Spectral and magnetic behaviour of some nickel(II) and cobalt(II) complexes of triazene 1-oxides

Some new nickel(II) and cobalt(II) complexes of triazene 1-oxides derived from amino pyridines are reported. Experimental evidence shows that the nickel(II) complexes are planar in the solid state but exhibit a planar⇋pseudooctahedral equilibrium. The pseudooctahedral species for the (RPyCl)₂Ni complexes involves chloro coordination. In chloroform solution the equilibrium shifts substantially to the right compared to benzene solution for these complexes. In the corresponding cobalt(II) complexes, the chloro-coordination is complete and the complexes have a distorted octahedral symmetry in both solid and solution phases.     

Crystal structures and magnetic properties of nitroxide radical-coordinated copper(II) and cobalt(II) complexes

Transition Metal Chemistry - The crystal structures and magnetic properties of three coordination compounds constructed from various nitroxide radicals L and MII(hfac)2(H2O)2 building blocks...     

Crystal structure and magnetic properties of two isomeric three-dimensional pyromellitate-containing cobalt(II) complexes

The hydrothermal preparation, crystal structure determination, and magnetic study of two isomers made up of 1,2,4,5-benzenetetracarboxylate and high-spin Co(II) ions of formula [Co2(bta)(H2O)4]n x 2n H2O (1 and 2; H4bta = 1,2,4,5-benzenetetracarboxylic acid) are reported. 1 and 2 are three-dimensional compounds whose structures can be described as (4,4) rectangular layers of trans-diaquacobalt(II) units with the bta(4-) anion acting as tetrakis-monodentate ligand through the four carboxylate groups, which are further connected through other trans-[Co(H2O)2](2+) (1) and planar [Co(H2O)4](2+) (2) entities, with the bridging units being a carboxylate group in either the anti-syn (1) or syn-syn (2) conformations and a water molecule (2). The study of the magnetic properties of 1 and 2 in the temperature range 1.9-300 K shows the occurrence of weak antiferromagnetic interactions between the high-spin Co(II) ions, with the strong decrease of chi(M)T upon cooling being mainly due to the depopulation of the higher energy Kramers doublets of the six-coordinated Co(II) ions. The computed values of the exchange coupling between the Co(II) ions across anti-syn carboxylate (1) and syn-syn carboxylate/water (2) bridges are J = -0.060 (1) and -1.90 (2) cm(-1) (with the Hamiltonian being defined as H = -Jsigma(i,j)S(i) x S(j)). These values follow the different conformations of the carboxylate bridge in 1 (anti-syn) and 2 (syn-syn) with the occurrence of a double bridge in 2 (water/carboxylate).     

Synthesis and magnetic properties of μ-phenolato oxovanadium(IV), cobalt(II) and zinc(II) binuclear complexes

Three binuclear complexes, (VO)₂(L)OMe (1), Co₂(L)OEt·3/2H₂O (2) and Zn₂(L)OMe·H₂O (3) have been prepared, where H₃L is the binucleating ligand, 2,6-diformyl-4-methylphenol di(benzoylhydrazone). The magnetic susceptibilities of (1) and (2) were measured over the 4.2–300 K range and the observed data were fitted to the Bleaney-Bowers equation by the least-squares method, giving the exchange integral 2J = −358.5cm⁻¹ for (1) and 2J = −6.6cm⁻¹ for (2). This procedure indicates the existence of an antiferromagnetic interaction between the metals. TMC 2699     

Local surrounding of cobalt(II) in dithiocarbamate complexes,their magnetic and spectral properties

[Co(S₂CNRR’)₂] complexes [R = R’ = CH₃, C₂H₅, C₃H₇, C₄H₉, or CH₂C₆H₅; RR’ = (CH₂)₅, (CH₂)₆, or (CH₂)₂O(CH₂)₂] were prepared via interaction of CoCl₂ with sodium dithiocarbamates in aqueous medium (pH 6–7). [Co(S₂CNRR’)₂] are low-spin compounds (μ_eff 2.19–2.45 μ_B) with distorted square-planar geometry of the CoS₄ coordination node. The Co-S bonds length is 2.22–2.26 Å, and the distance between cobalt and carbon atoms is 2.73–2.74 Å.     

A comparative study of the structures, NMR properties and magnetic behaviour of complexes of cobalt(II) with octamethylpyrophosphoramide and nonamethylimidodiphosphoramide

The structure of the complex Co(NIPA)₃(ClO₄)₂ has been determined by X-ray diffraction analysis and found to be very close to that of the corresponding OMPA complex. The magnetic susceptibilities of the OMPA and NIPA complexes have been measured by a thermomagnetic method and have allowed the calculation of χ_| and χ, the susceptibilities along the principal axes of the complex. The magnetic properties of the isomorphous nickel compounds have been studied for comparison. Results give evidence for the greater magnetic anisotropy of the NIPA complexes.     

Synthesis and magnetic properties of binuclear cobalt(Ⅱ), nickel(Ⅱ) and copper(Ⅱ) complexes bridged by oxamidate group

Four binuclear Co(Ⅱ), Ni(Ⅱ) and Cu(Ⅱ) complexes bridged by oxamidate (oxd) group have been synthesized, namely Co2(byp)2(oxd)(ClO4)2 (1), Co2(Me2bpy)2(oxd)(ClO4)2.H2O (2), Ni2(bpy)2(oxd)(ClO4)2.2H2O (3) and Cu2(Me2bpy)2(oxd)(NO3)2 (4). (bpy=2,2'-bipyridyl, Me2-bpy=4,4'-dimethylbipyridyl, oxd=oxamidate) The complexes are characterized by IR, UV spectra, EPR and variable-temperature magnetic susceptibility (4-300 K). The susceptibility data for. complexes 1 and 3 were least-squares fit to the susceptibility equation derived from the spin Hamiltonian H=-2J . S1 . S2. The exchange integral, J, was found to be equal to -3.62 cm-1 in 1 and -1.82 cm-1 in 3. This indicates a weak antiferromagnetic spin exchange interaction between the metal ions.     

Structure and magnetism of mono-, di-, and trinuclear benzoato cobalt(II) complexes

Three cobalt(II) - benzoato (bz) complexes have been prepared and structurally characterized. In the mononuclear complex trans-[Co(bz)₂(H₂O)₂(nca)₂] the benzoato ligand is unidentate (nca = nicotinamide). The dinuclear complex [(μ₂-bz)₄{Co(qu)}₂] is a structural analog of the copper acetate (qu = quinoline) where four bidentate benzoato ligands link two cobalt(II) pentacoordinate centers. The trinuclear complex of the composition [Co₃(bz)₆(inca)₆] contains a central hexacoordinate {(bz)₂Co(inca)₂(bz)₂} unit in which the bidentate benzoato ligands held the central and peripheral cobalt(II) centers (inca = iso-nicotinamide); the peripheral hexacoordinate {(bz)Co(inca)₂<} units contain the terminal benzoato ligand in its bidentate function. The magnetic susceptibility data down to T = 2 K and the magnetization data up to B = 7 T reveal a considerable magnetic anisotropy due to the single-ion zero-field splitting.     

Mesomorphic behaviour and TSDC measurements of ortho-metallated palladium(II) and platinum(II) complexes with S,O-donor co-ligands

A series of ortho-metallated Pd and Pt complexes containing an imine ligand carrying three alkoxy chains and N-benzoylthiourea derivatives as co-ligands were prepared and their liquid crystalline properties investigated. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy, whereas thermal properties were investigated by differential scanning calotimetry and polarising optical microscopy. All the compounds exhibit monotropic transitions involving nematic and smectic A phases, with the mesomorphic behaviour strongly related to the type of N-benzoylthiourea as well as the metal centre used. The thermally stimulated depolarisation current technique was employed to determine the conduction mechanism, phase transition temperature and the activation energies for one of the ortho-metallated Pd complexes.     

Synthesis and thermal behaviour of morpholine complexes with cobalt (II) and manganese (II) thiocyanates

The 1 4 complexes of cobalt (II) and manganese (II) thiocyanates with morpholine (Morph), [M(NCS)₂(Morph)₄] (M=Co, Mn), were prepared and studied by means of thermogravimetry, derivative thermogravimetry and differential scanning calorimetry. By thermal treatment of the above compounds, the 12 and 11 complexes, [M(NCS)₂(Morph)₂] (M=Co, Mn; n=1, 2), were formed. Magnetic data, infrared and electronic spectra and molar conductance values for the compounds are reported. All the complexes contain N-bonded morpholine and the 14 complexes are suggested to have a monomericcis pseudooctahedral structure with N-bonded thiocyanate, whereas the 12 and 11 complexes are considered to have a six-coordinated polymeric configuration involving bridging NCS groups.

---

Zusammenfassung Mittels. Thermogravimetrie, Derivativthermogravimetrie und Differential-Scanning-Kalorimetrie wurden die zuvor dargestellten 14 Komplexe von Kobalt(II)- und Mangan(II)thiozyanaten mit Morpholin (morph) [M(NCS)₂(morph)₄] mit M=Co, Mn untersucht. Durch Erhitzen obiger Verbindungen entstehen die 12- bzw. 11-Komplexe [M(NCS)₂(morph)_n] mit M=Co, Mn undn=1, 2. Magnetisierungsdaten, Infrarot- und Elektronenspektren sowie die molare Leitfähigkeit der Verbindungen wurden ermittelt bzw. angegeben. Alle Komplexe enthalten N-gebundenes Morpholin. Die 14 Komplexe besitzen eine monomere cis-pseudooktaedrische Struktur mit N-gebundenem Thiozyanat, während die 12- und 11-Komplexe eine hexakoordinierte polymere Struktur mit NCS-Gruppenbrücken zu besitzen scheinen.

---

, (.) [(S)₂(.)₄]. [ (S)₂(.) _n ], =1 2. , , . . 14 ( : ) - N- . 121 11 - , .

---

---

The authors express their thanks to Dirección Regional de Universidad e Investigación de la Comunidad Autónoma de Murcia for providing financial assistance.     

Studies on the magnetic properties of two cobalt(II) complexes bearing 1,4-phenylenediacetate ligands

One reported compound [Co(PDA)(4,4′-bipy)]_n·nH₂O and one new compound [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O were prepared by the reactions of Co(NO₃)₂·6H₂O or Co(OH)₂ with 1,4-phenylenediacetic acid (H₂PDA) in the presence of the ancillary ligands 4,4′-bipyridine (4,4′-bipy) or imidazole (Im), and their magnetic properties were investigated. The presence of 4,4′-bipy in [Co(PDA)(4,4′-bipy)]_n·nH₂O results in a μ ₃-bridging mode of the PDA²⁻ ligand with one μ ₂-carboxylato group and one chelating carboxylato group and the construction of a 2D framework as reported in the literature. The introduction of Im ligand in [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O helps to construct a one dimensional chain with the two carboxylato groups of PDA²⁻ ligand in monodentate coordination modes. The magnetic studies reveal the presence of dominant antiferromagnetic interaction in [Co(PDA)(4,4′-bipy)]_n·nH₂O with a field-induced magnetic transition due to spin-flop. Magnetically, [Co(PDA)(Im)₂(H₂O)₂]_n·nH₂O presents a mononuclear structure. This work reveals that the introduction of ancillary ligands in the Co(II)-PDA system adjusts the linking modes of PDA²⁻ and therefore the resulting frameworks and their magnetic properties.     

Diazabutadiene cobalt(II) complexes

Summary Studies on the chelates of cobalt(II) with the bidentate ligands 1,4-diphenyl(2,3-dimethyl-1,4-diazabutadiene) (PMB) and 1,4-di(p-methoxyphenyl)-2,3-dimethyl-1,4-diazabutadiene (MPMB) have been carried out. On the basis of elemental analyses, the complexes are [Co(PMB)Cl₂], [Co(PMB)₂(C1O₄)₂], [Co(MPMB)Cl₂] and [Co(MPMB)₂(ClO₄)₂].Both ligands are bidentatevia nitrogen atoms in all the complexes. The magnetic susceptibility and i.r. and u.v.-visible spectra are reported and discussed. The chloro-compounds involving two chlorine ligands and, in the perchlorate compounds, the ClO ₄ ^– groups are bound to the cobalt(II) centre.     

Redox properties of cobalt(II) complexes with isoindoline-based ligands

Cobalt bis-(N-arylimino)isoindolinates undergo electrostatic interactions with DNA or react with alkyl hydroperoxides to form ketones and alcohols. Redox behavior of the metal center should affect such reactivities; therefore, six neutral Co^II(L)₂ complexes with L = bis-(N-arylimino)isoindolinates have been synthesized to elucidate the effect of the aryl substituents on the redox potential of the metal center. Redox properties of various M^II(L)₂ complexes (M = Mn, Fe, Co, Ni) are compared. Moreover, data are presented on the dismutation rates of superoxide radical anion (a knowingly sensitive reagent on the redox properties of the metal center) in the presence of the various Co^II(L)₂ complexes among identical conditions.     

Synthesis, structure and magnetic properties of oligometallic systems derived from di- and trinuclear copper(II) amido-oximate complexes

Three heterometallic complexes [M(H(2)O)(n)][Cu(3)L(2)(H(2)O)] (M = Mn(2+), Co(2+) or Ba(2+)) and one dinuclear compound (CuDien)(CuL{H(2)O}) were prepared by interaction of anionic compounds Cu(3)L(2)(2-) or CuL(2-) with the corresponding cations (H(4)L = 1,9-dicyano-1,9-bis(hydroximino)-3,7-diazanonane-2,8-dione; Dien = 1,5-diamino-3-azapentane). The complexes [M(H(2)O)(n)][Cu(3)L(2)(H(2)O)] have a polymeric structure, formed via oligomerization of Cu(3)L(2)(2-) units and additionally, in the case of the Ba-salt, by binding of Cu(3)L(2)(2-) units through Ba(2+). Antiferromagnetic interactions occur in all the complexes, while for [Co(H(2)O)(6)][Cu(3)L(2)(H(2)O)] there is evidence of some ferromagnetic ordering at low temperatures. The values of J are lower in magnitude than for similar, previously reported systems, which is attributed to the electron-withdrawing effect of the ligand cyano groups.     

Synthesis,structures and magnetic properties of copper (II) and cobalt (II) complexes containing pyridyl-substituted nitronyl nitroxide and 3,5-dinitrobenzoate

Four new metal-radical complexes - [Cu(NIT3Py)₂(DTB)₂] 1, [Co(NIT3Py)₂(DTB)₂(CH₃OH)₂] 2, [Cu(NIT4Py)₂(DTB)₂(H₂O)₂] 3, [Co(NIT4Py)₂(DTB)₂(H₂O)₂] 4, (NIT3Py = 2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], NIT4Py = 2-(4^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], DTB = 3,5-dinitrobenzoic anion) have been synthesized by using transition metal ions, nitronyl nitroxide radicals as spin carriers, and incorporating 3,5-dinitrobenzoic acid (DTB) as a coligand.     

Cymantrenecarboxylate complexes of nickel(II) and cobalt(II)

Reactions of cymantrenecarboxylic acid (CO)₃MnC₅H₄COOH (CymCOOH) with Ni(II) and Co(II) pivalates in boiling THF followed by extraction of the products with diethyl ether or benzene and treatment with triphenylphosphine gave the binuclear complexes LM(CymCOO)₄ML (M = Ni (I) and Co (II); L = PPh₃). Treatment of the benzene extract of the intermediate cobalt cymantrenecarboxylate with 2,6-lutidine (L’) yielded the trinuclear complex L’Co(CymCOO)₃Co(CymCOO)₃CoL’ (III). Complex I is antiferromagnetic; μ_eff decreases from 3.7 to 0.9 μ_B in a temperature range from 300 to 2 K. Structures I-III were identified using X-ray diffraction. The frameworks of complexes I and II are like Chinese lanterns, having four carboxylate bridges and axial ligands L (Ni-P, 2.358(1) Å; Co-P, 2.412(2) Å). The metal atoms are not bonded to each other (Ni…Ni, 2.7583(9) Å; Co…Co, 2808 (2) Å). In complex III, either terminal Co atom is coordinated to one ligand L’ (Co-N, 2.059(2) Å). The Co atoms form a linear chain showing no M-M bonds (Co…Co, 3.346(1) Å), in which either terminal Co atom is linked with the central Co atom by three carboxylate bridges (on average, Co_centr-O, 2.164 Å; CO_term-O, 2.094 Å). In one of three carboxylate groups, only one carboxylate O atom serves as a bridge, while the other is bonded to the terminal Co atom only (Co_term-O, 2.094 and 2.389 Å); so this carboxylate group is a bridging and chelating ligand.