Jan G. H. du Preez

Substitution of nitrido by the oxo group in reactions of [ReNCl2(PPh3)2] with multidentate N,O–-donor chelates. Crystal structure of [ReOCl2(PPh3)(HL)][H2L = 2,6-bis(hydroxymethyl)pyridine]

The complex [ReNCl2(PPh3)2] reacts with the potentially bidentate 8-hydroxyquinoline (Hquin) and N-phenylsalicylideneimine (Hpsal), and potentially terdentate ligands di-2-pyridyl ketone and 2,6-bis(hydroxymethyl)pyridine (H2L) to form the products [ReOCl(quin)2], [ReOCl2(PPh3)(psal)], [ReOCl2{(C5H4N)2C(O)(OH)}] and cis-[ReOCl2(PPh3)(HL)], respectively. The first three products are identical to those isolated earlier by the reactions of trans-[ReOCl3(PPh3)2] with these ligands, while in the latter product the HL– ligand acts as a bidentate N,O–-donor, spanning one axial (O–trans to ReO) and one equatorial co-ordination site. These reactions present an alternative synthetic route to monooxorhenium(V) complexes. The complexes cis-[ReOCl2(PPh3)(HL)] crystallizes in the orthorhombic space group P212121 with cell parameters a= 10.019(3), b= 12.457(6), c= 19.53(1)A, U= 2436.5 A3, Z= 4, R= 0.059 and R′= 0.074 for 1330 reflections with Fo > 4σ(Fo).

Uranium(IV) poly(pyrazol-1-yl)borate complexes

Abstract The complexes [ThX n (HBPz 3 ) 4 − n ] ( Pz = C 3 H 3 N 2 , pyrazolyl; when n = 2, X = Cl or Br and when n = 1, X = Cl ), [ThCl 2 (HB(3,5Me 2 Pz) 3 ) 2 ], [ThBr 2 (BPz 4 ) 2 ], [ThCl 3 (HBPz 3 )(dma)(thf)], [Th(HBPz 3 ) 4 L x ] (when x = 1, L = thf and when x = 2, L = dma ) and K[Th(H 2 BPz 2 ) 5 ] have been prepared. The IR and 1 H NMR spectra of the complexes are reported; the latter indicate that in the complexes [ThX 2 (HBPz 3 ) 2 ] ( X = Cl , Br ) the HBPz 3 group is tridentate, whereas in [ThBr 2 (BPz 4 ) 2 ] an ionic structure of the type [(Pz 2 BPz 2 ) 2 Th(μPz 2 BPz 2 )Th(Pz 2 BPz 2 ) 2 ] 3+ [ThBr 6 (Pz 2 BPz 2 )] 3− is suggested.

The co-ordination chemistry of divalent cobalt, nickel, and copper. Part 13. Characterization and stability constants of copper(II) species isolated from mixed-ligand solutions; crystal structure of the complex (pyridine-2,6-dicarboxylato)(N,N,N′,N′-tetramethyl-1,3-diaminopropane)copper(II)

Six-co-ordinate complexes [Cu(pydca)(L)(H2O)]·H2O and five-co-ordinate complexes [Cu(pydca)(L)], where pydca = pyridine-2,6-dicarboxylate, L = en (1,2-diaminoethane), tmen (N,N,N′,N′-tetramethyl-1,2-diaminoethane), pn (1,3-diaminopropane), or pen [1,2-di(pyrrolidin-1-yl)ethane], were isolated and characterized by thermogravimetric, calorimetric, spectrophotometric, magnetic, and stability constant measurements. A structure determination on [Cu(pydca)(tmpn)](tmpn =N,N,N′,N′-tetramethyl-1,3-diaminopropane), which was monoclinic, with space group P21/c, a= 14.970(2), b= 7.290(1), c= 14.822(2)A, β= 106.64(2)°, Z= 4, indicated a distorted square-pyramidal co-ordination sphere with considerable steric interaction between the tertiary amine groups and the two carboxylate groups. The splitting of the νsym(COO) and νasym(COO) i.r. bands of all the above complexes having tertiary amine ligands was ascribed to the distortions resulting from this steric interaction. Stability constants for some complexes are reported.

Novel Technetium and Rhenium Complexes with Multidentate Nitrogen and Sulfur Donor Ligands

The structural characterization of the distorted octahedral complcx TcO(HAF)(PAC), containing the terdentate ONS^ donor Schiff base ligand HAF^ and the bidentate NS donor ligand PAC, is reported. The oxygen donor atom of the terdentate ligand occupies the coordination site trans to the Tc = 0 bond, with the N2S2 donors in the equatorial plane. It was previously implicated that complexes of this type could not be formed. The complex ReOCl3(PPh3)(HMEC), formed by the reaction of trans-ReOCl3(PPh3)2 with the potentially bidentate NS donor ligand methyl-2-(N-ethylamino)-l-cyclopentenedithiocarboxylate (HMEC) in acetone, was also structurally characterized. It was found that the ligand HMEC coordinates to the rhenium(V) in an unexpected monodentate manner through the neutral thiocarbonyl sulfur atom.

Pentahalogeno-oxouranates(VI)

Pentafluoro- and tetrabromochloro-oxouranate(VI) salts, [Ph4P][UOF5] ana [Ph4P][UOClBr4], have been prepared by reaction of [Ph4P][UOCl5] with hydrogen fluoride and bromide respectively. Hydrolysis of [Ph4P]-[UOCl5] leads to a uranium(VI) anion which may contain a cis-dioxouranium(VI) group. The electron-transfer and vibrational spectra of these salts are discussed and compared with those of the corresponding tungsten(VI) species. A simple method for the preparation of [Ph4P][WOF5] is also reported.

New uranium tetraiodide complexes

A new type of uranium tetraiodide complex, viz. Ul4L2(where L = a bulky amide or phosphine oxide ligand) and new suitable starting materials for the preparation of uranium(IV) iodo-complexes have been prepared.

The co-ordination chemistry of divalent cobalt, nickel, and copper. Part 10. Characterisation and stability constants of nickel(II) species isolated from a mixed-ligand solution: crystal structure of tris(1,2-diaminoethane)nickel(II) bis(pyridine-2,6-dicarboxylato)nickelate(II) tetrahydrate

The complexes, Ni(pydca)(en)·2H2O (1), Ni(pydca)(en)3·2H2O (2), and Ni(pydca)(en)1.5·2H2O (3) were isolated from solutions of nickel(II), pydca, and en (pydca = pyridine-2,6-dicarboxylate, en = 1,2-diaminoethane). Spectral and magnetic data indicate that species (1) and (2) are octahedral and can be formulated as [Ni(pydca)(en)(H2O)]·H2O and [Ni(en)3][pydca]·2H2O, respectively. The structure of (3) was shown by Patterson and Fourier methods to be in accordance with the formula [Ni(en)3][Ni(pydca)2]·4H2O, with a= 9.395(5), b= 10.924(5), c= 15.662(8)A, α= 70.95(2), β= 101.36(2), γ= 104.91(2)°, Z= 2, triclinic, and space group P. Heating (1) gave a compound with the empirical formula Ni(pydca)(en). Infrared and magnetic data indicate that this species is monomeric and five-co-ordinate. A compound with the same empirical formula, Ni(pydca)(en), was obtained by heating (3), but spectral data and a magnetic moment of 3.40 B.M. for this product suggest the formula [Ni(en)2][Ni(pydca)2], containing [Ni(en)2]2+ with Cs symmetry. A plot of complex-ion concentrations as a function of Ni : en ratio in solution was derived from measured stability constants and was used to explain the stepwise isolation of species (1), (3), and (2).

The chemistry of uranium. Part 20. Tetraphenylphosphonium pentachloro-oxouranate(VI): crystal structure and bonding characteristics

The crystal structure of the title complex has been determined from three-dimensional X-ray diffraction data collected on a four-circle automatic diffractometer. The complex crystallises in space group P4/n, with a=b= 13.264(5), c= 7.621(5)A, and Z= 2. The structure has been solved by Patterson and Fourier methods and refined to a final R of 0.024. The structure consists of octahedral anions and of cations with (S4) symmetry, both ions forming linear stacks parallel to c: U–O is 1.76(1)A, four Cl atoms form an equatorial plane with U–Cl 2.536(2)A, while the axial U–Cl bond, trans to U–O, is 2.433(4)A. The results are discussed in relation to structural data for similar actinoid complexes with metal oxidation states IV–VI; strong evidence is adduced that the bonding in such complexes is predominantly ionic in character and strongly influenced by ligand-ligand repulsion.

Complexation of thorium(IV) with 2-thenoic and 2-furoic acids in aqueous solution at low pH

The aqueous complexation chemistry of thorium(IV) with 2-thenoate and 2-furoate has been studied using precision analytical potentiometry (I= 0.5 mol dm–3 NaClO4, 25 °C) in the range pH 1.7–3.0. The best-fit model, which was tested by varying the data and pH range employed, took into account the competitive formation of the conjugate ligand acids and equilibrium hydroxothorium complexes. The formation constants of the complexes obtained, denoted by βpqr, where the subscripts p, q and r refer to the stoichiometric coefficients in the general formula [LpThqHr](–p+4q+r)(L = 2-thenoate or 2-furoate) have the values: 2-thenoate, log β101= 3.24 ± 0.00, log β110= 3.04 ± 0.07, log β11 – 1= 0.39 (invariant), log β210= 5.69 ± 0.05, log β312= 14.16 ± 0.05, log β412= 18.00 ± 0.03; 2-furoate, log β101= 3.01 ± 0.00, log β110= 2.85 ± 0.04, log β210= 5.11 ± 0.07, log β312= 12.78 ± 0.06, log β410= 10.07 ± 0.03, log β412= 15.14 ± 0.07. These results suggest that higher species of the type ThLnx+(n= 3 or 4) are partially protonated at the pH necessary to avoid hydrolytic precipitation of the actinide.

Di-iodotetrakis(triphenylarsine oxide)uranium(IV) hexaiodouranate(IV). A new type of actinoid co-ordination compound

A new type of co-ordination compound having UX4L2 stoicheiometry consisting of both cationic and anionic six co-ordinated metal species has been isolated (M = uranium, X = iodide, and L = neutral donor ligand).