Robert A. Coxall

β-diketonate derivatives of titanium alkoxides: X-ray crystal structures and solution dynamics of the binuclear complexes [{Ti(OR)3(dik)}2]

Abstract The crystal structures of the 2,4-pentanedionato (acetylacetonato, acac) and 2,2,6,6-tetramethylheptane-3,5-dionato (tmhd) compounds [{Ti(OR)3(dik)}2] (dik = acac, R = Me, Et, Pti; dik = tmhd, R = Me, Prn, Pri), obtained from reactions between Ti(OR)4 and one equivalent of dikH, have been determined for the first time. In the solid state, these compounds adopt centrosymmetric, alkoxide-bridged binuclear structures which in solution undergo ligand redistribution to give mixtures of [{Ti(OR)3(dik)}2], [Ti(OR)2 (dik)2] and Ti(OR)4. When R = Pri, the equilibrium favours the mononuclear compounds, whereas when R = Me, Et or Prn the binuclear compounds can be observed in the 1H NMR spectra. Variable-temperature 1H NMR spectra provide an insight into the dynamic behaviour of the methoxides [{Ti(OMe)3(dik)}2], and possible ligand exchange mechanisms are discussed. No conclusive evidence was obtained for the existence of dimeric or monomeric [Ti(OBui)3(dik)] in the solid state or in solution.

Synthesis, characterisation and magnetic properties of cobalt(II) complexes with picolinic acid derivatives: the crystal and molecular structures of [Co(MeC5H3NCOO)2(H2O)2] and [CoCl2(C5H4NCOOPri)2]

The reaction of Co(AcO) 2 with 6-methyl-2-pyridinecarboxylic acid, and that of CoCl 2 with the isopropyl ester of 2-pyridinecarboxylic acid, both with a 1:2 metal to ligand molar ratio, afford optimum yields for the synthesis of cis -[Co(MeC 5 H 3 NCOO) 2 (H 2 O) 2 ] and cis -[CoCl 2 (C 5 H 4 NCOOPr i ) 2 ], respectively. According to X-ray crystallography they both consist of mononuclear discrete molecules with octahedral coordination around Co(II). The ESR powder spectra of the related Zn phases doped with 0.25% Co(II) show the strong anisotropy of the g and A tensors. The magnetic behaviour of the solid complexes is characteristic of Co(II) systems with important spin–orbit coupling and weak antiferromagnetic interactions. Electronic UV–Vis and magnetic data indicate that these complexes, as well as the already known trans -[Co(C 5 H 4 NCOO) 2 (H 2 O) 2 ], have a high-spin octahedral geometry in solution.

Organophosphonate derivatives of titanium and niobium alkoxoanions

The organophosphonate-substituted alkoxides [Bu4nN]2[{Ti(OMe)3(O3PPh)}2] (1) and [Bu4nN]2[{Nb(OMe)3(O3PPh)}2(?-O)] (2) were prepd. from [Bu4nN][PhPO3H] and the metal alkoxides Ti(OMe)4 or Nb(OMe)5 resp. 1 And 2 were characterized by x-ray crystallog. (1�PhMe: monoclinic, space group C2, R = 0.0449; 2: monoclinic, space group P21/n, R = 0.0452). In 1, the bridging phenylphosphonates occupy trans coordination sites, whereas in 2, a cis-bridging geometry is adopted. [on SciFinder(R)]

Palladium(II) complexes with Pd2S2 rings. Synthesis and theoretical characterization of [Pd2(dppe)2(μ-S)2] and X-ray characterization of [Pd3(dppe)3(μ3-S)2]Cl2

Abstract The use of the dppe ligand and the fine tuning of the experimental conditions has allowed isolation of [Pd2(dppe)2)(μ-S)2], whose structural characterization has been achieved by ab initio MP2 calculations, and of [Pd3(dppe)3(μ3-S)2]Cl2, the X-ray structure of which is also reported.

Substitution of the chloro ligands in cis-[CoCl2(2-C5H4NCO2Pri)2]: structural characterization of four mononuclear products showing both cis and trans configurations at Co(II)

Abstract Cobalt(II) complexes obtained by the reaction of cis-[CoCl2(2-C5H4NCO2Pri)2] (1) with aqueous solutions of simple alkali metal salts have been prepared and characterized. While the reaction of 1 with KPF6 affords both trans-[Co(2-C5H4NCO2Pri)2(H2O)2](PF6)2·2(2-C5H4NCO2Pri) (2) and trans-[Co(2-C5H4NCO2Pri)2(H2O)2](PF6)2 (3), that with NaBPh4 leads to trans-[Co(2-C5H4NCO2Pri)2(H2O)2](BPh4)2·2H2O (5) exclusively. X-ray diffraction data show that the mononuclear cationic units in 2, 3 and 5 share common structural features. The reaction of 1 with KSCN leads to cis-[Co(NCS)2(2-C5H4NCO2Pri)2] (4), whose crystal structure shows that it consists of mononuclear discrete molecules. The analogous reaction with NaN3 yields the very slightly soluble complexes [Co(N3)2(2-C5H4NCO2Pri)] (7) and [Co2(N3)(2-C5H4NCO2Pri)4(H2O)]·3H2O (8) and that with NaOAc results in the formation of the already known complex trans-[Co(2-C5H4NCO2)2(H2O)2] (6) as the only product. Electronic UV–Vis and NIR spectral data for 2–5, 7 and 8 and the calculated magnetic moments from NMR measurements on 2–4 and 7 are indicative of high-spin octahedral Co(II) complexes, as already reported for 1 of known structure.

An alkoxide cluster with 18 Li+ ions encapsulating two borate anions, [(tBuO)12Li18(BO3)2]

The title compound, bis(borato)dodeca(tert-butoxo)octadecalithium, [Li(18)(BO(3))(2)(C(4)H(9)O)(12)], is formulated conveniently as [(((t)BuOLi)(3)(Li(3)BO(3)))(2)((t)BuOLi)(6)]. A central 12-membered ring and two outer six-membered rings are formed by alternating Li(+) cations and alkoxide O atoms. Sandwiched between the central ring and each of the outer rings is a planar array of three further Li(+) cations surrounding a [BO(3)](3-) anion. Thus, the molecule consists of a cationic [Li(18)(O(t)Bu)(12)](6+) cage encapsulating two borate anions. This compound is the first example of a structurally characterized polynuclear lithium borate, and a rare case of a lithium alkoxide cage with nuclearity greater than eight. All the alkoxide ligands are triply bridging, and the lithium ions have trigonal-planar, trigonal-pyramidal and fourfold coordination, all with major distortions from regular coordination geometry.

The first stable copper(II) complex containing four sulfide ligands: synthesis and structural characterization of [Pt2(dppe)2(µ-S)2] and [Cu{Pt2(dppe)2(µ3-S)2}2]2+

The synthesis and crystal structure of the novel heteropolymetallic aggregate [{Pt2(dppe)2(µ3-S)2}2Cu]- [PF6]2 2 and of its precursor [Pt2(dppe)2(µ-S)2] 1 are reported; 2 has been further characterized by EPR and electronic spectroscopies and the hinged Pt2S2 rings in 1 and 2 have been rationalized by ab initio MP2 calculations.