Copper(II) carboxylate dimers prepared from ligands designed to form a robust π···π stacking synthon: supramolecular structures and molecular properties

The reactions of bifunctional carboxylate ligands (1,8-naphthalimido)propanoate, (L(C2)(-)), (1,8-naphthalimido)ethanoate, (L(C1)(-)), and (1,8-naphthalimido)benzoate, (L(C4)(-)) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) in methanol or ethanol at room temperature lead to the formation of novel dimeric [Cu(2)(L(C2))(4)(MeOH)(2)] (1), [Cu(2)(L(C1))(4)(MeOH)(2)]·2(CH(2)Cl(2)) (2), [Cu(2)(L(C4))(4)(EtOH)(2)]·2(CH(2)Cl(2)) (3) complexes. When the reaction of L(C1)(-) with Cu(2)(O(2)CCH(3))(4)(H(2)O)(2) was carried out at -20 °C in the presence of pyridine, [Cu(2)(L(C1))(4)(py)(4)]·2(CH(2)Cl(2)) (4) was produced. At the core of complexes 1-3 lies the square Cu(2)(O(2)CR)(4) "paddlewheel" secondary building unit, where the two copper centers have a nearly square pyramidal geometry with methanol or ethanol occupying the axial coordination sites. Complex 4 contains a different type of dimeric core generated by two κ(1)-bridging carboxylate ligands. Additionally, two terminal carboxylates and four trans situated pyridine molecules complete the coordination environment of the five-coordinate copper(II) centers. In all four compounds, robust π···π stacking interactions of the naphthalimide rings organize the dimeric units into two-dimensional sheets. These two-dimensional networks are organized into a three-dimensional architecture by two different noncovalent interactions: strong π···π stacking of the naphthalimide rings (also the pyridine rings for 4) in 1, 3, and 4, and intermolecular hydrogen bonding of the coordinated methanol or ethanol molecules in 1-3. Magnetic measurements show that the copper ions in the paddlewheel complexes 1-3 are strongly antiferromagnetically coupled with -J values ranging from 255 to 325 cm(-1), whereas the copper ions in 4 are only weakly antiferromagnetically coupled. Typical values of the zero-field splitting parameter D were found from EPR studies of 1-3and the related known complexes [Cu(2)(L(C2))(4)(py)(2)]·2(CH(2)Cl(2))·(CH(3)OH), [Cu(2)(L(C3))(4)(py)(2)]·2(CH(2)Cl(2)) and [Cu(2)(L(C3))(4)(bipy)]·(CH(3)OH)(2)·(CH(2)Cl(2))(3.37) (L(C3)(-) = (1,8-naphthalimido)butanoate)), while its abnormal magnitude in [Cu(2)(L(C2))(4)(bipy)] was qualitatively rationalized by structural analysis and DFT calculations.     

Tetra-2,3-pyrazinoporphyrazines with externally appended pyridine rings. 1. Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine: a new macrocycle with remarkable electron-deficient properties

A new pyrazinoporphyrazine macrocycle carrying externally appended pyridine rings, tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine (hydrated), [Py(8)TPyzPzH(2)].2H(2)O, was prepared in high yield by direct cyclotetramerization of the precursor, 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)(2)Py(2)Pyz], in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The single-crystal X-ray structure of [(CN)(2)Py(2)Pyz] shows a noncoplanar positioning of the pyrazine and pyridine rings in the two slightly different independent molecular units present in the crystal. UV-vis spectra of [Py(8)TPyzPzH(2)] were measured in two nondonor solvents (CHCl(3), CH(2)Cl(2)), a slightly basic solvent (pyridine), and an acidic solvent (CH(3)COOH). In all cases, the spectral changes are consistent with the occurrence of molecular aggregation and colloidal dispersions which break up with time to give clear solutions containing exclusively the monomeric form of the macrocycle, either neutral [Py(8)TPyzPzH(2)] (in CHCl(3), CH(2)Cl(2), and CH(3)COOH) or dianionic [Py(8)TPyzPz](2)(-) (in pyridine). A spectrally monitored titration of [Py(8)TPyzPzH(2)] in CH(2)Cl(2) with TBA(OH) shows the loss of two protons from the macrocyclic core and quantitative conversion of [Py(8)TPyzPzH(2)] to [Py(8)TPyzPz](2)(-). Cyclic voltammetry and thin-layer spectroelectrochemical measurements show that [Py(8)TPyzPzH(2)] is present in CH(2)Cl(2) while [Py(8)TPyzPz](2)(-) is present in pyridine, but both forms of the compound exhibit identical electrochemical behavior, consistent with a conversion of the dianion to the neutral porphyrazine in pyridine prior to electroreduction via four reversible one-electron transfer steps. No oxidations of the macrocycle are observed in either solvent containing 0.1 M tetrabuthylammonium perchlorate (TBAP). A comparison of the electrochemical behavior for [Py(8)TPyzPzH(2)] with what is reported for related phthalocyanine and porphyrazine analogues highlights the remarkable electron-accepting properties of the presently investigated free-base macrocycle.     

Structure and properties of bivalent nickel and copper complexes with pyrazine-amide-thioether coordination: stabilization of trivalent nickel

Acyclic pyrazine-2-carboxamide and thioether containing hexadentate ligand 1,4-bis[o-(pyrazine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpzctb), in its deprotonated form, has afforded light brown [Ni(II)(bpzctb)](1)(S=1) and green [Cu(II)(bpzctb)](2)(S=1/2) complexes. The crystal structures of 1.CH(3)OH and 2.CH(2)Cl(2) revealed that in these complexes the ligand coordinates in a hexadentate mode, affording examples of distorted octahedral M(II)N(2)(pyrazine)N'(2)(amide)S(2)(thioether) coordination. Each complex exhibits in CH(2)Cl(2) a reversible to quasireversible cyclic voltammetric response, corresponding to the Ni(III)/Ni(II)(1) and Cu(II)/Cu(I)(2) redox process. The E(1/2) values reveal that the complexes of bpzctb(2-) are uniformly more anodic by approximately 0.2 V than those of the corresponding complexes with the analogous pyridine ligand, 1,4-bis[o-(pyridine-2-carboxamidophenyl)]-1,4-dithiobutane (H(2)bpctb), attesting that compared to pyridine, pyrazine is a better stabilizer of the Ni(ii) or Cu(i) state. Coulometric oxidation of the previously reported complex [Ni(II)(bpctb)] and 1 generates [Ni(III)(bpctb)](+) and [Ni(III)(bpzctb)](+) species, which exhibit a LMCT transition in the 470--480 nm region and axial EPR spectra corresponding to a tetragonally elongated octahedral geometry. Complex 2 exhibits EPR spectra characteristic of the d(z(2)) ground state.     

Synthesis, structure, and reactivity of rhodium and iridium complexes of the chelating bis-sulfoxide tBuSOC2H4SOtBu. Selective O-H activation of 2-hydroxy-isopropyl-pyridine

The chloro-bridged rhodium and iridium complexes [M2(BTSE)2Cl2] (M = Rh 1, Ir 2) bearing the chelating bis-sulfoxide tBuSOC2H4SOtBu (BTSE) were prepared by the reaction of [M2(COE)4Cl2] (M = Rh, Ir; COE = cyclooctene) with an excess of a racemic mixture of the ligand. The cationic compounds [M(BTSE)2][PF6] (M = Rh 3, Ir 4), bearing one S- and one O-bonded sulfoxide, were also obtained in good yields. The chloro-bridges in 2 can be cleaved with 2-methyl-6-pyridinemethanol and 2-aminomethyl pyridine, resulting in the iridium(I) complexes [Ir(BTSE)(Py)(Cl)] (Py = 2-methyl-6-pyridinemethanol 5, 2-aminomethyl-pyridine 6). In case of the bulky 2-hydroxy- isopropyl-pyridine, selective OH oxidative addition took place, forming the Ir(III)-hydride [Ir(BTSE)(2-isopropoxy-pyridine)(H)(Cl)] 7, with no competition from the six properly oriented C-H bonds. The cationic rhodium(I) and iridium(I) compounds [M(BTSE)(2-aminomethyl-pyridine)][X] (M = Rh 8, Ir 10), [Rh(BTSE)(2-hydroxy- isopropyl-pyridine)][X] 9(stabilized by intramolecular hydrogen bonding), [Ir(BTSE)(pyridine)2][PF6] 12, [Ir(BTSE)(alpha-picoline)2][PF6] 13, and [Rh(BTSE)(1,10-phenanthroline)][PF6] 14 were prepared either by chloride abstraction from the dimeric precursors or by replacement of the labile oxygen bonded sulfoxide in 3 or 4. Complex 14 exhibits a dimeric structure in the solid state by pi-pi stacking of the phenanthroline ligands.     

Chiral monomeric and homochiral dimeric copper(II) complexes of a new chiral ligand, N-(1,2-bis(2-pyridyl)ethyl)pyridine-2-carboxamide: an example of molecular self-recognition

Reaction of Cu(ClO(4))(2) x 6H(2)O with a racemic mixture of the novel chiral ligand N-(1,2-bis(2-pyridyl)ethyl)pyridine-2-carboxamide (PEAH) affords only the homochiral dimeric copper(II) complexes [Cu(2)((R)()PEA)(2)](ClO(4))(2) and [Cu(2)((S)()PEA)(2)](ClO(4))(2) in a 1:1 ratio. The phenomenon of molecular self-recognition is also observed when a racemic mixture of the monomeric copper(II) complex [Cu((R(S))()PEA)(Cl)(H(2)O)] is converted into the homochiral dimeric species [Cu(2)((R(S))()PEA)(2)](ClO(4))(2) via reaction with Ag(+) ion. This is the first report of direct conversion of a racemic mixture of a chiral monomeric copper(II) complex to a mixture of the homochiral dimers.     

Neutral (bis-beta-diketonato) iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) metallocycles: structural, electrochemical and solvent extraction studies

Neutral dimeric metallocyclic complexes of type [M(2)(L(1))(2)B(n)] (where M = cobalt(II), nickel(II) and zinc(II), L(1) is the doubly deprotonated form of a 1,3-aryl linked bis-beta-diketone ligand of type 1,3-bis(RC(O)CH(2)C(O))C(6)H(4) (R=Me, n-Pr, t-Bu) and B is pyridine (Py) or 4-ethylpyridine (EtPy)) have been synthesised, adding to similar complexes already reported for copper(II). New lipophilic ligand derivatives with R = octyl or nonyl were also prepared for use in solvent extraction experiments. Structural, electrochemical and solvent extraction investigations of selected metal complex systems from the above series are reported, with the X-ray structures of [Co(2)(L(1))(2)(Py)(4)] x 2.25CHCl(3) x 0.5H(2)O (R=Pr), [Co(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Ni(2)(L(1))(2)(EtPy)(4)] (R=t-Bu), [Zn(2)(L(1))(2)(EtPy)(2)] (R=Me) and [Zn(2)(L(1))(2)(EtPy)(4)] (R=t-Bu) being presented. The electrochemistry of H(2)L(1) (R=t-Bu) and of [Fe(2)(L(1))(3)], [Co(2)(L(1))(2)(Py)(4)], [Ni(2)(L(1))(2)(Py)(4)], [Cu(2)(L(1))(2)] and [Zn(2)(L(1))(2)(Py)(2)] has been examined. Oxidative processes for the complexes are dominantly irreversible, but several examples of quasireversible behaviour were observed and support the assignment of an anodic process, seen between +1.0 and +1.6 V, as a metal-centred oxidation. The reduction processes for the respective metal complexes are not simple, and irreversible in most cases. Solvent extraction studies (water/chloroform) involving variable concentrations of metal, bis-beta-diketone and heterocyclic base have been performed for cobalt(II) and zinc(II) using a radiotracer technique to probe the stoichiometries of the extracted species in each case. Synergism was observed when 4-ethylpyridine was added to the bis-beta-diketone ligand in the chloroform phase. Competitive extraction studies show a clear uptake preference for copper(II) over cobalt(II), nickel(II), zinc(II) and cadmium(II).     

New phenoxido-bridged quasi-tetrahedral and rhomboidal [Cu4] compounds bearing μ4-oxido or μ(1,1)-azido ligands: synthesis, chemical reactivity, and magnetic studies

[Cu(2)(μ(4)-O)Cu(2)] and [Cu(2)(μ(1,1)-N(3))(4)Cu(2)] geometrical arrangements are found in a new family of tetranuclear copper(II) complexes: [Cu(4)(μ(4)-O)(μ-cip)(2)Cl(4)] (1), [Cu(4)(μ(4)-O)(μ-cip)(2)(μ(1,3)-O(2)CPh)(4)]·2CH(3)OH (2·2CH(3)OH), and [Cu(4)(μ(1,1)-N(3))(4)(μ-cip)(2)(N(3))(2)]·DMF (3·DMF) [Hcip = 2,6-bis(cyclohexyliminomethylene)-4-methylphenol; CH(3)OH = methanol; DMF = dimethylformamide]. These complexes have been characterized by X-ray crystallography, and their magnetic properties have been studied. 1 and 2 form quasi-tetrahedral [Cu(4)(μ(4)-O)] complexes, and 3 is the first example of a rhomboidal [Cu(4)(μ(1,1)-N(3))] compound. Formation of the [Cu(4)] compounds is achieved via ligand-exchange reactions. The relative binding strength of the three ancillary ligands as N(3)(-) > PhCO(2)(-) > Cl(-) has been demonstrated from the core-conversion and peripheral ligand-exchange reactions. For the three complexes, the magnetic susceptibility measurements in the range of 1.8-300 K have been performed and modeled using two isolated S = (1)/(2) dimers based on the spin Hamiltonian H = -2J{S(Cu,1)·S(Cu,2)} with J/k(B) = -513, -340, and -315 K for 1-3, respectively (where J is the exchange constant through the oxido-phenoxido and azido-phenoxido bridges, respectively).     

Structure-activity relationships of highly cytotoxic copper(II) complexes with modified indolo[3,2-c]quinoline ligands

A number of indolo[3,2-c]quinolines were synthesized and modified at the lactam unit to provide a peripheral binding site able to accommodate metal ions. Potentially tridentate ligands HL(1a)-HL(4a) and HL(1b)-HL(4b) were reacted with copper(II) chloride in isopropanol/methanol to give novel five-coordinate copper(II) complexes [Cu(HL(1a-4a))Cl(2)] and [Cu(HL(1b-4b))Cl(2)]. In addition, a new complex [Cu(HL(5b))Cl(2)] and two previously reported compounds [Cu(HL(6a))Cl(2)] and [Cu(HL(6b))Cl(2)] with modified paullone ligands HL(5b), HL(6a), and HL(6b), which can be regarded as close analogues of indoloquinolines HL(1b), HL(4a), and HL(4b), in which the pyridine ring was formally substituted by a seven-membered azepine ring, were synthesized for comparison. The new ligands and copper(II) complexes were characterized by (1)H and (13)C NMR, IR and electronic absorption spectroscopy, ESI mass spectrometry, magnetic susceptibility measurements in solution at 298 K ([Cu(HL(1a))Cl(2)] and [Cu(HL(4b))Cl(2)]), and X-ray crystallography ([Cu(HL(3b))Cl(2)]·3DMF, [Cu(HL(4b))Cl(2)]·2.4DMF, HL(5b) and [Cu(HL(5b))Cl(2)]·0.5CH(3)OH). All complexes were tested for cytotoxicity in the human cancer cell lines CH1 (ovarian carcinoma), A549 (non-small cell lung cancer), and SW480 (colon carcinoma). The compounds are highly cytotoxic, with IC(50) values ranging from nanomolar to very low micromolar concentrations. Substitution of the seven-membered azepine ring in paullones by a pyridine ring resulted in a six- to nine-fold increase of cytotoxicity in SW480 cells. Electron-releasing or electron-withdrawing substituents in position 8 of the indoloquinoline backbone do not exert any effect on cytotoxicity of copper(II) complexes, whereas copper(II) compounds with Schiff bases obtained from 2-acetylpyridine and indoloquinoline hydrazines are 10 to 50 times more cytotoxic than those with ligands prepared from 2-formylpyridine and indoloquinoline hydrazines.     

Intra and intermolecular magnetic interactions in a series of dinuclear Cu(II)/hxta complexes [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: correlation of magnetic properties with geometry

Nine dinuclear copper(II) complexes with hxta5- ligands [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: [Cu2(MeO-hxtaH)(H2O)2] x 4H2O (1), [Na(micro-H2O)2(H2O)6][Cu2(Cl-hxta)(H2O)3]2 x 6H2O (2), [Cu(H2O)6][Cu2(Me-hxta)(H2O)2](NO3) x 2H2O (3), [Cu2(R-hxtaH)(H2O)3] x 3H2O [R = Cl (4), CH3 (5), and MeO (6)], [Cu2(MeO-hxtaH2)(micro-X)(CH3OH)] x 3CH3OH [X = Cl (7), Br (8)] and K5Na(micro-H2O)10[Cu2(micro-CO3)(Me-hxta)]2 x 4H2O (9), have been synthesized and structurally characterized. In complexes 4-7, the dinuclear units are linked via novel pairwise supramolecular interactions involving the ligand carboxylate groups. The intra- and intermolecular magnetic interactions have been quantified, and the coupling constants have been related to the structural geometries.     

Modeling Tyrosinase Monooxygenase Activity. Spectroscopic and Magnetic Investigations of Products Due to Reactions between Copper(I) Complexes of Xylyl-Based Dinucleating Ligands and Dioxygen: Aromatic Ring Hydroxylation and Irreversible Oxidation Products

A full account of a chemical system possessing features that mimic the reactivity aspects of tyrosinase is presented. Using dinucleating ligands with a m-xylyl spacer three new dicopper(I) complexes have been synthesized and their reactivity with dioxygen investigated. The six-membered chelate ring forming ligands provide only two nitrogen coordinations to each copper. The complexes [Cu(I)(2)L(CH(3)CN)(2)]X(2) (X = ClO(4)(-) (1a), SbF(6)(-) (1b)) and [Cu(I)(2)(L-NO(2))(CH(3)CN)(2)][SbF(6)](2) (1c) [L = alpha,alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; L-NO(2) = para-nitro derivative of L] have been characterized by IR and (1)H NMR spectroscopy. The reaction of O(2) with 1a-c in CH(2)Cl(2) or THF is instantaneous and causes stoichiometric xylyl hydroxylation reactions producing phenol products. Thus 1a produces phenoxo-/hydroxo-bridged product [Cu(II)(2)(L-O)(OH)][ClO(4)](2) (2a). The existence of putative peroxo-dicopper(II) species could not be detected even at -80 degrees C. A trend is observed for the extent of aromatic ring hydroxylation (298 K): CH(3)CN approximately DMF > CH(3)OH > CH(2)Cl(2). Cyclic voltammetric experiment of 1a in DMF reveals an appreciably low redox potential (E(1/2) = -0.26 V vs SCE) for the Cu(II)(2)/Cu(I)(2) redox process. Variable-temperature (25-300 K) magnetic susceptibility measurements establish that the copper(II) centers in 2a and the dihydroxo-bridged complex [Cu(II)(2)L'(OH)(2)][ClO(4)](2) (2b) [formed due to an impurity (L') present during the synthesis of L following Method A; L' = bis[alpha,alpha'-bis(N-methyl-N-(2-pyridylethyl)amino)-m-xylene]methylamine] are antiferromagnetically coupled, with 2a considerably more coupled than 2b. Reaction of 1a with O(2) in CH(2)Cl(2) (298 K) produces an additional unhydroxylated product of composition [Cu(II)(2)L(OH)(OH(2))][ClO(4)](3).2H(2)O.0.5HCl (3a). In agreement with its proposed hydroxo-/aquo-bridged structure, 3a is weakly antiferromagnetically coupled. In CH(3)CN solution, 3a rearranges to generate a doubly hydroxo-bridged species [Cu(II)(2)L(OH)(2)](2+). Using a solution-generated dicopper(I) complex of a closely similar ligand (L' ') providing five-membered chelate ring, the reactivity toward dioxygen was also investigated. It produces only an irreversibly oxidized product of composition Cu(II)(2)L' '(OH)(ClO(4))(3)(H(2)O)(2) (3b) (L' ' = alpha,alpha'-bis[N-methyl-N-(2-pyridylmethyl)amino]-m-xylene). For 3b the copper(II) centers are almost uncoupled.     

Monomeric, tetrameric, and polymeric copper di-tert-butyl phosphate complexes containing pyridine ancillary ligands

The reaction of di-tert-butyl phosphate (((t)BuO)(2)P(O)(OH), dtbp-H) with copper acetate in the presence of pyridine (py) and 2,4,6-trimethylpyridine (collidine) has been investigated. Copper acetate reacts with dtbp-H in a reaction medium containing pyridine, DMSO, THF, and CH(3)OH to yield a one-dimensional polymeric complex [Cu(dtbp)(2)(py)(2)(mu-OH(2))](n) (1) as blue hollow crystalline tubes. The copper atoms in 1 are octahedral and are surrounded by two terminal phosphate ligands, two pyridine molecules, and two bridging water molecules. The mu-OH(2) ligands that are present along the elongated Jahn-Teller axis are responsible for the formation of the one-dimensional polymeric structure. Recrystallization of 1 in a DMSO/THF/CH(3)OH mixture results in the reorganization of the polymer and its conversion to a more stable tetranuclear copper cluster [Cu(4)(mu(3)-OH)(2)(dtbp)(6)(py)(2)] (2) in about 60% yield. The molecular structure of 2 is made up of a tetranuclear core [Cu(4)(mu(3)-OH)(2)] which is surrounded by six bidentate bridging dtbp ligands. While two of the copper atoms are pentacoordinate with a tbp geometry, the other two copper atoms exhibit a pseudooctahedral geometry with five normal Cu-O bonds and an elongated Cu-O linkage. The pentacoordinate copper centers bear an axial pyridine ligand. The short Cu.Cu nonbonded distances in the tetranuclear core of 2 lead to magnetic ordering at low temperature with an antiferromagnetic coupling at approximately 20 K (J(P) = -44 cm(-1), J(c) = -66 cm(-1), g = 2.25, and rho = 0.8%). When the reaction between di-tert-butyl phosphate (dtbp-H) and copper acetate was carried out in the presence of collidine, large dark-blue crystals of monomeric copper complex [Cu(dtbp)(2)(collidine)(2)] (3) formed as the only product. A single-crystal X-ray diffraction study of 3 reveals a slightly distorted square-planar geometry around the copper atom. Thermogravimetric analysis of 1-3 revealed a facile decomposition of the coordinated ligands and dtbp to produce a copper phosphate material around 500 degrees C. An independent solid-state thermolysis of all the three complexes in bulk at 500-510 degrees C for 2 days produced copper pyrophosphate Cu(2)P(2)O(7) along with small quantities of Cu(PO(3))(2) as revealed by DR-UV spectroscopic and PXRD studies.     

Modular approach to tridentate N,O,N' ligands using pyrazolylborate chemistry

Two anionic tridentate N,O,N' chelators, [pz(Ph)B(mu-pz)(mu-O)B(Ph)pz](-) (3(-)) and [pz(Ph)(Ph)B(mu-pz)(mu-O)B(Ph)pz(Ph)](-) (4(-)), as well as the corresponding complexes [Fe(3)(py)Cl], [Fe(3)Cl(2)] and [Cu(3)Cl], have been synthesised and structurally characterised by X-ray crystallography (pz: pyrazolyl, pz(Ph): 3-phenylpyrazolyl, py: pyridine). Since our synthesis approach takes advantage of the highly modular pyrazolylborate chemistry, inexpensive and relatively resistant N,O,N' ligands of varying steric demand are readily accessible. The complexes [Fe(3)(py)Cl] and [Fe(3)Cl(2)] possess a distorted trigonal-bipyramidal configuration with the pyrazolyl rings occupying equatorial positions and the oxygen donor being located at an apical position. The complex [Cu(3)Cl] crystallises as chloro-bridged dimers featuring Cu(II) ions with ligand environments that are intermediate between a square-planar and a trigonal-bipyramidal geometry.     

Coinage metal complexes of a boron-substituted soft scorpionate ligand

An improved synthesis of lithium phenyltris(methimazolyl)borate, Li[PhTm(Me)], (methimazole = 1-methylimidazole-2-thione) is described, and the structure of the methanol-solvated [Li(OHMe)4][PhTm(Me)] has been determined. The syntheses and characterization of complexes [M(PhTm(Me))(PR3)] (M = Cu, Ag, Au; R = Et, Ph;) are reported, and the complexes [Cu(PhTm(Me))(PPh3)], [Ag(PhTm(Me))(PEt3)] and [Au(PhTm(Me))(PEt3)] are crystallographically characterized, showing a progression from pseudo-tetrahedral geometry (copper, S3P coordination) to trigonal planar geometry (silver, S2P coordination) to linear geometry (gold, SP coordination). In addition, the copper(I) and silver(I) triphenylphosphine complexes of the adventitiously formed phenylhydrobis(methimazolyl)borate ligand, [M(PhBm(Me))(PPh3)], have been crystallographically characterized, showing both species to have a trigonal planar primary coordination sphere, with a secondary M...H-B interaction. Finally, reaction of copper(II) chloride with Li[PhTm(Me)] results in formation of a compound analyzing as [Cu(II)(PhTm(Me))Cl], although its extreme insolubility and marked instability have precluded its complete characterization. Attempts to prepare this by ultra-slow diffusion of the reactants through solvent blanks has led to isolation of a mixed-valence copper(I/II) methimazolate cluster, [Cu(I)10Cu(II)2(mt)12Cl2] and a copper(I) dimeric complex [Cu2(PhTm(Me))2], indicating that copper(II) ions oxidatively decompose the phenyltris(methimazolyl)borate anion.     

Self-assembly of cuII and niII [2 x 2] grid complexes and a binuclear CuII complex with a new semiflexible substituted pyrazine ligand: multiple anion encapsulation and magnetic properties

With the new substituted pyrazine ligand pyrazine-2,3-dicarboxylic acid bis[(pyridin-2-ylmethyl)amide], H(2)L, a binuclear complex [Cu(2)(LH)(Cl(3))(H(2)O)].H(2)O (1) and two [2 x 2]G grid complexes, [[Cu(4)(LH)(4)](ClO(4))(4)].5CH(3)OH.4H(2)O (2) and [[Ni(4)(LH)(4)]Cl(4)].5CH(3)CN.13H(2)O (3), have been synthesized and characterized spectroscopically and crystallographically. The ligand H(2)L crystallized in the triclinic space group P1, with a = 4.9882(7) A, b = 12.079(2) A, c = 14.454(2) A, alpha = 107.08(2) degrees, beta = 98.61(2) degrees, gamma = 97.54(2) degrees, V = 808.8(2) A(3), Z = 2, R1 = 0.0747, and R(w) = 0.1829 for 1319 observed reflections [I > 2 sigma(I)]. The molecule is L-shaped with a strong intramolecular bifurcated hydrogen bond in half of the molecule. In the crystal the molecules are linked by an intermolecular hydrogen bond to form a 1D polymer. The binuclear complex [Cu(2)(LH)(Cl(3))(H(2)O)].H(2)O (1) crystallized in the monoclinic space group P2(1)/a, with a = 8.6859(7) A, b = 28.060(2) A, c = 9.5334(9) A, beta = 107.89(1) degrees, V = 2211.2(3) A(3), Z = 4, R1 = 0.039, and R(w) = 0.097 for 1408 observed reflections [I > 2 sigma(I)]. There are two independent copper atoms both having square pyramidal geometry. Both coordinate to a pyrazine, a pyridine, and an amide N atom. Two chlorines complete the coordination sphere of one of the copper atoms, while one chlorine atom and a water molecule complete the coordination sphere of the other. The copper(II) [2 x 2] grid complex [[Cu(4)(LH)(4)](ClO(4))(4)].5CH(3)OH.4H(2)O (2) crystallized in the triclinic space group P1, with a = 17.1515(14) A, b = 17.7507(13) A, c = 19.3333(15) A, alpha = 67.34(1) degrees, beta = 69.79(1) degrees, gamma = 71.50(1) degrees, V = 4980.3(7) A(3), Z = 2, R1 = 0.083, and R(w) = 0.207 for 5532 observed reflections [I > 2 sigma(I)]. The four Cu(II) atoms are octahedrally coordinated by two pyrazine, two pyridine, and two amide N atoms and occupy the corners of a [2 x 2] grid with edge lengths, Cu...Cu, varying from 7.01 to 7.39 A. The nickel(II) [2 x 2] grid complex [[Ni(4)(LH)(4)]Cl(4)].5CH(3)CN.13H(2)O (3) crystallized in the monoclinic space group C2/c, with a = 16.3388(10) A, b = 29.754(2) A, c = 20.857(1) A, beta = 101.845(1) degrees, V = 9923.6(12) A(3), Z = 4, R1 = 0.050, and wR2 = 0.101 for 3391 observed reflections [I > 2 sigma(I)]. Here the complex possesses C(2) symmetry and again each metal atom is octahedrally coordinated to two pyrazine, two pyridine, and two amide N atoms. They occupy the corners of a [2 x 2] grid with an average edge length, Ni.Ni, of 6.97 A. Of the four anions (ClO(4)(-)'s in 2 and Cl(-)'s in 3) required to equilibrate the charges in the grid complexes, two are encapsulated, one above and one below the plane of the four metal atoms. The remaining two anions are located between the "wings" of the ligands. Magnetic susceptibility measurements indicate that the binuclear complex 1 is antiferromagnetic, with a J value of -15.07 cm(-1). This is larger than the J values found for the Cu(II) (2) and Ni(II) (3) grid complexes, which were -5.87 and -2.64 cm(-1), respectively. DFT calculations have been carried out to explain the difference in the J values found for complexes 1 and 2.     

Assembling novel heterotrimetallic Cu/Co/Ni and Cu/Co/Cd cores supported by diethanolamine ligand in one-pot reactions of zerovalent copper with metal salts

The three novel heterotrimetallic complexes [Ni(H2L)2][CoCu(L)2(H2L)(NCS)]2(NCS)2 (1), [Ni(H2L)2][CuCo(L)2(H2L)(NCS)]2Br2.2H2O (2), and [CuCoCd(H2L)2(L)2(NCS)Br2].CH3OH (3) have been prepared using zerovalent copper; cobalt thiocyanate; nickel thiocyanate (1), nickel bromide (2), or cadmium bromide (3); and methanol solutions of diethanolamine in air. The most prominent feature of the structures of 1 and 2 is the formation of the "pentanuclear"aggregate [[Ni(H2L)2][CoCu(L)2(H2L)(NCS)]2]2+ made up of two neutral [CoCu(L)2(H2L)(NCS)] units and the previously unknown cation [Ni(H2L)2]2+ "glued together" by strong complementary hydrogen bonds. With Cd2+ instead of Ni2+, a different structure is obtained: the [CoCu(L)2(H2L)(NCS)] unit is now linked to the Cd center through coordination of the oxygens of L groups on the Co atom to form the discrete heterotrimetallic molecular species 3. Cryomagnetic measurements of the compounds show that, in all cases, the magnetic behavior is paramagnetic; the polycrystalline EPR spectra contain signals due to monomeric copper species only. At the same time, the EPR spectra of frozen DMF and methanol solutions of 1-3 reveal the presence of triplet-state species that can be generated only by a coupling of the Cu2+ centers within a dimer. The species responsible for the appearance of transitions within the triplet state are thought to be Cu(II) dimeric centers formed by aggregation of two [CuCo(H2L)(L)2] fragments of 1-3 present in solution. The residual monomeric spectra in the g approximately 2 region are indicative of the existence of an equilibrium in solution between the dimeric and monomeric Cu(II) centers in aggregated and free [CuCo(H2L)(L)2] fragments, respectively, with varying degrees of stability. The fragmentation process of 1-3 in solution was screened by electrospray ionization mass spectrometry.     

Charge-transfer photolysis of copper(II) dithiocarbamate mixed-ligand complexes in toluene/alcohol solutions

Charge-transfer (CT)-photolysis of Cu(II) dithiocarbamate mixed-ligand complexes Cu(II)(Et2dtc)X (X = Cl-, Br-) and Cu(II)(Et2dtc)(+)...Y- (Y = ClO4-, NO3-) has been studied in toluene/ROH and compared with our previous data obtained in chloromethane/ROH solutions, where chloromethane = CCl4, CHCl3 or CH2Cl2 and ROH = MeOH, EtOH, i-PrOH or i-BuOH. An EPR evidence is obtained about the formation of a new copper(II) dithiocarbamate mixed-ligand complex during simultaneous photolyses of Cu(II)(Et2dtc)+ and Cu(II)(Et2dtc)2 species in toluene/ROH. The role of the solvent is discussed from the combined analysis of spectrophotometric and EPR data and quantum yield results.     

Rhodium complexes with the chelating and binucleating ligands P(CH2CH2Py)nPh3-n (Py = 2-pyridyl; n = 1,2): structures and fluxional behavior

Several rhodium(I) complexes of the type [RhX(CO)(PePy2)], [Rh(diene)(PePy)]+, and [Rh(diene)(PePy2)]+ (PePyn = P(CH2CH2Py)nPh3-n; Py = 2-pyridyl; n = 1, 2) have been prepared. The two former are square planar; the latter are pentacoordinated for diene = tetrafluorobenzobarrelene or norbornadiene (confirmed by X-ray diffraction), but an equilibrium of 4- and 5-coordinate isomers exists in solution for diene = 1,5-cyclooctadiene. The fluxional behavior of all these complexes is studied by NMR spectroscopy. The complex [Rh(NBD)(PePy2)]PF6.Cl2CH2 crystallizes in the monoclinic space group P21/n with a = 8.455(1) A, b = 18.068(3) A, c = 19.729(3) A, beta = 99.658(3)degrees, and Z = 4. The complexes [Rh(diene)(PePy2)]+ react with CO to give the dimeric complex [Rh2(CO)2[P(CH2CH2Py)2Ph]2](BF4)2 with the pyridylphosphine acting as P,N-chelating and P,N-bridging.     

Tri- and tetranuclear copper(II) complexes consisting of mononuclear Cu(II) chiral building blocks with a sugar-derived Schiff's base ligand

A new sugar-derived Schiff's base ligand N-(3-tert-butyl-2-hydroxybenzylidene)-4,6-O-ethylidene-beta-D-glucopyranosylamine (H3L1) has been developed which afforded the coordinatively labile, alcoholophilic trinuclear Cu(II) complex [Cu3(L1)2(CH3OH)(H2O)] (1). Complex 1 has been further used in the synthesis of a series of alcohol-bound complexes with a common formula of [Cu3(L1)2(ROH)2] (R = Me (2), Et (3), nPr (4), nBu (5), nOct (6)). X-ray structural analyses of complexes 2-6 revealed the collinearity of trinuclear copper(II) centers with Cu-Cu-Cu angles in the range of 166-172 degrees . The terminal and central coppers are bound with NO3 and O4 atoms, respectively, and exhibit square-planar geometry. The trinuclear structures of 2-6 can be viewed as the two {Cu(L1)}- fragments capture a copper(II) ion in the central position, which is further stabilized by a hydrogen-bonding interaction between the alcohol ligands and the sugar C-3 alkoxo group. Complex 2 exhibits a strong antiferromagnetic interaction between the Cu(II) ions (J = -238 cm(-1)). Diffusion of methanol into a solution of complex 1 in a chloroform/THF mixed solvent afforded the linear trinuclear complex [Cu(3)(L1)2(CH3OH)2(THF)2] (7). The basic structure of 7 is identical to complex 2; however, THF binding about the terminal coppers (Cu-O(THF) = 2.394(7) and 2.466(7) A) has introduced the square-pyramidal geometry, indicating that the planar trinuclear complexes 2-6 are coordinatively unsaturated and the terminal metal sites are responsible for further ligations. In the venture of proton-transfer reactions, a successful proton transfer onto the saccharide C-3 alkoxo group has been achieved using 4,6-O-ethylidene-d-glucopyranose, resulting in the self-assembled tetranuclear complex, [Cu4(HL1)4] (8), consisting of the mononuclear Cu(II) chiral building blocks, {Cu(HL1)}.     

Complexes of copper(II) with 3-(ortho-substituted phenylhydrazo)pentane-2,4-diones: syntheses, properties and catalytic activity for cyclohexane oxidation

Reactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) bearing a substituent in the ortho-position [X = OH (H(2)L(1)) 1, AsO(3)H(2) (H(3)L(2)) 2, Cl (HL(3)) 3, SO(3)H (H(2)L(4)) 4, COOCH(3) (HL(5)) 5, COOH (H(2)L(6)) 6, NO(2) (HL(7)) 7 or H (HL(8)) 8] lead to a variety of complexes including the monomeric [CuL(4)(H(2)O)(2)]·H(2)O 10, [CuL(4)(H(2)O)(2)] 11 and [Cu(HL(4))(2)(H(2)O)(4)] 12, the dimeric [Cu(2)(H(2)O)(2)(μ-HL(2))(2)] 9 and the polymeric [Cu(μ-L(6))](n)] 13 ones, often bearing two fused six-membered metallacycles. Complexes 10-12 can interconvert, depending on pH and temperature, whereas the Cu(II) reactions with 4 in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H(2)O)(4){NCNC(NH(2))(2)}(2)](HL(4))(2)·6H(2)O 14 and the heteroligand polymer [Cu(μ-L(4))(im)](n)15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, (1)H and (13)C NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1-8 on the HOMO-LUMO gap and the relative stability of the model compounds [Cu(OH)(L(8))(H(2)O)]·H(2)O, [Cu(L(1))(H(2)O)(2)]·H(2)O and [Cu(L(4))(H(2)O)(2)]·H(2)O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12 and 13 act as catalyst precursors for the peroxidative oxidation (with H(2)O(2)) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H(2)O (total yields of ca. 20% with TONs up to 566), under mild conditions.     

Three supramolecular trinuclear nickel(II) complexes based on Salamo-type chelating ligand: syntheses,crystal structures,solvent effect,Hirshfeld surface analysis and DFT calculation

Transition Metal Chemistry - Three Ni(II) complexes {[NiL(μ-OAc)(CH3CH2OH)]2Ni} (1), {[NiL(μ-OAc)(CH3OH)]2Ni]·2CH2Cl2·2CH3OH (2) and {[NiL(μ-OAc)(CH3OH)]2Ni}·1.5CH3OH...