William E. Hatfield

New magnetic and structural results for uniformly spaced, alternatingly spaced, and ladder‐like copper (II) linear chain compounds (invited)

Results of recent synthetic, structural, and magnetic work on exchange coupled copper (II) ions bridged by nonmagnetic ligands are discussed, including the quasi‐linear chain compound bis (dimethyldithiocarbamato) copper (II) in which the copper (II) ions are antiferromagnetically exchange coupled. An unusual correlation exists in the structural and magnetic data for [Cu(dmtc)2]∞ and other known sulfur bridged copper compounds. Data are presented for the alternatingly spaced linear chain compounds di‐μ‐chlorobis‐(4‐methylpyridine)copper (II), and a series of dionebis‐(thiosemicarbazato)copper (II) compounds. Exchange coupling constants and alternation parameters were obtained from expressions which were empirically generated from calculations on rings of ten S = 1/2 ions for kT/‖J‖≳0.5 and J<0. Finally, new results for recently discovered spin ladder systems are presented.

Substituted pyridine N-oxide complexes. VI Spectral and magnetic properties of some 4-substituted pyridine N-oxide complexes with transition metal perchlorates

Abstract Visible spectra, infrared spectra and magnetic properties of 4-substituted pyridine N-oxide complexes of the general formula [M(4-RC 5 H 4 NO) 6 ](ClO 4 ) n , where R = OCH 3 , CH 3 , H, Cl and NO 2 ; M = Cr(III), Fe(III), Co(II) and Ni(II); and n = 2 or 3, are reported. For M = Cu(II); tetrakis derivatives are formed for all R substituents and the hexakis complex is additionally isolated with R = H. The magnetic and spectral data indicate that the six coordinate complexes are high-spin octahedral species and that the four coordinate copper(II) complexes are probably square planar. From infrared spectral measurements nitrogen-oxygen and metal-oxygen stretching vibrations are assigned and the former are found to correlate with the σ + values of the ligands. Crystal field parameters are evaluated from diffuse reflectance and mull spectra and differences and trends discussed.

The Coupled Representation Matrix of the Pair Hamiltonian.

A complete treatment of the spin hamiltonian for a pair of exchange coupled metal ions is given. The results obtained through the use of the Wigner-Eckart theorem are unrestricted with respect to the relative orientation of the single-ion tensors, and appropriate for both the S 1 = S 2 and S 1 ≠ S 2 cases. The necessary constants are derived so that matrix elements within a given spin multiplet can be treated by ordinary operator algebra with the coupled representation state vectors, |SM>, as a basis set. Explicit algebraic formulae for matrix elements between spin multiplets are presented for the first time. Symmetry restrictions are discussed in general and illustrated for the simple case of two ions related by an inversion centre, pair symmetry Ci .

Exchange coupling in the sulfur-bridged quasi-linear-chain compound bis(dimethyldithiocarbamato)copper(II). Observations on exchange in sulfur-bridged copper(II) compounds

Abstract : Magnetic susceptibility data have been collected on a powdered sample of the linear chain compound bis(dimethyldithiocarbamato) copper(II). The data are fitted to a Heisenberg linear chain odel for exchange coupled S=1/2 ions including an interchain correction term. The best fit parameters are J(interchain) = -1.22 /cm, J(interchain) = 0.47 /cm with the EPR average g value of 2.03. Data for Cu(dmtc)2 infinity and three other sulfur-bridged copper(II) compounds exhibit a correlation between the exchange coupling constant and the geometry of the Cu2S2 bridging unit. (Author)

Effect of Bridge Geometry on Exchange Coupling in Ligand-Bridged Copper(II) Dimers and Chains

Abstract The singlet triplet splitting resulting from exchange coupling in three series of ligand-bridged copper(II) complexes is primarily controlled by the angle at the bridging ligand atom and by the length of the superexchange pathway. Magnetic and structural data exist for chloro-, bromo-, and sulfur-bridged complexes. The smooth correlation between the exchange coupling constant J and the quotient of structural parameters φr 0 (where φ is the angle at the bridging ligand atom and r 0, is the long out-of-plane bond distance) may be explained in terms of extended Huckel molecular-orbital theory, but the theory does not permit an explanation why only complexes which obey the simple correlation exist. It is predicted that a family of such structurally and magnetically related complexes should exist.

The preparation and magnetic and structural examination of monomeric, dimeric, and polymeric adenine complexes of copper(II)

Abstract : Under acidic aqueous conditions, reaction of adenine with copper(II) yields monomeric (AdH2(2+)) CuCl6, dimeric (Ad)CuCl2, and linear chain polymeric (AdH+2)2CuCl4, as well as the previously reported trimeric (AdH+)2Cu3Cl8.4H2O. The crystal structure of (AdH+)2CuCl4 is analogous to that of (AdH+)2CuBr4. The chloro analogue crystallizes in the space group C2/c of the monoclinic system with the cell dimensions being a = 18.117(4), b = 8.576(1), c = 11.814(4) A and beta = 114.29(1) degrees with Z = 4. The copper atom is roughly tetrahedrally coordinated and lies on a crystallographic two-fold axis with the four coordination sites being occupied by two chloride ligands with a Cu-Cl distance of 2.228(1) A and by the N(9) atoms of two adeninium cations with a Cu-N(9) distance of 2.012(2) A. The cationic purine is protonated at N(1) and N(7). There are weak Cl...Cl interactions of length 3.755(2) A which link the monomeric units into zig-zag polymeric chains with a Cu-Cl...Cl angle of 169.23(7). The corresponding Br...Br contacts are calculated to be 3.791 A. These ligand-ligand contacts support Heisenberg linear chain antiferromagnetism with J(Cl) = -7.6/cm and J(Br) = -36.5/cm. The exchange coupling constant observed for dimeric (Ad)CuCl2 is -32/cm. (Author)

Single crystal magnetic susceptibility measurements on the linear chain polymer copper (II) pyrazine nitrate

Magnetic susceptibilities have been measured in the temperature region 1.7–60°K both parallel and perpendicular to the chemical chain on single crystals of Cu(pyrazine)(NO3)2. It has been shown that there is qualitative disagreement between experiment and theory if the appropriate equations derived for the Ising model in one dimension are applied. On the other hand, excellent agreement exists for the Heisenberg model with J/k = −5.3°K down to the lowest temperature achieved, along with closer agreement between the g values determined in this experiment and those obtained by EPR. A comparison is also made between the exchange pathway in Cu(NO3)2 · 2.5H2O and the probable pathway in Cu(pyrazine)(NO3)2.

The magnetic properties of several quasi two‐dimensional Heisenberg layer compounds: A new class of ferromagnetic insulators involving halocuprates

Magnetic susceptibility measurements on powdered samples of bis(benzylammonium) tetrachlorocuprate (II), bis(phenethylammonium) tetrachlorocuprate(II), bis(3‐phenyl‐1‐propylammonium) tetrachlorocuprate(II), and bis(benzylammonium) tetrabromocuprate(II) have shown that these four substances order ferromagnetically with Curie temperatures of 8.0±0.5, 9.0±0.2, 7.0±0.5, and 12.3±1.0 K, respectively. Fits of a series expansion for a two‐dimensional lattice to the magnetic susceptibility data obtained from powdered samples in the paramagnetic region yielded exchange constants J for the chloride compounds in the range 16.7–18.8 K, and a value of 25.3 K for the bromide compound. For these fits the <g≳ value of 2.14±0.01 determined from EPR measurements was used. Magnetic susceptibility measurements made at 10 Oe on a single crystal of bis(phenethylammonium) CuCl4 at temperatures just below Tc revealed ratios of susceptibilities of 30:7:1 along the c, a, and b axes, respectively, where the b axis is perpendicular ...

Effects of Iodination on the Electrical Conductivity of Hydrogen Bis(Phthalocyaninato) Neodymium(III)

Abstract Partial oxidation of hydrogen bis(phthalocyaninato) neodymium(III) by molecular iodine dramatically increases electrical conductivity. The results are discussed in terms of structural models.

Strong exchange coupling between the lanthanide ions and the phthalocyaninato ligand radical in bis(phthalocyaninato)lanthanide sandwich compounds

Abstract A series of lanthanide phthalocyanine sandwich compounds with the formula [(Pc2−)LnIII(Pc1−)] have been synthesized and characterized. To a first approximation, the lanthanide ions exist in their normal trivalent state, while one of the phthalocyanine ligands exists in the normal dianionic state and the other exists as a monoanionic phthalocyanine radical. It is obvious from the magnetic behavior of these compounds that there is a strong magnetic interaction between the lanthanide f electrons and the phthalocyanine radical electron. Both antiferro- and ferromagnetic ground states have been observed in this series of compounds which depends on the symmetry and occupancy of the magnetic orbitals on the lanthanide ion. In some cases both the antiferro- and ferromagnetic states of a single system are observed in the temperature range studied. In these cases, the energy separation between states has been evaluated from the magnetic data.