Mononuclear and binuclear copper(I) complexes ligated by bis(3,5-diisopropyl-1-pyrazolyl)methane: insight into the fundamental coordination chemistry of three-coordinate copper(I) complexes with a neutral coligand

By using the neutral bidentate nitrogen-containing ligand, bis(3,5-diisopropyl-1-pyrazolyl)methane (L1' '), the copper(I) complexes [Cu(L1' ')2](CuCl2) (1CuCl2), [Cu(L1' ')2](ClO4) (1ClO4), [Cu(L1' ')]2(ClO4)2 (2ClO4), [Cu(L1' ')]2(BF4)2 (2BF4), [Cu(L1' ')(NCMe)](PF6) (3PF6), [Cu(L1' ')(PPh3)](ClO4) (4ClO4), [Cu(L1' ')(PPh3)](PF6) (4PF6), [{Cu(L1' ')(CO)}2(mu-ClO4)](ClO4) (5ClO4), and the copper(II) complexes [{Cu(L1' ')}2(mu-OH)2(mu-ClO4)2] (6), and [Cu(L1' ')Cl2] (7) were systematically synthesized and fully characterized by X-ray crystallography and by IR and 1H NMR spectroscopy. In the case of copper(II), ESR spectroscopy was also applied. In comparison with the related neutral tridentate ligand L1', bis-chelated copper(I) complexes and binuclear linear-coordinated copper(I) complexes are easy to obtain with L1' ', like 1CuCl2, 1ClO4, 2ClO4, and 2BF4. Importantly, stronger and bulkier ligands such as acetonitrile (3PF6) and especially triphenylphosphine (4ClO4 and 4PF6) generate three-coordinate structures with a trigonal-planar geometry. Surprisingly, for the smaller ligand carbon monoxide, a mononuclear three-coordinate structure is very unstable, leading to the formation of a binuclear complex (5ClO4) with one bridging perchlorate anion, such that the copper(I) centers are four-coordinate. The same tendency is observed for the copper(II) bis(mu-hydroxo) compounds 6, which is additionally bridged by two perchlorate anions. Both copper(II) complexes 6 and 7 were obtained by molecular O2 oxidation of the corresponding copper(I) complexes. A comparison of the new copper(I) triphenylphosphine complexes 4ClO4 and 4PF6 with corresponding species obtained with the related tridentate ligands L1' and L1 (8ClO4 and 9, respectively) reveals surprisingly small differences in their spectroscopic properties. Density functional theory (DFT) calculations are used to shed light on the differences in bonding in these compounds and the spectral assignments. Finally, the reactivity of the different bis(pyrazolyl)methane complexes obtained here toward PPh3, CO, and O2 is discussed.     

Copper(I) complexes with fluorinated hydrotris(pyrazolyl)borate: Influence of electronic effects on their structure,physicochemical properties,and reactivity

Copper(I) coordination complexes of the anionic fluorinated ligand, hydrotris(3-trifluoromethyl-5-methyl-1-pyrazolyl)borate (L0f⁻), i.e. the copper(I) carbonyl complex, [Cu^I(L0f)(CO)] (1), the copper(I) triphenylphosphine complex, [Cu^I(L0f)(PPh₃)] (2), the copper(I) acetonitrile complex, [Cu^I(L0f)(NCMe)] (3), and the corresponding copper(I) triphenylphosphine complex with hydrotris(3,5-diisopropyl-1-pyrazolyl)-borate anion (L1⁻), i.e. [Cu^I(L1)(PPh₃)] (4), were synthesized in order to investigate the influence of the electron-withdrawing groups on the pyrazolyl rings. The structures of complexes 1, 2, and 4 were determined by X-ray crystallography. While X-ray crystallography did not show definitive trends in terms of copper(I) atom geometry, the clear influence of the electronic structure of the pyrazolyl rings is observed by spectroscopic techniques, namely, IR and multinuclear NMR spectroscopy. Finally, the relative stability of the copper(I) complexes is discussed.     

Impact of variations in design of flexible bitopic bis(pyrazolyl)methane ligands and counterions on the structures of silver(I) complexes: dominance of cyclic dimeric architecture

The new ligands 1,1,4,4-tetra(1-pyrazolyl)butane [CH(pz)(2)(CH(2))(2)CH(pz)(2), L2] and 1,1,5,5-tetra(1-pyrazolyl)pentane [CH(pz)(2)(CH(2))(3)CH(pz)(2), L3] have been prepared to determine the structural changes in silver(I) complexes, if any, that accompany the lengthening of the spacer group between two linked bis(pyrazolyl)methane units. Silver(I) complexes of both ligands with BF(4)(-) and SO(3)CF(3)(-) as the counterion have the formula [Ag(2)(micro-L)(2)](counterion)(2). These complexes have a cyclic dimeric structure in the solid state previously observed with the shorter linked ligand CH(pz)(2)CH(2)CH(pz)(2). Similar chemistry starting with AgNO(3) for L2 yields a complex of the empirical formula [Ag(2)[micro-CH(pz)(2)(CH(2))(2)CH(pz)(2)](3)](NO(3))(2) that retains the cyclic dimeric structure, but bonding of an additional ligand creates a coordination polymer of the cyclic dimers. In contrast, coordination of the nitrate counterion to silver in the complex of L3 leads to the formation of the coordination polymer of the empirical formula [Ag(micro-CH(pz)(2)(CH(2))(3)CH(pz)(2))]NO(3). All six new complexes have extended supramolecular structures based on noncovalent interactions supported by the counterions and the functional groups designed into the ligands.     

Mononuclear and dinuclear copper(I) complexes of bis(3,5-dimethylpyrazol-1-yl)methane: synthesis, structure, and reactivity

The synthesis and structures of a mononuclear copper(I) carbonyl complex [Cu(OClO3)(CO)(H2CPz2')] (3) and a dinuclear copper(I) carbonyl complex [{Cu(CO)(H2CPz2')}2(mu-pyrazine)](ClO4)2 (4), where H2CPz2' = bis(3,5-dimethylpyrazol-1-yl)methane, are described. These two compounds were generated by the carbonylation of the corresponding copper(I)-acetonitrile complexes, [Cu(H2CPz2')(MeCN)](ClO4) (1) and [{Cu(H2CPz2')(MeCN)}2(mu-pyrazine)](ClO4)2 (2). Alternatively, treatment of mononuclear 1 and 3, respectively, with pyrazine in a molar ratio of 2:1 produces the pyrazine-bridged dinuclear Cu(I) complexes 2 and 4. Each of the complexes 1-4 can react with PPh3 to generate a common three-coordinated copper(I) complex [Cu(PPh3)(H2CPz2')](ClO4) (5). The structures of complexes 1-5 were all confirmed by X-ray crystallography. Comparison of the Cu(I)-C(CO) bond distances and the CO stretching frequencies of 3 and 4 indicates the back-donating properties of d pi(Cu)-pi*(pyrazine) bonds in 4, and accordingly, stabilizes the mixed-valence species generated from 2. Complex 3, stabilized by the strong interaction between copper(I) ion and perchlorate counteranion (Cu(I)-O(ClO4) = 2.240(3) A), is a potential precursor for polynuclear copper(I) carbonyl complexes.     

Influence of second coordination sphere hydroxyl groups on the reactivity of copper(I) complexes

We report the enhanced reactivity of hydroxyl substituted CuN(3)(+) derivatives, where N(3) = tris(picolinyl)methane (tripic) and related derivatives, upon deprotonation of the O-H functionality. The work capitalizes on new methodology for incorporating hydroxyl groups into the second coordination sphere of copper centers. The key synthetic methodology relies on Pd-catalyzed coupling reactions of dilithiated 6-methyl-2-pyridone with bromopyridyl derivatives. These building blocks allow the preparation of tridentate N(3) ligands with OH and OMe substituents flanking the fourth coordination site of a tetrahedral complex. Coupling of these tridendate ligands gives the corresponding hydroxy- and methoxy-functionalized bistripodal ligands. [Cu[bis(2-methylpyrid-6-yl)(2-hydroxypyrid-6-yl)methane](NCMe)](+) ([Cu(2H)(NCMe)](+)) oxidizes readily in air to afford the mixed valence Cu(1.5) dimer ([Cu(2)(2)(2)](+)). Formation of [Cu(2)(2)(2)](+) is accelerated in the presence of base and can be reversed with a combination of decamethylferrocene and acid. The reactivity of [Cu(2H)(NCMe)](+) with dioxygen requires deprotonation of the hydroxyl substituent: neither [Cu(tripic)(NCMe)](+) nor the methoxy-derivatives displayed comparable reactivity. A related mixed valence dimer formed upon oxidation of the dicopper(I) complex of a tetrahydroxy bis(tridentate) ligand, [Cu(2)(6H(4))(NCMe)(2)](2+). The dicopper(I) complex of the analogous tetramethoxy N(6)-ligand, [Cu(2)(5)(NCMe)(2)](2+), instead reversibly binds O(2). Deprotonation of [Cu(2H)(CO)](+) and [Cu(2H)(NCMe)](+) afforded the neutral derivatives Cu(2)(CO) and Cu(2)(2)(2), respectively. The dicopper(I) derivative Cu(2)(2)(2) can be reoxidized, reprotonated, and carbonylated. The silver(I) complex, [Ag(2H)(NCMe)]BF(4), forms an analogous neutral dimer (Ag(2)(2)(2)) upon deprotonation of the hydroxyl group. The structures of ligand 2H, [Cu(2)(5)(NCMe)(2)](+), [Cu(2)(2)(2)](+), [Cu(2)(6H(2))](+), [Ag(2H)(NCMe)]BF(4), and Ag(2)(2)(2) were confirmed by single crystal X-ray diffraction.     

Synthesis and structures of homo- and heterobimetallic rhodium(I) and/or iridium(I) complexes of binucleating bis(1-pyrazolyl)methane ligands

The synthesis of a series of Rh(I) and Ir(I) homobimetallic complexes using three different linking scaffolds is described. The cyclooctadiene (COD) complexes [M(2)(COD)(2)(L(scaffold))][BAr(F)(4)](2) (2-7) where M = Rh(I) or Ir(I), and L(scaffold) = bis(1-pyrazolyl)methane ligands, p-C(6)H(4)[CH(pz)(2)](2) (1a), m-C(6)H(4)[CH(pz)(2)](2) (1b) and the anthracene-bridged 1,8-C(14)H(8)[CH(pz)(2)](2) (1c) were synthesized. The COD co-ligands of 2-7 were replaced with the carbonyl co-ligands to form the analogous homobimetallic complexes, [M(2)(CO)(4)(L(scaffold))][BAr(F)(4)](2) (8-13). The solid-state structures of the dicationic homobimetallic complexes 2, 3, 5, 6, 9, and 10, as well as cationic monometallic complexes 15 and 22 of ligands 1b and 1c respectively, were characterized using X-ray crystallography. The solid-state XRD structures of the resulting dirhodium and diiridium complexes with the para- and meta-phenylene and anthracene scaffolds show that there are distinct differences between structures of complexes 2-10 due to the variation in the scaffold structures, in particular the relative positions of the two metal centres. Heterobimetallic RhIr complexes of the m-C(6)H(4)[CH(pz)(2)](2) ligand were also synthesized using a stepwise approach, and the observed exchange of the metal centres in the heterobimetallic complexes was found to be dependent on the nature of the coligand.     

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.     

Copper(I) complexes of tripodal tris(imidazolyl) ligands: potential mimics of the Cu(A) site of hydroxylase enzymes

Copper(I) complexes of tripodal tris(N-methyl-4,5-diphenyl-imidazolyl)methane ligands, N3CR (1a-c, R = OH, OMe, H), have been prepared as models for the Cu(A) site of copper hydroxylase enzymes. In the absence of additional donors, the ligands 1 react with [Cu(CH3CN)4]PF6 (2) to produce dinuclear complexes [(N3CR)2Cu2](PF6)2 (3) in which the tripodal ligands bridge two trigonal Cu centers; the structures of 3b and 3c are established by X-ray diffraction. Mononuclear adducts [(N3CR)CuL]Z are produced with L = acetonitrile (4), carbon monoxide (5), and t-BuNC (6, 7). The carbonyl complexes 5 are in dynamic equilibrium with the dimeric complexes 3, but 5c (R = H) can be isolated. The structures of the isocyanide derivatives depend critically on the tripod methane substituent, R. Thus, the X-ray structures of 6 (R = OMe) and 7 (R = H) show trigonal and tetrahedral geometries, respectively, with bi- or tridentate coordination of the tripod. A trinuclear complex [Cu3(N3COH)2(t-BuNC)2](PF6)3 (8) is formed from N3COH (1a) which features both three-coordinate and two-coordinate Cu atoms and bidentate tripod coordination. Reactions of dioxygen with dinuclear 3c or mononuclear [(N3CR)CuL]Z are sluggish, producing from the latter in acetone [(N3CH)CuII(L)(L')](PF6)2 (9, L = acetone, L' = H2O).     

Copper complexes of nitrogen-anchored tripodal N-heterocyclic carbene ligands

Incorporation of a nitrogen functionality into a tripodal N-heterocyclic carbene ligand system affords the first N-anchored tetradentate tris-carbene ligands TIMEN(R) (R = Me (5a), t-Bu (5b), Bz (5c)). Treatment of the methyl derivatized [H(3)TIMEN(Me)](PF(6))(3) imidazolium salt (H(3)5a) with silver oxide yields the silver complex [(TIMEN(Me))(2)Ag(3)](PF(6))(3) (9), which, in a ligand transfer reaction, reacts with copper(I) bromide to give the trinuclear copper(I) complex [(TIMEN(Me))(2)Cu(3)](PF(6))(3) (10). Deprotonation of the tert-butyl and benzyl derivatives [H(3)TIMEN(t-Bu)](PF(6))(3) and [H(3)TIMEN(Bz)](PF(6))(3) yields the free tris-carbenes TIMEN(t-Bu) (5b) and TIMEN(Bz) (5c), which react readily with copper(I) salts to give mononuclear complexes [(TIMEN(t-Bu))Cu](PF(6)) (11b) and [(TIMEN(Bz))Cu]Br (11c). The solid-state structures of 10, 11b, and 11c were determined by single-crystal X-ray diffraction. While the TIMEN(Me) ligand yields trinuclear complex 10, with both T-shaped three-coordinate and linear two-coordinate copper(I) centers, the TIMEN(t-Bu) and TIMEN(Bz) ligands induce mononuclear complexes 11b and 11c, rendering the cuprous ion in a trigonal planar ligand environment of three carbenoid carbon centers and an additional, weak axial nitrogen interaction. Complexes 11b and 11c exhibit reversible one-electron redox events at half-wave potentials of 110 and -100 mV vs Fc/Fc(+), respectively, indicating sufficient electronic and structural flexibility of both TIMEN(R) ligands (R = t-Bu, Bz) to stabilize copper(I) and copper(II) oxidation states. Accordingly, a copper(II) NHC complex, [(TIMEN(Bz))Cu](OTf)(2) (12), was synthesized. Paramagnetic complex 12 was characterized by elemental analysis, EPR spectroscopy, and SQUID magnetization measurements.     

Complexes of functionalized dipyrido[3,2-a:2',3'-c]-phenazine: a synthetic, spectroscopic, structural, and density functional theory study

The ligands 11-bromodipyrido[3,2-a:2',3'-c]phenazine and ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate have been prepared and coordinated to ruthenium(II), rhenium(I), and copper(I) metal centers. The electronic effects of substitution of dipyrido[2,3-a:3',2'-c]phenazine (dppz) have been investigated by spectroscopy and electrochemistry, and some photophysical properties have been studied. The crystal structures of [Re(L)(CO)(3)Cl] (L = ethyl dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylate or 11-bromodipyrido[3,2-a:2',3'-c]phenazine) are presented. Density functional theory calculations on the complexes show only small deviations in bond lengths and angles (most bonds within 0.02 Angstroms, most angles within 2 degrees) from the crystallographic data. Furthermore, the vibrational spectra of the strongest Raman and IR bands are predicted to within an average 6 cm(-1) for the complexes [Re(L)(CO)(3)Cl] and [Cu(L)(triphenylphosphine)(2)]BF(4) (in the 1000-1700 cm(-1) region). Spectroscopic and electrochemical evidence suggest that reduction of the complex causes structural changes across the entire dppz ligand. This is unusual as dppz-based ligands typically have electrochemical properties that suggest charge localization with reduction on the phenazine portion of the ligand. The excited-state lifetimes of the complexes have been measured, and they range from ca. 200 ns for the [Ru(L)(2,2'-bipyridine)(2)](PF(6))(2) complexes to over 2 mus for [Cu(11-bromodipyrido[3,2-a:2',3'-c]phenazine)(PPh(3))(2)](BF(4)) at room temperature. The emission spectra suggest that the unusually long-lived excited states of the copper complexes result from metal-to-ligand charge transfer (MLCT) transitions as they are completely quenched in methanol. Electroluminescent films may be fabricated from these compounds; they show MLCT state emission even at low doping levels [<0.1% by weight in poly(vinylcarbazole) polymer matrix].     

Dinuclear copper(I) complexes with hexaaza macrocyclic dinucleating ligands: structure and dynamic properties

The synthesis and structural and spectroscopic characterization of a family of copper(I) complexes, containing a dinucleating hexaaza macrocyclic ligand, of general formula [Cu(2)(L)(X)(2)](2+) (L = Me2p, Me2m, Me3p, or Me3m; X = MeCN, n-PrCN, CO, t-BuNC, or PPh(3)) is described. This family of complexes contains ligands that differ from one another in the number of methylenic units linking the tertiary amines and in the meta or para substitution of their aromatic rings. The structural characterization in the solid-state includes a single-crystal X-ray diffraction analysis of [Cu(2)(Me2p)(CO)(2)](2+) and of [Cu(2)(Me2m)(t-BuNC)(2)](2+). In solution, those complexes are structurally characterized through NMR spectroscopy that also allows us to put forward and establish their fluxional behavior. Theoretical calculations at the DFT level have also been performed in order to further analyze the relative energy of the different potential isomers as well as to gain insight into their chemical properties. Finally, the influence of the hexaaza ligands over different structural aspects as well as on its potential chemical reactivity is discussed.     

Copper(II) complexes with neutral bis(pyrazolyl)methane ligands: The influence of steric hindrance on their structures and properties

By using the neutral bidentate nitrogen-containing ligands; bis(3,5-dimethyl-1-pyrazolyl)methane (L0″), bis(3,5-diisopropyl-1-pyrazolyl)methane (L1″), bis(3-tertiary-butyl-5-isopropyl-1-pyrazolyl)methane (L3″), and bis(3,5-ditertiary-butyl-1-pyrazolyl)methane (L4″), the copper(II) nitrato complexes [Cu(L0″)₂(NO₃)]NO₃ (1NO₃), [Cu(L0″)(NO₃)₂] (2), [Cu(L1″)(NO₃)₂] (3), [Cu(L3″)(NO₃)₂] (4), and [Cu(L4″)(NO₃)₂] (5), chloro complexes [Cu(L0″)₂Cl]₂(CuCl₄) (6CuCl₄), [Cu(L0″)₂Cl]₂(Cu₂Cl₆) (6Cu₂Cl₆), [Cu(L1″)Cl₂] (7), and [Cu(L3″)Cl₂] (8), nitrito complexes [Cu(L0″)(ONO)₂] (9) and [Cu(L1″)(ONO)₂] (10), and the complexes with perchlorate ions [Cu(L0″)₂(CH₃OH)](ClO₄)₂ (11ClO₄) and [Cu(L1″)₂(H₂O)](ClO₄)₂ (12ClO₄) were systematically synthesized and fully characterized by X-ray crystallography and by IR, far-IR, UV–Vis absorption, and ESR spectroscopy. In comparison with the obtained complexes with four bis(pyrazolyl)methanes having different bulkiness at pyrazolyl rings, the second coordination sphere effects on the ligands are discussed in detail. Moreover, the structures and physicochemical properties of these obtained complexes are compared with those of the related complexes with the neutral tridentate tris(pyrazolyl)methane ligand.     

Photoexcitation in Cu(I) and Re(I) complexes containing substituted dipyrido[3,2-a:2',3'-c]phenazine: a spectroscopic and density functional theoretical study

Copper(I) and rhenium(I) complexes [Cu(PPh(3))(2)(dppz-11-COOEt)]BF(4), [Cu(PPh(3))(2)(dppz-11-Br)]BF(4), [Re(CO)(3)Cl(dppz-11-COOEt)] and [Re(CO)(3)Cl(dppz-11-Br)] (dppz-11-COOEt = dipyrido-[3,2a:2',3'c]phenazine-11-carboxylic ethyl ester, dppz-11-Br = 11-bromo-dipyrido[3,2a:2',3'c]-phenazine) have been studied using Raman, resonance Raman, and transient resonance Raman (TR(2)) spectroscopy, in conjunction with computational chemistry. DFT (B3LYP) frequency calculations with a 6-31G(d) basis set for the ligands and copper(I) centers and an effective core potential (LANL2DZ) for rhenium in the rhenium(I) complexes show close agreement with the experimental nonresonance Raman spectra. Modes that are phenazine-based, phenanthroline-based, and delocalized across the entire ligand structure were identified. The nature of the absorbing chromophores at 356 nm for ligands and complexes was established using resonance Raman spectroscopy in concert with vibrational assignments from calculations. This analysis reveals that the dominant chromophore for the complexes measured at 356 nm is ligand-centered (LC), except for [Re(CO)(3)Cl(dppz-11-Br)], which appears to have additional chromophores at this wavelength. Calculations on the reduced complexes, undertaken to model the metal-to-ligand charge transfer (MLCT) excited state, show that the reducing electron occupies a ligand MO that is delocalized across the ligand structure. Resonance Raman spectra (lambda(exc) = 514.5 nm) of the reduced rhenium complexes show a similar spectral pattern to that observed in [Re(CO)(3)Cl(dppz)](*-); the measured bands are therefore attributed to ligand radical anion modes. These bands lie at 1583-1593 cm(-1) for [Re(CO)(3)Cl(dppz-11-COOEt)] and 1611 cm(-1) for [Re(CO)(3)Cl(dppz-11-Br)]. The thermally equilibrated excited states are examined using nanosecond-TR(2) spectroscopy (lambda(exc) = 354.7 nm). The TR(2) spectra of the ligands provide spectral signatures for the (3)LC state. A band at 1382 cm(-1) is identified as a marker for the (3)LC states of both ligands. TR(2) spectra of the copper and rhenium complexes of dppz-11-Br show this (3)LC band, but it is not prominent in the spectra of [Cu(PPh(3))(2)(dppz-11-COOEt)](+) and [Re(CO)(3)Cl(dppz-11-COOEt)]. Calculations suggest that the lowest triplet states of both of the rhenium(I) complexes and [Cu(PPh(3))(2)(dppz-11-Br)](+) are metal-to-ligand charge transfer in nature, but the lowest triplet state of [Cu(PPh(3))(2)(dppz-11-COOEt)](+) appears to be LC in character.     

Supramolecular copper hydroxide tennis balls: self-assembly, structures, and magnetic properties of octanuclear [Cu(8)L(8)(OH)(4)](4+) clusters (HL = N-(2-pyridylmethyl)acetamide)

The self-assembly of supramolecular copper "tennis balls" that possess unusual magnetic properties using a small pyridyl amide ligand is described. Copper(II) complexes of N-(2-pyridylmethyl)acetamide (HL) were synthesized in methanol. In the absence of base, the mononuclear complex [Cu(HL)(2)](ClO(4))(2) (1) was prepared. The structure of 1, determined by X-ray crystallography, contains a copper(II) ion surrounded by bidentate HL ligands coordinated via the pyridyl N atom and the carbonyl O atom in a trans, square planar arrangement. Reactions carried out in the presence of triethylamine resulted in cluster complexes [Cu(8)L(8)(OH)(4)](ClO(4))(4) and [Cu(8)L(8)(OH)(4)](CF(3)SO(3))(4) [2(ClO(4))(4) and 2(OTf)(4), respectively]. The cationic portions of 2(ClO(4))(4) and 2(OTf)(4) are isostructural, containing eight copper(II) ions, eight deprotonated ligands (L(-)), and four mu(3)-hydroxide ligands. The top and bottom halves of the cluster are related by a pseudo-S(4) symmetry operation and are held together by bridging L(-) ligands. Solutions of 2(ClO(4))(4) and 2(OTf)(4), which were shown to contain the full [Cu(8)L(8)(OH)(4)](4+) fragment by electrospray mass spectrometry and conductance experiments, are EPR silent. Magnetic susceptibility measurements for 2(ClO(4))(4) as a function of temperature and magnetic field showed the Cu ions all to exhibit magnetic moments in the range expected for the d(9) configuration. At low temperatures, the magnetization was reduced due to predominantly antiferromagnetic interactions between ions. Analysis showed that partially frustrated interactions among the four Cu ions making up each half of the cluster gave good agreement with the data once a large molecular anisotropy was taken into account, with J(c) = 106 cm(-1), D = 27 cm(-1), and g = 2.17.     

Metal complexes from 1,1'-di(pyrazinyl)ferrocene: coordination polymers and bridged diferrocenes

Ferrocene-based ligands 1,1'-di(pyrazinyl)ferrocene (L1) and 1,1'-di(2-pyrimidinyl)ferrocene (L2) were synthesized and copper and silver complexes were obtained from L1. Coordination polymers [{Cu(2)(PhCOO)(4)}(L1)](n) (1), [{Cu(2)(C(5)H(11)COO)(4)}(L1)](n) (2), and [{Cu(2)(OAc)(4)}(L1)](n).0.5n[Cu(2)(OAc)(4)(H(2)O)(2)].1.5nCH(3)CN (3) resulted from the reaction with the corresponding copper carboxylates. In all three complexes, L1 links the dinuclear copper carboxylate units to form one-dimensional step-like chains. In 2, these chains are further linked by [Cu(2)(OAc)(4)(H(2)O)(2)] dinuclear units via hydrogen bonding to form sheet structures. The reaction of L1 with copper(I) iodide resulted in a multinuclear complex [(CuI)(4)(L1)(2)].(L1) (4), which contains a [(CuI)(4)(L1)(2)] diferrocene unit with a step-like (CuI)(4) core. Reactions of L1 with silver(I) salts resulted in silver-bridged diferrocenes [Ag(2)(L1)(2)]X(2) (X = ClO(4) (5a, b), NO(3) (6a-c) and PF(6) (7)), some of which incorporate aromatic solvents into their crystal lattices. The intramolecular Ag...Ag separations in these metallamacrocycles (3.211-3.430 A) depended upon the counter-anions and on the coordination mode of the silver ions. In all of these coordination complexes, L1adopts a synperiplanar eclipsed conformation and acts as a bidentate ligand, with only the 5-nitrogen of each pyrazine ring involved in coordination.     

Syntheses of copper(I)cis-1,3,5-tri-iminocyclohexane complexes

Copper(I) complexes of the ligand cis-1,3,5-tris(cinnamylideneamino)cyclohexane (L) have been prepared from a versatile precursor complex, [Cu(I)(L)NCMe]BF4, which incorporates a labile acetonitrile ligand that can be exchanged to give a range of new Cu(L)X complexes (where X = Cl, Br, NO2, SPh). 1H NMR spectra and X-ray structures of the Cl, Br and NO2 complexes show L coordinated in a symmetric fashion about the copper centre. The complexes have been further characterised using UV/Visible spectroscopy and cyclic voltammetry. CuLCl shows an electrochemically reversible Cu(I/II) redox couple at 0.51 V (vs. Ag/AgCl) while the CuLNO2 complex shows an analogous quasi-reversible wave at 0.41 V (vs. Ag/AgCl).     

Reporting a unique example of electronic bistability observed in the form of valence tautomerism with a copper(II) helicate of a redox-active nitrogenous heterocyclic ligand

Valence tautomeric compounds involving nondixolene-type ligands are rare. The triple-helicate copper(II) complex [Cu(II)(2)(L)(3)](ClO(4))(4)·3CH(3)CN (1) containing a redox-active N-heterocyclic ligand (L) has been prepared and displays VT equilibrium in solution, as established by electronic spectroscopy, electron paramagnetic resonance spectroscopy, and cyclic and differential pulse voltammetry carried out at variable temperatures. The process involves intramolecular transfer of an electron from one of the L ligands to a copper(II) center, leading to the oxidation of L to an L(?+) radical with concomitant reduction of the Cu(II) center to Cu(I), as shown by the equilibrium [Cu(II)Cu(I)L(?+)L(2)](4+) ? [Cu(II)(2)L(3)](4+).     

Reaction behaviour of dinuclear copper(I) complexes with m-xylyl-based ligands towards dioxygen

Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L(1)(L(1)=alpha,alpha'-bis[(2-pyridylethyl)amino]-m-xylene) and L(3)(L(3)=alpha, alpha'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene). The dinuclear copper(I) complex [Cu(2)L(3)](ClO(4))(2) and the dicopper(II) complex [Cu(2)(L(1)-O)(OH)(ClO(4))]ClO(4) were characterized by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesized with the ligand L(2)-OH (structurally characterized [Cu(2)(L(2)-O)Cl(3)] with L(2)=alpha, alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; synthesized from the reaction between [Cu(2)(L(2)-O)(OH)](ClO(4))(2) and Cl(-)) and Me-L(3)-OH: [Cu(2)(Me-L(3)-O)(mu-X)](ClO(4))(2)xnH(2)O (Me-L(3)-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C(3)H(3)N(2)(-)(prz), MeCO(2)(-) and N(3)(-)). The magnetochemical characteristics of compounds were determined by temperature-dependent magnetic studies, revealing their antiferromagnetic behaviour [-2J(in cm(-1)) values: -92, -86 and -88; -374].     

Electronic and structural variation among copper(II) complexes with substituted phenanthrolines

A series of copper(II) complexes with substituted phenanthroline ligands has been synthesized and characterized electronically and structurally. The compounds that have been prepared include the monosubstituted ligand complexes of the general formula [Cu(5-R-phen)(2)(CH(3)CN)](BF(4))(2), where R = NO(2), Cl, H, or Me, and the disubstituted ligand complex [Cu(5,6-Me(2)-phen)(2)(CH(3)CN)](BF(4))(2). The complexes [Cu(5-NO(2)-phen)(2)(CH(3)CN](BF(4))(2) (1), [Cu(5-Cl-phen)(2)(CH(3)CN)](BF(4))(2) (2), [Cu(o-phen)(2)(CH(3)CN)](BF(4))(2) (3), and [Cu(5-Me-phen)(2)(CH(3)CN)](BF(4))(2) (4) each crystallize in the space group C2/c with compounds 1, 2, and 4 comprising an isomorphous set. The disubstituted complex [Cu(5,6-Me(2)-phen)(2)(CH(3)CN)](BF(4))(2) (5) crystallizes in the space group P2(1)/c. Each structure is characterized by a distorted trigonal bipyramidal arrangement of ligands around the central copper atom with approximate or exact C(2) symmetry. The progression from electron-withdrawing to electron-donating substituents on the phenanthroline ligands correlates with less accessible reduction potentials for the bis-chelate complexes.