Synthesis, characterization, and stereochemistry of S-bridged Co(III)MCo(III)(M = Pd(II), Pt(II)) trinuclear complexes containing two non-bridging thiolato groups: building blocks for the construction of chiral heterometallic aggregates

The reaction of fac(S)-[Co(aet)(3)](aet = aminoethanethiolate) with [PdCl(4)](2-) in a 2:1 ratio in water gave an S-bridged Co(III)Pd(II)Co(III) trinuclear complex composed of two mer(S)-[Co(aet)(3)] units, [Pd[Co(aet)(3)](2)](2+)([1](2+)). In [1](2+), each of the two mer(S)-[Co(aet)(3)] units is bound to a square-planar Pd(II) ion through two of three thiolato groups, leaving two non-bridging thiolato groups at the terminal. Of two geometrical forms, syn and anti, possible for [Pd[Co(aet)(3)](2)](2+), which arise from the difference in arrangement of two terminal non-bridging thiolato groups, [1](2+) afforded only the syn form. A similar reaction of fac(S)-[Co(aet)(3)] with [PtCl(4)](2-) or trans-[PtCl(2)(NH(3))(2)] produced an analogous Co(III)Pt(II)Co(III) trinuclear complex, [Pt[Co(aet)(3)](2)](2+)([2](2+)), but both the syn and anti forms were formed for [2](2+). Complexes [1](2+) and syn- and anti-[2](2+), which exclusively exist as a racemic(DeltaDelta/LambdaLambda) form, were successfully optically resolved with use of [Sb(2)(R,R-tartrato)(2)](2-) as the resolving agent. The reaction of syn-[2](2+) with [AuCl[S(CH(2)CH(2)OH)(2)]] led to the formation of an S-bridged Co(III)(4)Pt(II)(2)Au(I)(2) octanuclear metallacycle, [Au(2)[Pt[Co(aet)(3)](2)](2)](6+)([3](6+)), while the corresponding reaction of anti-[2](2+) afforded a different product ([[4](3+)](n)) that is assumed to have a polymeric structure in [[Au[Pt[Co(aet)(3)](2)]](3+)](n).     

Sulfur-bridged Co(III)Pt(II)Co(III) trinuclear complexes with mixed aliphatic and aromatic thiolate ligands: effect of nonbridging ligands on the homochiral linkage of cobalt(III) octahedrons by platinum(II)

The reaction of [Ni[Co(aet)(2)(pyt)](2)](2+) (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with [PtCl(4)](2)(-) gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex composed of two [Co(aet)(2)(pyt)] units, [Pt[Co(aet)(2)(pyt)](2)](2+) ([1](2+)). When a 1:1 mixture of [Ni[Co(aet)(2)(pyt)](2)](2+) and [Ni[Co(aet)(2)(en)](2)](4+) was reacted with [PtCl(4)](2)(-), a mixed-type S-bridged Co(III)Pt(II)Co(III) complex composed of one [Co(aet)(2)(pyt)] and one [Co(aet)(2)(en)](+) units, [Pt[Co(aet)(2)(en)][Co(aet)(2)(pyt)]](3+) ([2](3+)), was produced, together with [1](2+) and [Pt[Co(aet)(2)(en)](2)](4+). The corresponding Co(III)Pt(II)Co(III) trinuclear complexes containing pymt (2-pyrimidinethiolate), [Pt[Co(aet)(2)(pymt)](2)](2+) ([3](2+)) and [Pt[Co(aet)(2)(en)][Co(aet)(2)(pymt)]](3+) ([4](3+)), were also obtained by similar reactions, using [Ni[Co(aet)(2)(pymt)](2)](2+) instead of [Ni[Co(aet)(2)(pyt)](2)](2+). While [Pt[Co(aet)(2)(en)](2)](4+) formed both the deltalambda (meso) and deltadelta/lambdalambda (racemic) forms in a ratio of ca. 1:1, the preferential formation of the deltadelta/lambdalambda form was observed for [1](2+) (ca. deltalambda:deltadelta/lambdalambda = 1:3) and [2](3+) (ca. delta(en)lambda(pyt)/lambda(en)delta(pyt):deltadelta/lambdalambda = 1:2). Furthermore, [3](2+) and [4](3+) predominantly formed the deltadelta/lambdalambda form. These results indicate that the homochiral selectivity for the S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of two octahedral [Co(aet)(2)(L)](0 or +) units is enhanced in the order L = en < pyt < pymt. The isomers produced were separated and optically resolved, and the crystal structures of the meso-type deltalambda-[1]Cl(2).4H(2)O and the spontaneously resolved deltadelta-[4](ClO(4))(3).H(2)O were determined by X-ray analyses. In deltalambda-[1](2+), the delta and Lambda configurational mer(S).trans(N(aet))-[Co(aet)(2)(pyt)] units are linked by a square-planar Pt(II) ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In deltadelta-[4](3+), a similar linear-type trinuclear structure is constructed from the delta-mer(S).trans(N(aet))-[Co(aet)(2)(pymt)] and delta-C(2)-cis(S)-[Co(aet)(2)(en)](+) units that are bound by a Pt(II) ion with a slightly distorted square-planar geometry through four aet S atoms.     

Chemistry of cobalt acetate. 7. Electrochemical oxidation of mu3-oxo-centered cobalt(III) acetate trimers

Electrochemical and spectroelectrochemical properties of five cobalt(III) acetate complexes [CoIII3(mu3-O)(CH3CO2)5(OR)(py)3][PF6] are described, where py=pyridine and R=OCCH3 (A), H (B), CH3 (C), CH2CH=CH2 (D), and CH2C6H5 (E). Each is reduced irreversibly as observed by cyclic voltammetry at room temperature and at -40 degrees C in acetonitrile at scan rates up to 20 V s(-1), but oxidized reversibly to a mixed-valence Co(III)2Co(IV) species at approximately 1.23 V vs the ferrocenium/ferrocene couple. Controlled potential coulometry confirmed a one-electron-oxidation process. Spectroelectrochemical oxidation of A at 5 degrees C showed isosbestic points in the electronic absorption spectrum that showed the oxidized complex to be stable in solution for at least 1 h.     

High-nuclearity metal-cyanide clusters: synthesis,magnetic properties,and inclusion behavior of open-cage species incorporating [(tach)M(CN)3] (M = Cr,Fe, Co) complexes

The use of 1,3,5-triaminocyclohexane (tach) as a capping ligand in generating metal-cyanide cage clusters with accessible cavities is demonstrated. The precursor complexes [(tach)M(CN)(3)] (M = Cr, Fe, Co) are synthesized by methods similar to those employed in preparing the analogous 1,4,7-triazacyclononane (tacn) complexes. Along with [(tach)Fe(CN)(3)](1)(-), the latter two species are found to adopt low-spin electron configurations. Assembly reactions between [(tach)M(CN)(3)] (M = Fe, Co) and [M'(H(2)O)(6)](2+) (M' = Ni, Co) in aqueous solution afford the clusters [(tach)(4)(H(2)O)(12)Ni(4)Co(4)(CN)(12)](8+), [(tach)(4)(H(2)O)(12)Co(8)(CN)(12)](8+), and [(tach)(4)(H(2)O)(12)Ni(4)Fe(4)(CN)(12)](8+), each possessing a cubic arrangement of eight metal ions linked through edge-spanning cyanide bridges. This geometry is stabilized by hydrogen-bonding interactions between tach and water ligands through an intervening solvate water molecule or bromide counteranion. The magnetic behavior of the Ni(4)Fe(4) cluster indicates weak ferromagnetic coupling (J = 5.5 cm(-)(1)) between the Ni(II) and Fe(III) centers, leading to an S = 6 ground state. Solutions containing [(tach)Fe(CN)(3)] and a large excess of [Ni(H(2)O)(6)](2+) instead yield a trigonal pyramidal [(tach)(H(2)O)(15)Ni(3)Fe(CN)(3)](6+) cluster, in which even weaker ferromagnetic coupling (J = 1.2 cm(-)(1)) gives rise to an S = (7)/(2) ground state. Paralleling reactions previously performed with [(Me(3)tacn)Cr(CN)(3)], [(tach)Cr(CN)(3)] reacts with [Ni(H(2)O)(6)](2+) in aqueous solution to produce [(tach)(8)Cr(8)Ni(6)(CN)(24)](12+), featuring a structure based on a cube of Cr(III) ions with each face centered by a square planar [Ni(CN)(4)](2)(-) unit. The metal-cyanide cage differs somewhat from that of the analogous Me(3)tacn-ligated cluster, however, in that it is distorted via compression along a body diagonal of the cube. Additionally, the compact tach capping ligands do not hinder access to the sizable interior cavity of the molecule, permitting host-guest chemistry. Mass spectrometry experiments indicate a 1:1 association of the intact cluster with tetrahydrofuran (THF) in aqueous solution, and a crystal structure shows the THF molecule to be suspended in the middle of the cluster cavity. Addition of THF to an aqueous solution containing [(tach)Co(CN)(3)] and [Cu(H(2)O)(6)](2+) templates the formation of a closely related cluster, [(tach)(8)(H(2)O)(6)Cu(6)Co(8)(CN)(24) superset THF](12+), in which paramagnetic Cu(II) ions with square pyramidal coordination are situated on the face-centering sites. Reactions intended to produce the cubic [(tach)(4)(H(2)O)(12)Co(8)(CN)(12)](8+) cluster frequently led to an isomeric two-dimensional framework, [(tach)(H(2)O)(3)Co(2)(CN)(3)](2+), exhibiting mer rather than fac stereochemistry at the [Co(H(2)O)(3)](2+) subunits. Attempts to assemble larger edge-bridged cubic clusters by reacting [(tach)Cr(CN)(3)] with [Ni(cyclam)](2+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) complexes instead generated extended one- or two-dimensional solids. The magnetic properties of one of these solids, two-dimensional [(tach)(2)(cyclam)(3)Ni(3)Cr(2)(CN)(6)]I(2), suggest metamagnetic behavior, with ferromagnetic intralayer coupling and weak antiferromagnetic interactions between layers.     

Encapsulation of cyanometalates by a tris-macrocyclic ligand tricopper(II) complex: syntheses, structural variation, and magnetic exchange coupling pathways

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.     

Synthesis and DNA binding of novel water-soluble cationic methylcobalt porphyrins

Organocobalt derivatives of tetracationic water-soluble porphyrins are difficult to prepare via the typical reductive alkylation of the Co(II)(por) (porH(2) = porphyrin ligand). None have been reported. The problem may arise because the porphyrin core is made relatively electron poor by the positively charged peripheral groups. We have circumvented this problem by using the [Co(III)(NH(3))(5)CH(3)](2+) reagent, which inserts the Co(III)-CH(3) moiety directly into porH(2) in water under basic conditions. The method afforded two new [CH(3)Co(por)](4+) derivatives, [CH(3)CoTMpyP(4)](4+) and [CH(3)CoTMAP](4+), where [TMpyP(4)](4+) and [TMAP](4+) are the coordinated, NH-deprotonated forms of meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin and meso-tetrakis(N,N,N-trimethylaniliniumyl)porphyrin, respectively. The binding of the two new [CH(3)Co(por)](4+) cations to DNA and to the synthetic DNA polymers [poly(dA-dT)](2) and [poly(dG-dC)](2) was studied. Using published criteria by which changes in DNA viscosity and in the visible and CD spectra in the Soret region can be used to assess DNA binding, we conclude that both are outside binders. A large hypochromicity of the Soret bands of the [CH(3)Co(por)](4+) cations observed upon outside binding to DNA may indicate a high degree of self-stacking. The visible absorption and CD spectra of the [CH(3)Co(por)](4+) cations in the presence of 1:1 mixtures of [poly(dA-dT)](2) and [poly(dG-dC)](2) are nearly identical to those with [poly(dA-dT)](2) alone and are very different from those of [poly(dG-dC)](2) alone. Thus, both cations show a high preference for outside binding at AT-rich over GC-rich DNA sites. Upon binding of each of the [CH(3)Co(por)](4+) cations to all of the DNA polymers, the Soret bands exhibit blue shifts, whereas the Soret bands of the corresponding [(H(2)O)(2)Co(por)](5+) cations exhibit red shifts. The blue shifts strongly suggest that the [CH(3)Co(por)](4+) cations, particularly [CH(3)CoTMAP](4+), become five-coordinate forms to some extent on DNA binding; this result is the first good evidence for the presence at equilibrium of five-coordinate CH(3)Co(III)(N(4)) forms in water.     

Synthesis and characterization of iron(III)-substituted, dimeric polyoxotungstates, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](n-) (n = 6, X = As(III), Sb(III); n = 4, X = Se(IV), Te(IV))

Interaction of the lacunary [alpha-XW(9)O(33)](9-) (X = As(III), Sb(III)) with Fe(3+) ions in acidic, aqueous medium leads to the formation of dimeric polyoxoanions, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)) in high yield. X-ray single-crystal analyses were carried out on Na(6)[Fe(4)(H(2)O)(10)(beta-AsW(9)O(33))(2)] x 32H(2)O, which crystallizes in the monoclinic system, space group C2/m, with a = 20.2493(18) A, b = 15.2678(13) A, c = 16.0689(14) A, beta = 95.766(2) degrees, and Z = 2; Na(6)[Fe(4)(H(2)O)(10)(beta-SbW(9)O(33))(2)] x 32H(2)O is isomorphous with a = 20.1542(18) A, b = 15.2204(13) A, c = 16.1469(14) A, and beta = 95.795(2) degrees. The selenium and tellurium analogues are also reported, [Fe(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](4-) (X = Se(IV), Te(IV)). They are synthesized from sodium tungstate and a source of the heteroatom as precursors. X-ray single-crystal analysis was carried out on Cs(4)[Fe(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)] x 21H(2)O, which crystallizes in the triclinic system, space group P macro 1, with a = 12.6648(10) A, b = 12.8247(10) A, c = 16.1588(13) A, alpha = 75.6540(10) degrees, beta = 87.9550(10) degrees, gamma = 64.3610(10) gamma, and Z = 1. All title polyanions consist of two (beta-XW(9)O(33)) units joined by a central pair and a peripheral pair of Fe(3+) ions leading to a structure with idealized C(2h) symmetry. It was also possible to synthesize the Cr(III) derivatives [Cr(4)(H(2)O)(10)(beta-XW(9)O(33))(2)](6-) (X = As(III), Sb(III)), the tungstoselenates(IV) [M(4)(H(2)O)(10)(beta-SeW(9)O(33))(2)]((16)(-)(4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Zn(2+), Cd(2+), and Hg(2+)), and the tungstotellurates(IV) [M(4)(H(2)O)(10)(beta-TeW(9)O(33))(2)]((16-4n)-) (M(n+) = Cr(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Hg(2+)), as determined by FTIR. The electrochemical properties of the iron-containing species were also studied. Cyclic voltammetry and controlled potential coulometry aided in distinguishing between Fe(3+) and W(6+) waves. By variation of pH and scan rate, it was possible to observe the stepwise reduction of the Fe(3+) centers.     

Electron and hydrogen-atom self-exchange reactions of iron and cobalt coordination complexes

Reported here are self-exchange reactions between iron 2,2'-bi(tetrahydro)pyrimidine (H(2)bip) complexes and between cobalt 2,2'-biimidazoline (H(2)bim) complexes. The (1)H NMR resonances of [Fe(II)(H(2)bip)(3)](2+) are broadened upon addition of [Fe(III)(H(2)bip)(3)](3+), indicating that electron self-exchange occurs with k(Fe,e)(-) = (1.1 +/- 0.2) x 10(5) M(-1) s(-1) at 298 K in CD(3)CN. Similar studies of [Fe(II)(H(2)bip)(3)](2+) plus [Fe(III)(Hbip)(H(2)bip)(2)](2+) indicate that hydrogen-atom self-exchange (proton-coupled electron transfer) occurs with k(Fe,H.) = (1.1 +/- 0.2) x 10(4) M(-1) s(-1) under the same conditions. Both self-exchange reactions are faster at lower temperatures, showing small negative enthalpies of activation: DeltaH++(e(-)) = -2.1 +/- 0.5 kcal mol(-1) (288-320 K) and DeltaH++(H.) = -1.5 +/- 0.5 kcal mol(-1) (260-300 K). This behavior is concluded to be due to the faster reaction of the low-spin states of the iron complexes, which are depopulated as the temperature is raised. Below about 290 K, rate constants for electron self-exchange show the more normal decrease with temperature. There is a modest kinetic isotope effect on H-atom self-exchange of 1.6 +/- 0.5 at 298 K that is close to that seen previously for the fully high-spin iron biimidazoline complexes.(12) The difference in the measured activation parameters, E(a)(D) - E(a)(H), is -1.2 +/- 0.8 kcal mol(-1), appears to be inconsistent with a semiclassical view of the isotope effect, and suggests extensive tunneling. Reactions of [Co(H(2)bim)(3)](2+)-d(24) with [Co(H(2)bim)(3)](3+) or [Co(Hbim)(H(2)bim)(2)](2+) occur with scrambling of ligands indicating inner-sphere processes. The self-exchange rate constant for outer-sphere electron transfer between [Co(H(2)bim)(3)](2+) and [Co(H(2)bim)(3)](3+) is estimated to be 10(-)(6) M(-1) s(-1) by application of the Marcus cross relation. Similar application of the cross relation to H-atom transfer reactions indicates that self-exchange between [Co(H(2)bim)(3)](2+) and [Co(Hbim)(H(2)bim)(2)](2+) is also slow, < or =10(-3) M(-1) s(-1). The slow self-exchange rates for the cobalt complexes are apparently due to their interconverting high-spin [Co(II)(H(2)bim)(3)](2+) with low-spin Co(III) derivatives.     

Gas-phase coordination complexes of dipositive plutonyl, PuO2(2+): chemical diversity across the actinyl series

We report the first transmission of solvent-coordinated dipositive plutonyl ion, Pu(VI)O(2)(2+), from solution to the gas phase by electrospray ionization (ESI) of plutonyl solutions in water/acetone and water/acetonitrile. ESI of plutonyl and uranyl solutions produced the isolable gas-phase complexes, [An(VI)O(2)(CH(3)COCH(3))(4,5,6)](2+), [An(VI)O(2)(CH(3)COCH(3))(3)(H(2)O)](2+), and [An(VI)O(2)(CH(3)CN)(4)](2+); additional complex compositions were observed for uranyl. In accord with relative actinyl stabilities, U(VI)O(2)(2+) > Pu(VI)O(2)(2+) > Np(VI)O(2)(2+), the yields of plutonyl complexes were about an order of magnitude less than those of uranyl, and dipositive neptunyl complexes were not observed. Collision-induced dissociation (CID) of the dipositive coordination complexes in a quadrupole ion trap produced doubly- and singly-charged fragment ions; the fragmentation products reveal differences in underlying chemistries of plutonyl and uranyl, including the lower stability of Pu(VI) as compared with U(VI). Particularly notable was the distinctive CID fragment ion, [Pu(IV)(OH)(3)](+) from [Pu(VI)O(2)(CH(3)COCH(3))(6)](2+), where the plutonyl structure has been disrupted and the tetravalent plutonium hydroxide produced; this process was not observed for uranyl.     

Excellent correlation between drug release and portal size in metalla-cage drug-delivery systems

A series of large cationic hexanuclear metalla-prisms, [Ru(6)(p-iPrC(6)H(4)Me)(6)(tpt)(2)(donq)(3)](6+), [Ru(6)(p-iPrC(6)H(4)Me)(6)(tpt)(2)(doaq)(3)](6+) and [Ru(6)(p-iPrC(6)H(4)Me)(6)(tpt)(2)(dotq)(3)](6+), composed of p-cymene-ruthenium building blocks bridged by OO∩OO ligands (donq=5,8-dioxido-1,4-naphthoquinonato; doaq=5,8-dioxido-1,4-anthraquinonato, dotq=6,11-dioxido-5,12-naphthacenedionato) and connected by two 2,4,6-tripyridin-4-yl-1,3,5-triazine (tpt) panels, which encapsulate the guest molecules 1-(4,6-dichloro-1,3,5-triazin-2-yl)pyrene and Pd(acac)(2), have been prepared. The host-guest properties of these water-soluble delivery systems were studied in solution by NMR and fluorescence spectroscopy, providing the stability constants (K) for these host-guest systems. Moreover, the ability of the hosts to deliver the guests into cancer cells was evaluated and the uptake mechanism studied; the rate of release of the guest molecule was found to depend on the portal size of the host.     

Redox-switched complexation/decomplexation of K(+) and Cs(+) by molecular cyanometalate boxes

The reaction of [N(PPh(3))(2)][CpCo(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6) (Cb* = C(4)Me(4)) in the presence of K(+) afforded {K subset[CpCo(CN)(3)](4)[Cb*Co](4)}PF(6), [KCo(8)]PF(6). IR, NMR, ESI-MS indicate that [KCo(8)]PF(6) is a high-symmetry molecular box containing a potassium ion at its interior. The analogous heterometallic cage {K subset[Cp*Rh(CN)(3)](4)[Cb*Co](4)}PF(6) ([KRh(4)Co(4)]PF(6)) was prepared similarly via the condensation of K[Cp*Rh(CN)(3)] and [Cb*Co(NCMe)(3)]PF(6). Crystallographic analysis confirmed the structure of [KCo(8)]PF(6). The cyanide ligands are ordered, implying that no Co-CN bonds are broken upon cage formation and ion complexation. Eight Co-CN-Co edges of the box bow inward toward the encapsulated K(+), and the remaining four mu-CN ligands bow outward. MeCN solutions of [KCo(8)](+) and [KRh(4)Co(4)](+) were found to undergo ion exchange with Cs(+) to give [CsCo(8)](+) and [CsRh(4)Co(4)](+), both in quantitative yields. Labeling experiments involving [(MeC5H4)Co(CN)(3)]- demonstrated that Cs(+)-for-K(+) ion exchange is accompanied by significant fragmentation. Ion exchange of NH(4+) with [KCo(8)](+) proceeds to completion in THF solution, but in MeCN solution, the exclusive products were [Cb*Co(NCMe)(3)]PF(6) and the poorly soluble salt NH(4)CpCo(CN)(3). The lability of the NH(4+)-containing cage was also indicated by the rapid exchange of the acidic protons in [NH(4)Co(8)](+). Oxidation of [MCo(8)](+) with 4 equiv of FcPF(6) produced paramagnetic (S = 4/2) [Co(8)](4+), releasing Cs(+) or K(+). The oxidation-induced dissociation of M(+) from the cages is chemically reversed by treatment of [Co(8)](4+) and CsOTf with 4 equiv of Cp(2)Co. Cation recognition by [Co(8)] and [Rh(4)Co(4)] cages was investigated. Electrochemical measurements indicated that E(1/2)(Cs(+))--E(1/2)(K(+)) approximately 0.08 V for [MCo(8)](+).     

New polydentate ligand and catalytic properties of the corresponding ruthenium complex during sulfoxidation and alkene epoxidation

Bis(diimine)-ruthenium complexes constitute a class of catalysts with good activity for oxidation reactions, such as sulfoxidation and epoxidation. The synthesis and the full characterization of a new ruthenium complex bearing an original pentadentate ligand (L5pyr for 2,6-bis-(6-ethyl-2,2'-bipyridyl)-pyridine) is reported. Comparison of its activity with regard to[Ru(bpy)2(CH3CN)2](2+) and [Ru(bpy)2(py)(CH3CN)](2+) during alkene and sulfide oxidation allowed us to conclude that the addition of a fifth pyridine ligand in the coordination sphere improves the efficiency of the catalyst. Moreover, under these oxidation conditions a hydroxylation of the ligand L5pyr led to a better activity than its analogue [Ru(bpy)2(py)(CH3CN)](2+), especially during epoxidation of alkenes by PhI(OAc)2.     

Facially coordinating cyclic triamines, part I. The coordination chemistry of cis-3,5-diaminopiperidine and substituted derivatives

An efficient and convenient method for the preparation of cis-3,5-diaminopiperidine (dapi) has been established and the coordination chemistry of this ligand with CoII, CoIII, NiII, CuII, ZnII, and CdII has been investigated in the solid state and in aqueous solution. Potentiometric measurements revealed a generally high stability for the bis complexes of the divalent cations with maximum stability for NiII (log beta2 = 21.2, beta2 = [M(dapi)2][M](-1)[dapi](-2), 25 degrees C, mu = 0.1 mol dm(-3)). Cyclic voltammetry established quasi-reversible formation of [Ni(dapi)2]3+ with a redox potential of 0.91 V (versus NHE) for the Ni(II/III) couple. [Co(dapi)2]3+ was prepared by aerial oxidation of the corresponding CoII precursor. The two isomers trans-[Co(dapi)2]3+ (1(3+), 26%) and cis-[Co(dapi)2]3+ (2(3+), 74%), have been separated and isolated as solid Cl- and CF3SO3- salts. In a non-aqueous medium 1(3+) and 2(3+) reacted with paraformaldehyde and NEt3 to give the methylidene-imino derivatives 3(3+) and 4(3+), in which the two piperidine rings are bridged by two or one N-CH2-O-CH2-N bridges, respectively. Crystal structure analyses were performed for H3dapi[ZnCl4]Cl, 1Cl3 x 2H2O, 2Cl3 x H2O, 3[ZnCl4]Cl, 4[ZnCl4]Cl, [Ni(dapi)2]Cl2 x H2O, [Cu(dapi)2](NO3)2, [Cu(dapi)Cl2], [(dapi)ClCd-(mu2-Cl)2-CdCl(dapi)], and [Co(dapi)(NO2)(CO3)]. The stability of [M(II)(dapi)]2+ and [M(II)(dapi)2]2+ complexes in aqueous solution, particularly the remarkably high tendency of [M(dapi)]2+ to undergo coordinative disproportionation is discussed in terms of the specific steric requirements of this ligand. Molecular mechanics calculations have been performed to analyze the different types of strain in these complexes. A variety of alkylated derivatives of dapi have been prepared by reductive alkylation with formaldehyde, benzaldehyde, salicylaldehyde, and pyridine-2-carbaldehyde. The NiII complexes of the pentadentate N3,N5-bis(2-pyridinylmethyl)-cis-3,5-diaminopiperidine (py2dapi) and the hexadentate N3,N5,1-tris(2-pyridinylmethyl)-cis-3,5-diaminopiperidine (py3dapi) have been isolated as crystalline ClO4- salts [Ni(py2dapi)Cl]ClO4 and [Ni(py3dapi)](ClO4)2 x H2O and characterized by crystal structure analyses.     

Thermodynamics of formation of urea complexes with manganese(II), nickel(II) and zinc(II) ions in N,N-dimethylformamide

The complexation of urea (ur) with manganese(II), nickel(II) and zinc(II) ions has been studied by titration calorimetry in N,N-dimethylformamide (DMF) containing 0.4M (C(2)H(5))(4) NBF(4) as a constant ionic medium at 25 degrees C. The calorimetric data were well explained in terms of the formation of [Mn(ur)](2+), [Mn(ur)(2)](2+) and [Mn(ur)(4)](2+) for manganese(II), [Ni(ur)](2+) for nickel(II) and [Zn(ur)](2+) and [Zn(ur)(2)](2+) for zinc(II), and their formation constants, reaction enthalpies and entropies were determined. The complexation of the nickel(II)-urea system in DMF has also been studied by means of spectrophotometric titration and electronic spectra of individual nickel(II) complexes were determined. On the basis of the stepwise thermodynamic quantities and the individual electronic spectra of the complexes, it is revealed that the [Mn(ur)](2+), [Mn(ur)(2)](2+), [Ni(ur)](2+), [Zn(ur)](2+) and [Zn(ur)(2)](2+) complexes have a six-coordinate octahedral structure, while the [Mn(ur)(4)](2+) complex has a four-coordinate tetrahedral structure.     

Simplest homoleptic metal-centered tetrahedrons, [M(OH2)4]2+, in 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid (M = Co, Ni, Cu)

Dissolution of a tetrafluoroborate or perchlorate salt of [M(OH(2))(6)](2+) (M = Co, Ni, Cu) in 1-ethyl-3-methylimidazolium tetraluforoborate ionic liquid ([emim]BF(4)) results in significant solvatochromism and increasing intensity of color. These observations arise from partial dehydration from the octahedral [M(OH(2))(6)](2+) and formation of the tetrahedral [M(OH(2))(4)](2+). This reaction was monitored by the intense absorption band due to the d-d transition in the UV-vis absorption spectrum. The EXAFS investigation clarified the coordination structures around M(2+) {[Co(OH(2))(4)](2+), R(Co-O) = 2.17 ?, N = 4.2; [Cu(OH(2))(4)](2+), R(Cu-O) = 2.09 ?, N = 3.8}. (1)H and (19)F NMR study suggested that both [emim](+) and BF(4)(-) are randomly arranged in the second-coordination sphere of [M(OH(2))(4)](2+).     

Lanthanide(III) and group 13 metal ion complexes of tripodal amino phosphinate ligands

The tripodal amino-phosphinate ligands, tris(4-(phenylphosphinato)-3-benzyl-3-azabutyl)amine (H(3)ppba.2HCl.H(2)O) and tris(4-(phenylphosphinato)-3-azabutyl)amine (H(3)ppa.HCl.H(2)O) were synthesized and reacted with Al(3+), Ga(3+), In(3+) and the lanthanides (Ln(3+)). At 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(3)ppba)(2)](3+)(M = Al(3+), Ga(3+), In(3+), Ho(3+)-Lu(3+)) were isolated. The bicapped [Ga(H(3)ppba)(2)](NO(3))(2)Cl.3CH(3)OH was structurally characterized and was shown indirectly by various techniques to be isostructural with the other [M(H(3)ppba)(2)](3+) complexes. Also, at 2 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)(2)](5+)(M = La(3+)-Tb(3+)) were characterized, and the X-ray structure of [Gd(H(4)ppba)(2)](NO(3))(4)Cl.3CH(3)OH was determined. At 1 : 1 H(3)ppba to metal ratios, complexes of the type [M(H(4)ppba)](4+)(M = La(3+)-Er(3+)) were isolated and characterized. Elemental analysis and spectroscopic evidence supported the formation of a 1 : 1 monocapped complex. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+), complex of the type [Ga(ppa)].3H(2)O was obtained. Reaction of 1 : 1 ratios of H(3)ppa with Ln(3+) and In(3+) yielded complexes of the type [M(H(3)ppa)](3+)(M = La(3+)-Yb(3+)) but with Ga(3+) a neutral complex [Ga(ppa)].3H(2)O was obtained. The formation of an encapsulated 1 : 1 complex is supported by elemental analysis and spectroscopic evidence.     

Complexes of a novel multinucleating poly-beta-diketonate ligand

The synthesis of the new polynucleating ligand 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-benzene (H4L) is reported along with the preparation, structure and properties of its dinuclear complexes [Cu(2)(H(2)L)(2)(py)(2)](1), [Ni(2)(H(2)L)(2)(py)(4)](2), [Mn(2)(H(2)L)(2)(dmf)(4)](3), [Co(2)(H(2)L)(2)(dmf)(4)](4) and [Co(2)(H(2)L)(2)(MeOH)(4)](5), respectively. In complexes 1 to 5, the polydentate ligand is in its bis-deprotonated form, chelating the metals through its [small beta]-diketonate moieties. Magnetic measurements show that the metals within these molecules are maintained almost mutually independent.     

Determination of potassium with alkali-heavy metal cobaltinitrites

A procedure is proposed for the removal and determination of K(+) by precipitation with [Co(NO(2))(6)](3-) in the presence of Pb(2+) and H(2)O(2). The whole precipitate is dissolved, the Co(3+) estimated colorimetrically, and the K(+) content calculated, with a relative error of 1%. The potassium-containing precipitate may also be dissolved in NaOH + NH(3) solution, the Co(3+) titrated complexometrically, and the potassium content deduced. These two procedures may be modified for the removal and determination of Pb(2+), Co(2+), Co(3+) and NO(2)(-). Na(+) ions do not interfere.     

Scandium ion-enhanced oxidative dimerization and N-demethylation of N,N-dimethylanilines by a non-heme iron(IV)-oxo complex

Oxidative dimerization of N,N-dimethylaniline (DMA) occurs with a nonheme iron(IV)-oxo complex, [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), to yield the corresponding dimer, tetramethylbenzidine (TMB), in acetonitrile. The rate of the oxidative dimerization of DMA by [Fe(IV)(O)(N4Py)](2+) is markedly enhanced by the presence of scandium triflate, Sc(OTf)(3) (OTf = CF(3)SO(3)(-)), when TMB is further oxidized to the radical cation (TMB(?+)). In contrast, we have observed the oxidative N-demethylation with para-substituted DMA substrates, since the position of the C-C bond formation to yield the dimer is blocked. The rate of the oxidative N-demethylation of para-substituted DMA by [Fe(IV)(O)(N4Py)](2+) is also markedly enhanced by the presence of Sc(OTf)(3). In the case of para-substituted DMA derivatives with electron-donating substituents, radical cations of DMA derivatives are initially formed by Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), giving demethylated products. Binding of Sc(3+) to [Fe(IV)(O)(N4Py)](2+) enhances the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), whereas binding of Sc(3+) to DMA derivatives retards the electron-transfer reaction. The complicated kinetics of the Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+) are analyzed by competition between binding of Sc(3+) to DMA derivatives and to [Fe(IV)(O)(N4Py)](2+). The binding constants of Sc(3+) to DMA derivatives increase with the increase of the electron-donating ability of the para-substituent. The rate constants of Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+), which are estimated from the binding constants of Sc(3+) to DMA derivatives, agree well with those predicted from the driving force dependence of the rate constants of Sc(3+) ion-coupled electron transfer from one-electron reductants to [Fe(IV)(O)(N4Py)](2+). Thus, oxidative dimerization of DMA and N-demethylation of para-substituted DMA derivatives proceed via Sc(3+) ion-coupled electron transfer from DMA derivatives to [Fe(IV)(O)(N4Py)](2+).     

Direct intercalation of bis-2,2',2″,6-terpyridylcobalt(III) into zirconium phosphate layers for biosensing applications

The direct intercalation reaction of [Co(tpy)(2)](2+) with the highly hydrated θ phase of layered zirconium phosphate (θ-ZrP) resulted in the formation of the oxidized [Co(tpy)(2)](3+) ion within the ZrP material. The X-ray powder diffraction patterns showed that the interlayer distance increases from 10.3 ? in θ-ZrP to 14.9 ? in the dry [Co(tpy)(2)](3+)-intercalated ZrP {[Co(tpy)(2)](3+):ZrP} phase. The complex remains electroactive within the layers of ZrP. The formal potential of a carbon paste electrode (CPE) modified with [Co(tpy)(2)](3+):ZrP (E°' = 40.8 mV versus Ag/AgCl, 3.5 M NaCl) is non-pH-dependent. However, the sensitivity of the [Co(tpy)(2)](3+):ZrP-modified CPE for the detection of reduced nicotinamide adenine dinucleotide (NADH) electrooxidation was lower than that of a previously reported CPE modified with [Ru(phend)(2)bpy](2+)-intercalated ZrP. (1) To improve the characteristics of NADH electrooxidation of the [Co(tpy)(2)](3+):ZrP-modified CPE, we included the enzyme diaphorase in solution, which increased the electrocatalytic current for NADH oxidation. A bienzymatic lactate biosensor was constructed and used for lactate sensing.