Search

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(μ-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(μ-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4−8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(μ-MeO)(μ-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structu...

The complexes [Ag(etu)2]ClO4 (1) and [{Ag(py2tH)2}(ClO4)(H2O)0.5]n (2) have been obtained from the reactions of AgClO4 with the corresponding thioamide ligands (etu = imidazolidine-2-thione; py2tH = pyridine-2-thione). Complex 1, consisting of centrosymmetric monomeric [Ag(etu)2]+ cations and ClO4− counterions, constitutes the first bis[thio(mono- or di)amide] complex (M = Cu, Ag) known thus far to possess a linear MS2 mononuclear core. Component ions behave in the crystal structure as complementary partners, with all four N−H groups of each [Ag(etu)2]+ cation and all four oxygen atoms of each ClO4− anion involved in N−H···O−Cl hydrogen bonding associations. This leads to the assembly of a three-dimensional supramolecular network. Complex 2, whose previously reported structure has been redetermined with higher precision, contains catena-[Ag(py2tH)2]nn+ polymeric cations consisting of linear chains of linked Ag2(μ-S)2 rings, with distorted tetrahedral AgS4 centres. Supramolecular association through N−H···O−Cl, N−H···O(water) and Cl−O···H−O−H···O−Cl hydrogen bonding, where all N−H groups and H2O molecules and only one or two oxygen atoms of each ClO4− anion are involved, leads to the formation of a two-dimensional layered supramolecular structure. A correlation of some stereochemical parameters and a simple qualitative sulfur-bridge bonding model has been developed for 2 and other related thioamide complexes containing M2(μ-S)2 rings or M−S−M′ single bridges. For these structural units, suitable ranges of tilt and twist dihedral angles have been estimated and assigned to different bonding types. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

We have determined by X-ray crystallography the structures of three dinuclear zirconium(IV) complexes containing the heptadentate ligand dhpta (where H(5)dhpta = 1,3-diamino-2-propanol-N,N,N',N'-tetraacetic acid, 1) and different countercations: K(2)[Zr(2)(dhpta)(2)].5H(2)O (2.5H(2)O), Na(2)[Zr(2)(dhpta)(2)].7H(2)O.C(2)H(5)OH (3.7H(2)O.C(2)H(5)OH), and Cs(2)[Zr(2)(dhpta)(2)].H(5)O(2).Cl.4H(2)O (4.H(5)O(2).Cl.4H(2)O). In the K(I) complex 2, crystallized from water, the two Zr(IV) ions are 3.5973(4) A apart and bridged via two alkoxo groups (average Zr-O 2.165 A). Each Zr(IV) is eight-coordinate and also bound to two N atoms (average Zr-N 2.448 A), and four carboxylate O atoms (average Zr-O 2.148 A). The two dhpta ligands in the dinuclear unit have different conformations. One face of the complex contains an array of 14 oxygen atoms and interacts strongly with the two K(I) ions, one of which is 6-coordinate, the other 8-coordinate, which are 3.922(4) A apart and bridged by a carboxylate O and by two water molecules. The structures of the dinuclear anion [Zr(2)(dhpta)(2)](2-) in the Na(I) complex 3 and in the Cs(I) complex 4 are essentially identical to that found in complex 2, although the alkali metal ions coordinate differently to the oxygen-rich face. All Zr(IV) ions have a distorted triangulated dodecahedral geometry. Although the crystal structure of complex 2 does not indicate the presence of acidic protons, in 4 an [H(5)O(2)](+) unit is strongly H-bonded to an oxygen atom of a coordinated carboxylate group. 1D and 2D (1)H and (13)C NMR spectroscopic and potentiometric studies reveal two deprotonations with pK(a) values of 9.0 and 10.0. At low pH, two carboxylate groups appear to undergo protonation accompanied by chelate ring-opening, and the complex exhibits dynamic fluxional behavior in which the two magnetically nonequivalent dhpta ligands exchange at a rate of 11 s(-1) at pH 3.30, 298 K, as determined from 2D EXSY NMR studies. Ligand interchange is not observed at high pH (>11). The same crystals of complex 2 were obtained from solutions at pH 3 or 12. The dynamic configurational change is therefore mediated by the aqueous solvent.

Four polymetallic iron complexes have been synthesised by a high-temperature route. Two complexes have a [Fe 6 O 2 (OH) 2 ] 12+ core, one containing benzoate ligands and the other pivalates. The other two have a [Fe 11 O 6 (OH) 6 ] 15+ core, with benzoate or t -butylacetate bridging ligands, respectively. These complexes have been characterised by X-ray crystallography, elemental analysis and magnetochemistry. All four complexes consist of Fe III ions, and anti-ferromagnetic exchange between the metal centres lead to low spin ground states.

A new high-yield synthesis of [(PhCH(2))(2)Mg(thf)(2)] and [[(PhCH(2))CH(3)Mg(thf)](2)] via benzylpotassium has allowed a simple entry into benzylmagnesium coordination chemistry. The syntheses and X-ray crystal structures of both [(eta(2)-Me(2)NCH(2)CH(2)NMe(2))Mg(CH(2)Ph)(2)] and [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] (Ar'=2,6-diisopropylphenyl) are reported. The latter beta-diketiminate complex reacts with dioxygen to provide a 1:2 mixture of dimeric benzylperoxo and benzyloxo complexes. The benzylperoxo complex [[eta(2)-HC[C(CH(3))NAr'](2)Mg(mu-eta(2):eta(1)-OOCH(2)Ph)](2)] is the first example of a structurally characterised Group 2 metal-alkylperoxo complex and contains the benzylperoxo ligands in an unusual mu-eta(2):eta(1)-coordination mode, linking the two five-coordinate magnesium centres. The O[bond]O separation in the benzylperoxo ligands is 1.44(2) A. Reaction of the benzylperoxo/benzyloxo complex mixture with further [eta(2)-HC[C(CH(3))NAr'](2)Mg(CH(2)Ph)(thf)] results in complete conversion of the benzylperoxo species into the benzyloxo complex. This reaction, therefore, establishes the cleavage of dioxygen by this system as a two-step process that involves initial oxygen insertion into the Mg[bond]CH(2)Ph bond followed by O[bond]O/Mg[bond]C sigma-bond metathesis of the resulting benzylperoxo ligand with a second Mg[bond]CH(2)Ph bond. The formation of a 1:2 mixture of the benzylperoxo and benzyloxo species indicates that the rate of the insertion is faster than that of the metathesis, and this is shown to be consistent with a radical mechanism for the insertion process.

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.

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.

Visible light irradiation of inert [PtIV(diam(m)ine)(diazide)] complexes leads to reductive elimination of the azide ligands, production of N2, and formation of bifunctional adducts with guanine bases of the type which are lethal to cancer cells.

The structure of the gallane adduct Me3P·GaH3 in the vapour and crystalline states has been investigated. The gas-phase electron-diffraction (GED) pattern has been analysed using the SARACEN method to determine the most reliable structure of the gaseous molecule. Salient structural parameters (rh1 structure) were found to be: r(Ga–H) 159.0(11), r(Ga–P) 244.3(6), r(P–C) 184.0(2), r(C–H) 108.3(7) pm; H–Ga–P 98.4(12) and Ga–P–C 117.7(3)°. The structure of a single crystal at 150 K shows that the adduct retains the same monomeric unit in the crystalline phase, with dimensions generally close to those of the gaseous molecule and an eclipsed conformation of the C3PGaH3 skeleton. The results are discussed and analysed in the light of quantum chemical calculations and of the properties of related adducts of Group 13 metal hydrides.

Ditopic ligands have been designed and synthesized for the solvent extraction and membrane transport of transition metal salts for application in metal separation and purification processes. Tetradentate salicylaldimine ligands of the H2salen type bearing pendant tertiary amine groups undergo a zwitterionic transformation when binding metal salts, forming overall neutral assemblies which can be transferred into non-polar, water-immiscible solvents. A comparison of the solid state structures of copper(II) sulfate and neutral copper-only complexes demonstrates how incorporation of the metal ion into the salen2− unit preorganises the anion binding site to accommodate the sulfate group. The extraction/recovery characteristics of copper and sulfate are reported for a ligand which has been modified to lower the strength of copper-binding and thus facilitate copper-recovery and ligand-recycling. An X-ray structure determination of this 2,2′-biphenylene-bridged ligand indicates a predisposition towards the provision of a non-planar N2O22− donor-set. This is exemplified by its cis-octahedral nickel(II) sulfate complex in which the sulfate acts as a bidentate ligand. Competitive metal ion transport experiments show the selectivity of this ligand for copper(II) transport over a range of other metals including nickel(II) and zinc(II). The pH profiles for loading of Cu2+ (pH1/2 2.0, i.e. pH at 50 percent extraction) and of SO42− (pH1/2 9.7) into the ligand zwitterion in chloroform have been determined and this has allowed the demonstration of a protocol for loading of CuSO4, stripping of copper and sulfate separately and recycling of the extractant. Such a protocol provides proof-of-concept for application of these ditopic ligands in metal recovery from sulfide leaching or from acid mine drainage streams.

The nucleophilicity of the [Pt(2)S(2)] core in [[Ph(2)P(CH(2))(n)PPh(2)]Pt(mu-S)(2)Pt[Ph(2)P(CH(2))(n)PPh(2)]] (n = 3, dppp (1); n = 2, dppe (2)) metalloligands toward the CH(2)Cl(2) solvent has been thoroughly studied. Complex 1, which has been obtained and characterized by X-ray diffraction, is structurally related to 2 and consists of dinuclear molecules with a hinged [Pt(2)S(2)] central ring. The reaction of 1 and 2 with CH(2)Cl(2) has been followed by means of (31)P, (1)H, and (13)C NMR, electrospray ionization mass spectrometry, and X-ray data. Although both reactions proceed at different rates, the first steps are common and lead to a mixture of the corresponding mononuclear complexes [Pt[Ph(2)P(CH(2))(n)PPh(2)](S(2)CH(2))], n = 3 (7), 2 (8), and [Pt[Ph(2)P(CH(2))(n)PPh(2)]Cl(2)], n = 3 (9), 2 (10). Theoretical calculations give support to the proposed pathway for the disintegration process of the [Pt(2)S(2)] ring. Only in the case of 1, the reaction proceeds further yielding [Pt(2)(dppp)(2)[mu-(SCH(2)SCH(2)S)-S,S']]Cl(2) (11). To confirm the sequence of the reactions leading from 1 and 2 to the final products 9 and 11 or 8 and 10, respectively, complexes 7, 8, and 11 have been synthesized and structurally characterized. Additional experiments have allowed elucidation of the reaction mechanism involved from 7 to 11, and thus, the origin of the CH(2) groups that participate in the expansion of the (SCH(2)S)(2-) ligand in 7 to afford the bridging (SCH(2)SCH(2)S)(2-) ligand in 11 has been established. The X-ray structure of 11 is totally unprecedented and consists of a hinged [(dppp)Pt(mu-S)(2)Pt(dppp)] core capped by a CH(2)SCH(2) fragment.

Addition of a coligand in reactions of phosphonates with salts of late 3d metals can lead to more soluble and tractable materials, such as the {Co13 } cage shown (Co: green; P: purple). The structure contains two central PhPO32- ligands, surrounded by a hexanuclear cobalt helix, capped by seven further cobalt sites.

A series of oxo-centered metal carboxylate triangles have been heated to 200–400°C under a stream of N2. The products of this treatment depend on the metal, carboxylate, and counterion present. Heating [Cr3O(O2CC6H4Cl)6(H2O)3][NO3]to 200°C gives a compound that crystallizes as [Cr(OH)(O2CC6H4Cl)2]8 [Cr3O(O2CC6H4Cl)6]2[O2CC6H4Cl], indicating incomplete dehydration of [Cr3O(O2CC6H4Cl)6(H2O)3][NO3] at this temperature. For [Cr3O(O2CCMe3)6][O2CCMe3] heating to 400°C gives a new salt containing the hexanuclear cages [Cr6O2(OH)2(O2CCMe3)11] [Cr6O4(O2CCMe3)11]. For [Mn3O(O2CPh)6(NC5H5)2(H2O)] a reduction of the metal occurs and a polymeric complex [Mn4(O2CPh)8(EtOH)6]n can be crystallized from EtOH.

The molecular structures of 1,1‘-di-tert-butylferrocene (1) and isopropylferrocene (2) have been examined by solid-state X-ray crystallography, gas-phase electron diffraction, and DFT and molecular...

Treatment of dimethylmagnesium with Ar‘NC(tBu)CHC(tBu)NHAr‘ (Ar‘ = 2,6-diisopropylphenyl) in THF provides the β-diketiminate complex [CH3Mg(THF){η2-(Ar‘NCtBu)2CH}]. The THF ligand may be removed fr...

The series of compounds ButX2SiSiX2But (X = Cl, Br and I) have been studied by X-ray crystallography, vibrational spectroscopy and ab initio calculations. The solids were all found to be anti and the vibrational spectra are consistent with this observation. The molecular structure of 1,2-di-tert-butyltetrachlorodisilane, ButCl2SiSiCl2But, has also been determined in the gas phase by electron diffraction (GED) and ab initio molecular-orbital calculations. The conformation is distorted slightly from the fully staggered arrangement, with ϕ(CSiSiC) 167.7(11)°. Important structural parameters (ra) include: Si–Si 238.0(7) pm, Si–C 187.2(7) pm, C–C 154.3(2) pm, C–H 114.2(4) pm, Si–Si–C 119.8(6)°, Cl–Si–Cl 105.5(8)° and C–Si–Si–C 167.7(11)°. These experimental observations are supported by theoretical predictions obtained at the MP2/6-31G* level.

The adduct Me2(H)N·AlH3 (1) has been isolated for the first time at low temperatures from the reaction of [Me2NH2]Cl with LiAlH4 in Et2O solution at ca. 250 K. Single crystals of this and of the corresponding gallane Me2(H)N·GaH3 (2) have been grown, also at low temperature; the structures of these at 150 K determined by X-ray diffraction reveal dimeric units Me2(H)N·H2M(μ-H)2MH2·N(H)Me2 with highly unsymmetrical M–H⋯M hydrogen bridges, as well as evidence of significant intermolecular N–H⋯H–M interactions, particularly for M = Al. The M–N distances are quite similar [1 2.028(1), 2 2.079(3) A], but the M⋯M distance in 2 [3.7519(15) A] is much longer than in 1 [2.8743(8) A]. The adducts decompose at ambient temperatures, rapidly in the case of 1, slowly in the case of 2, with the elimination of H2 and the formation of the corresponding dimethylamido derivative. Unlike the vapour at low pressure in which the dimeric molecule predominates, crystals of the gallane (3) at 150 K are composed of trimers [Me2NGaH2]3 structurally analogous to the corresponding alane, with a chair-like conformation and a mean Ga–N distance of 1.981(3) A.

The reaction of Zn(II) and Co(II) with thiosalicylic acid, o-HSC6H4COOH, and its methyl ester has led to the following complexes: [Zn(SC6H4COO)] (1), (NEt4)Na[Zn(SC6H4COO)2].H2O (2), (NEt4)2Na[Co(SC6H4COO)3].2H2O (3), (NEt4)3Na3[(Co(SC6H4COO)3)2].6MeOH (4), [Zn(SC6H4COOMe)2] (5), and [Co(SC6H4COOMe)n], n = 2 (6), 3 (7). These ligands have not allowed stabilization of Co(II) in a sulfur-oxygen coordination environment. The structures of complexes 2-4 and 7 have been determined crystallographically. Those of 2-4 show significant similarities such as the behavior of the -SC6H4COO- anion as chelating ligand and the involvement of sodium ions as a structural element. Thus, the structure of the [Na(Zn(SC6H4COO)2)(H2O)]- anion in complex 2 can be described as infinite chains of consecutive [Zn(SC6H4COO)2]2- metalloligands linked by [Na(H2O)]+ centers, that of the [Na(Co(SC6H4COO)3(H2O)2)]2(4-) anion in 3 as a centrosymmetric tetranuclear Co2Na2 dimer with a (CoIII(S[symbol: see text]O)3)Na(mu-H2O)2Na(CoIII(S[symbol: see text]O)3) core, and that of the pentanuclear [Na3(Co(SC6H4COO)3)2(MeOH)6]3- anion in 4 as two dinuclear [(CoIII(S[symbol: see text]O)3)Na(MeOH)3] fragments linked to a central sodium ion, which appears to be the first structurally characterized example of a NaS6 site. The use of the o-HSC6H4COOMe ligand allowed the synthesis of [Co(SC6H4COOMe)2] (6) but not its full structural characterization. Instead, [Co(SC6H4COOMe)3] (7) was obtained and structurally characterized. It consists of mononuclear molecules containing an octahedral CoIIIS3O3 core. The selection of 2,2-diphenyl-2-mercaptoacetic acid as ligand with reductive properties has afforded the first mononuclear complex containing a CoIIS2O2 core and thus an unprecedented model for Co(II)-substituted metalloproteins containing tetrahedral MS2O2 active sites. The synthesis and full structural characterization of the isostructural complexes (NEt4)2[Zn(Ph2C(S)COO)2] (8) and (NEt4)2[Co(Ph2C(S)COO)2] (9) show that they consist of discrete [M(Ph2C(S)COO)2]2- anions, with a distorted tetrahedral coordination about the metal. In addition, the stability conferred by the ligand on the CoIIS2O2 core has allowed its characterization in solution by paramagnetic 1D and 2D 1H NMR studies. The longitudinal relaxation times of the hyperfine-shifted resonances and NOESY spectra have led to the assignment of all resonances of the cobalt complex and confirmed that it maintains its tetrahedral geometry in solution. Magnetic measurements (2-300 K) for complex 9 and 9.2H2O are in good agreement with distorted tetrahedral and octahedral environments, respectively.

Two ligands have been synthesized by derivatisation of cyanuric chloride: 6-(diethylamino)-2,4-disulfanyl-1,3,5-triazine (H2SSta) 1 and 6-(diethylamino)-2-hydroxo-4-sulfanyl-1,3,5-triazine (H2OSta) 2 have been characterised by X-ray crystallography, which shows intermolecular hydrogen bonding in the solid state, leading to dimers of 1 and ribbons of 2. On reaction with metal salts both ligands undergo oligomerisation reactions. Compound 1 reacts with nickel chloride to form a mononuclear complex, [Ni{(Sta)S(S2ta)}] 3. In 3 two triazine ligands have reacted, to form a tetradentate ligand in which two triazine rings are bridged by a sulfur group, with a co-ordinated disulfide group present on one ring and a co-ordinated thiolate on the second. Compound 2 reacts with cobalt(II) chloride to form a cage complex, [Co6NaO(OStaH)7{S(Ota)2}2(O2CPh)2(H2O)2] 4. This complicated structure contains two polydentate ligands formed by linking triazine groups through a bridging sulfur. The cage contains four cobalt(II) and two cobalt(III) sites which are assigned by bond length considerations. The compound [Co(OSta)3] 5 co-crystallises with 4, and its structure has also been determined.

The reaction of [Pt2(dppe)2(µ-S)2] 1, with metal complexes or metal salts gave different types of complexes depending on the nature of the heterometal and of the stoichiometric ratios employed. Thus, a trinuclear complex of formula [Pt(dppe){Pt2(dppe)2(µ3-S)2}]Cl2 2 and an apparently mixed PdxPt3-x product 3 have been prepared and characterised. Alternatively, dissolution of 1 in chlorinated solvents affords 2 easily and 3 is formed from 1 with [PdCl2(dppe)]. The pentanuclear complexes of formula [M{Pt2(dppe)2(µ3-S)2}2]X2 (M = Zn 4 or Cd 5, X = ClO4; M = Cd, X2 = [CdCl4] 5′; M = Hg, X2 = [PF6][HgCl4]0.5 6) have been obtained. The structures of complexes 2, 3, 4, 5, 5′ and 6 have been determined crystallographically. Complex 2 comprises three slightly distorted square-planar cis-PtP2S2 co-ordination planes sharing two µ3-S ligands. X-Ray data and NMR studies in solution of different crops of crystals support that 3 is essentially a simple solid-solution mixture of pure complexes [Pd(dppe){Pt2(dppe)2(µ3-S)2}][BPh4]2 3′ and [Pt(dppe){Pd2(dppe)2(µ3-S)2}][BPh4]2 3″ in variable proportions with at most a minor component of the homometallic complex 2. The structure of the cations of complexes 4, 5, 5′ and 6 comprises two {Pt2S2} butterflies linked through sulfur to the metal(II) ion, which shows a significantly distorted tetrahedral environment. All complexes have been fully characterised by multinuclear NMR techniques and the corresponding parameters are reported.

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.

The organophosphonate-substituted alkoxides [Bu4nN]2[{Ti(OMe)3(O3PPh)}2] (1) and [Bu4nN]2[{Nb(OMe)3(O3PPh)}2(μ-O)] (2) have been prepared from [Bu4nN][PhPO3H] and the metal alkoxides Ti(OMe)4 or Nb(OMe)5 respectively. In 1, the bridging phenylphosphonates occupy trans coordination sites, whereas in 2, a cis–bridging geometry is adopted.

The tetra-n-butylammonium (TBA) salt of [(MeO)TiW(5)O(18)](3-) 1 was reacted with alcohols ROH to give primary, secondary and tertiary alkoxide derivatives [(RO)TiW(5)O(18)](3-) (R = Et 2, (i)Pr 3 and (t)Bu 4), whilst hydrolysis afforded [(mu-O)(TiW(5)O(18))(2)](6-) 5 rather than the hydroxo derivative (R = H). In reactions with (i)PrOH and (t)BuOH, impurity peaks observed at 1015 and 1020 ppm in the (17)O NMR spectra indicate alkoxide degradation and Ti=O bond formation via reactions analogous to those occurring at the surfaces of solid heteropolyacids. Aryloxides [(ArO)TiW(5)O(18)](3-) were prepared by reacting 1 with phenols ArOH (Ar = C(6)H(5) 6, C(6)H(4)Me-4 7, C(6)H(4)(t)Bu-4 8, C(6)H(4)OH-4 9, C(6)H(4)OH-3 10, C(6)H(3)(OH)(2)-3,5 11 and C(6)H(4)CHO-2 13). TiW(5)O(18) units were linked by reacting 1 with 9 to give [(mu-1,4-OC(6)H(4)O)(TiW(5)O(18))(2)](6-) 12. (17)O and (183)W NMR spectra are reported and X-ray crystal structures were obtained for TBA salts of anions 3-10 and 13, which showed that the titanium is six-coordinate in all cases. Reactions were monitored by (1)H NMR, including a 2D-EXSY study of methoxo exchange, and the slow rates observed are probably associated with the reluctance of titanium in these anions to achieve seven-coordination.

The methoxo-bridged, dimeric, ZrIV-substituted Lindqvist-type polyoxometalate (POM) (nBu4N)6[{(mu-MeO)ZrW5O18}2], (TBA)61, has been synthesized by stoichiometric hydrolysis of Zr(OnPr)4, [{Zr(OiPr)3(mu-OnPr)(iPrOH)}2], or [{Zr(OiPr)4(iPrOH)}2] and [{WO(OMe)4}2] in the presence of (nBu4N)2WO4, providing access to the systematic nonaqueous chemistry of ZrW5 POMs for the first time and an efficient route to 17O-enriched samples for 17O NMR studies. 1H NMR provided no evidence for dissociation of 1 in solution, although exchange with MeOH was shown to be slow by an EXSY study. Reactions with HX at elevated temperatures gave a range of anions [{XZrW5O18}n]3n- (X = OH, 3; OPh, 4; OC6H4Me-4, 5; OC6H4(CHO)-2, 6; acac, 7; OAc, 8), where n = 2 for 3 and n = 1 for 4-8, while 1H and 17O NMR studies of hydrolysis of 1 revealed the formation of an intermediate [(mu-MeO)(mu-HO)(ZrW5O18)2]6-. Electrospray ionization mass spectrometry of 1 and 3 illustrated the robust nature of the ZrW5O18 framework, and X-ray crystal structure determinations showed that steric interactions between ligands X and the ZrW5O18 surface are important. The coordination number of Zr is restricted to six in aryloxides 4 and 5, while seven-coordination is achieved in the chelate complexes 6-8. Given the inert nature of the methoxo bridges in 1, protonation of ZrOW sites is proposed as a possible step in reactions with HX. The diphenylphosphinate ligand in [(Ph2PO2)ZrW5O18]3- was found to be labile and upon attempted recrystallization the aggregate [(mu3-HO)2(ZrW5O18)3H]7- 9 was formed, which was found to be protonated at ZrOZr and ZrOW sites. This work demonstrates the flexibility of the {ZrW5O18}2- core as a molecular platform for modeling catalysis by tungstated zirconia surfaces.

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.

Errington, John/0000-0001-5696-0332; Clegg, William/0000-0003-1643-5298; WOS: 000181609600023 The title compound, (CH3CNLiOC6H5)(4) or [Li-4 (C6H5O)(4) (C2H3N)(4)], is tetrameric with a distorted Li4O4 cube core. The molecule has crystallographic (4) over bar symmetry. Each Li atom has distorted tetrahedral coordination, with bonds to three triply bridging phenoxo ligands and a terminal acetonitrile ligand derived from the solvent in the synthesis.

Errington, John/0000-0001-5696-0332; Clegg, William/0000-0003-1643-5298 WOS: 000183345100017 PubMed: 12794331 The title compound, bis(borato) dodeca(tert-butoxo)octadeca-lithium, [Li-18(BO3)(2)(C4H9O)(12)], is formulated conveniently as [{((BuOLi)-Bu-t)(3)(Li3BO3)}(2)((BuOLi)-Bu-t)(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 [BO3](3-) anion. Thus, the molecule consists of a cationic [Li-18((OBu)-Bu-t)(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.

Organometallic ruthenium(II) arene anticancer complexes of the type [(eta(6)-arene)Ru(II)(en)Cl][PF(6)] (en = ethylenediamine) specifically target guanine bases of DNA oligomers and form monofunctional adducts (Morris, R., et al. J. Med. Chem. 2001). We have determined the structures of monofunctional adducts of the "piano-stool" complexes [(eta(6)-Bip)Ru(II)(en)Cl][PF(6)] (1, Bip = biphenyl), [(eta(6)-THA)Ru(II)(en)Cl][PF(6)] (2, THA = 5,8,9,10-tetrahydroanthracene), and [(eta(6)-DHA)Ru(II)(en)Cl][PF(6)] (3, DHA = 9,10-dihydroanthracene) with guanine derivatives, in the solid state by X-ray crystallography, and in solution using 2D [(1)H,(1)H] NOESY and [(1)H,(15)N] HSQC NMR methods. Strong pi-pi arene-nucleobase stacking is present in the crystal structures of [(eta(6)-C(14)H(14))Ru(en)(9EtG-N7)][PF(6)](2).(MeOH) (6) and [(eta(6)-C(14)H(12))Ru(en)(9EtG-N7)][PF(6)](2).2(MeOH) (7) (9EtG = 9-ethylguanine). The anthracene outer ring (C) stacks over the purine base at distances of 3.45 A for 6 and 3.31 A for 7, with dihedral angles of 3.3 degrees and 3.1 degrees, respectively. In the crystal structure of [(eta(6)-biphenyl)Ru(en)(9EtG-N7)][PF(6)](2).(MeOH) (4), there is intermolecular stacking between the pendant phenyl ring and the purine six-membered ring at a distance of 4.0 A (dihedral angle 4.5 degrees). This stacking stabilizes a cyclic tetramer structure in the unit cell. The guanosine (Guo) adduct [(eta(6)-biphenyl)Ru(en)(Guo-N7)][PF(6)](2).3.75(H(2)O) (5) exhibits intramolecular stacking of the pendant phenyl ring with the purine five-membered ring (3.8 A, 23.8 degrees) and intermolecular stacking of the purine six-membered ring with an adjacent pendant phenyl ring (4.2 A, 23.0 degrees). These occur alternately giving a columnar-type structure. A syn orientation of arene and purine is present in the crystal structures 5, 6, and 7, while the orientation is anti for 4. However, in solution, a syn orientation predominates for all the biphenyl adducts 4, 5, and the guanosine 5'-monophosphate (5'-GMP) adduct 8 [(eta(6)-biphenyl)Ru(II)(en)(5'-GMP-N7)], as revealed by NMR NOE studies. The predominance of the syn orientation both in the solid state and in solution can be attributed to hydrophobic interactions between the arene and purine rings. There are significant reorientations and conformational changes of the arene ligands in [(eta(6)-arene)Ru(II)(en)(G-N7)] complexes in the solid state, with respect to those of the parent chloro-complexes [(eta(6)-arene)Ru(II)(en)Cl](+). The arene ligands have flexibility through rotation around the arene-Ru pi-bonds, propeller twisting for Bip, and hinge-bending for THA and DHA. Thus propeller twisting of Bip decreases by ca. 10 degrees so as to maximize intra- or intermolecular stacking with the purine ring, and stacking of THA and DHA with the purine is optimized when their tricyclic ring systems are bent by ca. 30 degrees, which involves increased bending of THA and a flattening of DHA. This flexibility makes simultaneous arene-base stacking and N7-covalent binding compatible. Strong stereospecific intramolecular H-bonding between an en NH proton oriented away from the arene (en NH(d)) and the C6 carbonyl of G (G O6) is present in the crystal structures of 4, 5, 6, and 7 (average N...O distance 2.8 A, N-H...O angle 163 degrees ). NMR studies of the 5'-GMP adduct 8 provided evidence that en NH(d) protons are involved in strong H-bonding with the 5'-phosphate and O6 of 5'-GMP. The strong H-bonding from G O6 to en NH(d) protons partly accounts for the high preference for binding of [(eta(6)-arene)Ru(II)en](2+) to G versus A (adenine). These studies suggest that simultaneous covalent coordination, intercalation, and stereospecific H-bonding can be incorporated into Ru(II) arene complexes to optimize their DNA recognition behavior, and as potential drug design features.

Two new octanuclear cages are reported which feature formate as a bridging carboxylate which has been formed in situ from decomposition of triphenylacetate used as a ligand.

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.

Treatment of dimethylmagnesium with bulky alpha-diimine ligands provides either the biradical methyl-bridged complexes [(alpha-diimine-.)Mg+(mu-CH3)]2 via single electron transfer (SET), or the product of methyl transfer to an imine carbon atom depending upon conditions.