Molecular and electronic structures of bis(pyridine-2,6-diimine)metal complexes [ML2](PF6)n (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn)

A series of mononuclear, octahedral first-row transition metal ion complexes mer-[M(II)L0(2)](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II) ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of Cu(II) and Zn(II)) can be reversibly one-electron-oxidized, yielding the respective trications [M(III)L0(2)]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [Mn(III)L1(2)]PF6 and [Co(I)L0(2)]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV-vis, NMR, X-band EPR, Mossbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [M(III)L0(2)]3+, and the dications are [M(II)L0(2)]2+. The monocations are described as [Mn(III)L1(2)]+ (S = 0), [Fe(II)L0L1]+ (S = 1/2), [Co(I)L0(2)]+ (S = 1), [Ni(I)L0(2)]+ (S = 1/2), [Cu(I)L0(2)]+ (S = 0), [Zn(II)L1L0]+ (S = 1/2) where the Mn(II) and Fe(II) ions are low-spin-configurated. The neutral species are described as [Mn(II)L1(2)]0, [Fe(II)L1(2)]0, [Co(I)L0L1]0, [Ni(I)L0L1]0, and [Zn(II)L1(2)]0; their electronic ground states have not been determined.     

[Co(tp)~2(Me-en)]ClO~4配合物不对称氮的翻转及重氢化动力学研究

本文合成了[Co(tp)~2(Me-en)]ClO~4(tp:2-羟基-2,4,6-环庚三烯-1-酮负离子;Me-en:N-甲基乙二胺)三元不对称配合物, 用离子交换法分离了该配合物的Λ(R)△(S)和Λ(S)△(R)两对对映体, 用高效液相色谱法测定了对映体的不对称配位氮的翻转速率常数k~e~p(差向立体异构化速率常数), 用^1HNMR法测定了对映体的不对称配位氮的重氢化质子交换)速率常数k~D, 并与同属CoO~4~2型的Na[Co(OX)~2(Me-en)](OX:草酸根)、[Co(acac)~2(Me-en)]ClO~4(acac:2,4-戊二酮负离子)配合物的k~e~p、k~D值进行了比较, 讨论了影响质子交换、不对称氮翻转速率的因素及反应机理。     

Theoretical insights into the ferromagnetic coupling in oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear complexes with aromatic diimine ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.     

Electronic structure of mononuclear bis(1,2-diaryl-1,2-ethylenedithiolato)iron complexes containing a fifth cyanide or phosphite ligand: a combined experimental and computational study

A series of mononuclear square-based pyramidal complexes of iron containing two 1,2-diaryl-ethylene-1,2-dithiolate ligands in various oxidation levels has been synthesized. The reaction of the dinuclear species [Fe(III)2(1L*)2(1L)2]0, where (1L)2- is the closed shell di-(4-tert-butylphenyl)-1,2-ethylenedithiolate dianion and (1L*)1- is its one-electron-oxidized pi-radical monoanion, with [N(n-Bu)4]CN in toluene yields dark green crystals of mononuclear [N(n-Bu)4][Fe(II)(1L*)2(CN)] (1). The oxidation of 1 with ferrocenium hexafluorophosphate yields blue [Fe(III)(1L*)2(CN)] (1ox), and analogously, a reduction with [Cp2Co] yields [Cp2Co][N(n-Bu)4][Fe(II)(1L*)(1L)(CN)] (1red); oxidation of the neutral dimer with iodine gives [Fe(III)(1L*)2I] (2). The dimer reacts with the phosphite P(OCH3)3 to yield [Fe(II)(1L*)2{P(OCH3)3}] (3), and [Fe(III)2(3L*)2(3L)2] reacts with P(OC6H5)3 to give [Fe(II)(3L*)2{P(OC6H5)3}] (4), where (3L)2- represents 1,2-diphenyl-1,2-ethylenedithiolate(2-). Both 3 and 4 were electrochemically one-electron oxidized to the monocations 3ox and 4ox and reduced to the monoanions 3red and 4red. The structures of 1 and 4 have been determined by X-ray crystallography. All compounds have been studied by magnetic susceptibility measurements, X-band EPR, UV-vis, IR, and M?ssbauer spectroscopies. The following five-coordinate chromophores have been identified: (a) [Fe(III)(L*)2X]n, X = CN-, I- (n = 0) (1ox, 2); X = P(OR)3 (n = 1+) )3ox, 4ox) with St = 1/2, SFe = 3/2; (b) [Fe(II)(L*)2X]n, X = CN-, (n = 1-) (1); X = P(OR)3 (n = 0) (3, 4) with St = SFe = 0; (c) [Fe(II)(L*)(L)X]n <--> [Fe(II)(L)(L*)X]n, X = CN- (n = 2-) (1red); X = P(OR)3 (n = 1-) (3red, 4red) with St = 1/2, SFe = 0 (or 1). Complex 1ox displays spin crossover behavior: St = 1/2 <--> St = 3/2 with intrinsic spin-state change SFe = 3/2 <--> SFe = 5/2. The electronic structures of 1 and 1(ox) have been established by density functional theoretical calculations: [Fe(II)(1L*)2(CN)]1- (SFe = 0, St = 0) and [Fe(III)(1L*)2(CN)]0 (SFe = 3/2, St = 1/2).     

Magnetostructural D correlations in hexacoordinated cobalt(II) complexes

The magnetostructural D correlation for hexacoordinated cobalt(II) complexes is outlined. The structural and magnetic properties of a series of mononuclear cobalt(II) complexes with the general formulas [Co(II)(L)(6)]X(2), [Co(II)(L)(2)X(2)], and [Co(II)(L)(2)(H(2)O)(2)(car)(2)] have been investigated where the coordination sphere is formed by nitrogen/oxygen-donor heterocycle (L), carboxylato (car), aqua, and chlorido ligands. The chromophores of these compounds involve {CoN(6)}, {CoO(6)}, {CoO(4)O'(2)}, {CoN(2)O(2)O'(2)}, and {CoN(2)O(2)Cl(2)}. All complexes were subjected to magnetochemical investigation down to 2 K (SQUID susceptibility and magnetization measurements). Most of the studied complexes show magnetic behavior typical for zero-field-splitting systems. The magnetism of the complex [Co(H(2)O)(6)](6-OHnic)(2) reflects the presence of the magnetic angular momentum in the ground-state crystal-field term. The obtained values of the magnetic anisotropy (D or δ) have been correlated with the structural distortion of the coordination polyhedron. This correlation can be understood with the help of crystal-field theory, where the magnetic anisotropy parameters are related to the splitting of the lowest crystal-field multiplets.     

Temperature-dependent in situ ligand cyclization via C═C coupling and formation of a spin-crossover iron(II) coordination polymer

The reaction of N(1),N(2)-bis(pyridin-4-ylmethylene)ethane-1,2-diamine (L) with Fe(NCS)(2) under various temperatures gave rise to three iron(II) coordination polymers, namely, one-dimensional [Fe(L')(NCS)(2)] (1), two-dimensional [Fe(L)(2)(NCS)(2)]·H(2)O (2), and one-dimensional [Fe(L)(2)(NCS)(2)]·2CH(2)Cl(2)·4MeOH (3). The formation of 1 involved an in situ C═C coupling reaction, L to L' [L' = 5,6-di(pyridin-4-yl)-1,2,3,4-tetrahydropyrazine], which was catalyzed by cyanide ions decomposed from thiocyanates; the manganese(II) (1a) and zinc(II) (1b) analogues of 1 were also synthesized for comparison. Magnetic studies showed that complex 1 underwent a pressure-dependent one-step incomplete spin transition whereas complexes 2 and 3 were paramagnetic in the whole temperature range.     

Homobinuclear cyanide-bridged linkage isomers containing the redox-active unit [(micro-XY)Ru(CO)2L(o-O2C6Cl4)] (XY=CN or NC)

The salts [NEt4][Ru(CN)(CO)2L(o-O2C6Cl4)] {L=PPh3 or P(OPh)3}, which undergo one-electron oxidation at the catecholate ligand to give neutral semiquinone complexes [Ru(CN)(CO)2L(o-O2C6Cl4)], react with the dimers [{Ru(CO)2L(micro-o-O2C6Cl4)}2] {L=PPh3 or P(OPh)3} to give [NEt4][(o-O2C6Cl4)L(OC)2Ru(micro-CN)Ru(CO)2L'(o-O2C6Cl4)] {L or L'=PPh3 or P(OPh)3}. The cyanide-bridged binuclear anions are, in turn, reversibly oxidised to isolable neutral and cationic complexes [(o-O2C6Cl4)L(OC)2Ru(micro-CN)Ru(CO)2L'(o-O2C6Cl4)] and [(o-O2C6Cl4)L(OC)2Ru(micro-CN)Ru(CO)2L'(o-O2C6Cl4)]+ which contain one and two semiquinone ligands respectively. Structural studies on the redox pair [(o-O2C6Cl4)(Ph3P)(OC)2Ru(micro-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]- and [(o-O2C6Cl4)(Ph3P)(OC)2Ru(micro-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)] confirm that the C-bound Ru(CO)2(o-O2C6Cl4) fragment is oxidised first. Uniquely, [(o-O2C6Cl4){(PhO)3P}(OC)2Ru(micro-CN)Ru(CO)2(PPh3)(o-O2C6Cl4)]- is oxidised first at the N-bound fragment, indicating that it is possible to control the site of electron transfer by tuning the co-ligands. Crystallisation of [(o-O2C6Cl4)(Ph3P)(OC)2Ru(micro-CN)Ru(CO)2{P(OPh)3}(o-O2C6Cl4)] resulted in the formation of an isomer in which the P(OPh)3 ligand is cis to the cyanide bridge, contrasting with the trans arrangement of the X-Ru-L fragment in all other complexes of the type RuX(CO)2L(o-O2C6Cl4).     

Cationic and neutral diphenyldiazomethanerhodium(I) complexes as catalytically active species in the C-C coupling reaction of olefins and diphenyldiazomethane

Cationic rhodium(I) complexes cis-[Rh(acetone)2(L)(L')]+ (2: L = L'=C8H14; 3: L=C8H14; L'=PiPr3; 4: L=L'=PiPr3), prepared from [RhCl(C8H14)2]2] and isolated as PF6 salts, catalyze the C-C coupling reaction of diphenyldiazomethane with ethene, propene, and styrene. In most cases, a mixture of isomeric olefins and cyclopropanes were obtained which are formally built up by one equivalent of RCH=CH2 (R = H, Me, Ph) and one equivalent of CPh2. The efficiency and selectivity of the catalyst depends significantly on the coordination sphere around the rhodium(I) center. Treatment of 4 with Ph2CN2 in the molar ratio of 1:1 and 1:2 gave the complexes trans-[Rh(PiPr3)2(acetone)(eta1-N2CPh2)]PF6 (8) and trans-[Rh(PiPr3)2(eta1-N2CPh2)2]PF6 (9), of which 8 was characterized by X-ray crystallography. Since 8 and 9 not only react with ethene but also catalyze the reaction of C2H4 and free Ph2CN2, they can be regarded as intermediates (possibly resting states) in the C-C coupling process. The lability of 8 and 9 is illustrated by the reactions with pyridine and NaX (X=Cl, Br, I, N3) which afford the mono(diphenyldiazomethane)rhodium(I) compounds trans-[Rh(PiPr3)2(py)(eta1-N2CPh2)]PF6 (10) and trans-[RhX(eta1-N2CPh2)(PiPr3)2] (11-14), respectively. The catalytic activity of the neutral complexes 11 - 14 is somewhat less than that of the cationic species 8, 9 and decreases in the order Cl > Br> I > N3.     

Syntheses of 8-quinolinolatocobalt(III) complexes containing cyclen based auxiliary ligands as models for hypoxia-activated prodrugs

New ligands H(2)L2-H(2)L6 comprise the cyclen macrocycle which is N,N'-dialkylated at the 1,7-nitrogen atoms by three- and four-carbon alkyl chains bearing terminal sulfonic (C(3) H(2)L2), phosphonic (C(3) H(2)L3, C(4) H(2)L4) or carboxylic acid (C(3) H(2)L5, C(4) H(2)L6) groups, and HL7 is N-monoalkylated by a four-carbon sulfonic acid group. The ligands were prepared by alkylation of a bridged bisaminal intermediate. The syntheses of cobalt(III) complexes containing a tetradentate cyclen, N,N'-1,7-Me(2)cyclen, cyclam or L2-L7 ligand together with the bidentate 8-quinolinato (8QO(-)) ligand, of interest as it is a model for a more potent cytotoxic analogue, were investigated. Coordination of ligands (L) cyclen, N,N'-1,7-Me(2)cyclen or cyclam to cobalt(III) was achieved using Na(3)[Co(NO(6))] to form [Co(L)(NO(2))(2)](+). HOTf (trifluoromethansulfonic acid) was used to prepare the triflato complexes [Co(L)(OTf)(2)](+), followed by substitution of the labile triflato ligands to yield [Co(L)(8QO)](ClO(4))(2) isolated as the perchlorate salts. One further example containing cyclam and the 5-hydroxymethyl-8-quinolinato ligand was also prepared by this method. Complexes containing the pendant arm ligands L2-L6 were prepared from the cobalt precursor trans-[Co(py)(4)Cl(2)](+). Reaction of this complex with H(2)L2·4HCl and 8QOH produced [Co(L2)(8QO)] in one step and contains two deprotonated sulfonato pendant arms. The reaction of H(2)L3·4HBr with [Co(py)(4)Cl(2)](+) gave [Co(L3)]Cl in which L3 acts as a hexadenate ligand with the three-carbon phosphonato side chains coordinated to cobalt. H(2)L5·4HCl bearing three-carbon carboxylic acid pendant arms gave a similar result. The four-carbon ligands were coordinated to cobalt by reaction of [Co(py)(4)Cl(2)](+) with H(2)L4·4HBr or H(2)L6·4HCl to give [Co(HL4)Cl(2)] or [Co(H(2)L6)Cl(2)]Cl, which in turn with 8QOH gave the 8QO(-) complexes [Co(L4)(8QO)] bearing anionic phosphate pendant arms or [Co(H(2)L6)(8QO)]Cl(2) containing neutral carboxylic acid side chains. The reaction of Na(3)[Co(CO(3))(3)] with the mono-N-alkylated ligand HL7·4HCl and then HOTf gave [Co(L7)(CO(3))] and then in turn [Co(L7)(OTf)(2)]. The carbonato complex [Co(L7)(CO(3))] with [8QO](2)[SO(4)] produced [Co(L7)(CO(3))]. All complexes containing L7 bear an anionic sulfonato group on the side chain. The synthesis and characterisation of the six new ligands based on N-alkylated cylen ligand and the cobalt complexes outlined above are described, along with cyclic voltammograms of the 8QO(-) complexes and the molecular structures determined by X-ray crystallography of [Co(cyclen)(H(2)O)(2)](OTf)(3) (formed by aquation of the triflato complex), [Co(cyclen)(8QO)](ClO(4))(2), Co(L2)(8QO)·2H(2)O, Co(L4)(8QO)·6H(2)O and [Co(H(2)L6)Cl(2)]Cl·H(2)O. These demonstrate the coordination of the cyclen ligand in the folded anti-O,syn-N configuration with the N-alkylated nitrogens occupying apical positions.     

SYNTHESIS,CRYSTAL STRUCTURE AND ANTIMICROBIAL ACTIVITY OF COBALT(III) COMPLEXES WITH SCHIFF BASE LIGANDS

Journal of Structural Chemistry - Three new mononuclear cobalt(III) complexes, [CoL1(4-Brsal)] (1), [CoL3(4-Brsal)] (2), and [Co(L2)2]NO3 (3), where L1, L2, L3 and 4-Brsal are the deprotonated form...     

Dinuclear cyano complexes of cobalt(III) and Iron(III) containing noninnocent 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene bridging ligands

Two new dinucleating ligands 1,2,4,5-tetrakis(2-pyridinecarboxamido)benzene, H(4)(tpb), and 1,2,4,5-tetrakis(4-tert-butyl-2-pyridinecarboxamido)benzene, H(4)(tbpb), have been synthesized, and the following dinuclear cyano complexes of cobalt(III) and iron(III) have been isolated: Na(2)[Co(III)(2)(tpb)(CN)(4)] (1); [N(n-Bu)(4)](2)[Co(III)(2)(tbpb)(CN)(4)] (2); [Co(III)(2)(tbpb(ox2))(CN)(4)] (3); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(N(3))(4)] (4); [N(n-Bu)(4)](2)[Fe(III)(2)(tpb)(CN)(4)] (5); [N(n-Bu)(4)](2)[Fe(III)(2)(tbpb)(CN)(4)] (6). Complexes 2-4 and 6 have been structurally characterized by X-ray crystallography at 100 K. From electrochemical and spectroscopic (UV-vis, IR, EPR, M?ssbauer) and magnetochemical investigations it is established that the coordinated central 1,2,4,5-tetraamidobenzene entity in the cyano complexes can be oxidized in two successive one-electron steps yielding paramagnetic (tbpb(ox1))(3)(-) and diamagnetic (tbpb(ox2))(2)(-) anions. Thus, complex 6 exists in five characterized oxidation levels: [Fe(III)(2)(tbpb(ox2))(CN)(4)](0) (S = 0); [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Fe(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Fe(III)Fe(II)(tbpb)(CN)(4)](3)(-) (S = (1)/(2)); [Fe(II)(2)(tbpb)(CN)(4)](4)(-) (S = 0). The iron(II) and (III) ions are always low-spin configurated. The electronic structure of the paramagnetic iron(III) ions and the exchange interaction of the three-spin system [Fe(III)(2)(tbpb(ox1))(CN)(4)](-) are characterized in detail. Similarly, for 2 three oxidation levels have been identified and fully characterized: [Co(III)(2)(tbpb)(CN)(4)](2)(-) (S = 0); [Co(III)(2)(tbpb(ox1))(CN)(4)](-) (S = (1)/(2)); [Co(III)(2)(tbpb(ox2))(CN)(4)](0). The crystal structures of 2 and 3 clearly show that the two electron oxidation of 2 yielding 3 affects only the central tetraamidobenzene part of the ligand.     

Unusual iron(II) and cobalt(II) complexes derived from monodentate arylamido ligands

The coordination chemistry of the N-substituted arylamido ligands [N(R)(C6H3R'2-2,6)] [R = SiMe3, R' = Me (L1); R = CH2But, R' = Pri (L2)] toward FeII and CoII ions was studied. The monoamido complexes [M(L1)(Cl)(tmeda)] [M = Fe (1), Co (2)] react readily with MeLi, affording the mononuclear, paramagnetic iron(II) and cobalt(II) methyl-arylamido complexes [M(L1)(Me)(tmeda)] [M = Fe (3), Co (4)]. Treatment of 2:1 [Li(L2)(THF)2]/FeCl2 affords the unusual two-coordinate iron(II) bis(arylamide) [Fe(L2)2] (5).     

Mo and W dihalide complexes with uncommon trigonal-prismatic geometry imposed by the linear tetraphosphine ancillary ligand and their reactivities toward diazoalkanes

New Mo and W tetraphosphine-dihalide complexes [MX2(kappa4-P4)] (2, MX=MoCl, MoBr, WBr; P4=meso-o-C6H4(PPhCH2CH2PPh2)2) with uncommon trigonal-prismatic geometries have been prepared. Treatment of ethyl diazoacetate with 2 (MX=MoCl) resulted in catalytic carbenoid-group coupling to give diethyl maleate and fumarate, whereas reactions of 2 with trimethylsilyldiazoalkane formed the diazoalkane complexes trans-[MX(NN=CHSiMe3)-(kappa4-P4)]+ (3+) and cis,mer-[MoCl2(NN=CHSiMe3)(kappa3-P4)]. The molecular structures of 2 (MX=MoCl) and 3[PF6] (MX=WBr) were crystallographically determined.     

Syntheses and structures of three complexes of formulas [L3Co(μ2-O2P(Bn)2)3CoL'][L"], featuring octahedral and tetrahedral cobalt(II) geometries; variable-temperature magnetic susceptibility measurement and analysis on [(py)3Co(μ2-O2PBn2)3Co(py)][ClO4

The syntheses and structural properties of three dinuclear complexes [L(3)Co(μ(2)-O(2)P(Bn)(2))(3)CoL'][L"] [one ionic L(3) = py(3), L' = py, L" = ClO(4)(-) (1) and two molecular L(3) = py(3), L' = Cl (2) and L(3) = py, μ(2)-NO(3)(-), L' = py (3)] are reported. Complexes feature octahedral Co(II) sites bridged by three dibenzylphosphinate ligands to a tetrahedrally ligated Co(II) site, with the remaining coordination sites occupied by py, nitrato, and Cl ligands. The Co-Co distances are 4.248 ? at 291 K and 4.265 ? at 100 K for 1 and 4.278 and 4.0313(7) ? for 2 and 3, respectively at 100 K. A fit of the low-temperature magnetic susceptibility data was derived for complex 1 with g = 2.25, TIP = 700 × 10(-6) cm(3) mol (-1), λ = -173 cm(-1), κ = 0.93, ν = -3.9, Δ = 630 cm(-1), J = 0.15 cm(-1), and θ = -1.8 resulting in R(χ(M)) = 2.5 × 10(-5) and R(χ(M)T) = 5.8 × 10(-5).     

Redox-noninnocence of the S,S'-coordinated ligands in bis(benzene-1,2-dithiolato)iron complexes

The electronic structures of complexes of iron containing two S,S'-coordinated benzene-1,2-dithiolate, (L)(2)(-), or 3,5-di-tert-butyl-1,2-benzenedithiolate, (L(Bu))(2)(-), ligands have been elucidated in depth by electronic absorption, infrared, X-band EPR, and Mossbauer spectroscopies. It is conclusively shown that, in contrast to earlier reports, high-valent iron(IV) (d(4), S = 1) is not accessible in this chemistry. Instead, the S,S'-coordinated radical monoanions (L(*))(1)(-) and/or (L(Bu)(*))(1)(-) prevail. Thus, five-coordinate [Fe(L)(2)(PMe(3))] has an electronic structure which is best described as [Fe(III)(L)(L(*))(PMe(3))] where the observed triplet ground state of the molecule is attained via intramolecular, strong antiferromagnetic spin coupling between an intermediate spin ferric ion (S(Fe) = (3)/(2)) and a ligand radical (L(*))(1)(-) (S(rad) = (1)/(2)). The following complexes containing only benzene-1,2-dithiolate(2-) ligands have been synthesized, and their electronic structures have been studied in detail: [NH(C(2)H(5))(3)](2)[Fe(II)(L)(2)] (1), [N(n-Bu)(4)](2)[Fe(III)(2)(L)(4)] (2), [N(n-Bu)(4)](2)[Fe(III)(2)(L(Bu))(4)] (3); [P(CH(3))Ph(3)][Fe(III)(L)(2)(t-Bu-py)] (4) where t-Bu-py is 4-tert-butylpyridine. Complexes containing an Fe(III)(L(*))(L)- or Fe(III)(L(Bu))(L(Bu)(*))- moiety are [N(n-Bu)(4)][Fe(III)(2)(L(Bu))(3)(L(Bu)(*))] (3(ox)()), [Fe(III)(L)(L(*))(t-Bu-py)] (4(ox)()), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))] (7), [Fe(III)(L(Bu))(L(Bu)(*))(PMe(3))(2)] (8), and [Fe(III)(L(Bu))(L(Bu)(*))(PPr(3))] (9), where Pr represents the n-propyl substituent. Complexes 2, 3(ox)(), 4, [Fe(III)(L)(L(*))(PMe(3))(2)] (6), and 9 have been structurally characterized by X-ray crystallography.     

Phenylthiyl radical complexes of gallium(III), iron(III), and cobalt(III) and comparison with their phenoxyl analogues.

Three hexadentate, asymmetric pendent arm macrocycles containing a 1,4,7-triazacyclononane-1,4-diacetate backbone and a third, N-bound phenolate or thiophenolate arm have been synthesized. In [L(1)](3)(-) the third arm is 3,5-di-tert-butyl-2-hydroxybenzyl, in [L(2)](3)(-) it is 2-mercaptobenzyl, and in [L(3)](3)(-) it is 3,5-di-tert-butyl-2-mercaptobenzyl. With trivalent metal ions these ligands form very stable neutral mononuclear complexes [M(III)L(1)] (M = Ga, Fe, Co), [M(III)L(2)] (M = Ga, Fe, Co), and [M(III)L(3)] (M = Ga, Co) where the gallium and cobalt complexes possess an S = 0 and the iron complexes an S = (5)/(2) ground state. Complexes [CoL(1)].CH(3)OH.1.5H(2)O, [CoL(3)].1.17H(2)O, [FeL(1)].H(2)O, and [FeL(2)] have been characterized by X-ray crystallography. Cyclic voltammetry shows that all three [M(III)L(1)] complexes undergo a reversible, ligand-based, one-electron oxidation generating the monocations [M(III)L(1)(*)](+) which contain a coordinated phenoxyl radical as was unambiguously established by their electronic absorption, EPR, and M?ssbauer spectra. In contrast, [M(III)L(2)] complexes in CH(3)CN solution undergo an irreversible one-electron oxidation where the putative thiyl radical monocationic intermediates dimerize with S-S bond formation yielding dinuclear disulfide species [M(III)L(2)-L(2)M(III)](2+). [GaL(3)] behaves similarly despite the steric bulk of two tertiary butyl groups at the 3,5-positions of the thiophenolate, but [Co(III)L(3)] in CH(2)Cl(2) at -20 to -61 degrees C displays a reversible one-electron oxidation yielding a relatively stable monocation [Co(III)L(3)(*)](+). Its electronic spectrum displays intense transitions in the visible at 509 nm (epsilon = 2.6 x 10(3) M(-)(1) cm(-)(1)) and 670sh, 784 (1.03 x 10(3)) typical of a phenylthiyl radical. The EPR spectrum of this species at 90 K proves the thiyl radical to be coordinated to a diamagnetic cobalt(III) ion (g(iso) = 2.0226; A(iso)((59)Co) = 10.7 G).     

Synthesis, structure and magnetic properties of two new azido-Co(II) coordination architectures: from ferromagnetic coupling to single-chain-magnets

Two new azido-Co(II) complexes with pyrazine carboxylato ligands, [Co(N(3))(L)·H(2)O](n) (L = pyrazine-2-carboxylato) (1) and [CoNa(N(3))(2)(L)](n) (2), have been obtained by carefully tuning the Co(II):N(3)(-) ratio. Here we present the structural and magnetic characterization of these new species. Modulation of the coordination environment of Co(II) leads to a variation of the magnetic properties of the obtained compounds. Complex 1 exhibits ferromagnetically coupled [Co(2)] units that form the rungs of the ladder with a nearly negligible coupling between these units, while complex 2 is a 2D arrangement of 1D Co(II) single-chain magnets.     

Studies on the bacterial activity of cobalt(III) complexes. Part II. Cobalt(III) aminoacidato-complexes

Summary Cobalt(III) complexes of the typetrans-[Co(AA)₂(ox)] (where AA = aminoacidato, gly = glycinato, sar = sarcosinato, DL-ala = DL-alaninato, L-ala = L-alaninato; ox = oxalate); [Co(L-val)₂CO₃] and DL-[Co(en)₂sar]I₂ where L-val = L-valinato, en = ethylenediamine) have been investigated for their bacterial activity againstEscherichia coli B using well-cultured techniques on EMB agar and in minimal glucose media. The activities decrease in the order:trans-(N)(+)K[Co(sar)₂(ox)] >trans-(N)(+)K[Co(L-ala)₂(ox)] >trans-(N)(–)K[Co (gly)₂(ox)] >trans-(N)(+)K[Co(DL-ala)₂(ox)] >trans-(N)(+)K[Co(gly)₂(ox)] >trans(+)K[Co(DL-ala)₂(ox)] >trans-K[Co(L-val)₂CO₃].     

Increasing the ordering temperatures in oxalate-based 3D chiral magnets: the series [Ir(ppy)2(bpy)][M(II)M(III)(ox)3] x 0.5 H2O (M(II)M(III) = MnCr, FeCr, CoCr, NiCr, ZnCr, MnFe, FeFe); bpy = 2,2'-bipyridine; ppy = 2-phenylpyridine; ox = oxalate dianion)

The synthesis, structure, and physical properties of a novel series of oxalate-based bimetallic magnets obtained by using the Ir(ppy)2(bpy)]+ cation as a template of the bimetallic [M(II)M(III)(ox)3]- network are reported. The compounds can be formulated as [Ir(ppy)2(bpy)][M(II)Cr(III)(ox)3] x 0.5 H2O (M(II) = Ni, Mn, Co, Fe, and Zn) and [Ir(ppy)2(bpy)]-[M(II)Fe(III)(ox)3] x 0.5 H2O (M(II) = Fe, Mn) and crystallize in the chiral cubic space group P4(1)32 or P4(3)32. They show the well-known 3D chiral structure formed by M(II) and M(III) ions connected through oxalate anions with [Ir(ppy)2(bpy)]+ cations and water molecules in the holes left by the oxalate network. The M(II)Cr(III) compounds behave as soft ferromagnets with ordering temperatures up to 13 K, while the Mn(II)Fe(III) and Fe(II)Fe(III) compounds behave as a weak ferromagnet and a ferrimagnet, respectively, with ordering temperatures of 31 and 28 K. These values represent the highest ordering temperatures so far reported in the family of 3D chiral magnets based on bimetallic oxalate complexes.     

The remarkable reactivity of high oxidation state ruthenium and osmium polypyridyl complexes

There is a remarkable redox chemistry of higher oxidation state M(IV)-M(VI) polypyridyl complexes of Ru and Os. They are accessible by proton loss and formation of oxo or nitrido ligands, examples being cis-[RuIV(bpy)2(py)(O)]2+ (RuIV=O2+, bpy=2,2'-bipyridine, and py=pyridine) and trans-[OsVI(tpy)(Cl)2(N)]+ (tpy=2,2':6',2' '-terpyridine). Metal-oxo or metal-nitrido multiple bonding stabilizes the higher oxidation states and greatly influences reactivity. O-atom transfer, hydride transfer, epoxidation, C-H insertion, and proton-coupled electron-transfer mechanisms have been identified in the oxidation of organics by RuIV=O2+. The Ru-O multiple bond inhibits electron transfer and promotes complex mechanisms. Both O atoms can be used for O-atom transfer by trans-[RuVI(tpy)(O)2(S)]2+ (S=CH3CN or H2O). Four-electron, four-proton oxidation of cis,cis-[(bpy)2(H2O)RuIII-O-RuIII(H2O)(bpy)2]4+ occurs to give cis,cis-[(bpy)2(O)RuV-O-RuV(O)(bpy)2]4+ which rapidly evolves O2. Oxidation of NH3 in trans-[OsII(tpy)(Cl)2(NH3)] gives trans-[OsVI(tpy)(Cl)2(N)]+ through a series of one-electron intermediates. It and related nitrido complexes undergo formal N- transfer analogous to O-atom transfer by RuIV=O2+. With secondary amines, the products are the hydrazido complexes, cis- and trans-[OsV(L3)(Cl)2(NNR2)]+ (L3=tpy or tpm and NR2-=morpholide, piperidide, or diethylamide). Reactions with aryl thiols and secondary phosphines give the analogous adducts cis- and trans-[OsIV(tpy)(Cl)2(NS(H)(C6H4Me))]+ and fac-[OsIV(Tp)(Cl)2(NP(H)(Et2))]. In dry CH3CN, all have an extensive multiple oxidation state chemistry based on couples from Os(VI/V) to Os(III/II). In acidic solution, the OsIV adducts are protonated, e.g., trans-[OsIV(tpy)(Cl)2(N(H)N(CH2)4O)]+, and undergo proton-coupled electron transfer to quinone to give OsV, e.g., trans-[OsV(tpy)(Cl)2(NN(CH2)4O)]+ and hydroquinone. These reactions occur with giant H/D kinetic isotope effects of up to 421 based on O-H, N-H, S-H, or P-H bonds. Reaction with azide ion has provided the first example of the terminal N4(2-) ligand in mer-[OsIV(bpy)(Cl)3(NalphaNbetaNgammaNdelta)]-. With CN-, the adduct mer-[OsIV(bpy)(Cl)3(NCN)]- has an extensive, reversible redox chemistry and undergoes NCN(2-) transfer to PPh3 and olefins. Coordination to Os also promotes ligand-based reactivity. The sulfoximido complex trans-[OsIV(tpy)(Cl)2(NS(O)-p-C6H4Me)] undergoes loss of O2 with added acid and O-atom transfer to trans-stilbene and PPh3. There is a reversible two-electron/two-proton, ligand-based acetonitrilo/imino couple in cis-[OsIV(tpy)(NCCH3)(Cl)(p-NSC6H4Me)]+. It undergoes reversible reactions with aldehydes and ketones to give the corresponding alcohols.