Catalytic activity of some new copper(II) azo-complexes

Copper(II) complexes [Cu(L)₂]?·?nH₂O, where L is 3-(p-X-)-4-hydroxy-l,2-naphthoquinone (for L1, X?=?H; L2, X?=?CH₃; L3, X?=?Cl; L4, X?=?Br; and L5, X?=?NO₂), have been synthesized and characterized by analytical, electrochemical, spectroscopic (IR, UV-Vis, ESR, and ¹H NMR), and magnetic methods. From the data obtained, square-planar geometry has been assigned for all the complexes. [CuL1]?·?H₂O exhibits catalytic activity for oxidation of benzyl alcohol, piperonyl alcohol, and cinnamyl alcohol into their respective aldehydes in the presence of H₂O₂ as co-oxidant and in CH₃CN and H₂O as solvents at room temperature.     

Synthesis,characterization, and optoelectronic properties of heteroleptic iridium complexes containing substituted 1,3,4-oxadiazole and β-diketone as ligands

The new heteroleptic iridium(III) complexes (BuOXD)₂Ir(tta) and (BuOXD)₂Ir(tmd) [BuOXD?=?2-(4-butyloxyphenyl)-5-phenyl[1,3,4]oxadiazolato-N4,C2, tta?=?1,1,1-trifluoro-4-thienylbutane-2,4-dionato, tmd?=?2,2,6,6-tetramethylheptane-3,5-dionato] have been synthesized and characterized. These complexes have two cyclometalated ligands (C^N) and a bidentate diketone ligand (X) [C^N)₂Ir(X)], where X is a β-diketone with trifluoromethyl, theonyl or t-butyl groups. The color tuning with the change in electronegativity of substituents in the β-diketones has been studied. Photoluminescence spectra of the complexes showed peak emissions at 523 and 549?nm, respectively. The electroluminescent properties of these complexes have been studied by fabricating multi layer devices with device structure ITO/α-NPD/8% iridium complex doped CBP/BCP/Alq₃/LiF/Al. The electroluminescence spectra also showed peak emissions at 526 and 570?nm for (BuOXD)₂Ir(tta) and (BuOXD)₂Ir(tmd), respectively. These metal complexes showed good thermal stability in air to 340°C.     

Some novel manganese(III) porphyrins with catalytic properties

Abstract

A series of manganese(III) porphyrins with 4-methylimidazole have been prepared. These are high-spin complexes having general formula [Mn^III(THMPP)X(4-MeIm)], where THMP?=?5,10,15,20-tetra(4-hydroxy-3-methoxyphenyl)porphine ligand, X?=?Cl^?, Br^?, NCS^?, or N₃^? and 4-MeIm?=?4-methylimidazole. All the complexes have been characterized by UV-visible, FT-IR, ESI-MS spectra, elemental analyses and magnetic susceptibility measurements. These manganese(III) porphyrins oxidize aromatic alcohols to aldehydes. The oxidation reactions have been carried out at room temperature in the presence of oxidants such as NaIO₄, H₂O₂, and NaOCl. The comparative studies proved that NaIO₄ behaves as the most efficient oxidant in these oxidative transformation reactions.     

2-Chloro-3-fluoropyridine copper(II) complexes and the effect of structural changes on magnetic behavior

Abstract

A family of copper(II) compounds has been prepared with the general formula (2-chloro-3-fluoro-pyridine)₂CuX₂·n(Y), where X?=?Cl, Br, n?=?0,1, and Y?=?methanol or water. For the copper chloride complexes, only solvated structures were obtained (1, X?=?Cl, Y?=?H₂O; 2, X?=?Cl, Y?=?CH₃OH) while for the copper bromide compounds, both a desolvated structure and the methanol solvate were prepared (3, X?=?Br, Y?=?none; 4, X?=?Br, Y?=?CH₃OH). Each compound has been characterized by IR, powder X-ray diffraction, single-crystal X-ray diffraction, and temperature-dependent magnetic susceptibility measurement. Compounds 1 and 4 are isostructural, in the space group Cm, and neither exhibits significant magnetic exchange although superexchange pathways are present. Compound 2 also crystallizes in the Cm space group and exhibits weak ferromagnetic interactions (J/k_B?=?1.72(2) K from the 1D-ferromagnetic chain model) which are likely propagated by hydrogen bonding. Compound 3 crystallizes in the space group P2₁/n with the Cu(II) ion sitting on a crystallographic inversion center. Compound 3 exhibits weak antiferromagnetic exchange via two-halide superexchange typical for similar complexes. The magnetic data for 3 were fit to the 1D-antiferromagnetic chain model resulting in J/k_B?=??1.21(1).     

Transition metal salts of quinoline: synthesis,structure and magnetic behavior of (QuinH)2[MX4]·2H2O [Quin = quinoline; M = Mn,Co, Cu,Zn], (QuinH)2[MnBr2(H2O)2](Br)2 and (QuinH)[Cu(Quin)Br3]

Abstract

A family of compounds of general formula (QuinH)₂MX₄·2H₂O has been prepared and characterized [Quin?=?quinoline; M, X?=?Co,Cl (1); M, X?=?Co,Br (2); M, X?=?Zn,Br (3); M, X?=?Mn,Cl (4)]. The complexes crystallize in the monoclinic space group C2/c as well-isolated layers containing the MX₄^?2 anions and water molecules, separated by the quinolinium cations. The bromide analogue of 4, compound 5 (QuinH)₂[MnBr₂(H₂O)₂](Br)₂, also crystallizes in the C2/c space group, but comprises a co-crystal of manganese bromide dihydrate and quinolinium bromide. The temperature dependent magnetic properties of the complexes are described, along with the tetrachlorocuprate analogue (7). All compounds show weak antiferromagnetic interactions (J/k_B?～?0.06–1.4 K) and good one- or two-dimensional isolation. In addition, the crystal structure of the mixed quinoline/quinolinium complex (QuinH)[Cu(Quin)Br₃] (triclinic, P-1) is reported.     

Influence of modifiers and glass-forming ions on the crystallization of glasses of the NaCaPO4–SiO2 system

Silicate?Cphosphate glasses of the XYPO₄?CSiO₂ and XYPO₄?CSiO₂?CAlPO₄ (where X?=?Na⁺ and/or K⁺ and Y?=?Ca²⁺ and/or Mg²⁺) systems have been the subject of the presented investigations. Bioactive glasses from these systems are the base for obtaining glass-crystalline biomaterials through a direct crystallization. However, growth of crystalline phases very adversely affects the bioactivity of the glasses. Uncontrolled growth of crystalline phases can be reduced by means of a glass phase separation phenomenon in the silicate?Cphosphate glasses because boundaries of inclusion-matrix phase may be a barrier limiting the growth of crystalline phases. Microscopic and EDX investigations which have been carried out have shown that glass phase separation occurs in glasses belonging to XYPO₄?CSiO₂ and XYPO₄?CSiO₂?CAlPO₄ systems. Introduction of aluminum ions into the glass structure leads to a rapid homogenization of its texture. Based on DSC examinations it has been found out that crystallization of the glasses of XYPO₄?CSiO₂ systems is a multistep process. The presence of several (the number depends on the type of modifiers and glass-forming ions) clearly separated exothermic peaks in DSC curves of investigated glasses makes it possible to crystallize only the inclusions with the matrix remaining amorphous or vice versa. It has been shown that, crystallization of glasses of XYPO₄?CSiO₂?CAlPO₄ system is single-stage process, which is the consequence of the homogenizing effect of aluminum ions on their texture.     

Comparative Computational Study of Hydrogen Abstraction Reactions of CY3H + XO− (X,Y = F,Cl, and Br)

The effects of halogen substituents on the reactivity are characterized by the hybrid B3LYP and BHandHLYP functionals of density functional theory using the aug‐cc‐pVDZ basis set. The species XO⁻ and CY₃H, where X, Y = F, Cl, and Br, have been chosen as model reactants in this work. Also, the mechanism of the hydrogen abstraction (HAT) reaction has been used to study the chemical reactivity of these anionic reactions. Our theoretical findings suggest that the relative reactivity of the CY₃H + XO⁻ reactions increases as Y goes from F to Br and decreases as X goes from F to Br. Moreover, among all reactions investigated in this study, the special role of the Y has very dominant effect on activation of the C–H bond in CY₃H when XO⁻ attacks the CY₃H. Again, through the transition state theory the rate constants at 298–1000 K are also evaluated for the HAT reactions, indicating the lower the temperature the faster is the chemical reaction.     

Syntheses,characterizations, and antimicrobial activities of binuclear ruthenium(III) complexes containing 2-substituted benzimidazole derivatives

Binuclear ruthenium(III) complexes [RuX₃L]₂?·?nH₂O (X?=?Cl, L?=?L¹, L², L³; n?=?1, L⁴ and L⁵, X?=?Br; L?=?L³), [RuX₃L_1.5]₂?·?nH₂O (X?=?Br, L?=?L¹; n?=?0, L⁴; n?=?6 and L⁵; n?=?10), and [RuX₃L₂]₂ (X?=?Br, L?=?L²) have been isolated by treatment of hydrated RuX₃ (X?=?Cl/Br) in acetone with 2-(2′-aminophenylbenzimidazole) (L¹), 2-(3′-aminophenylbenzimidazole) (L²), 2-[(3′-N-salicylidinephenyl)benzimidazole] (L³), 2-(3′-pyridylbenzimidazole) (L⁴), and 2-(4′-pyridylbenzimidazole) (L⁵) in acetone. The complexes were characterized by elemental analysis, conductivity and magnetic susceptibility measurements, IR, electronic, EPR, and mass spectral studies. The complexes were dimeric; based on analytical and spectral studies, an octahedral geometry was proposed for the complexes. The synthesized complexes were screened against Gram-positive and Gram-negative bacteria and fungi.     

Symmetric Ni(II) dithiocarbamates with bidentate phosphines ligands

Ni(II) mononuclear dithiocarbamate complexes with bidentate P,P ligands of composition [Ni(R₂dtc)(P,P)]X {R?=?pentyl (pe), benzyl (bz); dtc?=?S₂CN^?; P,P?=?1,2-bis(diphenylphosphino)ethane (dppe), 1,4-bis(diphenylphosphino)butane (dppb), 1,1′-bis(diphenylphosphino) ferrocene (dppf); X?=?ClO₄, Cl, Br, NCS} and binuclear complexes of composition [Ni₂(μ-dpph)(R₂dtc)₂]X₂ with a P,P-bridging ligand {P,P?=?1,6-bis(diphenylphosphino)hexane (dpph); X?=?Cl, Br, NCS} have been synthesized. The complexes have been characterized by elemental and thermal analysis, IR, electronic and ³¹P{¹H}-NMR spectroscopy, magnetochemical and conductivity measurements. Single crystal X-ray analysis of [Ni(pe₂dtc)(dppf)]ClO₄ confirmed a distorted square planar coordination in the NiS₂P₂ chromophore. For selected samples, the catalysis of graphite oxidation was studied.     

Syntheses and characterization of new tetraazamacrocyclic copper(II) complexes as a dual functional mimic enzyme (catalase and superoxide dismutase)

A series of macrocyclic complexes, [Cu(TAAP)]X₂, X?=?ClO₄ and CH₃COO; [Cu(TAAP)X]X, X?=?NO₃, Cl, and Br, have been synthesized by self-condensation of 5-amino-3-methyl-l-phenylpyrazole-4-carbaldehyde (AMPC) in the presence of copper(II). Elemental analyses and conductivity measurements confirm the stoichiometry of the ligand and complexes, while the characteristic absorption bands in IR spectra confirmed the formation of ligand framework around copper. Square-pyramidal and square-planar stereochemistries have been proposed for the five-coordinate (nitrato and halogeno) and four-coordinate (perchlorate and acetate) complexes. The electrochemical properties and thermal behaviors have been studied by cyclic voltammetry and TGA. Mimetics of antioxidant enzymes such as superoxide dismutase (SOD) and catalase demonstrated that there is a correlation between the observed redox properties and the SOD and catalase biomimetic catalytic activities of the copper(II) complexes.     

Synthesis and characterization of tungsten carbonyl complexes containing N-methyl substituted urea and thiourea ligands

Six new mixed-ligand tungsten carbonyl complexes containing N-methyl substituted urea and thiourea of the type W(CO)₄[RCH₂N-(C=X)NH₂] where X?=?O or S and R?=?morpholine, piperidine and diphenylamine are reported. These have been prepared by refluxing hexacarbonyl tungsten(0) with corresponding ligands in THF to produce cis-disubstituted products, [(L-L)W(CO)₄] where L-L?=?a chelating bidentate ligand, morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU), piperidinomethyl thiourea (PMTU), diphenylaminomethyl urea (DAMU) and diphenylaminomethyl thiourea (DAMTU). The compounds have been characterized by elemental analysis, IR, electronic and ¹³C NMR spectra, magnetic moments and conductivity measurements. The IR spectra suggests that in all the complexes, the ligands are bidentate chelating, coordinating the metal through carbonyl oxygen or thiocarbonyl sulphur and the ring nitrogen or tert-nitrogen of diphenylamine. The CO force constants and CO–CO interaction constants for these derivatives have also been calculated using Cotton–Kraihanzel secular equations, which indicate poor π-bonding ability of the ligands. ¹³C NMR and electronic spectra reveal loss of cis-carbonyl ligands to produce cis-disubstituted tetracarbonyl derivatives. Molecular modeling studies have been carried out using Hyperchem release 7.52 which suggest a distorted octahedral geometry for these complexes.     

Heteroatom Tuning of Bimolecular Criegee Reactions and Its Implications

High‐level quantum‐chemical calculations have been performed to understand the key reactivity determinants of bimolecular reactions of Criegee intermediates and H₂X (X=O, S, Se, and Te). Criegee intermediates are implicated as key intermediates in atmospheric, synthetic organic, and enzymatic chemistry. Generally, it is believed that the nature and location of substituents at the carbon of the Criegee intermediate play a key role in determing the reactivity. However, the present work suggests that it is not only the substitution of the Criegee intermediate, but the nature of the heteroatom in H₂X that also plays a crucial role in determining the reactivity of the interaction between the Criegee intermediate and H₂X. The barriers for the reactions of Criegee intermediates and H₂X satisfy an inverse correlation with the bond strength of X−H in H₂X, and a direct correlation with the first pK_a of H₂X. This heteroatom tuning causes a substantial barrier lowering of 8–11 kcal mol⁻¹ in the Criegee reaction barrier in going from H₂O to H₂Te. An important implication of these results is that the reaction of the Criegee intermediate and H₂S could be a source of thioaldehydes, which are important in plantery atmospheres and synthetic organic chemistry. By performing the reaction of Criegee intermediates and H₂S under water or acid catalysis, thioladehydes could be detected in a hydrogen‐bonded complexed state, which is significantly more stable than their uncomplexed form. As a result, simpler aliphatic thioaldehydes could be selectively synthesized in the laboratory, which, otherwise, has been a significant synthetic challenge because of their ability to oligomerize.     

Dramatic substituent effects on the mechanisms of nucleophilic attack on Se—S bridges

The reactions of XSeSX, XSeSY, and YSeSX (X, Y = CH₃, NH₂, OH, F) with F^? and CN^? nucleophiles have been investigated by means of B3PW91/6‐311+G(2df,p) and G4 calculations. In systems where the two substituents are not identical (XSeSY), the more stable of the two possible isomers corresponds to those in which the most electronegative substituent is attached to Se. Nucleophilic attack takes place at Se, independent of the nature of the nucleophile, with the only exception being XSeSF (X = CH₃, NH₂, OH), in which case the attack occurs at S. In agreement with recent results for disulfide and diselenide linkages, the mechanisms leading to Se—S bond cleavage are not always the more favorable ones because for highly electronegative substituents the most favorable process is fission of the chalcogen‐substituent bond. These dissimilarities in the observed reactivity pattern as a function of the electronegativity of the substituents are due to the fact that the σ‐type Se—S antibonding orbital, which for low‐electronegative substituents is the lowest unnoccupied molecular orbital (LUMO), becomes strongly destabilized when the electronegativity of the substituent increases, and is replaced by an antibonding π‐type Se‐X (or S‐X) orbital. In contrast, however, with what has been found for disulfide and diselenide derivatives, the observed reactivity does not change with the nature of the nucleophile. The activation strain model provides interesting insight into these processes, showing that in most cases the activation barriers are the consequence of subtle differences in the strain or in the interaction energies. © 2013 Wiley Periodicals, Inc.     

Manganese(I) tricarbonyl complexes: UV-dependent antioxidant activity,electrochemistry, and DFT/TDDFT calculation

Abstract

As important catalysts, metal carbonyl complexes have received considerable attention in recent years owing to their ability to store and transport carbon monoxide that have been proven to function as antiinflammatory, antiapoptotic, and antiproliferative agents. In addition, imidazole/benzimidazole derivative molecules have been known to be bioactive owing to their antihypertensive, antiinflammatory, and antimicrobial properties. Combining these two bioactive species could be a good idea for possible synergistic effect. In this study, [Mn(CO)₃(bpy)L]X (bpy =2,2-bipyridyl; X?=?PF₆, SO₃CF₃, L?=?imidazole, N-methylimidazole, benzimidazole, N-benzylbenzimidazole, N-4-chlorobenzylbenzimidazole) complexes have been characterized electrochemically and related to CO-releasing properties. The molecules have been theoretically analyzed in terms of electronic transitions and spin-density plot in water, acetonitrile, and gas phase for having insight that promote CO-releasing and electroactivity characteristics. Antioxidant activity of the complexes has also been analyzed in order to gain a possible relationship with CO-releasing properties of the complexes.     

Synthesis,crystal structure,and luminescence of a quaternary binuclear europium complex [Eu2(phth)2(Hphth)2(phen)2(H2O)4]

A quaternary binuclear europium complex [Eu₂(phth)₂(Hphth)₂(phen)₂(H₂O)₄] (H₂phth?=?phthalic acid, phen?=?1,10-phenanthroline) has been synthesized. The structure was determined by X-ray crystallography which reveals that it is binuclear with each europium nine-coordinate. Intermolecular hydrogen bonds link the complex units to form a 3D supermolecular network. Its properties have been studied by means of luminescence spectrum and thermal analysis. Fluorescence spectra show that the complex exhibits strong red emission.     

Syntheses and characterization of nickel(II), zinc(II) and palladium(II) complexes derived from three pyrazole-based polydentate ligands

Two pyrazole-based polydentate ligands, 1,3-bis(5-methyl-3-phenylpyrazol-1-yl)-propan-2-ol (Hmppzpo) and 1,3-bis(5-methyl-3-p-isopropylphenylpyrazol-1-yl)-propan-2-ol (Hmcpzpo), have been synthesized. A third ligand, 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-2-ol (Hdmpzpo), has been synthetically modified. Seven new M(II) coordination compounds of general formula M₂L₂X₂ (M?=?Zn, Ni; X?=?NO₃ or ClO₄; L?=?dmpzpo, mppzpo or mcpzpo) or MLX (M?=?Pd; L?=?dmpzpo; X?=?Cl) were synthesized and structurally characterized by elemental analysis and FT-IR analysis. The crystal structures of [Zn₂(μ-dmpzpo-O,N,N′)₂(NO₃)₂]?·?2H₂O (1?·?2H₂O), [Ni₂(μ-dmpzpo-O,N,N′)₂(CH₃CN)₂](ClO₄)₂ (2) and Pd(μ-dmpzpo-N,N′)Cl₂ (4) were determined by single-crystal X-ray crystallography. The crystal structures show that complexes 1?·?2H₂O and 2 are center-symmetric dinuclear compounds, with two metal ions bridged by two alkoxo groups and each metal ion with a distorted square-pyramidal environment. The palladium complex, 4, displayed square-planar coordination geometry around the Pd(II) ion with trans arrangement.     

Thiophene series. XV The effect of leaving groups on the reactivity of nitro-activated thiophene derivatives with sodium thiophenoxide

The effect of leaving groups on the reactivity of 3-X-2-nitrothiophene (1), 2-X-3-nitrothiophene (II) and 2-X-5-nitrothiophene (III) (X = Cl, Br, I, OC₆H₄NO₂(p), SO₂C₆ H₅) with sodium thiophenoxide has been examined. The results show that the reactivity ratio kIII/kII is always greater than unity and is relatively uninfluenced by changing leaving groups compared to the ratio kI/kII. The ratio kI/kII is greater or smaller than unity, according to following patterns of leaving groups Examination of the reactivity of the three series of compounds having Cl, Br, I and C₆H₄NO₂(p) as leaving groups showed the absence of an “element effect” which indicates that in the transition states of these displacement reactions there is little breaking of the bond to the group being displaced.     

Reactivity of Nitroalkyl Anions Addition to Substituted Benzylidenecyanoacetates: Electrophilicity Parameters and Free Energy Relationships

The kinetics of the reactions of benzylidenecyanoacetates 1a–d (X = H, Me, OMe, and NMe₂) with nitroalkyl anions 2a–c have been studied in aqueous solution at 20°C. The second‐order rate constants are used to evaluate the electrophilicity parameter E of these series of Michael acceptors 1a–d according to the linear free enthalpy relationship log k (20°C) = s_N (E + N ). The measured E values were found to cover a domain of reactivity, ranging from −10.07 for the most reactive electrophile 1a (X = H) to −14.04 for the less electrophile 1d (X = NMe₂). Mayr's approach was found to correctly predict the rate constants for the reactions of these series of olefins 1a–d with the hydroxide ion in water and 50% water–50% acetonitrile at 20°C. Analysis of the kinetic measurements using the Brönsted relationship shows that β_nuc values remain remarkably constant for changes in the nature of the substituent X. A notable finding of this work is perhaps provided by the observed large changes in the electrophilicity parameter E on going from benzylidenecyanoacetates 1 to their analogues benzylidenemalonates 3 (ΔE ∼ 9.06–10.48), whereas the replacement of second CO₂Et group by the CN group in 1 to give benzylidenemalononitriles 4 has little effect on electrophilic reactivity, i.e., ΔE ∼ 0.65–0.95. This abnormal pattern in the E values has been attributed to the resonance interaction and salvation effects. On the other hand, the effect of benzylidenecyanoacetate substituents on the electrophilic reactivity was examined quantitatively on the basis of the electrophilicity parameter E , leading to linear correlation of E with Hammett–Brown substituent constants (). More importantly, the four electrophiles have comparable log k _o values, which are located at a relatively low level, i.e., log k _o ≤ 4–5, in the intrinsic reactivity scale.     

AC conductivity studies and relaxation behaviour in (LiX) y [(Li2O)0.6(P2O5)0.4](1 − y) glasses

The electrical conductivity of (LiX) _y [(Li₂O)_0.6(P₂O₅)_0.4]_(1???y) (X?=?Cl, Br, y?=?0, 0.1, 0.15, 0.2) glasses has been determined over a wide range of temperature and frequency by means of impedance spectroscopy. The real part of the frequency-dependent conductivity exhibits a simple power law feature, and the dimensionless frequency exponent n has been determined. The conductivity spectra show scaling behaviour when the conductivity spectra are scaled by ω/(σ _dc T) and ω/ω _p . The conductivity relaxation time and activation energy have been estimated from the modulus spectra. Increases of ionic conductivity values with addition of LiX content are in line with the decrease of activation energy and relaxation time.     

Bis(2-Amino-5-bromopyrimidinium) Tetrahalometallates: Crystal structures of (2-amino-5-bromopyrimidinium)2 MCl4 (M = Co,Zn)

The reactions of metal(II) chlorides and bromides with 2-amino-5-bromopyrimidine (2-abpm) in neutral and acidic solution were investigated. The reaction with ZnCl₂, ZnBr₂, CoCl₂, CoBr₂ and MnCl₂ in acidic nitromethane solution gave complexes of the formula (2-abpmH)₂MX₄ (1, M?=?Zn, X?=?Cl; 2, M?=?Zn, X?=?Br; 3, M?=?Co, X?=?Cl; 4, M?=?Co, X?=?Br; 5, M?=?Mn, X?=?Cl). Crystals of 1 and 3 suitable for single crystal X-ray diffraction were obtained. Crystal data: For (1): triclinic, P-1, a?=?6.2485(13), b?=?9.0520(14), c?=?15.334(4)?Å, α?=?94.81(2), β?=?95.224(17), γ?=?98.027(17)°, V?=?851.1(3)?ų, Z?=?2, R?=?0.0596 for [|I|?≥?2σ(I)]. For (3): triclinic, P-1, a?=?6.2438(13), b?=?9.0597(15), c?=?15.318(3)?Å, α?=?94.749(18), β?=?95.343(15), γ?=?98.021(17)°, V?=?850.2(3)?ų, Z?=?2, R?=?0.0452 for [|I|?≥?2σ(I) ]. Variable temperature magnetic susceptibility data indicates weak antiferromagnetic interactions in the cobalt and manganese complexes.