Coordination complexes of 1-(4-[N-tert-butyl-N-aminoxyl]phenyl)-1H-1,2,4-triazole with paramagnetic transition metal dications

1-(4-(N-tert-Butyl-N-aminoxylphenyl))-1H-1,2,4-triazole (NIT-Ph-Triaz) forms isostructural cyclic 2:2 dimeric complexes with M(hfac)(2), M = Mn, Ni, Co, hfac = hexafluoroacetylacetonate. For M = Cu, only a sufficient sample for crystallographic analysis was isolated. For M = Mn, Ni, and Co, the M-NIT exchange is strongly antiferromagnetic. The intradimer exchange coupling between M-NIT units is J/k = +0.53 K for M = Mn, J/k = (-)3.5 K for M = Ni. For M = Co, J/k < 0 K, with the magnetic susceptibility tending toward zero at low temperatures. The exchange behavior is consistent with an intradimer spin polarization mechanism linking M-NIT units through the conjugated pi-system of the radical. Computational modeling of NIT-Ph-Triaz gives Mulliken spin populations in good accord with experimental electron spin resonance hyperfine coupling constants, and is consistent with the presumed radical spin density distribution in the complexes. The results provide useful guidelines to anticipate spin polarization effects in organic pi-radical building blocks in magnetic materials, particularly when qualitative connectivity-based analyses are clouded by nonalternant molecular connectivities.     

Donor-acceptor biradicals as ground state analogues of photoinduced charge separated states

A Valence Bond Configuration Interaction (VBCI) model is used to relate the intraligand magnetic exchange interaction (J) to the electronic coupling matrix element (HAB) in Tp(Cum,MeZn)(SQNN), a compound that possesses a Donor-Acceptor (D-A) SemiQuinone-NitronylNitroxide (SQNN) biradical ligand. Within this framework, an SQ --> NN charge transfer state mixes with the ground state and stabilizes the spin triplet (S = 1). This charge-transfer transition is observed spectroscopically and probed using resonance Raman spectroscopy. In addition, the temperature-dependent electronic absorption spectrum of the Ni(II) complex, Tp(Cum,MeNi)(SQNN), has been studied. Exchange coupling between the S = 1 Ni(II) ion and S = 1 SQNN provides a mechanism for observing the formally spin-forbidden, ligand-based 3GC --> 1CTC transition. This provides a means of determining U, the mean GC --> CTC energy, and a one-center exchange integral, K(0). The experimental determination of J, U, and K(0) permits facile calculation of HAB, and we show that this methodology can be extended to determine the electronic coupling matrix element in related SQ-Bridge-NN molecules. As magnetic susceptibility measurements are easily acquired in the solid state, H(AB) may be effectively determined for single molecules in a known geometry, provided a crystal structure exists for the biradical complex. Thus, SQ-Bridge-NN molecules possess considerable potential for probing both geometric and electronic structure contributions to the magnitude of the electronic coupling matrix element associated with a given bridge fragment.     

Synthesis,Spectral and Magnetic Studies of Mononuclear and Binuclear Mn(Ii), Co(Ii), Ni(Ii) and Cu(Ii) Complexes with Semicarbazone Ligands Derived from Sulfonamide

Mononuclear and binuclear Mn(II), Co(II), Ni(II) and Cu(II) complexes of new semicarbazone ligands derived from sulfonamide were synthesized and characterized by elemental analysis and IR spectra. In mononuclear complexes, the semicarbazone behaves as a monoanionic terdentate or neutral terdentate ligand towards the metal ion. However, in binuclear complexes, it behaves as a monoanionic terdentate towards one of the bivalent metal ions and monoanionic bidentate ligand towards the other metal ion in the same complex. Electronic spectra and magnetic susceptibility measurements of the solid complexes indicated octahedral geometry around Mn(II), Co(II) and Ni(II) and square planar around the Cu(II) ion. These geometries were confirmed by the results obtained from thermal analyses. The antifungus properties of the ligands and their complexes were investigated.     

Preparation and characterization of Cr(III), Mn(II), Fe(II), Co(II) and Ni(II) complexes of a hexaazadithiophenolate macrocycle

The ligating properties of the 24-membered macrocyclic dinucleating hexaazadithiophenolate ligand (L(Me))2- towards the transition metal ions Cr(II), Mn(II), Fe(II), Co(II), Ni(II) and Zn(II) have been examined. It is demonstrated that this ligand forms an isostructural series of bioctahedral [(L(Me))M(II)2(OAc)]+ complexes with Mn(II) (2), Fe(II) (3), Co(II) (4), Ni(II) (5) and Zn(II) (6). The reaction of (L(Me))2- with two equivalents of CrCl2 and NaOAc followed by air-oxidation produced the complex [(L(Me))Cr(III)H2(OAc)]2+ (1), which is the first example for a mononuclear complex of (L(Me))2-. Complexes 2-6 contain a central N3M(II)(mu-SR)2(mu-OAc)M(II)N3 core with an exogenous acetate bridge. The Cr(III) ion in is bonded to three N and two S atoms of (L(Me))2- and an O atom of a monodentate acetate coligand. In 2-6 there is a consistent decrease in the deviations of the bond angles from the ideal octahedral values such that the coordination polyhedra in the dinickel complex 5 are more regular than in the dimanganese compound 2. The temperature dependent magnetic susceptibility measurements reveal the magnetic exchange interactions in the [(L(Me))M(II)2(OAc)]+ cations to be relatively weak. Intramolecular antiferromagnetic exchange interactions are present in the Mn(II)2, Fe(II)2 and Co(II)2 complexes where J = -5.1, -10.6 and approximately -2.0 cm(-1) (H = -2JS1S2). In contrast, in the dinickel complex 5 a ferromagnetic exchange interaction is present with J = +6.4 cm(-1). An explanation for this difference is qualitatively discussed in terms of the bonding differences.     

Designing binuclear transition metal complexes: a new example of the versatility of N,N'-bis(2-aminobenzyl)-4,13-diaza-18-crown-6

N,N'-Bis(2-aminobenzyl)-4,13-diaza-18-crown-6 (L) is a versatile receptor able to adapt to the coordinative preferences of different metal cation guests. With first-row transition metal ions, L tends to form binuclear complexes but, depending on the nature of the particular metal ion, the structure of the binuclear complex may be very different. Herein we report a study of the structure and magnetic properties of the corresponding nickel(II) and cobalt(II) complexes. The X-ray crystal structure of the nickel complex (1), with formula [Ni2(L)(CH3CN)4](ClO4)4.CH3CN, shows that this compound presents a symmetric coordination environment with L adopting an anti arrangement. Each Ni(II) ion is six-coordinate in a distorted octahedral environment, and both metal ions are quite far from each other. On the other hand, the X-ray crystal structure of the cobalt complex (2), with formula [Co(L)(mu-OH)Co(CH3CN)](ClO4)3, reveals a rather different structure. Coordination number asymmetry is found: one of the Co(II) is five-coordinate in a distorted trigonal-bipyramidal coordination environment, while the second Co(II) ion is six-coordinate in a distorted octahedral arrangement. Now L adopts a syn arrangement and a hydroxide group acts as a bridge between both cobalt ions. This hydroxo-bridged Co(II) binuclear complex shows structural features that mimic the active site of methionine aminopeptidases. The magnetic properties of 1 and 2 have been investigated in the temperature range 2.0-300 K. Whereas 1 displays a Curie law except for temperatures below 50 K where zero-field splitting of the S= 1 ground state is observed, antiferromagnetic exchange in the singular asymmetric binuclear Co(II) complex 2 has been observed. This magnetic behaviour has been fitted considering first-order spin-orbit coupling in the assumed axially distorted octahedral site and totally quenched orbital contribution in the five-coordinate site in which zero-field splitting of the S= 3/2 ground state is operative.     

Neutral bis(alpha-iminopyridine)metal complexes of the first-row transition ions (Cr, Mn, Fe, Co, Ni, Zn) and their monocationic analogues: mixed valency involving a redox noninnocent ligand system

A series of bis(alpha-iminopyridine)metal complexes featuring the first-row transition ions (Cr, Mn, Fe, Co, Ni, and Zn) is presented. It is shown that these ligands are redox noninnocent and their paramagnetic pi radical monoanionic forms can exist in coordination complexes. Based on spectroscopic and structural characterizations, the neutral complexes are best described as possessing a divalent metal center and two monoanionic pi radicals of the alpha-iminopyridine. The neutral M(L*)2 compounds undergo ligand-centered, one-electron oxidations generating a second series, [(L(x))2M(THF)][B(ArF)4] [where L(x) represents either the neutral alpha-iminopyridine (L)0 and/or its reduced pi radical anion (L*)-]. The cationic series comprise mostly mixed-valent complexes, wherein the two ligands have formally different redox states, (L)0 and (L*)-, and the two ligands may be electronically linked by the bridging metal atom. Experimentally, the cationic Fe and Co complexes exhibit Robin-Day Class III behavior (fully delocalized), whereas the cationic Zn, Cr, and Mn complexes belong to Class I (localized) as shown by X-ray crystallography and UV-vis spectroscopy. The delocalization versus localization of the ligand radical is determined only by the nature of the metal linker. The cationic nickel complex is exceptional in this series in that it does not exhibit any ligand mixed valency. Instead, its electronic structure is consistent with two neutral ligands (L)0 and a monovalent metal center or [(L)2Ni(THF)][B(ArF)4]. Finally, an unusual spin equilibrium for Fe(II), between high spin and intermediate spin (S(Fe) = 2 <--> S(Fe) = 1), is described for the complex [(L*)(L)Fe(THF)][B(ArF)4], which consequently is characterized by the overall spin equilibrium (S(tot) = 3/2 <--> S(tot) = 1/2). The two different spin states for Fe(II) have been characterized using variable temperature X-ray crystallography, EPR spectroscopy, zero-field and applied-field M?ssbauer spectroscopy, and magnetic susceptibility measurements. Complementary DFT studies of all the complexes have been performed, and the calculations support the proposed electronic structures.     

First row divalent transition metal complexes of aryl-appended tris((pyridyl)methyl)amine ligands: syntheses, structures, electrochemistry, and hydroxamate binding properties

Divalent manganese, cobalt, nickel, and zinc complexes of 6-Ph(2)TPA (N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-Ph(2)TPA)Mn(CH(3)OH)(3)](ClO(4))(2) (1), [(6-Ph(2)TPA)Co(CH(3)CN)](ClO(4))(2) (2), [(6-Ph(2)TPA)Ni(CH(3)CN)(CH(3)OH)](ClO(4))(2) (3), [(6-Ph(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (4)) and 6-(Me(2)Ph)(2)TPA (N,N-bis((6-(3,5-dimethyl)phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; [(6-(Me(2)Ph)(2)TPA)Ni(CH(3)CN)(2)](ClO(4))(2) (5) and [(6-(Me(2)Ph)(2)TPA)Zn(CH(3)CN)](ClO(4))(2) (6)) have been prepared and characterized. X-ray crystallographic characterization of 1A.CH(3)()OH and 1B.2CH(3)()OH (differing solvates of 1), 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN revealed mononuclear cations with one to three coordinated solvent molecules. In 1A.CH(3)()OH and 1B.2CH(3)()OH, one phenyl-substituted pyridyl arm is not coordinated and forms a secondary hydrogen-bonding interaction with a manganese bound methanol molecule. In 2.2CH(3)()CN, 3.CH(3)()OH, 4.2CH(3)()CN, and 6.2.5CH(3)()CN, all pyridyl donors of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands are coordinated to the divalent metal center. In the cobalt, nickel, and zinc derivatives, CH/pi interactions are found between a bound acetonitrile molecule and the aryl appendages of the 6-Ph(2)TPA and 6-(Me(2)Ph)(2)TPA ligands. (1)H NMR spectra of 4 and 6 in CD(3)NO(2) solution indicate the presence of CH/pi interactions, as an upfield-shifted methyl resonance for a bound acetonitrile molecule is present. Examination of the cyclic voltammetry of 1-3 and 5 revealed no oxidative (M(II)/M(III)) couples. Admixture of equimolar amounts of 6-Ph(2)TPA, M(ClO(4))(2).6H(2)O, and Me(4)NOH.5H(2)O, followed by the addition of an equimolar amount of acetohydroxamic acid, yielded the acetohydroxamate complexes [((6-Ph(2)TPA)Mn)(2)(micro-ONHC(O)CH(3))(2)](ClO(4))(2) (8), [(6-Ph(2)TPA)Co(ONHC(O)CH(3))](ClO(4))(2) (9), [(6-Ph(2)TPA)Ni(ONHC(O)CH(3))](ClO(4))(2) (10), and [(6-Ph(2)TPA)Zn(ONHC(O)CH(3))](ClO(4))(2) (11), all of which were characterized by X-ray crystallography. The Mn(II) complex 8.0.75CH(3)()CN.0.75Et(2)()O exhibits a dinuclear structure with bridging hydroxamate ligands, whereas the Co(II), Ni(II), and Zn(II) derivatives all exhibit mononuclear six-coordinate structures with a chelating hydroxamate ligand.     

Synthesis and characterization of some pyrimidine, purine, amino acid and mixed ligand complexes

Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of barbital, thiouracil, adenine, amino acids (methionine, lysine and alanine) and some mixed ligands were prepared and characterized by elemental analyses, IR, electronic spectra, magnetic susceptibility and ESR spectra. Coordination of the metallic centre to the oxygen and nitrogen atoms of barbital, thiouracil, amino acids and coordinate to amino group and nitrogen atom of adenine occurred. Electronic spectra and magnetic susceptibility measurements were utilized to infer the structure of the complexes which are octahedral for Mn(II), Fe(III), Co(II), Ni(II) and Cd(II) and tetrahedral for Mn(II), Cu(II), Zn(II) complexes. ESR spectra were observed for copper complexes with a d(x2)-(y2) ground state with small g(||) values indicating strong interaction between the ligands and their metal ions.     

A phosphorus supported multisite coordinating tris hydrazone P(S)[N(Me)N=CH-C6H4-o-OH]3 as an efficient ligand for the assembly of trinuclear metal complexes: synthesis, structure, and magnetism

A phosphorus supported multisite coordinating ligand P(S)[N(Me)N=CH-C(6)H(4)-o-OH](3) (2) was prepared by the condensation of the phosphorus tris hydrazide P(S)[N(Me)NH(2)](3) (1) with o-hydroxybenzaldehyde. The reaction of 2 with M(OAc)(2).xH(2)O (M = Mn, Co, Ni, x = 4; M = Zn, x = 2) afforded neutral trinuclear complexes [P(S)[N(Me)N=CH-C(6)H(4)-o-O](3)](2)M(3) [M = Mn (3), Co (4), Ni (5), and Zn (6)]. The X-ray crystal structures of compounds 2-6 have been determined. The structures of 3-6 reveal that the trinculear metal assemblies are nearly linear. The two terminal metal ions in a given assembly have an N(3)O(3) ligand environment in a distorted octahedral geometry while the central metal ion has an O(6) ligand environment also in a slightly distorted octahedral geometry. In all the complexes, ligand 2 coordinates to the metal ions through three imino nitrogens and three phenolate oxygens; the latter act as bridging ligands to connect the terminal and central metal ions. The compounds 2-6 also show intermolecular C-H...S=P contacts in the solid-state which lead to the formation of polymeric supramolecular architectures. The observed magnetic data for the (s = 5/2)3 L(2)(Mn(II))(3) derivative, 3, show an antiferromagnetic nearest- and next-nearest-neighbor exchange (J = -4.0 K and J' = -0.15 K; using the spin Hamiltonian H(HDvV) = -2J(S(1)S(2) + S(2)S(3)) - 2J'S(1)S(3)). In contrast, the (s = 1)(3) L(2)(Ni(II))(3) derivative, 5, displays ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchange interactions (J = 4.43 K and J' = -0.28 K; H = H(HDvV)+ S(1)DS(1) + S(2)DS(2)+ S(3)DS(3)). The magnetic behavior of the L(2)(Co(II))(3) derivative, 4, reveals only antiferromagnetic exchange analogous to 3 (J = -4.5, J' = -1.4; same Hamiltonian as for 3).     

Spectral, XRD, SEM and biological activities of transition metal complexes of polydentate ligands containing thiazole moiety

Metal complexes of o-vanillidene-2-aminobenzothiazole have been prepared and characterized by elemental and spectral (vibrational, electronic, 1H NMR and EPR) data as well as magnetic susceptibility measurements and thermo gravimetric analysis (TG/DTA). The low molar conductance values reveal the non-electrolytic nature of these complexes. The elemental analysis suggests that the stoichiometry to be 1:2 (metal:ligand). Magnetic susceptibility data coupled with electronic spectra suggest that two ligands coordinate to each metal atom by phenolic oxygen and imino nitrogen to form high spin octahedral complex with Co(II), Mn(II) and Ni(II). The fifth and sixth position of metal ion is satisfied with water molecules. The thermal behaviour (TG/DTA) of the synthesised complexes shows that the complexes loss water molecules in the first step followed by decomposition of the ligand. Spin Hamiltonian parameters predict a distorted tetrahedral geometry for the copper complex. XRD and SEM analysis provide the crystalline nature and the morphology of the metal complexes. The in vitro biological activity of the metal chelates is tested against the Gram positive bacteria (Bacillus amyloliquifacians) and gram negative bacteria (Pseudomonas species), fungus (Aspergillus niger) and yeast (Sacchromyces cereviaceae). Most of the metal chelates exhibited higher biological activities.     

Periodic trends within a series of five-coordinate thiolate-ligated [MII(SMe2N4(tren))]+ (M = Mn, Fe, Co, Ni, Cu, Zn) complexes, including a rare example of a stable CuII-thiolate

A series of five-coordinate thiolate-ligated complexes [M(II)(tren)N4S(Me2)]+ (M = Mn, Fe, Co, Ni, Cu, Zn; tren = tris(2-aminoethyl)amine) are reported, and their structural, electronic, and magnetic properties are compared. Isolation of dimeric [Ni(II)(SN4(tren)-RS(dang))]2 ("dang"= dangling, uncoordinated thiolate supported by H bonds), using the less bulky [(tren)N4S](1-) ligand, pointed to the need for gem-dimethyls adjacent to the sulfur to sterically prevent dimerization. All of the gem-dimethyl derivatized complexes are monomeric and, with the exception of [Ni(II)(S(Me2)N4(tren)]+, are isostructural and adopt a tetragonally distorted trigonal bipyramidal geometry favored by ligand constraints. The nickel complex uniquely adopts an approximately ideal square pyramidal geometry and resembles the active site of Ni-superoxide dismutase (Ni-SOD). Even in coordinating solvents such as MeCN, only five-coordinate structures are observed. The MII-S thiolate bonds systematically decrease in length across the series (Mn-S > Fe-S > Co-S > Ni-S approximately Cu-S < Zn-S) with exceptions occurring upon the occupation of sigma* orbitals. The copper complex, [Cu(II)(S(Me2)N4(tren)]+, represents a rare example of a stable CuII-thiolate, and models the perturbed "green" copper site of nitrite reductase. In contrast to the intensely colored, low-spin Fe(III)-thiolates, the M(II)-thiolates described herein are colorless to moderately colored and high-spin (in cases where more than one spin-state is possible), reflecting the poorer energy match between the metal d- and sulfur orbitals upon reduction of the metal ion. As the d-orbitals drop in energy proceeding across the across the series M(2+) (M= Mn, Fe, Co, Ni, Cu), the sulfur-to-metal charge-transfer transition moves into the visible region, and the redox potentials cathodically shift. The reduced M(+1) oxidation state is only accessible with copper, and the more oxidized M(+4) oxidation state is only accessible for manganese.     

High-spin metal complexes containing a ferromagnetically coupled tris(semiquinone) ligand

The tris-bidentate ligand 1,3,5-tris(5'-tert-butyl-3',4'-dihydroxyphenyl)benzene ((TBCat)(3)Ph) was synthesized. The reaction of this molecule in basic solution with two paramagnetic acceptors, i.e., a nickel(II)minus signtetraazamacrocyclic ligand complex (Ni(CTH)) (CTH = dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) and manganese(II)-hydrotris[3-(4'-cumenyl)-5-methylpyrazolyl]borate (Mn(Tp(Cum,Me))), yielded two complexes whose analytical formulas are consistent with those of trinuclear complexes. Spectroscopic and magnetic measurements suggest that these derivatives contain divalent metal ions coordinated to the tris(semiquinone) form of the ligand. Analysis of the magnetic data shows that the pi-connectivity of the ligand enforces ferromagnetic coupling between the three semiquinone units of the molecule, giving rise to complexes with S = 9/2 (M = Ni(II)) and S = 6 (M = Mn(II)) ground states. The coupling within the tris(semiquinone) unit is quite large (J = -26 cm(-1) for the nickel(II) derivative and J = -40 cm(-1) for the manganese(II) one, using the general exchange Hamiltonian H = sigma J(ij)S(i)S(j)), and it is of the same order of magnitude as that observed in an analogous series of bis(semiquinone) complexes that we recently reported.     

Mono{hydrotris(mercaptoimidazolyl)borato} complexes of manganese(II), iron(II), cobalt(II), and nickel(II) halides

A series of [Tm(Me)M(mu-Cl)]2 and Tm(R)MCl (Tm(R) = tris(mercaptoimidazolyl)borate; R = Me, tBu, Ph, 2,6-iPr2C6H3 (Ar); M = Mn, Fe, Co, Ni) complexes have been prepared by treatment of NaTm(Me) or LiTm(R) with an excess amount of metal(II) chlorides, MCl2. Treatment of Tm(R)MCl (R = tBu, Ph, Ar) with NaI led to a halide exchange to afford Tm(R)MI. The molecular structures of [Tm(Me)M(mu-Cl)]2 (M = Mn, Ni), [Tm(Me)Ni(mu-Br)]2, Tm(tBu)MCl (M = Fe, Co), Tm(Ph)MCl (M = Mn, Fe, Co, Ni), Tm(Ar)MCl (M = Mn, Fe, Co, Ni), Tm(Ph)MI (M = Mn, Co), and Tm(Ar)MI (M = Fe, Co, Ni) have been determined by X-ray crystallography. The Tm(R) ligands occupy the tripodal coordination site of the metal ions, giving a square pyramidal or trigonal bipyramidal coordination geometry for Tm(Me)M(mu-Cl)]2 and a tetrahedral geometry for the Tm(R)MCl complexes, where the S-M-S bite angles are larger than the reported N-M-N angles of the corresponding hydrotris(pyrazolyl)borate (Tp(R)) complexes. Treatment of Tm(Ph)2Fe with excess FeCl2 affords Tm(Ph)FeCl, indicating that Tm(R)2M as well as Tm(R)MCl is formed at the initial stage of the reaction between MCl2 and the Tm(R) anion.     

Molecular structure and spectroscopic studies on novel complexes of coumarin-3-carboxylic acid with Ni(II), Co(II), Zn(II) and Mn(II) ions based on density functional theory

Novel Ni(II), Co(II), Zn(II) and Mn(II) complexes of coumarin-3-carboxylic acid (HCCA) were studied at experimental and theoretical levels. The complexes were characterised by elemental analyses, FT-IR, (1)H NMR, (13)C NMR and UV-Vis spectroscopy and by magnetic susceptibility measurements. The binding modes of the ligand and the spin states of the metal complexes were established by means of molecular modelling of the complexes studied and calculation of their IR, NMR and absorption spectra at DFT(TDDFT)/B3LYP level. The experimental and calculated data verified high spin Ni(II), Co(II) and Mn(II) complexes and a bidentate binding through the carboxylic oxygen atoms (CCA2). The model calculations predicted pseudo octahedral trans-[M(CCA2)(2)(H(2)O)(2)] structures for the Zn(II), Ni(II) and Co(II) complexes and a binuclear [Mn(2)(CCA2)(4)(H(2)O)(2)] structure. Experimental and calculated (1)H, (13)C NMR, IR and UV-Vis data were used to distinguish the two possible bidentate binding modes (CCA1 and CCA2) as well as mononuclear and binuclear structures of the metal complexes.     

Magnetic anisotropy of two trinuclear and tetranuclear Cr(III)Ni(II) cyanide-bridged complexes with spin ground states S = 4 and 5

The trinuclear and the tetranuclear complexes [[iPrtacnCr(CN)3]2[Ni(cyclam)]](NO3)2.5H2O 1 (cyclam = 1,4,8,11-tetraazacyclotetradecane, iPrtacn = 1,4,7-tris-isopropyl-1,4,7-triazacyclononane) and [[iPrtacnCr(CN)3Ni(Me2bpy)2]2](ClO4)4.2CH3CN 2 (Me2bpy = 4,4-dimethyl-2,2-bipyridine) were synthesized by reacting (iPrtacn)Cr(CN)3 with [Ni(cyclam)](NO3)2 and [Ni(Me2bpy)2(H2O)2](ClO4)2, respectively. The crystallographic structure of the two compounds was solved. The molecular structure of complex 1 consists of a linear Cr-Ni-Cr arrangement with a central Ni(cyclam) unit surrounded by two Cr(iPrtacn)(CN)3 molecules through bridging cyanides. Each peripheral chromium complex has two pending CN ligands. Complex 2 has a square planar arrangement with the metal ions occupying the vertices of the square. Each Cr(iPrtacn)(CN)3 molecule has two bridging and one non-bridging cyanide ligands. The magnetic properties of the two complexes were investigated by susceptibility vs. temperature and magnetization vs. field studies. As expected from the orthogonality of the magnetic orbitals between Cr(III) (t2g3) and Ni(II) (e(g)2) metal ions, a ferromagnetic exchange interaction occurs leading to a spin ground states S = 4 and 5 for 1 and 2, respectively. The magnetization vs. field studies at T = 2, 3 and 4 K showed the presence of a magnetic anisotropy within the ground spin states leading to zero-field splitting parameters obtained by fitting the data D4 = 0.36 cm(-1) and D5 = 0.19 cm(-1) (the indices 4 and 5 refer to the ground states of complexes 1 and 2, respectively). In order to quantify precisely the magnitude of the axial (D) and the rhombic (E) anisotropy parameters, High-field high frequency electron paramagnetic resonance (HF-HFEPR) experiments were carried out. The best simulation of the experimental spectra (at 190 and 285 GHz) gave the following parameters for 1: D4 = 0.312 cm(-1), E4/D4 = 0.01, g4x = 2.003, g4y = 2.017 and g4z = 2.015. For complex 2 two sets of parameters could be extracted from the EPR spectra because a doubling of the resonances were observed and assigned to the presence of complexes with slightly different structures at low temperature: D5 = 0.154 (0.13) cm(-1), E5/D5 = 0.31 (0.31) cm(-1), g4x = 2.04 (2.05), g4y = 2.05 (2.05) and g4z = 2.03 (2.02). The knowledge of the magnetic anisotropy parameters of the mononuclear Cr(iPrtacn)(CN)3, Ni(cyclam)(NCS)2 and Ni(bpy)2(NCS)2 complexes by combining HF-HFEPR studies and calculation using a software based on the angular overlap model (AOM) allowed to determine the orientation of the local D tensors of the metal ions forming the polynuclear complexes. We, subsequently, show that the anisotropy parameters of the polynuclear complexes computed from the projection of the local tensors are in excellent agreement with the experimental ones extracted from the EPR experiments.     

Schiff碱双核配合物的磁性及模拟甲烷单加氧酶催化性能的研究

存在于生命体中的甲烷单加氧酶是一种双金属单加氧酶,其结构及催化作用机制目前还不十分清楚．为了模拟甲烷单加氧酶的催化作用,探讨甲烷单加氧酶中两个金属离子间是否存在协同作用,本文按前文方法合成了双[N,N’-亚乙基-2,2’-(苯亚甲基)二(3,4-二甲基吡咯-5-醛缩亚胺)]合单金属配合物MH2L(1～7)及双金属配合物MnML(8-14)(结构见Scheme 1)．     

Polynuclear complexes of the pendent-arm ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane

The ligand 1,4,7-tris(acetophenoneoxime)-1,4,7-triazacyclononane (H(3)L) has been synthesized and its coordination properties toward Cu(II), Ni(II), Co(II), and Mn(II) in the presence of air have been investigated. Copper(II) yields a mononuclear complex, [Cu(H(2)L)](ClO(4)) (1), cobalt(II) and manganese(II) ions yield mixed-valence Co(III)(2)Co(II) (2a) and Mn(II)(2)Mn(III) (4) complexes, whereas nickel(II) produces a tetranuclear [Ni(4)(HL)(3)](2+) (3) complex. The complexes have been structurally, magnetochemically, and spectroscopically characterized. Complex 3, a planar trigonal-shaped tetranuclear Ni(II) species, exhibits irregular spin-ladder. Variable-temperature (2-290 K) magnetic susceptibility analysis of 3 demonstrates antiferromagnetic exchange interactions (J = -13.4 cm(-1)) between the neighboring Ni(II) ions, which lead to the ground-state S(t) = 2.0 owing to the topology of the spin-carriers in 3. A bulk ferromaganetic interaction (J = +2 cm(-1)) is prevailing between the neighboring high-spin Mn(II) and high-spin Mn(III) ions leading to a ground state of S(t) = 7.0 for 4. The large ground-state spin value of S(t) = 7.0 has been confirmed by magnetization measurements at applied magnetic fields of 1, 4 and 7 T. A bridging monomethyl carbonato ligand formation occurs through an efficient CO(2) uptake from air in methanolic solutions containing a base in the case of complex 4.     

Preparation, UV-vis, IR, EPR and resonance Raman study of Fe, Ni, Co and Zn dioxolene complexes

An UV-vis, Raman, IR and EPR spectroscopic study was performed for the water soluble complexes of Fe(III), Ni(II), Co(II) and Zn(II) coordinated to dioxolene ligands derived from oxidized dopamine. The complexes were obtained and stabilized at neutral pH by the strong reducing agent sodium thiosulfate. Iron(III) stabilizes the ligand in catecholate form as [Fe(III)(Cat)2]1-, Cat=dopacatecholate, and the divalent metals as dopasemiquinone (SQ): [Ni(SQ)3]1-, [Co(SQ)3]1- and [Zn(SQ)3]1-. The resonance Raman spectra of the solid complexes as [CAT][Ni(SQ)3], [CTA][Co(SQ)3] and [CTA][Zn(SQ)3], CTA is the cetyltrimethylammonium, are very similar to the spectra of the complexes in solution, while the Fe(III) complex is a mixture of two iron complexes, with catecholate or dopasemiquinone ligands.     

Self-assembled polynuclear clusters derived from some flexible polydentate dihydrazide ligands

Polynuclear manganese(II), cobalt(II)/(III), iron(II)/(III) and nickel(II) complexes of a group of flexible polydentate dihydrazone ligands, based on pyridine-2,6-dipicolinic (A), oxalic (B) and malonic (C) subunits are described. Structural details are reported for the linear dinuclear complexes [Ni2(2poap)2(H2O)2](NO3)4 . 2CH3OH . 2.5H2O (1), [Mn2(pttp)(NO3)2(CH3OH)2(H2O)2](NO3)2 . H2O (2) and [Mn2(mapttp)2(NO3)2(H2O)2](NO3)2 . 10H2O (3), a square tetranuclear complex [Co4(pttp)4]Br6 . 9H2O (4), a tetranuclear tetrahedral complex [Ni4(pttp)6](BF4)6F2 . 14H2O (7), and a mixed spin state tetranuclear Ni(II) complex [(2pyoap)2Ni4(CH3OH)4] . 1.5CH3OH (10), with a diamond-like arrangement of metal ions. The paramagnetic metal centers are well separated in each case, leading to weak antiferromagnetic coupling or non-existent spin exchange.