David A. Brown

Transition metal complexes of monohydroxamic acids

Complexes of monohydroxamic acids and Fe(III), Co(II), Ni(II) and Cu(II) are shown to involve chelation via the oxygen atoms of the donor ligand. Spectral and magnetic properties of the complexes of Fe(III), Co(II), and Ni(II) indicate octahedral coordination with the latter two metal ions forming polymeric species. The monohydroxamic acid complexes show slightly larger 10Dq values than the corresponding aquo and acetylacetonato complexes. Cu(II) forms a square planar complex probably with a dxy ground state.

Metal‐Metal Bonding in Dicobalt Hexacarbonyl Diphenylacetylene

The nature of the bonding between the two cobalt atoms in dicobalt hexacarbonyl diphenylacetylene is discussed in terms of simple molecular‐orbital theory. It is shown that, in addition to bonding via the π orbitals of the acetylene residue, it is essential to consider direct overlap between the 4p orbitals of the cobalt atoms. Master formulas and numerical tables are derived for the integrals S(4pσ4pσ), S(4pπ4pπ).

A new type of isomerism in some phosphine and phosphite derivatives of the metal carbonyls

Abstract A new type of isomerism is reported for a wide variety of transition metal carbonyl complexes of the general type (π-Ring)M(CO)(L)X where L is a tertiary phosphine or phosphite ligand. The effects of solvent and temperature upon this isomerism are described, and possible reasons for it are discussed.

Kinetics of substitution reactions of cyclopentadienyl metal carbonyl halides

Abstract The kinetics of the substitution reactions of the iron cyclopentadienyl carbonyl halides and iron methylcyclopentadienyl carbonyl halides are reported for a series of phosphite ligands. A dissociative mechanism is observed in all cases. Detailed solvent studies are presented and a rationalization of these is given in terms of conjugation effects.

Ni(II) complexes as models for inhibited urease

Abstract Nickel(II) complexes with the ligands 2,2′-dipyridyl ketone (dpk) and 2,2′-bipyridine (bipy) were prepared in order to study the mode of bonding of hydroxamic acid as secondary ligand. The structures of the novel complexes 1–3 were characterised by X-ray structure determination and IR spectroscopy. [Ni4(dpkOH)4(CH3CO2)4]·4CH3CH2OH (1) is monoclinic, space group P21/c, with a=12.646(3) A, b=14.031(3) A, c=18.731(4) A, β=105.80(3)°. Substitution of 1 equiv. of Ni(CH3CO2)2 by acetohydroxamic acid (aha) results in the formation of [Ni4(dpkOH)2(dpkOCH2CH3)2(CH3CONHO)2]Cl2 (2) (triclinic, space group P 1 , a=10.872(2) A, b=12.252(2) A, c=12.348(2) A, α=76.90(3)°, β=74.70(3)°, γ=76.57(3)°). [Ni2(bipy)2(CH3CO2)3(CH3CONHO)]·CH3CH2OH (3) is triclinic, space group P 1 with a=8.800(2) A, b=9.193(2) A, c=22.091(4) A, α=95.30(3)°, β=92.85(3)°, γ=111.55(3)°). The coordination spheres of 2 and 3 are similar to that found in the active site of the acetohydroxamate-inhibited C319A variant of Klebsiella aerogenes urease.

The infrared spectra of monohydroxamic acid complexes of copper, iron and nickel

A normal coordinate treatment of Cu(MAHA)2, Fe(MAHA)2 and Ni(MAHA)2, (MAHA = N-methylhydroxamic acid) has been carried out, using a 1:1 metal-ligand model and a Urey-Bradley force field. The methyl group was treated as a point mass. Very satisfactory agreements of observed and calculated inplane infrared frequencies were obtained for copper(II) and iron(III); the metal-oxygen bonds are equivalent, having force constants of ca. 1.08 mdyn/ A. Delocalization does occur over the chelate system resulting in significant double bond character of the Cue5f8N bond, and to a lesser extent of the Nue5f8O bond.

Reactions of some Group 15 ligands with [(η5-indenyl)Fe(CO)3]BF4

Abstract [(η 5 -Indenyl)Fe(CO) 3 ]BF 4 ( I ) undergoes facile monocarbonyl substitution at room temperature in acetone by monophosphines, monophosphites and MPh 3 (M =1cr; As, Sb, Bi) ligands (L) to form [(η 5 -Indenyl)Fe(CO) 2 L]BF 4 . Ditertiary phosphines, PPh 2 (CH 2 ) n PPh 2 ( n = 1, 2, 4, 6, 8) and both the arsines, AsPh 2 (CH 2 ) 2 AsPh 2 and AsMe 2 (CH 2 ) 5 AsMe 2 react similarly to form monosubstituted complexes e.g. [(η 5 -Indenyl)Fe(CO) 2 (η 1 - PPh 2 (CH 2 ) n PPh 2 )]BF 4 and dimeric complexes, e.g. [{(η 5 -Indenyl) Fe(CO) 2 } 2 -μ-PPh 2 (CH 2 ) n PPh 2 )] [BF 4 ] 2 Prolonged refluxing of I with these ligands gives the chelates, e.g. [(η 5 -Indenyl)Fe(CO)(η 2 - PPh 2 (CH 2 ) n PPh 2 )]BF 4 . The enhanced reactivity of the [(η 5 -Indenyl)Fe(CO) 3 ] + cation over that of [(η 5 ,-C 5 H 5 )Fe(CO) 3 ] + in solvents such as acetone may be attributed to the “indenyl” effect, i.e. ring slippage from η 5 to η 3 . However, no evidence was obtained for intermediates such as [(η 3 -C 9 H 7 )Fe(CO) 3 (acetone)] + , and so the effect must operate solely in the transition state of the reaction.

Monohydroxamic acid complexes of iron(II and III), cobalt(II and III), copper(II) and zinc(II)

Abstract Iron(II) and Cobalt(III) complexes of monohydroxamic acids (aceto-, propiono- and steareo-) are reported for the first time. Spectral and magnetic properties indicate octahedral coordination via the oxygen atoms of the deprotonated hydroxamic acid ligand. Both series are relatively unstable, the former undergoing rapid oxidation to Fe(III) and the latter reduction to Co(II) with concomitant oxidation of the ligand to acetate. Complexes of Fe(III), Co(II), Cu(II) and Zn(II) are also reported.

Synthesis of dioxouranium dialkylhydromates - cluster formation in fast atom bombardment mass spectra (FAB-MS)

Abstract The synthesis of a series of dioxouranium(VI) dialkylhydromates, UO 2 (CH 3 (CH 2 ) n CONHO) 2 , n = 4, 5 and 6, is reported together with spectroscopic data. Surprisingly, the fast atom bombardment mass spectra of these complexes all show cluster formation of the form (UO 2 ) n + ( n =1–6) very similar to those recently reported for UO 2 (acetate) 2 .

Discussion of Slater Parameters for Elements of the First Long Period

Slater‐Condon parameters are calculated for elements of the first long period in terms of Slater functions. By comparison with the observed spectroscopic data it is found that the Slater rules predict reasonable values for the exponents of these functions, with certain important qualifications regarding the variation of the screening number with configuration. The exchange integral between the 3d and 4s functions is less satisfactory. By means of the derived results the reduction of Slater‐Condon parameters within complexes is attributed in part to a polarization of the 3d functions so as to achieve near equality of Slater exponents with those of the ligands.