Magnetochemistry: advances in theory and experimentation

The coordination chemistry of pyrazole-derived ligands

Maleic anhydride (MA) is an important intermediate in a large number of chemtcal processes. World capacity is of the order of 700,000 tonnes/yr, and its major use is in the manufacture of unstaurated polyester resins, which accounts for 60–70% of production [1,2]. Other uses are summarized in Table 1

Vanadium-phosphorus Oxide Catalysts for the Selective Oxidation of C-4 Hydrocarbons To Maleic-anhydride

The uses of passive measurement of acoustic emissions from chemical engineering processes

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.

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

Crystal and molecular structure, spectroscopy, and magnetism of diaquobis(imidazole)catena-.mu.-(squarato-1,3)-nickel(II). A one-dimensional polymer

Magnetic susceptibility data have been measured in the temperature range 1.75 to 60 K for the following structurally characterized, single chloride-bridged copper(II) chain compounds: dichlorobis(dimethyl sulphoxide)copper(II), dichlorobis(imidazole)copper(II), aquo(caffeine)dichlorocopper(II), and dichloro[2-(2′-methylaminoethyl)pyridine]copper(II). The first two compounds exhibit antiferromagnetic intrachain interactions with exchange coupling constants of –6.1 and –2.1 cm–1, respectively, while the second two compounds exhibit ferromagnetic interactions with J values of 0.48 and 1.58 cm–1 respectively. Except for dichlorobis(imidazole)copper(II), which undergoes long-range magnetic ordering below 7.7 K, the exchange coupling constants become more negative as the angle at the chloride bridge increases from 113.6° in dichloro[2-(2′-methylaminoethyl)pyridine]copper(II) to 144.6° in dichlorobis(dimethyl sulphoxide)copper(II).

Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

Coordination compounds having the general formula ML2Ox are described, with Ox = oxalato dianion; M = Ni, Co and Zn; 1 = water and imidazoles. The compounds are characterised by chemical analyses, i.r., far-i.r., Raman, ligand field and e.s.r. spectra. Magnetic susceptibility measurements at low temperatures indicate a polymeric structure of ant i-ferromagnetically coupled M2+ ions.

Polymeric coordination compounds of nickel(II), cobalt(II), and zinc(II) with oxalate ions as symmetric tetradentate bridging ligands

Acoustic emission during the preparation of dichloro(pyrazine)zinc(II)

Variable-temperature (4.2–80.0 K) magnetic-susceptibility data are reported for compounds CuX2L2[X = Cl or Br; L = imidazole (imH), N-methylimidazole (mim), pyrazole (Hpz), and indazole (Hindi)]. The magnetic data have been analysed with five different equations, i.e. the Heisenberg polynomial, the lsing expression, the parallel component of the lsing expression, the Monte-Carlo calculation of Jotham, and the dimeric Bleaney–Bowers expression. Ligand-field and e.s.r. spectra (X- and Q-band) are also presented. The magnetic properties of none of the compounds can be described with the lsing model of anisotropic coupling. For the compounds CuBr2L2(L = Hpz or Hind) excellent fits are obtained with the Heisenberg model of isotropic coupling, yielding J=–19.0 cm–1 and g 2.06, and J=–18.7 cm–1 and g 2.06 respectively. For CuCl2L2(L = imH or mim) and CuBr2(mim)2 the Jotham expression gives the best results, with J=–5.36 cm–1 and g 2.19, J=–2.88 cm–1 and g 2.36, and J=–11.7 cm–1 and g 2.15 respectively. The magnetism of CuCl2(Hpz)2 can best be described with the dimeric Bleaney–Bowers expression (J=–1.3 cm–1 and g 2.18). In CuCl2(Hind)2 the copper(II) ions appear to be coupled ferromagnetically. Unfortunately no unique fit has been obtained; both the parallel lsing and Bleaney–Bowers expressions fit the data (J= 0.9 cm–1 and g 2.21, and J= 5.2 cm–1 and g 2.10 respectively).

Johannes A. C. van Ooijen

Papers

Crystal and molecular structure, spectroscopy, and magnetism of diaquobis(imidazole)catena-.mu.-(squarato-1,3)-nickel(II). A one-dimensional polymer

Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

Polymeric coordination compounds of nickel(II), cobalt(II), and zinc(II) with oxalate ions as symmetric tetradentate bridging ligands

Acoustic emission during the preparation of dichloro(pyrazine)zinc(II)

Magnetic exchange in some polynuclear bis(azole)dihalogenocopper(II) complexes