An unprecedented copper(I,II)-octacyanotungstate(V) 2-D network: crystal structure and magnetism of [CuII(tren)]{CuI[W(V)(CN)8]} . 1.5H2O

A novel two-dimensional cyanide-bridged polymer [CuII(tren)]{CuI[W(V)(CN)8]} . 1.5H2O (tren = tris(2-aminoethyl)amine) formed via the simultaneous in situ metal-ligand redox reaction of [Cu(tren)(OH2)]2+ and self-assembly with [W(V)(CN)8]3- consists of a {CuI[W(V)(CN)8]} square grid built of CuI centres of tetrahedral geometry coordinatively saturated by CN bridges and [W(V)(CN)8]3- capped by [CuII(tren)]2+ moieties; it exhibits ferromagnetic coupling J1 = +5.8(1) cm(-1) within the CuII-W(V) dinuclear subunits and weak antiferromagnetic coupling J2 = -0.03(1) cm(-1) between them through diamagnetic CuI spacers.     

Cyanide-bridged tetradecanuclear RuII3MII11 clusters (MII=ZnII and CuII) based on the high connectivity building block [Ru3(HAT)(CN)12]6-: structural and photophysical properties

Reaction of the anionic cyanometallate chromophore [{Ru(CN)4}3(micro3-HAT)]6- with [MII(tren)]2+ complexes (M=ZnII, CuII) provides discrete tetradecanuclear clusters of formula [{MII(tren)(micro-CN)}11{Ru3(HAT)(CN)}]16+; the weak luminescence of the Ru3 chromophore is substantially enhanced in the presence of ZnII ions, whereas it is completely quenched when CuII centers are present.     

2-D soft ferromagnet based on [Wv(CN)8]3- and CuII with a Tc of 34 K

Self-assembly of [Cu(tetren)]2+ (tetren = tetraethylenepentamine) and [W(CN)8]3- in acidic aqueous solution yields the double-layered square grid cyanide-bridged polymer of ((tetrenH5)0.8CuII4[Wv(CN)8](4).7.2H2O)n with Cu(II) centres of square pyramidal geometry coordinatively saturated solely by CN bridges supplied by five [W(CN)8]3- ions; it exhibits soft ferromagnetic behaviour with an ordering temperature Tc of 34 K.     

Ferromagnetism in malonato-bridged copper(II) complexes. Synthesis,crystal structures,and magnetic properties of [[Cu(H2O)3][Cu(mal)2(H2O)]]n and [[Cu(H2O)4]2[Cu(mal)2(H2O)]][Cu(mal)2(H2O)2][[Cu(H2O)4][Cu(mal)2(H2O)2][(H2mal = malonic acid)

Three malonato-bridged copper(II) complexes of the formulas [[Cu(H2O)3][Cu(C3H2O4)2(H2O)]]n (1), [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]] [Cu(C3H2O4)2(H2O)2][[Cu(H2O)4][Cu(C3H2O4)2(H2O)2]] (2), and [Cu(H2O)4][Cu(C3H2O4)2(H2O)2] (3) (C3H2O4 = malonate dianion) have been prepared, and the structures of the two former have been solved by X-ray diffraction methods. The structure of compound 3 was already known. Complex 1 crystallizes in the orthorhombic space group Pcab, Z = 8, with unit cell parameters of a = 10.339(1) A, b = 13.222(2) A, and c = 17.394(4) A. Complex 2 crystallizes in the monoclinic space group P2/c, Z = 4, with unit cell parameters of a = 21.100(4) A, b = 21.088(4) A, c = 14.007(2) A, and beta = 115.93(2) degrees. Complex 1 is a chain compound with a regular alternation of aquabis(malonato)copper(II) and triaquacopper(II) units developing along the z axis. The aquabis(malonato)copper(II) unit acts as a bridging ligand through two slightly different trans-carboxylato groups exhibiting an anti-syn coordination mode. The four carboxylate oxygens, in the basal plane, and the one water molecule, in the apical position, describe a distorted square pyramid around Cu1, whereas the same metal surroundings are observed around Cu2 but with three water molecules and one carboxylate oxygen building the equatorial plane and a carboxylate oxygen from another malonato filling the apical site. Complex 2 is made up of discrete mono-, di-, and trinuclear copper(II) complexes of the formulas [Cu(C3H2O4)2(H2O)2]2-, [[Cu(H2O)4] [Cu(C3H2O4)2(H2O)2]], and [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]]2+, respectively, which coexist in a single crystal. The copper environment in the mononuclear unit is that of an elongated octahedron with four carboxylate oxygens building the equatorial plane and two water molecules assuming the axial positions. The neutral dinuclear unit contains two types of copper atoms, one that is six-coordinated, as in the mononuclear entity, and another that is distorted square pyramidal with four water molecules building the basal plane and a carboxylate oxygen in the apical position. The overall structure of this dinuclear entity is nearly identical to that of compound 3. Finally, the cationic trimer consists of an aquabis(malonato)copper(II) complex that acts as a bismonodentate ligand through two cis-carboxylato groups (anti-syn coordination mode) toward two tetraaqua-copper(II) terminal units. The environment of the copper atoms is distorted square pyramidal with four carboxylate oxygens (four water molecules) building the basal plane of the central (terminal) copper atom and a water molecule (a carboxylate oxygen) filling the axial position. The magnetic properties of 1-3 have been investigated in the temperature range 1.9-290 K. Overall, ferromagnetic behavior is observed in the three cases: two weak, alternating intrachain ferromagnetic interactions (J = 3.0 cm-1 and alpha J = 1.9 cm-1 with H = -J sigma i[S2i.S2i-1 + alpha S2i.S2i+1]) occur in 1, whereas the magnetic behavior of 2 is the sum of a magnetically isolated spin doublet and ferromagnetically coupled di- (J3 = 1.8 cm-1 from the magnetic study of the model complex 3) and trinuclear (J = 1.2 cm-1 with H = -J (S1.S2 + S1.S3) copper(II) units. The exchange pathway that accounts for the ferromagnetic coupling, through an anti-syn carboxylato bridge, is discussed in the light of the available magneto-structural data.     

Synthesis, structure, and magnetic properties of valence ambiguous dinuclear antiferromagnetically coupled cobalt and ferromagnetically coupled iron complexes containing the chloranilate(2-) and the significantly stronger coupling chloranilate(*3-) radical trianion

Dinuclear [(TPyA)MII(CA2-)MII(TPyA)]2+ [TPyA=tris(2-pyridylmethyl)amine; CA2-=chloranilate dianion; M=Co (1(2+)), Fe (2(2+))] complexes have been prepared by the reaction of M(BF4)(2).6H2O, TPyA, H2CA, and triethylamine in MeOH solution. Their reduced forms [(TPyA)MII(CA*3-)MII(TPyA)]+ [M=Co(1+), Fe (2+)] have been synthesized by using cobaltocene, and oxidized forms of 1, [(TPyA)CoIII(CAn)CoIII(TPyA)]z+ [z=3, n=3- (1(3+)); z=4, n=2- (1(4+))], have been obtained by using FcBF4 and ThianBF4 (Fc=ferrocenium; Thian=thianthrinium), respectively. The dinuclear compound bridged chloranilates (CA2- or CA*3-) were isolated and characterized by X-ray crystallography, electrochemistry, magnetism, and EPR spectroscopy. Unlike the other redox products, valence ambiguous 13+ forms via a complex redox-induced valence electron rearrangement whereby the one-electron oxidation of the [CoIICA2-CoII]2+ core forms [CoIIICA*3-CoIII]3+, not the expected simple 1-e- transfer mixed-valent [CoIICA2-CoIII]3+ core. The M ions in 1 and 2 have a distorted octahedral geometry by coordination with four nitrogens of a TPyA, two oxygens of a chloranilate. Due to the interdimer offset face-to-face pi-pi and/or herringbone interactions, all complexes show extended 1-D and/or 2-D supramolecular structures. The existence of CA*3- in 1(3+) is confirmed from both solid-state magnetic and solution EPR data. Co-based 1n+ exhibit antiferromagnetic interactions [1(2+): g=2.24, J/kB=-0.65 K (-0.45 cm-1); 1+: g=2.36, J/kB=-75 K (52 cm-1)], while Fe-based 2n+ exhibit ferromagnetic interactions [2(2+): g=2.08, J/kB=1.0 K (0.70 cm-1); 2+: g=2.03, J/kB=28 K (19 cm-1)] [H=-2JS1.S2 for 12+ and 2(2+); H=-2J(S1.S2+S2.S3) for 1+ and 2+]. Thus, due to direct spin exchange CA*3- is a much strong spin coupling linkage than the superexchange spin-coupling pathway provided by CA2-.     

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).     

Mononuclear to polynuclear transition induced by ligand coordination: synthesis, X-ray structure, and properties of mono-, di-, and polynuclear copper(II) complexes of pyridyl-containing azo ligands

Reactions of two hydrated cupric salts (CuCl(2).2H(2)O and Cu(ClO(4))(2).6H(2)O) with three azopyridyl ligands, viz. 2-[(arylamino)phenylazo]pyridine [aryl = phenyl (HL(1a)), p-tolyl (HL(1b)), and 2-thiomethyl phenyl (HL(1c))], 2-[2-(pyridylamino)phenylazo]pyridine (HL(2)), and 2-[3-(pyridylamino)phenylazo]pyridine (HL(3)), afford the mononuclear [CuClL(1)] (1), dinuclear [Cu(2)X(2)L(2)(2)](n)()(+) (X = Cl, H(2)O, ClO(4); n = 0, 1; 2, 3), and polynuclear [CuClL(3)](n)() (4) complexes, respectively, in high yields. Representative X-ray structures of these complexes 1-4 are reported. X-ray structure analysis of 4 reveals an infinite 1D zigzag chain that adopts a saw-tooth-like structure. Variable-temperature cryomagnetic measurements (2-300 K) on the complexes 2-4 have revealed weak magnetic interactions between the copper centers with J values -1.04, 9.88, and -1.31 cm(-1), respectively. Positive ion ESI mass spectra of the soluble complexes 1-3 are studied which provide the evidence for the integrity of the complexes also in solution. Visible range spectra of the complexes 1-3 in solution consist of intense and broad transitions in the range 700-600 nm. The solid-state spectrum of the insoluble copper complex 4, on the other hand, shows a structured band near 700 nm. The intensities of the transitions of the dinuclear complexes are much higher than those of the corresponding mononuclear copper complexes. Redox properties of the present copper complexes are reported. Notably, the dinuclear complex, 3, displays two successive redox processes: Cu(II)Cu(II) right harpoon over left harpoon Cu(II)Cu(I) right harpoon over left harpoon Cu(I)Cu(I). It catalyzes aerial oxidation of L-ascorbic acid. The catalytic cycle is most effective up to H(2)A/3 (H(2)A = L-ascorbic acid) molar ratio of 20:1.     

Nature of copper(II)-lanthanide(III) magnetic interactions and generation of a large magnetic moment with magnetic anisotropy of 3d-4f cyclic cylindrical tetranuclear complexes [CuIILLnIII(hfac)2]2, (H3L = 1-(2-hydroxybenzamido)-2-(2-hydroxy-3-methoxybenzylideneamino)ethane and Hhfac = hexafluoroacetylacetone,LnIII = Eu,Gd, Tb,Dy)

A cyclic cylindrical 3d-4f tetranuclear structure, in which the 3d and 4f magnetic ions are arrayed alternately, has been found to be a suitable molecular design to produce a large magnetic moment and large magnetic anisotropy. Complexes 3-10 with the chemical formula [MLLn(hfac)2]2 ((MII, LnIII) = (Cu, Eu) (3), (Cu, Gd) (4), (Cu, Tb) (5), (Cu, Dy) (6), (Ni, Eu) (7), (Ni, Gd) (8), (Ni, Tb) (9), (Ni, Dy) (10)) have been synthesized, where H3L = 1-(2-hydroxybenzamido)-2-(2-hydroxy-3-methoxybenzylideneamino)ethane and Hhfac = hexafluoroacetylacetone. The powder X-ray diffractions and FAB-mass spectra demonstrated that these complexes assume a similar tetranuclear structure. The crystal structures of 4 and 5 showed that each complex has a cyclic cylindrical tetranuclear CuII2LnIII2 structure, in which the CuII complex functions as a "bridging ligand-complex" to two adjacent LnIII ions. The temperature-dependent magnetic susceptibilities from 2 to 300 K and the field-dependent magnetizations at 2 K from 0 to 5 T have been measured for four pairs of CuII2LnIII2 and NiII2LnIII2, in which compound NiII2LnIII2 containing diamagnetic NiII ion was used as the reference complex to evaluate the CuII-LnIII magnetic interaction. Comparison of the magnetic properties of the CuII2LnIII2 complex with those of the corresponding NiII2LnIII2 complex showed that the magnetic interaction between CuII and EuIII ions is weakly ferromagnetic and that between CuII and either of GdIII, TbIII, and DyIII ions is ferromagnetic. Complex CuII2GdIII2, 4, has an S = 8 spin ground state, due to the ferromagnetic spin coupling between SGd = 7/2 and SCu = 1/2 with coupling constants of J1 = +3.1 cm-1 and J2 = +1.2 cm-1. The magnetic measurements showed that compounds 5 and 6, CuII2LnIII2 (LnIII = Tb, Dy), exhibit large magnetic moments and large magnetic anisotropy due to the LnIII ion.     

Mono- and dinuclear zinc complexes derived from unsymmetric binucleating ligands: synthesis, characterization, and formation of tetranuclear arrays

Zinc complexes of the unsymmetric, binucleating Schiff base ligands 3-(N-[2-(dimethylamino)ethyl]iminomethyl)-salicylic acid (H2L1) and 3-[N-(2-pyridylmethyl)iminomethyl]-salicylic acid (H2L2) have been studied in the solid state as well as in solution. Reaction of ZnX2 (X = NO3-, CH3CO2-) with 3-formylsalicylic acid and N,N-dimethylethylenediamine at neutral or slightly acidic pH afforded the dinuclear complexes [Zn2(HL1)2(H2O)2](NO3)2.2H2O (1a) and [Zn2(HL1)2(CH3CO2)2].6H2O (1b). The Zn ions, which are 3.126(1) A (1a) and 3.2665(7) A (1b) apart, are bridged by two phenolate oxygens. Further coordination sites of the ligand are the imine nitrogen and carboxylate oxygen, while the amino nitrogen is protonated. On dissolution in DMSO or DMF, 1a and 1b are converted into the mononuclear species [Zn(HL1)]+. Cleavage of the dinuclear complexes is accompanied by migration of the ammonium proton to the carboxylate group and coordination of the amino nitrogen to Zn. Reaction of 1b with base yielded the novel tetranuclear Zn complex [Zn4(L1)4].6.5H2O (2) that exhibits coordination number asymmetry. The four Zn ions having N2O3 and N2O4 coordination environments are located at the corners of a nearly square-planar rectangle. H2L2 binds Zn via the phenolate oxygen and, imine and pyridine nitrogens in acidic solution. Deprotonation of the carboxyl group in alkaline solution gave the tetranuclear compound [Zn4(L2)4].4.5H2O (4) with a cubane-like Zn4O4 core.     

Ditopic hexaazamacrocycles containing pyridine: synthesis, protonation and complexation studies

Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n]py2N4 n= 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]-py2N4 are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degrees C in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22]py2N4 show significant differences from those described previously, while [24]py2N4 has not been studied before and [26]py2N4 is a new compound. Mononuclear and dinuclear complexes of the divalent metal ions studied with [22]- to [26]-py2N4 were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving-Williams order: NiL2+ < CuL2+ > ZnL2+ > PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu2([20]py2N4)(H2O)4][Cu(H2O)6](SO4)3 x 3H2O and [Cu(2)([20]py(2)N4)(CH3CN)4][Ni([20]py2N4)]2(ClO4)8 x H2O, which are composed of homodinuclear [Cu2([20]py2N4])(H2O)4]4+ and [Cu2([20]py2N4])(CH3CN))4]4+, and mononuclear species, [Cu(H2O)6]2+ and [Ni([20]py2N4)]2+, respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in and acetonitrile in . The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) A in 1a and 2a, respectively. The mononuclear complex [Ni([20]py2N4])]2+ displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.     

Self-encapsulation of [MII(phen)2(H2O)2]2+ (M=Co, Zn) in one-dimensional nanochannels of [MII(H2O)6(BTC)2]4- (M=Co, Cu, Mn): a high HQ/CAT ratio catalyst for hydroxylation of phenols

Four novel three-dimensional (3D) microporous supramolecular compounds containing nanosized channels, namely, [Co(phen)2(H2O)2]2[Co(H2O)6].2BTC.21.5H2O (1), [Co(phen)2(H2O)2]2[Cu(H2O)6].2BTC.21.5H2O (2), [Co(phen)2(H2O)2]2[Mn(H2O)6].2BTC.18H2O (3), and [Zn(phen)2(H2O)2]2[Mn(H2O)6].2BTC.22.5H2O (4), were synthesized from 1,3,5-benzenetricarboxylate (BTC), 1,10-phenanthroline (phen), and the transition-metal salt(s) by self-assembly. Single-crystal X-ray structural analysis showed that the resulting 3D microporous supramolecular frameworks consist of a two-dimensional (2D) hydrogen-bonded host framework of [MII(H2O)6(BTC)2]4- (M=Co for 1, Cu for 2, Mn for 3, 4) with rectangular-shaped cavities containing [MII(phen)2(H2O)2]2+ (M=Co for 1-3, Zn for 4) guests. The guest complex is encapsulated in the 2D hydrogen-bonded host framework by hydrogen bonding and aromatic pi-pi stacking interactions, forming the 3D hydrogen-bonded framework. The catalytic activities of 1, 2, 3, and 4 were studied using hydroxylation of phenols with 30% aqueous H2O2 as a test reaction. The compounds displayed a good phenol conversion ratio and excellent channel selectivity in the hydroxylation reaction, with a maximum hydroquinone (HQ)/catechol (CAT) ratio of 3.9.     

Novel manganese(II) sulfonate-phosphonates with dinuclear, tetranuclear, and hexanuclear clusters

Hydrothermal reactions of manganese(II) salts with m-sulfophenylphosphonic acid (m-HO3S-Ph-PO3H2, H3L) and 1,10-phenanthroline (phen) led to six novel manganese(II) sulfonate-phosphonates, namely, [Mn2(HL)2(phen)4][Mn2(HL)2(phen)4(H2O)](2).6H2O (1), [Mn4(L)2(phen)8(H2O)2][ClO4](2).3H2O (2), [Mn(phen)(H2O)4]2[Mn4(L)4(phen)4].10H2O (3), [Mn6(L)4(phen)8(H2O)2].4H2O (4), [Mn6(L)4(phen)8(H2O)2].24H2O (5), and [Mn6(L)4(phen)6(H2O)4].5H2O (6). The structure of 1 contains two types of dinuclear manganese(II) clusters, and 2-3 exhibit two types of tetranuclear manganese(II) cluster units. 4-5 feature two different types of isolated hexanuclear manganese(II) clusters, whereas the hexanuclear manganese(II) clusters in 6 are bridged by sulfonate-phosphonate ligands into a 1D chain. Magnetic property measurements indicate that there exist weak antiferromagnetic interactions between magnetic centers in all six compounds.     

Synthesis and spectroscopic and X-ray structural characterization of R2Sn(IV)-oxydiacetate and -iminodiacetate complexes

Seven novel R2Sn(IV)-oxydiacetate (oda) and -iminodiacetate (ida) compounds of the form [R2Sn(oda)(H2O)]2 (R = Me, nBu, and Ph) (1-3), [(R2SnCl)2(oda)(H2O)2]n (R = Et, iBu, and tBu) (4-6), and [Me2Sn(ida)(MeOH)]2 (7) have been synthesized and characterized by IR, 1H, 13C, and 119Sn NMR (solution), solid-state 119Sn CPMAS NMR, and (119m)Sn M?ssbauer spectroscopy. The crystal structure of [Me2Sn(oda)(H2O)]2, 1, shows it to be dinuclear (centrosymmetric), with two seven-coordinated tin atoms, bridged by one arm of the carboxylate group from each oda. By contrast, the crystal structure of [(Et2SnCl)2(oda)(H2O)2]n, 4, comprises a zigzag polymeric assembly containing a pair of different alternating subunits, {Et2SnCl(H2O)} and {Et2SnCl(H2O)(oda)}, which are connected by way of bridging oda carboxylates, thus giving seven-coordinate tin centers in both components. Finally, the structure of [Me2Sn(ida)(MeOH)]2, 7, also centrosymmetric dinuclear, is comprised of a pair of mononuclear units with seven-coordinate tin. The 119Sn solid-state CPMAS NMR and (119m)Sn Mossbauer suggest the presence of seven-coordinate Sn metal atoms in some derivatives and the existence of two different tin sites in the [(R2SnCl)2(oda)(H2O)2]n compounds.     

Equilibria and structure of the lanthanide(III)-2-hydroxy-1,3-diaminopropane-N,N,N',N'-tetraacetate complexes: formation of alkoxo-bridged dimers in solid state and solution

The complex formed between 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid (H4L-OH) and Nd3+ at pH 7.5 was found to be a dinuclear dimer in the solid state by X-ray crystallography. In the complex K4[Nd2(L-O)2(H2O)2].14H2O each ligand is coordinated to both Nd3+ atoms with an iminodiacetate group (the Nd3+-Nd3+ distance is 3.9283(8) A). The alcoholic OH groups are deprotonated, and the alkoxo oxygens are coordinated to both Nd3+ in a bridging position. The Nd3+ ions are nine-coordinated with one water molecule per Nd(III) ion in the inner sphere. The complex K4[Nd2(L-O)2(H2O)2].14H2O has an inversion center, and the space group is P1. Two of the K+ counterions are six-coordinated, while the other two K+ ions are eight-coordinated; polar polymeric water-K+ layers are formed between the apolar ligand layers via the bridging water molecules. The dinuclear dimer complexes are also present in aqueous solution. The proton relaxivities of the Gd3+ complex decrease with the increase of pH, and at pH > 6, the low relaxivity values indicate the probable absence of H2O in the inner sphere and the predominance of the eight-coordinated dimer species [Gd2(L-O)2].4- The results of ESI-TOF MS studies of the complexes of La3+, Nd3+, and Lu3+ proved the formation of dinuclear dimers in dilute (0.25 mM) solutions. pH-potentiometric titrations indicate the formation of complexes with 1:1 (Ln(L-OH)-, Ln(HL-OH), and Ln2(L-O)24-) and 2:1 (Ln2(L-O)+) metal-to-ligand ratios. The stability constants of the Ln(L-OH)- species increase from La3+ (log K = 10.19) to Lu3+ (log K = 14.08). The alcoholic OH group of the Ln(L-OH)- species dissociates at unusually low pH values. The pH range of dissociation shifts to lower and lower pH's with the increasing atomic number of the lanthanides. This pH range is about 4-7 for the La3+ complex and 1-4 for the Lu3+ complex. The results of 1D and 2D 1H and 13C NMR studies of the La3+ complex, the number and multiplicity of signals, and the values of coupling constants are in agreement with the dinuclear dimer structure of the complex in solution.     

Mono-, di- and trinuclear 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz)-containing copper(II) complexes: syntheses, crystal structures and magnetic properties

Three new copper(ii) complexes of formula [Cu(tppz)(NCO)(2)].0.4H(2)O (1), [Cu(2)(tppz)Br(4)](2) and [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)].7H(2)O (3)[tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; C(5)O(5)(2-) = croconate, dianion of 4,5-dihydroxycyclopent-4-ene-1,2,3-trione] have been synthesised and structurally characterized by X-ray diffraction methods. The structure of complex is made up of neutral [Cu(tppz)(NCO)(2)] mononuclear units and uncoordinated water molecules. The mononuclear units are grouped by pairs to give a rather short copper-copper distance of 3.9244(4) angstroms. The structure of complex 1 consists of neutral tppz-bridged [Cu(2)(tppz)Br(4)] dinuclear units, the copper-copper separation across tppz being 6.6198(1) angstroms. The dinuclear units are further connected through weak, double out-of-plane Cu-Br...Cu bridges [Br(1)...Cu(1a) 4.0028(17) angstroms] creating tetranuclear entities, the copper-copper separation through this interaction being 4.3299(21) angstroms. The structure of complex 3 is built of neutral [Cu(3)(tppz)(C(5)O(5))(3)(H(2)O)(3)] trinuclear units and uncoordinated water molecules. Tppz and one of the croconate groups act as bridging ligands, the former exhibiting the bis-terdentate coordination mode and the latter adopting an unusual asymmetrical bis-bidentate bridging mode through three adjacent oxygen atoms. The other two croconate groups exhibit the bidentate coordination mode. The intramolecular copper-copper separations are 6.5417(9)(across tppz) and 4.3234(9) angstroms (through bis-bidentate croconato). The magnetic properties of 2 and 3 have been investigated in the temperature range 1.9-300 K. The magnetic behaviour of complex 2 is that of an antiferromagnetically coupled copper(II) dimer (J = -40.9 cm(-1), the Hamiltonian being H = -JS(A).S(B)). In the case of compound , the chi(M) T vs. T plot is typical of an overall antiferromagnetic coupling with a low-lying spin doublet being fully populated at T < 10 K. The values of the intramolecular antiferromagnetic interactions in 3 are -19.9 (across tppz) and -32.9 cm(-1)(through bridging croconato). Density functional type calculations were performed on model dinuclear fragments of 3 in order to analyze the efficiency of the exchange pathways involved and also to substantiate the coupling parameters.     

Synthesis, crystal structure and magnetic properties of novel heterobimetallic malonate-bridged MIIReIV complexes (M = Mn, Fe, Co and Ni)

Five novel ReIV-MII bimetallic complexes of formula [ReCl4(mu-mal)M(dmphen)2].MeCN [M = Co (1), Fe (2) and Ni (3)], [ReCl4(mu-mal)Ni(dmphen)(MeCN)2(H2O)].(MeCN)0.5(H2O)0.5 (4), and [ReCl4(mu-mal)Mn(dmphen)(H2O)2].dmphen.MeCN.H2O (5) (mal = malonate dianion, dmphen = 2,9-dimethyl-1,10-phenanthroline) have been synthesized, and the structures of 1, 2, 4, and 5 determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of neutral [ReCl4(mu-mal)M(dmphen)2] dinuclear units where the metal ions are linked through a malonate ligand which adopts simultaneously the bidentate (at ReIV) and monodentate (at MII) coordination modes. The bridging carboxylate-malonate group in them exhibits the anti-syn conformation. The rhenium atom is six-coordinated with four chloro atoms and two carboxylate-oxygens from a bidentate malonate group in a distorted octahedral environment. The M atom is five-coordinated being surrounded by four nitrogen atoms of two bidentate dmphen ligands and one oxygen atom of the malonato ligand. There are also ReIV(mu-mal)NiII dinuclear units in 4 with the same type of bridge, but the nickel atom is six-coordinated with one bidentate dmphen, two molecules of acetonitrile and one water molecule as peripheral ligands. Compound 5 is a neutral chain compound with regular alternating rhenium(IV) and manganese(II) ions. The [ReCl4(mal)]2- units in each chain act as bismonodenate ligands through two carboxylate-oxygen atoms toward [Mn(dmphen)(H2O)2]2+ entities. Variable-temperature magnetic measurements of 1-5 in the temperature range 2.0-300 K show the occurrence of weak antiferromagnetic interactions which are rationalized on the basis of the structural knowledge and simple orbital considerations. Very noticeable is compound 5, a ferrimagnetic chain with regular alternating ReIV and MnII cations.     

Synthesis, reactivity, and X-ray crystallographic characterization of mono-, di-, and tetranuclear palladium(II)-metalated species

The reactivity of the tetranuclear metallated palladium compound (Pd[mu 2-(C6H4)PPh2]Br)4 (1) with different ligands has been investigated with the aim of evaluating the influence of the entering ligand on the nature of the reaction products. The results confirmed the ability of the ligand [(C6H4)PPh2]- to expand a bridging [mu 2-] or a chelating [eta 2-] coordination mode, depending on the auxiliary ligands present in the complex. Bulky phosphines stabilize mononuclear species of formula (Pd[eta 2-(C6H4)PPh2]Br[P]), with a four-atom metallocycle, while small phosphines give dinuclear compounds. The molecular structures of three different metalated palladium compounds have been determined by single-crystal X-ray crystallography; the tetranuclear (Pd[mu 2-(C6H4)PPh2]Cl)4 (2), the dinuclear(Pd[mu 2-(C6H4)PPh2]Br[PMe3])2 (3), and the mononuclear (Pd[eta 2-(C6H4)PPh2]Br[PCBr]), (PCBr = P(o-BrC6H4)Ph2) (9) were obtained, the first one by halogen exchange reaction and the others by frame degradation of 1.     

Synthesis and characterization of vanadium(IV) complexes with cis-inositol in aqueous solution and in the solid-state

The complex formation of vanadium(IV) with cis-inositol (ino) and the corresponding trimethyl ether 1,3,5-trideoxy-1,3,5-trimethoxy-cis-inositol (tmci) was studied in aqueous solution and in the solid-state. With increasing pH, the formation of [VO(H-2L)], [(VO)2L2H-5]-, [VO(H-3L)]- (L = ino) or [(VO)2L2H-6]2- (L = tmci), [V(H-3L)2]2-, and [VO(H-3L)(OH)2]3- was observed. For the vanadium(IV)/ino system, [(VO)2L2H-7]3- was observed as an additional dinuclear species. The formation constants of these complexes were determined by potentiometric titrations (25 degrees C, 0.1 M KCl). In addition, the vanadium(IV)/ino system was investigated by means of UV-vis spectrophotometric methods. EPR spectroscopy and cyclic voltammetry confirmed this complexation scheme. EPR measurements indicated the formation of three distinct isomers of the non-oxo complex [V(H-3ino)2]2- in weakly basic solution. This type of isomerism, which is not observed for the vanadium(IV)/tmci system, was assigned to the ability of ino to bind the vanadium(IV) center with three alkoxo groups having either a 1,3,5-triaxial or an 1,2,3-axial-equatorial-axial arrangement. The structures of [V(H-3ino)2][K2(ino)2].4H2O (1) and [Na6V(H-3ino)2](SO4)2.6H2O (2) were determined by single-crystal X-ray analysis. In both compounds, the coordination of each ino molecule to the vanadium(IV) center via three axial deprotonated oxygen donors was confirmed. The centrosymmetric structure of the coordination spheres corresponds to an almost regular octahedral geometry with a twist angle of 60 degrees. The crystal structure of the potassium complex 1 represents an unusual 1:1 packing of [V(H-3ino)2]2- dianions and [K2(ino)2]2+ dications, in which both K+ ions have a coordination number of nine and are bonded simultaneously to a 1,3,5-triaxial and an 1,2,3-axial-equatorial-axial site of ino. In 2, the [V(H-3ino)2]2- complexes are surrounded by six Na+ counterions that are bonded to the axial alkoxo oxygens and to the equatorial hydroxy oxygens of the cis-inositolato moieties. The six Na+ centers are further interlinked by bridging sulfate ions. According to EPR spectroscopy, the D3d symmetric structure of the [V(H-3ino)2]2- anion is retained in H2O, in dimethylformamide, and in a mixture of CHCl3/toluene 60:40 v/v.     

Synergic effect of two metal centers in catalytic hydrolysis of methionine-containing peptides promoted by dinuclear palladium(II) hexaazacyclooctadecane complex

The species obtained by the reaction of [Pd2([18]aneN6)Cl2](ClO4)2(where [18]aneN6 is 1,4,7,10,13,16-hexaazacyclooctadecane) with AgBF4 have been determined by electrospray ionization mass spectrometry (ESI-MS) to be an equilibrium mixture of three major types of dinuclear Pd(II) complex cations, [Pd2(mu-O)([18]aneN6)]2+, [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)](3+), in aqueous solution. The hydroxo-group-bridged one, [Pd2(mu-OH)([18]aneN6)]3+, is a dominant species, whose crystal structure has been obtained. The crystal structure of [Pd2(mu-OH)([18]aneN6)](ClO4)3 shows that each Pd(II) ion in the dinuclear complex is tetra-coordinated by three nitrogen atoms and one hydroxo group bridge in a distorted square configuration. The two Pd(II) ions are 3.09 A apart from each other. The dinuclear Pd(II) complex cations [Pd2(mu-OH)([18]aneN6)]3+ and [Pd2(H2O)(OH)([18]aneN6)]3+ can efficiently catalyze hydrolysis of the amide bond involving the carbonyl group of methionine in methionine-containing peptides with turnover number of larger than 20. In these hydrolytic reactions, the two Pd(II) ions are synergic; one Pd(II) ion anchors to the side chain of methionine and the other one delivers hydroxo group or aqua ligand to carbonyl carbon of methionine, or acts as a Lewis acid to activate the carbonyl group of methionine, resulting in cleavage of Met-X bond. The binding constant of dinuclear Pd(II) complex cations with AcMet-Gly and AcMet were determined by 1H NMR titration to be 282 +/- 2 M(-1) and 366 +/- 4 M(-1), respectively. The relatively low binding constants enable the catalytic cycle and the possible catalytic mechanism is proposed. This is the first artificial mimic of metallopeptidases with two metal active centers.     

Heterotrimetallic oxalato-bridged ReIV2MII complexes (M=Mn, Co, Ni, Cu): synthesis, crystal structure, and magnetic properties

The use of the (NBu4)2[ReIVCl4(ox)] mononuclear species as a ligand toward divalent first row transition metal ions in the presence of imidazole affords the new trinuclear compounds of formula (NBu4)2[{ReIVCl4(mu-ox)}2MII(Him)2] [NBu4+=tetra-n-butylammonium cation, ox=oxalate dianion, Him=imidazole; M=Mn (1), Co (2), Ni (3), Cu (4)] whose preparation, crystal structures, and magnetic properties are reported. 1-4 are isostructural complexes which are made up of discrete trinuclear [{ReIVCl4(mu-ox)}2MII(Him)2]2- anions and bulky NBu4+ cations. The Re and M atoms exhibit somewhat distorted octahedral surroundings which are built by four chloro and two oxalate oxygens (Re) and two imidazole nitrogen and four oxalate oxygen atoms (M), the central M atom being linked to the two peripheral Re atoms through bis-bidentate oxalate. The values of the Re...M separation across bridging oxalate vary in the range 5.646(2) (M=Ni) to 5.794(2) A (M=Mn). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range 1.9-300 K show the occurrence of significant intramolecular antiferro- (1) and ferromagnetic (2-4) interactions. The nature and magnitude of the magnetic coupling in 1-4 are qualitatively understood through orbital symmetry considerations.