Structures and magnetic properties of dicopper(II) and dinickel(II) complexes with end-on azido bridges

An asymmetric single EO azido bridged dinuclear copper(II) complex, [Cu₂(dmterpy)₂(μ-1,1-N₃)(N₃)₂] · NO₃ · (H₂O)₂1 [dmterpy = 5,5″-dimethyl-2,2′:6′,2″-terpyridine], and a double EO azido bridged dinuclear nickel(II) complex, [Ni₂(pbdiim)₄(μ-1,1-N₃)₂] · 2(N₃) · 6(H₂O) 2 [pbdiim = 2-(2′-pyridyl)benzo[1,2-d:4,5-d′]diimidazole], have been synthesized and characterized structurally and magnetically. Compound 1 consists of a single EO azido bridged Cu^II dimer in which each Cu^II ion is five-coordinated in the form of a distorted square-based pyramid. The N_(μ−1,1) atom holds on the apical position of one Cu^II pyramid with an elongated bond length of 2.305 Å and on the basal plane of another distorted Cu^II pyramid with a bond length of 1.991 Å. The Cu-N_(μ−1,1)-Cu angle is 117.4 (2)°. The copper(II) dimer forms a 1 D zig-zag chain via hydrogen bondings between azide ions, water molecules and the nitrate anion. Compound 2 consists of a double EO azido bridged Ni^II dimer with the Ni-N_(μ−1,1)-Ni bond angle of 102.96 (13)°. The coordination geometry of Ni^II is octahedral. Their magnetic properties have been measured in the range from 300 to 2 K and correlated with the molecular structures. Compound 1 shows weak ferromagnetic interactions within the copper(II) dimer (J = 2.88 cm⁻¹), despite the large EO azide bridge angle (117.4 (2)°). The intramolecular coupling between the Ni^II (S = 1) ions in compound 2 was found to be ferromagnetic (J = 27.87 cm⁻¹).     

Syntheses, crystal structures and magnetic properties of trinuclear and [3 × 1 + 1 × 2] pentanuclear complexes derived from a compartmental ligand: Role of solvent on nuclearity and number of components

Reaction of [Cu^IIL⊂(H₂O)] (H₂L = N,N′-ethylenebis(3-ethoxysalicylaldimine)) with nickel(II) perchlorate in 1:1 ratio in acetone produces the trinuclear compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂ (1). On the other hand, on changing the solvent from acetone to methanol, reaction of the same reactants in same ratio produces the pentametallic compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)]·2MeOH (2A), which loses solvated methanol molecules immediately after its isolation to form [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)] (2B). Clearly, formation of 1 versus 2A and 2B is solvent dependent. Crystal structures of 1 and 2A have been determined. Interestingly, compound 2A is a [3 × 1 + 1 × 2] cocrystal. The cryomagnetic profiles of 1 and 2B indicate that the two pairs of copper(II)···nickel(II) ions in the trinuclear cores in both the complexes are coupled by almost identical moderate antiferromagnetic interaction (J = −22.8 cm⁻¹ for 1 and −26.0 cm⁻¹ for 2B).     

Synthesis, crystal structures and magnetic studies of terephthalato- and fumarato-bridged dinickel(II) complexes with tripodal poly-benzimidazole ligand

Two novel dinuclear nickel(II) complexes [Ni₂(ntb)₂(μ-tp)(H₂O)_1.61(CH₃OH)_0.39](NO₃)₂·5.13CH₃OH·2.25H₂O (1) and [Ni₂(ntb)₂(μ-fum)(H₂O)(CH₃OH)](NO₃)₂·6CH₃OH·H₂O (2) (tp = terephthalate dianion, fum = fumarate dianion, ntb = tris(2-benzimidazolylmethyl)amine) containing tetradentate poly-benzimidazole ligand were synthesized and structurally characterized by IR spectra, UV-Vis, elemental analysis and X-ray crystallography. The Ni(II) ions in 1 and 2 have distorted octahedral geometry with four nitrogen atoms of ntb, one oxygen atom of water and one oxygen atom supplied by the carboxylate group of the bridged dicarboxylato ligand. Complexes 1 and 2 consist of terephthalato- and fumarato-bridged dinickel(II) centers in bis(monodentate) bonding fashion. The Ni?Ni distances are 11.333 Å for 1 and 8.966 Å for 2. The magnetic susceptibility measurements at variable temperature show that two complexes exhibit weak antiferromagnetic interactions between nickel(II) ions with J values of −0.25 cm⁻¹ and −0.36 cm⁻¹, respectively.     

Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties

Three new coordination compounds, [Ni(Pht)(Py)₂(H₂O)₃] (1), [Ni(Pht)(β- Pic)₂(H₂O)₃] · H₂O (2) and [Ni(Pht)(1-MeIm)₂(H₂O)₃] (3) (where Pht²⁻ = dianion of o-phthalic acid; Py = pyridine, β-Pic = 3-methylpyridine, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy and thermogravimetric analysis. Crystallographic studies 1-3 reveal that each Ni(II) center has a distorted octahedral geometry being coordinated by two nitrogen atoms of aromatic amines, one oxygen atom from a carboxylate group of a phthalate ligand and three water molecules. Pht²⁻ anions act as monodentate ligands, while the remaining uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonding. The uncoordinated oxygen atoms form hydrogen bonds with the coordinated water molecules from adjacent complexes creating a centrosymmetric dimer unit. Further, these dimer units are connected by O-H?O hydrogen bonds in double-chains. Depending on the nature of aromatic amines, the arrangement of these double-chains differs. The double-chains are held together only by van der Waals interactions in 1. In contrast, in 2 these chains form layers by π-π interactions between antiparallel molecules of β-Pic as well as by π-π interactions between β-Pic and Pht aromatic rings. In complex 3, the double-chains are knitted together via C-H?O hydrogen bonds between the methyl group of 1-MeIm and the coordinated carboxylate oxygen atom of Pht, as well as π-π contacts involving antiparallel 1-MeIm cycles. The thermal dependence of the magnetic susceptibilities for compounds 1 and 2 shows a weak antiferromagnetic interaction between the two Ni²⁺ ions of the hydrogen bonded dimers. For compound 3, a ferromagnetic interaction could be observed. Modeling the experimental data with MAGPACK resulted in: g = 2.22, |D| = 4.11 cm⁻¹ and J = −0.29 cm⁻¹ for compound 1, g = 2.215, |D| = 3.85 cm⁻¹ and J = −0.1 cm⁻¹ for compound 2 and g = 2.23, |D| = 4.6 cm⁻¹ and J = 0.22 cm⁻¹ for compound 3.     

Dinuclear terephthalato-bridged nickel(II) complexes. Structural characterization and magnetic properties

The dinuclear terephthalato-bridged nickel(II) complexes [Ni₂(cyclen)₂(μ-tp)](ClO₄)₂ (1) [Ni₂(trpn)₂(μ-tp)(H₂O)₂](ClO₄)₂ (2) and [Ni₂(3,3,3-tet)₂(μ-tp)(H₂O)₂](ClO₄)₂ · 2H₂O (3), where tp = terephthalate dianion, cyclen = 1,4,7,10-tetraazacyclododecane, trpn = tris(3-aminopropyl)amine and 3,3,3-tet = 1,5,9,13-tetraazatridecane, were synthesized and structurally characterized by X-ray crystallography. Their magnetic susceptibilities were also determined at variable temperatures over the range 2-300 K. The structures of these complexes consist of μ-tp bridging two Ni(II) centers in a bis(bidentate) bonding fashion in 1 and in bis(monodentate) bonding fashion in 2 and 3. The coordination geometry around the Ni(II) ions in these compounds has a distorted octahedral geometry with four nitrogen atoms from the amine ligand (cyclen, trpn or 3,3,3-tet) and two coordinated oxygen atoms supplied by the chelated carboxylate group of the bridged terephthalate ligand in 1, and by one tp-carboxylate-oxygen in 2 and 3. The sixth coordination site in the last two complexes 2 and 3 is achieved via an oxygen atom from a coordinated water molecule. The intradimer Ni…Ni distances in these complexes are 10.740, 11.428 and 11.537 Å for 1, 2 and 3, respectively. The electronic spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Ni(II) centers. Also, the analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(bidentate) and bis(monodentate) coordination modes for the bridged terephthalate ligand in 1, 2 and 3, respectively. Despite the different coordination modes of the tp bridging ligand in these complexes, they all exhibit very weak antiferromagnetic coupling. The coupling constants J were found to be −2.2, −0.6 and −1.5 cm³ K mol⁻¹ for the complexes 1, 2 and 3, respectively. The structural and magnetic results of 1-3 are discussed in relation to the other related published μ-terephthalato dinuclear Ni(II) compounds.     

Synthesis, structure, and magnetic properties of dinuclear nickel(II) complexes with a phenol-based dinucleating ligand with four methoxyethyl chelating arms

Dinuclear nickel(II) complexes [Ni₂(bomp)(MeCO₂)₂]BPh₄ (1) and [Ni₂(bomp)(PhCO₂)₂]BPh₄ (2) were synthesized with the dinucleating ligand 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenol [H(bomp)]. X-Ray analysis revealed that the complex 1 · 0.5CHCl₃ contains two nickel(II) ions bridged by phenolic oxygen and two acetate groups, forming a μ-phenoxo-bis(μ-acetato)dinickel(II) core. Electronic spectra were investigated for 1 and 2 in the range of 400-1800 nm, and the data were typical for the octahedral high-spin nickel(II) complexes. Obtained spectral components were well simulated based on the angular overlap model assuming the trigonally distorted octahedral geometry. Magnetic susceptibility was measured for 1 and 2 over a temperature range of 4.5-300 K. The optimized magnetic data were J = 1.75 cm⁻¹, zJ′ = −0.234 cm⁻¹, g = 2.21, D = 15.1 cm⁻¹, and TIP = 370 × 10⁻⁶ cm⁻¹ for complex 1 and J = 3.55 cm⁻¹, zJ′ = −0.238 cm⁻¹, g = 2.23, D = 21.8 cm⁻¹, and TIP = 470 × 10⁻⁶ cm⁻¹ for complex 2. The data revealed ferromagnetic interactions between the two nickel(II) ions.     

Structures, magnetic properties, and XPS of one-dimensional cyanide-bridged Cu-Ni/Pt bimetallic assembly complexes

Synthesis, crystal structures, and spectroscopic and magnetic properties of new one-dimensional cyano-bridged bimetallic complexes, [Cu^II(N-Eten)₂][M^II(CN)₄] (N-Eten = N-ethylethylenediamine; M^II = Ni^II (1) and Pt^II (2)), have been reported. Both complexes consist of one-dimensional alternate chains of Cu^II and M^II moieties. The Pt-C bond distances of 1.997(3) and 2.001(3) Å for 2 are considerably longer than the Ni-C bond lengths of 1.866(3) and 1.872(3) Å for 1. Because of pseudo Jahn-Teller distortion, the axial Cu-N bond distances of 2.554(2) and 2.550(3) Å for 1 and 2 are longer than those of equatorial ones of 2.008(2) and 2.056(2) Å for 1 and 2.010(2) and 2.054(2) Å for 2. In contrast to M^II-C bond distances, the Cu-N ones of 1 are similar to those of 2 regardless of element-substitution. These complexes indicate weak antiferromagnetic interactions with Weiss constants = − 4.68 and −3.95 K for 1 and 2, respectively. The emission spectrum of 2 (λ_ex = 360 nm) exhibits a broad band with peaks at 22 800 and 24 000 cm⁻¹ at 298 K. The Cu 2p_1/2 and 2p_3/2 peaks of XPS spectra are compared systematically to various copper(II) complexes showing different bridging features or distorted coordination geometries as models for excited structures induced by external physical conditions. The spectroscopic properties are discussed from the viewpoint of magneto-optical properties.     

Coordination chemistry of pyrazolylbis((alkylthio)methyl)borates: Hybrid nitrogen and sulfur donor ligands

The synthesis of iron(II), cobalt(II) and nickel(II) complexes supported by chelating borate ligands containing one pyrazole and two thioethers, phenyl(pyrazolyl)bis((alkylthio)methyl)borates, [Ph(pz)Bt^R], is described. The six-coordinate complexes [Ph(pz)Bt]₂M, M = Fe (1Fe), Co (1Co) and Ni (1Ni), form exclusively the cis isomers as confirmed by X-ray diffraction analyses. Whereas 1Co and 1Ni are high spin, 1Fe exhibits a room temperature magnetic moment, μ_eff = 4.1 μ_B, consistent with spin-crossover behavior. Quantitative analysis of the electronic spectrum of 2Ni leads to a value of D_q = 1086 cm⁻¹, reflective of a ligand field strength somewhat weaker than those imposed by the related tridentate borate ligands Tp or PhTt. Replacement of the methylthioether substituent with the sterically more demanding tert-butylthioether leads to the isolation of [Ph(pz)Bt^tBu]MX, M = Co, X = Cl (2Co); M = Ni, X = Cl (2Ni) or acac (3). The solid state structures of 2Co and 2Ni are chloride-bridged dimers. Additional high-spin cobalt(II) complexes, accessible under distinct preparative conditions, [κ²-Ph(pzH)Bt^tBu] CoCl₂·THF (4) and [κ²-Ph(pz)Bt^tBu]₂Co (5), have been fully characterized.     

Solution and solid-state complexes of the potentially tetradentate pyridyl-thiazole ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine with Co, Ni, Cu, Cd, Hg, Cu and Ag

Reaction of the potentially tetradentate N-donor ligand 6,6′-bis(4-methylthiazol-2-yl)-2,2′-bipyridine (L¹) with the transition metal dications Co^II, Ni^II, Cu^II, Cd^II and Hg^II results in the formation of mononuclear [M(L¹)]²⁺ complexes, in which a planar ligand coordinates to the metals via all four N-donors. In contrast, reaction of L¹ with Cu^I and Ag^I monocations, affords dinuclear double stranded helicate species [M₂(L¹)₂]²⁺ (where M = Cu^I or Ag^I), in which partitioning of the ligand into two bis-bidentate pyridyl-thiazole chelating units allows each ligand to bridge both metal centres. X-Ray crystallography, electrospray mass spectroscopy and NMR spectroscopy reveal that the complexes [M_n(L¹)_m]^z+ (where n = 1, m = 1 and z = 2, when M = Co^II, Ni^II, Cu^II, Cd^II and Hg^II; n = 2, m = 2 and z = 2, when M = Cu^I), retain their solid-state structures in solution. Conversely, whilst ¹H NMR studies suggest that combination of equimolar amounts of Ag(X)(where ) and L¹ (in either nitromethane or acetonitrile) results in the formation of a helicate in solution, in the solid-state, an anion-templating effect gives rise to either mononuclear or dinuclear helicate structures [Ag_n(L¹)_n][X]_n (where n = 2 when X = OTf⁻; n = 1 when ).     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

3D hydrogen bonded heteronuclear Co, Ni, Cu and Zn aqua complexes derived from dipicolinic acid

The heteronuclear water-soluble and air-stable compounds [M(H₂O)₅M′(dipic)₂] · mH₂O (M/M′ = Cu^II/Co^II (1), Cu^II/Ni^II (2), Cu^II/Zn^II (3), Zn^II/Co^II (4), Ni^II/Co^II (5), m = 2-3; H₂dipic = dipicolinic acid) have been prepared by self-assembly synthesis in aqueous solution at room temperature, and characterized by IR, UV-Vis and atomic absorption spectroscopies, elemental and X-ray diffraction single crystal (for 1 and 2) analyses. 1-5 represent the first examples of heteronuclear dipicolinate compounds with 3d metals. Extensive H-bonding interactions involving all aqua ligands, dipicolinate oxygens and lattice water molecules further stabilize the dimetallic units by linking them to form three-dimensional polymeric networks.     

The effects of point of substitution on the electrochemical behavior of new manganese phthalocyanines, tetra-substituted with diethylaminoethanethiol

The syntheses and comparative studies of the spectral, voltammetry and spectroelectrochemical properties of new manganese phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral positions (complex 3b) are reported. Solution electrochemistry of complex 3a showed quasi-reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.07 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.78 V vs. Ag|AgCl) reductions, but no ring-based oxidation. However, complex 3b showed weak irreversible ring-oxidation signal (E_p = +0.86 vs. Ag|AgCl). Reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.04 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.68 V vs. Ag|AgCl) reductions were also observed for complex 3b. Spectroelectrochemistry was used to confirm these processes. Reduction process involving the metal (Mn^IIIPc⁻²/Mn^IIPc⁻²) was associated with the formation of manganese μ-oxo complex in complex 3a.     

Copper(II) complexes derived from tripodal tris[(2-ethyl-(1-pyrazolyl)]amine

Three mono-nuclear copper(II) complexes [Cu(tepza)X]ClO₄ (X = Cl, 1; X = NCS, 2; X = dca, 3) and two dinuclear bridging complexes [Cu₂(tepza)₂(μ-C₄O₄)](ClO₄)₂·H₂O(4) and [Cu₂(tepza)₂(μ-C₅O₅)](ClO₄)₂(5) where tepza = tris[2-ethyl(1-pyrazolyl)]amine, dca = dicyanamide, C₄O₄²⁻ = 3,4-dihydroxycyclobut-3-ene-1,2-dionate (squarate dianion) and C₅O₅²⁻ = 4,5-dihydroxycyclopent-4-ene-1,2,3-trionate (croconate dianion) were synthesized and structurally characterized by IR and UV-Vis spectroscopy as well as by single X-ray crystallography. In the solid state, the geometry of copper(II) centers in these complexes are as follows: close to SP in 2, distorted TBP in 3, predominant SP in 4, and distorted octahedral in 5, whereas in solution distorted SP geometry was generally found. The squarato and the croconato dianions in complexes 4 and 5 are bridging the two copper(II) centers in cis-bis-monodentate and bis-bidentate bonding modes, respectively. Magnetic susceptibility measurements at variable temperatures (2-300 K) reveal the weak antiferromagnetic coupling in the two bridging dinuclear complexes 4 (J = −24.9 cm⁻¹) and 5 (J = −3.1 cm⁻¹).     

Three trinuclear Cu-M-Cu (M = Co, Ni and Zn) complexes including macrocyclic oxamido bridge: Synthesis, structures and magnetic properties

Based on the complex ligand (CuL H2L = 2,3-dioxo-5,6:15,16-dibenzo-1,4,8,13-tetraazacyclotetradeca-7,13-diene), which includes macrocyclic oxamido bridge, three trinuclear complexes were prepared. They are of the formula [(CuL)₂M(ClO₄)₂] (M = Co(1), Ni(2)) and [(CuL)₂Zn(CH₃OH)₂] · (ClO₄)₂ (3). The crystal structures of the three complexes have been determined and the M(II) of the three complexes all exist on the mirror plane. Complex 1 is the first Cu-Co complex bridged by oxamido. Their magnetic properties were studied by susceptibility versus temperature measurement, the best fitting of the experimental data led to J = −28.12 cm⁻¹ for 1, J = −42.88 cm⁻¹ for 2, and J = −2.13 cm⁻¹ for 3.     

Synthesis, crystal structures and magnetic characterization of heterodinuclear CuGd and CuTb Schiff base complexes

Preparation, crystal structures and magnetic properties of new heterodinuclear Cu^IIGd^III (1) and Cu^IITb^III (2) complexes [CuLn(L)(NO₃)₂(H₂O)₃MeOH]NO₃·MeOH (where Ln = Gd, Tb) with the hexadentate Schiff-base compartmental ligand N,N′-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine (H₂L = C₁₉H₂₀N₂O₄Br₂) (0) have been described. Crystal structure analysis of 1 and 2 revealed that they are isostructural and form discrete dinuclear units with dihedral angle between the O1Cu1O2 and O1Gd1/Tb1O2 planes equal to 2.5(1)° and 2.6(1)°, respectively. The variable-temperature and variable-field magnetic measurements indicate that the metal centers in 1 and 2 are ferromagnetically coupled (J = 7.89 cm⁻¹ for 1). Crystal and molecular structure of the Schiff base ligand (0) has been also reported. The complex formation changes the conformation of Schiff base ligand molecule.     

Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

Synthesis, structure, sorption and magnetic properties of Ni(II) and Cu(II) complexes with thiosemicarbazone of 2-hydroxybenzaldehyde, bridged by 4,4′-bipyridine

(ML)₂(bipy) complexes (LH₂ = thiosemicarbazone of 2-hydroxybenzaldehyde, bipy = 4,4′-bipyridine, M = Ni(II), 1, or Cu(II), 2) were synthesized and characterized by X-ray crystallography. Compound 1 possessed porous structure due to peculiarities of crystal packing, whereas 2 formed infinite zig-zag chains with dense non-porous packing. It was shown that 1 absorbed 0.013 cm³/g of methanol vapor in two steps. Complex 1 was diamagnetic; for 2, the dependency of χ versus T could be interpreted by Bleaney-Bowers expression in 20-300 K temperature range (J = −6.8 cm⁻¹, g = 2.07).     

Synthesis, characterization, and magnetic study of pyrazine bridged polymeric complexes of copper(II)

The synthesis, structural characterization and magnetic property of two new coordination polymers [Cu(pyz)(μ-CH₃CO₂)₄]_n (1) and [Cu(pyz)(μ-CCl₃CO₂)₄]_n (2) (pyz = pyrazine) are reported. Here, the carboxylato bridged two dinuclear copper(II) complexes are linked through pyrazine giving a 1-D alternating chain. The magnetic property of the complexes indicates a significant difference originated from the introduction of electron withdrawing substituent on the bridging dicarboxylate. Complex 1 exhibits strong antiferromagnetic interactions with J = −344.61 cm⁻¹, whereas 2 exhibits comparatively less strong antiferromagnetic coupling with J = −238.53 cm⁻¹.     

Pseudohalide-bridged five-coordinate Ni(II) or Co(II) complexes with bulky bidentate ligands: Magneto-structural correlationship

Bidentate ligands 2,2′-biquinoline (biq) and 6,6′-dimethyl-2,2′-bipyridine (dmbpy) with steric hindrance substituents cis to the nitrogen atoms have been used in the synthesis of transition metal complexes. Six new doubly end-on azido-bridged binuclear complexes [M₂(biq)₂(μ_1,1-N₃)₂(N₃)₂] (M = Ni (1), M = Co (2)), [M₂(biq)₂(μ_1,1-N₃)₂Cl₂] (M = Ni (3), M = Co (4)), [M₂(dmbpy)₂(μ_1,1-N₃)₂(N₃)₂] (M = Ni (5), M = Co (6)) and one end-to-end thiocyanato-bridged polymeric [Ni(dmbpy)(μ_1,3-SCN)(NCS)]_n (7) have been synthesized and characterized by single crystal X-ray diffraction analysis and magnetic studies. Complexes 1-6 comprise five-coordinate M(II) ions bridged by two end-on azide ligands. The bridging M-N-M bond angles are in the small range 104.1-105.2°. Complex 7 consists of a singly thiocyanate-bridged Ni(II) chain in which Ni(II) ions are five-coordinate. This research suggests that the bulky ligands play a key role in the formation of five-coordinate coordination structure. All complexes display intramolecular intermetallic ferromagnetic coupling with J_NiNi and J_CoCo of ca. 23 or 13 cm⁻¹ based on the Hamiltonian (S₁ = S₂ = 1 for Ni₂, or 3/2 for Co₂). The singly SCN⁻-bridged chainlike complex 7 shows intrachain ferromagnetic interaction with J = 3.96(2) cm⁻¹ and D = −4.55(8) cm⁻¹ (. Magneto-structural correlationship has been investigated.     

Preparation and characterization of macrocyclic dinickel complexes coligated by monoalkyl- and dialkylcarbamates

The dinuclear nickel(II) complex [Ni₂L(Cl)]⁺ (1), where (L)²⁻ represents a 24-membered binucleating hexamine-dithiophenolate ligand, reacts readily with primary and secondary amines RR′NH in the presence of CO₂ (1 bar) to give dinuclear monoalkyl- and dialkylcarbamate complexes [Ni₂L(O₂CNRR′)]⁺ (R = H, R′ = CH₂Ph (2), R = H, R′ = n-Bu (3), R = H, R′ = n-Oct (4), R = H, R′ = CH₂CH₂OH (5), R = R′ = Et (6), and R = R′ = CH₂CH₂OH (7)). Complexes 2-7 can also be prepared by the reaction of 1 with CO₂(air)/amine. The carbamate complexes are hydrolyzed in methanolic solution to give the known alkylcarbonate complex [Ni₂L(O₂COMe)]⁺ (8). These conversions are less rapid than the transesterification reactions of 8, due to a less electron-demanding carboxyl C(carbamate) atom. All new complexes were either isolated as perchlorate or tetraphenylborate salts and fully characterized by elemental analysis, UV/Vis, and IR spectroscopy. The structures of 2[BPh₄] and 7[BPh₄] have also been determined by X-ray crystallography. They confirm the presence of μ_1,3-bridging alkylcarbamate units in the products.