Raymond J. Butcher

Peroxo aminopolycarboxylato vanadate(V) of an unusually low toxicity: synthesis and structure of the very stable K2[VO(O2)(C6H6NO6)]·2H2O

The synthesis and structure of a monoperoxo vanadate(V) of the formula K2[VO(O2)NTA]·2H[2O, where NTA = C6H6NO6 3−, the nitrilotriacetate, is described. This stable compound crystallizes in the orthorhombic system (space group Pna21): a = 7.621(1), b = 13.002(3), c = 13.155(1) A. A tetradentate NTA encloses vanadium in a distorted pentagonal bipyramid with an apical V = O group. Cis to it, in the pentagonal plane, a non-symmetrically coordinated peroxo group is located with an (OO) bond length of 1.438(4) A. Complex IR spectra display rich absorption due to coordinated NTA, in addition to the characteristic V = O and (OO) stretching vibrations. Aqueous solutions of the complex show a (peroxo → V(V)) charge transfer band at γmax = 425 nm.

Synthesis and crystal structure of bis-µ-(5-chloro-2-hydroxy-N-methyl-α- phenylbenzylideneiminato-N,O)-bis[ethanol(nitrato-O,O′)nickel(II)]: a new type of nickel(II) dimer

The title complex (4) is formed by reaction of nickel(II) dinitrate hexahydrate and triethoxymethane (tem) with bis(5-chloro-2-hydroxy-N-methyl-α-phenylbenzylideneiminato)nickel(II); its crystal and molecular structure were determined by single-crystal X-ray diffraction. The two nickel atoms are in distorted octahedral environments with a shared edge formed by the phenolic oxygens of the Schiff-base ligands, each of which bonds to both metal atoms. Like the Schiff-base ligands, the nitrato-groups are bidentate, and an ethanol molecule bonded at oxygen completes the octahedron. The ethanol is formed by the reaction of hydrate water with tem. These results are in contrast with those of related nickel complexes and nickel nitrate which form trinuclear complexes, in which the solvent plays no part. An analogous reaction proceeds in other solvents. e.g. ethanol and methanol, but the product is difficult to control because water and solvent molecules compete for the sixth ligand position on the metal.Crystals of (4) Are triclinic, space group P, unit-cell parameters: a= 8.969(7), b= 9.601(3), c= 11.926(7)A, α= 100.32(5), β= 92.12(7), γ= 114.01(3)°, Z= 1 dimer. The structure was solved by the heavy-atom method from diffractometer data, and refined by least squares to R 0.029 for 2 090 observed reflections.

Nature and mechanism of high spin-low spin crossovers and the existence of intermediate spin states

Temperature- and pressure-dependent spectroscopic and magnetic, and X-ray crystallographic studies show that, in some FeIII and FeII crossover systems, rapid thermal equilibria occur between high spin, low spin and sometimes intermediate spin states, with solvent molecules sometimes inducing specific spin states; it is of relevance to biological systems that the single ‘spin-mixed’ state model is inapplicable in every well studied case.

Crystal and molecular structure of aquadibromo[2-(2-pyridyl)quinolinyl]manganese(II), and the relation between structure and magnetic properties of manganese(II) complexes

The crystal and molecular structure of the title complex has been determined by heavy-atom techniques. Crystal are monoclinic, a= 8.172(3), b= 11.868(4), c= 16.456(5)A, β= 98.83(4)°, space group P21/c. The structure was refined by least squares to R 8% for 1 577 reflections measured by diffractometer. The complex consists of well-isolated units of five-co-ordinated MnII molecules. permitting no significant magnetic exchange interaction between neighbouring paramagnetic centres. Comparison with a related structure [Mn2(biq)2Cl4](biq = 2.2′-biquinolyl) indicates that the presence of the co-ordinated water molecule (Mn–O 2.27 A) prevents dimerisation of the complex via bromide bridges. The MnN2X2(X = Br or Cl) chromophore in this type of complex seeks out an extra ligand to become distorted trigonal bipyramidal five-co-ordinate.

Crystal and molecular structures of dichloromethane-solvated tris(morpholinocarbodithioato)-complexes of chromium(III), manganese(III), and rhodium(III). Comparison of co-ordination spheres

The title complexes [(I)–(III)] are nearly isomorphous with the known cobalt(III) analogue (IV). The principal differences between (I)–(III) arise from the nature of the central metal atoms, packing and other effects being essentially the same. They may be considered as trigonally distorted octahedral, with an approximate three-fold rotation axis. The manganese complex (II) deviated most significantly from this model, with elongated bonds in the z and slightly elongated bonds along the x direction, which can only be attributed to Jahn–Teller effects. The MS6 co-ordination sphere is highly symmetrical in the chromium complex(I), as expected for the 4A ground-state, even more so than in (IV). The mean increase in metal-ligand bond distance from CoIII to RhIII, with identical d6(1A1) configurations, is very close to 0.1 A. The ‘bite’ angle of the bidentate ligand appears to be determined largely by M–L distance.Crystal data: (I), space group P, Z= 2, a= 13.255(9), b= 10.642(5), c= 11.395(1)A, α= 115.16(4), β= 104.4(1), γ= 100.19(6)°, R= 4.3%, 2 218 reflections; (II), space group P, a= 13.067(3), b= 10.824(6), c= 11.475(5)A, α= 116.23(5), β= 104.06(3), γ= 100.19(4)°. R 4.0%, 2 062 reflections; (III), space group. PZ= 2, a= 13.343(4), b= 10.596(1), c= 11.191 (1)A, α= 114.20(1), β= 103.18(2), γ= 101.29(2)°. R 4.3% 3 529 reflections.

Novel nickel(II) dimers

Syntheses of nickel dimers derived from bidentate Schiff bases (bsb) and nitrato ligands, analogous to [Cu(bsb)halide]2 dimers, are reported for the first time and their structures and magnetism compared with [Cu(bsb)NO3]2, whose structure is also reported.