Jeffrey H. Helms

Preparation and Properties of Single Crystals of Hydrogen Bis(Phthalocyaninato) Neodymium(III).

Abstract Single crystals of hydrogen bis(phthalo-cyaninato)neodymium(III) have been synthesized by electrochemical means. The crystals are semiconductors and follow Curie-Weiss behavior.

A study of the ferrimagnetic ordering of the complex bimetallic salt hexaaminechromium (III) hexachloroferrate (III), [Cr (NH3)6] [FeCl6]

The magnetic susceptibility of a powdered sample of [Cr (NH3)6][FeCl6] has been measured in the temperature range 1.85 to 110 K in applied magnetic fields of 100 and 10 000 Oe. A magnetic phase transition near 2.8 K is apparent in the low field data set. The transition is confirmed by zero field Mossbauer spectroscopy data. The magnetic data above the phase transition may be fit to the Neel hyperbola for a ferrimagnet: χ−1=(T−θ)/C−ζ/(T−θ’) with best-fit values of C=6.58 emu K, θ=−14.1 K, θ’=2.22 K, and ζ=10.1 emu K. Assuming a structure similar to [Co(NH3)6] [FeCl6] and mean field theory, the intrasublattice coupling constants are 0.12 cm−1, and the intersublattice coupling constant, Jab, is −0.21 cm−1. The value of Jab is confirmed by a change in slope of the magnetization data near 2000 Oe.

Crystal structure and mössbauer spectroscopy studies of the ferrimagnetic complex bimetallic salt hexaamminechromium (III) hexachloroferrate (III), [Cr(NH3)6][FeCl6]

SummaryThe crystal and molecular structures of the ferrimagnetic bimetallic complex salt hexaamminechromium(III) hexachloroferrate(III), [Cr(NH3)6][FeCl6], have been determined from single-crystal, three-dimensional x-ray diffraction counter data. The compound crystallizes as orange coloured crystals in the space groupC2/c of the monoclinic system with Z=4 and has cell dimensionsa=11.325(1) Å,b=11.387(1) Å,c=11.233(1) Å, and β=90.83(1)Å. The structure was refined by using segmented block diagonal least-squares techniques to discrepancy indices R and Rw of 0.0233 and 0.0285, respectively. The metal ions occupy sites with symmetry

Cluster Calculations on the Chain Compound Aqua[N- (Salicyclaldiminato) Glycinato] Copper(II) Hemihydrate

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Electronic structure of the oxidation catalyst cis(bipyridine)oxo(pyridine) ruthenium(IV) diperchlorate

and are nearly octahedrally coordinated. In the [FeCl6]3− anion there are three independent Fe−Cl distances with a mean of 2.393(2) Å, and the maximum angular deviation from octahedral geometry is 1.20. In the [Cr(NH3)6]3+ cation, the mean of the three independent Cr−N distances is 2.079 (7) Å, and the maximum angular deviation from octahedral geometry is 0.70. The structural data provide an explanation for the observed quadrupole splitting of 0.214 mms−1 as seen in the Mössbauer spectrum at 292.6 K and reveal superexchange pathwaysvia close amine proton-chloride anion contacts with lead to 3D-ferrimagnetic ordering near 2.8 K.

Effect of Meso Substituents on Exchange-Coupling Interactions in μ-Oxo Iron(III) Porphyrin Dimers

Abstract The structure of the mixed ligand complex bis-μ-chloro-bis[chloro(4-methylthiazole)dimethylformamidecopper(II)] has been determined from three-dimensional X-ray counter data. The complex [Cu-(C4H5NS)(DMF)Cl2]2 crystallizes in the monoclinic space group P 2 1 n with two formula units in a cell of dimensions a = 7.349(7), b = 20.306(7), c = 8.909(3) A and β = 112.53(6)°. The final weighted R factor is 0.032 based on 1646 data. In this first example of a mixed ligand bis-μ-chloro-copper(II) complex, copper is five-coordinate, with the coordination geometry being distorted from an idealized tetragonal pyramidal. The Cu2Cl2 bridging unit is constrained to be planar by the presence of a center of symmetry, and the CuCl distances are 2.296(2) and 2.724(1) A with a CuCl⋯Cu′ angle of 95.29(7)°. Magnetic susceptibility measurements reveal antiferromagnetic exchange coupling, and the best fit of equation for an exchange coupled pair of S = 1 2 ions yields J = −1.7 cm−1 and g = 2.105. The exchange coupling constant lies in the range of values for a φ R o value of 35 deg A−1. The quality of the fit is markedly improved if intermider exchange interactions are taken into account. The dimers pack in the solid state to form a ladder-like structure with copper(II)sulfur contacts of 3.906(3) A. Best fit exchange coupling constants for the spin ladder of −1.17 and −1.0 cm−1 were obtained from a calculation on a closed ring of 10 spins with nearest neighbor and next-nearest neighbor interactions.

Exchange interactions in a "bicapped-cubane" Cu6O8 cluster. Crystal structure and magnetic susceptibility of tetrakis(.mu.3-2-amino-2-methyl-1-propanolato)tetrakis(.mu.-2-amino-2-methyl-1-propanolato)hexacopper(II) perchlorate

The spin analog of the regular Peierls distortion1 of a quasi-one-dimensional system containing paramagnetic transition metal ions has recently been suggested for the linear chain compound aqua[N-(salicylaldiminato)glycinato] copper(II) hemihydrate, CuNSG.2 Theoretically the spin-Peierls (SP) transition may arise in electrically insulating, antiferromagnetically coupled, uniformly spaced spin chains, but it had previously been restricted to those systems in which the unpaired spins are delocalized on large flat organic molecules.3 The absence of SP phase transitions in the numerous antiferromagnetically coupled, uniform spin chains containing metal ion localized unpaired spin density can be attributed to long range 3-dimensional ordering at temperatures above the potential SP ordering temperature, Tsp. Cluster calculations on the temperature dependent magnetization at varying applied external fields verify the SP phenomenon in CuNSG.

Preparation and characterization of the μ-oxo dimer and hydroxo complexes of (tetrakis(pentafluorophenyl)porphinato)iron(III)

The crystal and molecular structure of cobalt(II) oxydiacetate trihydrate, Co(C4H4O5)·3H2O, has been determined from single-crystal, three-dimensional x-ray diffraction counter data. The compound crystallizes as dark red violet platelets in space groupP21/n of the monoclinic system withZ=4 and having cell dimensionsa=7·128(1)A,b=10·384(2)A,c=11·122(1)A, and β=91·51(1)A. The structure was refined toR=0·042 andRw=0·053. The cobalt(II) ion has a distorted octahedral coordination in which the oxydiacetate acts as a tridentate chelate and the three remaingng coordination sites are occupied by two water molecules and an oxygen atom from a carboxylate group of an adjacent oxydiacetate dianion. This latter linkage forms a chain structure. The chains are packed in layers and there is extensive hydrogen bonding between the layers. The magnetic susceptibility of cobalt(II) oxydiacetate trihydrate is dependent on the applied magnetic field. In an applied magnetic field of 1,000 Oe, the maximum susceptibility occurs at 2·51 K, and the inflection point belowTmax lies at 2·40 K. (χmax,Tmax) at 100 Oe and 10,000 Oe are (0·257 emu/mole, 2·63 K) and (0·227, 1·76 K).