluctuation model and scaling concepts. In particular, we focus on the mean-square displacement of single monomers and of the center of mass of the chains. The characteristic time tau of the fluctuations of a free chain in a good solvent grows as tau approximately N(a), where the coefficient a obeys a=2nu+1. We show that the same coefficient also holds at the critical point of adsorption. At intermediate time scales single monomers show subdiffusive behavior; this concurs with the behavior calculated from scaling arguments based on the dynamical exponent a. In the adsorbed state tau(perpendicular), the time scale for the relaxation in the direction perpendicular to the surface, becomes independent of N; tau(perpendicular) is then the relaxation time of an adsorption blob. In the direction parallel to the surface the motion is similar to that of a two-dimensional chain and is controlled by a time scale given by tau(parallel) approximately N(2nu(2)+1)L(-2Delta(nu/nu)), where nu(2) is the Flory exponent in two dimensions, nu is the Flory exponent in three dimensions, and Deltanu=nu(2)-nu. For the motion parallel to the surface we find dynamical scaling over a range of about four decades in time.     

Novel chiral three-dimensional iron(III) compound exhibiting magnetic ordering at T(c) = 40 K

The preparation and crystal structure determination of the iron(III) compound of formula [(NH(4))(2)[Fe(2)O(ox)(2)Cl(2)].2H(2)O](n) (1) (ox = oxalate dianion) are reported here. Complex 1 crystallizes in the orthorhombic system, space group Fdd2, with a = 14.956(7) A, b = 23.671(9) A, c = 9.026(4) A, and Z = 8. The structure of complex 1 consists of the chiral anionic three-dimensional network [Fe(2)O(ox)(2)Cl(2)](2-) where the iron(III) ions are connected by single oxo and bisbidentate oxalato groups. The metal-metal separations through these bridging ligands are 3.384(2) and 5.496(2) A, respectively. Ammonium cations and crystallization water molecules are located in the helical pseudohexagonal tunnels defined by iron atoms. The longest iron-iron distance in the pseudohexagonal tunnel is 15.778(2) A whereas the shortest one is 8.734(2) A. The iron atoms are hexacoordinated: a terminal chloro ligand and five oxygen atoms, that of the oxo group and four from two cis coordinated oxalate ligands, build a distorted octahedral environment around the metal atom. The Fe-O(oxo) bond distance [1.825(2) A] is significantly shorter than the Fe(III)-O(ox) [average value 2.103(4) A] and Fe(III)-Cl bond distances [2.314(2) A]. Magnetic susceptibility measurements of 1 in the temperature range 2.0-300 K reveal the occurrence of a susceptibility maximum at 195 K and a transition toward a magnetically ordered state in the lower temperature region with T(c) = 40 K. The strong antiferromagnetic coupling through the oxo bridge (J = -46.4 cm(-1), the Hamiltonian being H = -JS(A).S(B)) accounts for the susceptibility maximum whereas a weak spin canting of approximately 0.3 degrees due to the antisymmetric magnetic exchange within the chiral three-dimensional network is responsible for the magnetic ordering. The values of coercive field (H(c)) and remnant magnetization (M(r)) obtained from the hysteresis loop of 1 at 5 K are 4000 G and 0.016 micro(B).     

Efficient enantiomeric analysis of primary amines and amino alcohols by high-performance liquid chromatography with precolumn derivatization using novel chiral SH-reagent N-(R)-mandelyl-(S)-cysteine

Novel N-acylated-(S)-cysteine derivative-N-(R)-mandelyl-(S)-cysteine (R-NMC), containing additional chiral center, aromatic and polar alpha-substituents in contrast to the traditionally used enantiomerically pure thiols, has been demonstrated to be an efficient SH-reagent for enantiomeric HPLC analysis of primary nonfunctionalized amines and amino alcohols after precolumn derivatization with o-phthalaldehyde. The R-NMC-derived isoindoles as well as adducts formed using traditional SH-reagents had a characteristic absorption maximum at 340 nm with a molar absorbance 6000 M(-1) cm(-1), were stable during the HPLC-analysis and highly fluorescent allowing to detect 1 fmol of amino compound. Using diastereomeric R-NMC all tested amino alcohols were resolved effectively as well as nonfunctionalized amines, some of which were not resolved by a direct method on a chiral phase. Applying traditional enantiomeric N-acetyl-(S)-cysteine (NAC) only some isoindoles formed by aliphatic amino alcohols have been separated satisfactorily. The enhanced selectivity for R-NMC-derived isomers has been achieved, obviously, due to the involvement of the substituents at an extra chiral center into additional intramolecular interactions.     

High-resolution submicron patterning of self-assembled monolayers using a molecular fluorine laser at 157 nm

Using a molecular fluorine laser at 157 nm wavelength, submicron patterning of organosilane self-assembled monolayers (SAMs) is demonstrated utilizing mask-contact photolithography. An organosilane, namely, octadecyltrimethoxysilane [ODS, CH(3)(CH(2))(17)Si(OCH(3))(3)], SAM is chemisorbed onto Si substrates covered with a 2 nm thick oxide layer and subsequently patterned using the laser. The optical path of the laser beam and the photomask-sample space are evacuated and then backfilled and purged with nitrogen during laser firing. The resulting pattern is investigated using various measurement techniques. The scanning probe microscopy images show that patterns are transferred to the SAM-covered Si substrates and that 500 nm features are successfully photoprinted in this way.