Phenoxo Oxygen Atoms Research Articles

Mono, di and trinuclear photo-luminescent cadmium(II) complexes with N2O and N2O2 donor salicylidimine Schiff bases: Synthesis, structure and self assembly

Four new octahedral cadmium(II) complexes, [(Cd)(L1)(HL1)](ClO4) (1), [Cd2(L2)2(SCN)2(CH3OH)2] (2), [(CdL3)3(μ-1,1,1-OH)](ClO4)2 (3) and [Cd2(L4)2(SCN)(NO3)] (4) have been synthesized using four Schiff bases, HL1, HL2, HL3 and HL4, (where HL1=2-(2-(ethylamino)ethyliminomethyl)phenol, HL2=2-(2-(dimethylamino)ethyliminomethyl)-4-bromophenol, HL3=2-(2-(diethylamino)ethyliminomethyl)-6-methoxyphenol and HL4=2-(2-(ethylamino)ethyliminomethyl)-6-methoxyphenol). All four complexes have been characterized by elemental and spectral analysis and structures have been confirmed by single crystal X-ray diffraction studies. Complex 1 is a mononuclear cationic bis-ligand complex. Complex 2 features a double end-to-end thiocyanate bridged dinuclear cadmium(II) complex. Complex 3 has a partial cubane [Cd3O4] core in which three [CdL3] subunits are interconnected through two types of oxygen bridges afforded by phenoxo oxygen atoms of ligands and a central hydroxo group. Complex 4 has a double phenoxo bridged dinuclear structure. Supramolecular interactions in all four complexes were also explored. All four complexes show fluorescence.

Cyanide- and Phenoxo-Bridged Heterobimetallic Fe(III)-Mn(III) Coordination Polymer: Synthesis, Crystal Structures and Magnetic Properties

Two two-dimensional cyanide- and phenoxo-bridged heterometallic M(II)-Mn(III) (M = Ni, Pd) coordination polymers <TEX>$\{[Mn(saltmen)]_4[Ni(CN)_4]\}(ClO_4)_2{\cdot}CH_3OH{\cdot}H_2O$</TEX> (1) and <TEX>$\{[Mn(saltmen)]_4[Pd(CN)_4]\}(ClO_4)_2{\cdot}CH_3CN{\cdot}H_2O$</TEX> (2) (<TEX>$saltmen^{2-}$</TEX> = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneaminato)dianion) have been obtained by using <TEX>$K_2[M(CN)_4]$</TEX> as building blocks and a salen-tpye Schiff-base manganese(III) compound as assembling segment. Single X-ray analysis reveals their isostrutural cyanide-bridged <TEX>$MMn_4$</TEX> pentanuclear cationic structure. The four Schiff base manganese units of the pentanuclear entity are self-complementary through the phenoxo oxygen atoms from the neighboring complex, therefore forming cyanide- and phenoxo-bridged 2D sheet-like structure. Investigation over magnetic susceptibilities reveals the overall ferromagnetic coupling between the adjacent Mn(III) ions bridged by the phenoxo oxygen atoms with J = 2.13 and <TEX>$2.21cm^{-1}$</TEX> for complexes 1 and 2, respectively.

Synthesis, crystal structure, spectral properties and catalytic activity of binuclear copper(II), mononuclear nickel(II) and cobalt(III) complexes containing Schiff base ligand

Newly designed tridentate ligand, HL 1 derived from 2-(benzylthio)aniline and 2-hydroxy-1-naphthaldehyde, upon reaction with Cu(II), Ni(II) and Co(III) nitrate separately in methanol yielded binuclear Cu(II) complex, [Cu2(L)2(NO3)2] 2, and mononuclear [Ni(L)2] 3 and [Co(L)2](NO3) 4 which were characterized by spectral data and authenticated by single crystal X-ray diffraction of 2 and 3. The diffraction analysis revealed that the ligand binds to metals in (O, N, S) fashion. Single crystal X-ray diffraction studies confirmed that the [Cu2(L)2(NO3)2] complex consist of centrosymmetric binuclear entities containing square-pyramidal copper(II) ions bridged through the phenoxo oxygen atoms. The emission and redox properties of both the ligand and corresponding complexes were examined. The redox property of the complexes has been qualitatively explained by single point DFT calculations. The catalytic activities of Cu(II) complex [Cu2(L)2(NO3)2] towards oxidation of benzyl alcohol derivatives to carbonyl compounds was tested using H2O2 as the oxidant.

Exploration of heterometallic systems containing silver(I) in acyclic Schiff base ligands: Finite and infinite self-assemblies as a result of silver(I)–carbon bond and silver(I)⋯silver(I) interaction

The work in this report describes the syntheses and crystal structures of nine copper(II)–silver(I) compounds derived from some single-compartment N(imine)2O(phenoxo)2 or double-compartment N(imine)2O(phenoxo)2–O(phenoxo)2O(methoxy/ethoxy)2 acyclic Schiff base ligands. The nine compounds are [{CuII(ClO4)Lsal–enAgI}2{CuII(ClO4)Lsal–enAgI(H2O)}]n (1), [CuIILsal–pnAgI(ClO4)]n (2), [{CuIILsal–pnAgI(NO3)}2] (3), [(CuIILacpn–en)2AgI(MeCN)2](ClO4) (4), [{CuIILOMe–enAgI(NO3)}2] (5), [{CuIILOMe–pnAgI(NO3)}2] (6), [{CuIILOMe–pnAgI(NO3)}2]·2H2O (7), [{CuIILOEt–enAgI(NO3)}2] (8) and [{CuIILOEt–opAgI(MeOH)}2](ClO4)2 (9), where the superscripts in the ligand symbols mean the following: (i) sal, acpn, OMe and OEt indicate that the aldehyde counterpart is salicylaldehyde, 2-hydroxyacetophenone, 3-methoxysalicylaldehyde and 3-ethoxysalicylaldehyde, respectively; (ii) en, pn and op indicate that the diamine counterpart is ethylenediamine, 1,3-diaminopropane and o-phenylenediamine, respectively. Copper(II) in all these compounds occupies a N2O2 compartment and the two phenoxo oxygen atoms in all cases bridge one copper(II) and one silver(I) centers. Compound 4 is a trinuclear CuIIAgICuII system. Compounds 3 and 5–9 are dimer-of-dinuclear compounds, in which the dimerization takes place due to interdinuclear Cu–O(nitrate) and Ag⋯Ag interactions in 3, 5 and 6 and due to Ag–π (η1-/η2-) bonds in 7–9. Compounds 2 and 1 are one-dimensional coordination polymers due to Ag–π (η2-)/Ag–π (η3-) bonds. CSD search/analysis reveals some definite significant aspects in both the Ag–π and Ag⋯Ag bonded systems in the present investigation.

Abrupt Spin Transition with Thermal Hysteresis of Iron(III) Complex [FeIII(Him)2(hapen)]AsF6 (Him = Imidazole, H2hapen = N,N′-Bis(2-hydroxyacetophenylidene)ethylenediamine)

The solvent-free spin crossover iron(III) complex [Fe(III)(Him)2(hapen)]AsF6 (Him = imidazole, H2hapen = N,N'-bis(2-hydroxyacetophenylidene)ethylenediamine), exhibiting thermal hysteresis, was synthesized and characterized. The Fe(III) ion has an octahedral coordination geometry, with N2O2 donor atoms of the planar tetradentate ligand (hapen) and two nitrogen atoms of two imidazoles at the axial positions. One of two imidazoles is hydrogen-bonded to the phenoxo oxygen atom of hapen of the adjacent unit to give a hydrogen-bonded one-dimensional chain, while the other imidazole group is free from hydrogen bonding. The temperature dependencies of the magnetic susceptibilities and Mössbauer spectra revealed an abrupt spin transition between the high-spin (S = 5/2) and low-spin (S = 1/2) states, with thermal hysteresis.

Formation of bis(μ-tetrazolato)dinickel(ii) complexes with N,N,O-donor Schiff bases via in situ 1,3-dipolar cyclo-additions: isolation of a novel bi-cyclic trinuclear nickel(ii)–sodium(i)–nickel(ii) complex

A dinuclear and a novel bi-cyclic hetero trinuclear bis(μ-tetrazolato) bridged nickel(II) Schiff base complexes [Ni2(L(1))2(PTZ)2] (1) and [Ni2(L(2))2(PTZ)2Na(H2O)]ClO4·H2O (2) {where HL(1) = 2-((2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol, HL(2) = 2-((2-(methylamino)ethylimino)methyl)-6-methoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole} have been synthesized by in situ 1,3-dipolar cyclo-addition and characterized by spectral analysis, X-ray crystallography, and variable-temperature magnetic susceptibility measurements. Both the complexes crystallize in monoclinic space group P2(1)/c. Both the complexes feature double μ-NN'-tetrazolato bridged dinickel(II) structures, in which each nickel(II) is coordinated meridionally by a depronated terdentate Schiff base [(L(1))(-) for 1 and (L(2))(-) for 2] and two nitrogen atoms of the (PTZ)(-). A nitrogen atom from a symmetry related bridging (PTZ)(-) coordinates to complete the distorted octahedral geometry of nickel(II). The phenoxo and methoxo oxygen atoms from two [NiL(2)] units and a water molecule coordinate to a sodium(I) to form the unique bi-cyclic trinuclear nickel(II)-sodium(I)-nickel(II) core in complex 2. Very strong π···π stacking is observed in complex 2 to form a supramolecular chain. The variable-temperature (1.8-300 K) magnetic susceptibility measurements show the presence of anti-ferromagnetic coupling between two nickel(II) centers for both complexes with J = -2.14(1) cm(-1) (for 1) and J = -1.20(2) cm(-1) (for 2). To obtain a better understanding of the magnetic exchange mechanism, quantum mechanical (DFT) calculations have been performed. The calculated J values [J(theo) = -4.53 cm(-1) (for 1) and J(theo) = -2.48 cm(-1) (for 2)] are in agreement with the values obtained experimentally.

Synthesis, structure, antioxidation, and DNA-binding studies of a binuclear ytterbium(III) complex with bis(N-salicylidene)-3-oxapentane-1,5-diamine

A new complex of ytterbium(III) nitrate with bis(N-salicylidene)-3-oxapentane-1,5-diamine (H2L), with the composition Yb2(L)2(NO3)2·2H2O, was synthesized and characterized by physic-chemical and spectroscopic methods. The crystal structure of the ytterbium(III) complex has been determined by single-crystal X-ray diffraction. It reveals a centrosymmetric binuclear neutral entity where Yb(III) metal centers are bridged by two phenoxo oxygen atoms. Electronic absorption titration spectra, ethidium bromide displacement experiments, and viscosity measurements indicate that both the ligand and the Yb(III) complex can bind calf thymus DNA, presumably via a groove binding mechanism. Furthermore, the antioxidant activities of the Yb(III) complex were determined by a superoxide and hydroxyl radical scavenging method in vitro, which indicates that it is a scavenger for OH and O2− radicals.

Two-Dimensional Coordination Polymers Constructed by [NiIILnIII] Nodes and [WIV(bpy)(CN)6]2– Spacers: A Network of [NiIIDyIII] Single Molecule Magnets

Three isomorphous two-dimensional (2D) coordination polymers of general formula {[Ni(II)(valpn)Ln(III)(NO3)(H2O)(μ-NC)4W(IV)(bipy)(CN)2]·xH2O·yCH3CN}n have been synthesized by reacting Ph4P[W(V)(CN)6(bipy)] with the heterodinuclear [Ni(II)Ln(III)(valpn)(O2NO)3] complexes [H2valpn = 1,3-propanediyl-bis(2-iminomethylene-6-methoxyphenol), bipy = 2,2'-bipyridine, and Ln = Gd (1), Dy (2), and Tb (3) with x = 2 (1), 3.9 (2), and 3.35 (3) and y = 2.50 (1), 2 (2), and 1.8 (3)]. Their crystal structures consist of [Ni(II)Ln(III)] 3d-4f nodes which are connected by [W(IV)(bipy)(CN)6](2-) diamagnetic linkers resulting from the reduction of W(V) to W(IV) during the reaction process. The Ni(II) and Ln(III) ions occupy the inner and outer coordination sites of the dideprotonated valpn ligand, respectively, and they are doubly bridged by the phenoxo oxygen atoms of such a ligand. The value of Ni(II)···Ln(III) separation through this bridge is 3.4919(10) (1), 3.4760(10) (2), and 3.4799(9) (3) Å, and those of the angles at the bridgehead phenoxo atoms are 106.6(2) and 107.3(2) (1), 106.9(2), and 107.8(2) (2) and 106.5(2)-106.8(2)° (3). Each W(IV) is eight-coordinated with a bidentate bipy molecule and six cyanide-carbon atoms building a somewhat distorted square antiprism environment. The rare-earth cations are nine-coordinated, the donor atoms describing a monocapped square antiprism for 1 and 3 and a tricapped trigonal prism for 2. Magnetic susceptibility measurements in the temperature range 1.9-300 K show the occurrence of ferromagnetic interactions between the Ni(II) and Ln(III) ions in 1-3. Frequency-dependent alternating susceptibility signals were observed for the Dy(III) derivative below 8.0 K under an applied dc field of 2500 G indicating the presence of slow magnetic relaxation with values of the pre-exponential factor (τ0) and energy barrier (E(#)) of ca. 5.7 × 10(-8) s and 15.9 cm(-1), respectively. Complex 2 constitutes the first example of a 2D 3d-4f heterobimetallic single molecule magnet (SMM).

First examples of 3d-uranium compounds derived from single-compartment Schiff base ligands: Syntheses, crystal structures and d–d band correlation

This paper deals with the syntheses, characterization, crystal structures and UV–Vis spectroscopy of three diphenoxo-bridged dinuclear CuII(UVIO2) compounds [CuII(MeCN)L1(UVIO2)(NO3)2] (1), [CuII(MeCN)L2(UVIO2)(NO3)2] (2) and [CuII(MeCN)L3(UVIO2)(NO3)2] (3) derived from the single-compartment Schiff base ligands H2L1 (2:1 condensation product of salicylaldehyde and 1,3-diaminopropane), H2L2 (2:1 condensation product of salicylaldehyde and 1-ethyl-1,3-diaminopropane) and H2L3 (2:1 condensation product of 2-hydroxyacetophenone and 1,3-diaminopropane). While copper(II) occupies the N2O2 compartment, uranium(VI) center is linked with Schiff base ligand through the two bridging phenoxo oxygen atoms. Copper(II) is pentacoordinated and distorted square pyramidal, while the uranium(VI) center is octacoordinated and distorted hexagonal bipyramidal in which the two uranyl oxygen atoms occupy the apical positions. Electronic spectra of 1–3 and the corresponding mononuclear CuII compounds have been recorded and a previously reported but practically unexplored correlation regarding d–d band position has been highlighted. Although the correlation is not valid for only mononuclear or only dinuclear compounds derived from different ligands, a nice correlation is found out on comparing the spectra of dinuclear compounds with the corresponding mononuclear compounds.

Synthesis, X-ray crystal structure, and electrochemistry of polynuclear azido-bridged manganese(III) and copper(II) Schiff base complexes

Abstract New azido-bridged [MnIII(salabza)(μ-1,3-N3)]n (1), and [CuII4(salabza)2(μ-1,1-N3)2(N3)2(HOCH3)2],(2) complexes with an unsymmetrical Schiff base ligand, {H2salabza = N,N’-bis(salicylidene)-2-aminobenzylamine}, have been synthesized, characterized by spectroscopic and electrochemical methods, and their crystal structures have been determined by X-ray diffraction. In complex 1, each manganese(III) atom is coordinated with N2O2 donor atoms from salabza and two adjacent Mn(III) centers are linked by an end-to-end (EE) azide bridge to form a helical polymeric chain with octahedral geometry around the Mn(III) centers. Complex 2 is a centrosymmetric tetranuclear compound containing two types of Cu(II) centers with square pyramidal geometry. Each terminal copper atom is surrounded by N2O2 atoms of a salabza ligand, and the oxygen atom of the methanol molecule. Each central copper(II) ion is coordinated with two phenoxo oxygen atoms from one salabza, one terminal azido, and two end-on (EO) bridging azido ligands. The central copper(II) ions are linked to each other by the two end-on (EO) azido groups.

Synthesis, Crystal Structure, DNA-binding Properties and Antioxidant Activities of a Lutetium(III) Complex with the Bis(N-salicylidene)-3- oxapentane-1,5-diamine Ligand

A Schiff base ligand bis(N-salicylidene)-3-oxapentane-1,5-diamine (H2L) and its lutetium(III) complex, with composition Lu2(L)2(NO3)2, were synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structure of the Lu(III) complex has been determined by single-crystal X-ray diffraction. It reveals a centrosymmetric binuclear neutral entity where Lu(III) metal centers are bridged by two phenoxo oxygen atoms. The DNA-binding properties of the Lu(III) complex were investigated by spectrophotometric methods and viscosity measurements, and the results suggest that the Lu(III) complex binds to DNA via a groove binding mode. Additionally, the antioxidant activity of the Lu(III) complex was determined by the superoxide and hydroxyl radical scavenging methods in vitro, which indicate that it is a scavenger for OH· and O-· 2 radicals.

Syntheses, three types of hydrogen-bonded assembly structures, and magnetic properties of [FeIII(Him)2(hapen)]Y·solvent (Him = imidazole, hapen =N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, Y = BPh4−, CF3SO3−, PF6−, ClO4−, and BF4−)

Five iron(III) complexes of [FeIII(Him)2(hapen)]Y·solvent with five different counter anions were synthesized, where Him=imidazole, H2hapen=N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, Y=BPh4− (1), CF3SO3− (2), PF6− (3), ClO4− (4), and BF4− (5), and solvent=methanol or H2O. Each FeIII ion has octahedral coordination geometry with N2O2 donor atoms of the equatorial tetradentate ligand (hapen) and two nitrogen atoms of two imidazoles at the axial positions. The imidazole group is hydrogen-bonded to the phenoxo oxygen atom of hapen of the adjacent unit and/or to the counter anion or solvent molecule, to give three types of assembly structures involving linear dimer, cyclic dimer, and one-dimensional zigzag chain. Compound 1, with a cyclic dimer, and 2 and 3, with a one-dimensional chain, showed spin-equilibrium behavior between high-spin (S=5/2) and low-spin (S=1/2) states, whereas 4 and 5, with linear dimers, are high-spin complexes. Compound 3 shows abrupt spin transition with small thermal hysteresis.

A new synthetic route towards binuclear 3d–4f complexes, using non-compartmental ligands derived from o-vanillin. Syntheses, crystal structures, magnetic and luminescent properties

Sixteen new 3d–4f binuclear complexes have been obtained using two Schiff-base ligands, Hvalampy and Hvalaepy, derived from the reaction of o-vanillin and 2-aminomethyl-pyridine or 2-(2-aminoethyl)-pyridine, respectively. Hvalaepy ligand: [Zn(valaepy)2Sm(O2NO)3]·CH3CN 1; [Ni(valaepy)2Eu(O2NO)3(H2O)]·CH3CN 2; [Ni(valaepy)2Gd(O2NO)3(H2O)]·CH3CN 3; [Ni(valaepy)2Dy(O2NO)3(H2O)]·CH3CN 4; [Ni(valaepy)2Ho(O2NO)3(H2O)]·CH3CN 5; [Cu(valaepy)2Eu(O2NO)3]·CH3CN 6; [Cu(valaepy)2Gd(O2NO)3]·CH3CN 7; Hvalampy ligand: [Zn(valampy)2Pr(O2NO)3]·CH3CN 8, [Zn(valampy)2Sm(O2NO)3]·CH3CN 9; [Zn(valampy)2Gd(O2NO)3]·CH3CN 10; [Zn(valampy)2Tb(O2NO)3]·CH3CN 11; [Zn(valampy)2Dy(O2NO)3]·CH3CN 12; [Zn(valampy)2Eu(O2NO)3]·CH3CN 13; [Ni(valampy)2La(O2NO)3(H2O)2]·2H2O 14, [Ni(valampy)2Sm(O2NO)3(H2O)2]·2H2O 15; [Ni(valampy)2Eu(O2NO)3(H2O)]·2CH3CN 16. The crystal structures of the sixteen compounds can be described as resulting from the coordination of two valaepy− (or valampy−) ligands to the 3d metal ions through two phenoxo oxygen atoms and nitrogen atoms, arising from the pyridyl and azomethynic groups. In all these compounds the 3d and 4f metal ions are bridged by the phenoxo oxygen atoms. The comparative analysis of the crystal structures shows several differences, which arise mainly from the stereochemical preference of the 3d metal ions. These ions arrange the two organic ligands in positions that favour or not the coordination of the methoxy groups to the lanthanide ions. The magnetic properties of compounds 2, 3, 4, 5, 7, 14, 15, and 16 have been investigated. The exchange interactions between NiII and GdIII in 3, and between CuII and GdIII in 7 were found to be ferromagnetic (JNiGd = 1.56 cm−1; JCuGd = 4.94 cm−1; H = −JSGdSM). For the 3d–4f binuclear complexes derived from the Hvalampy ligand (namely 8–13) the photoluminescence (PL) properties were investigated in the Vis spectral region. The results provide evidence for the relatively stronger antenna effect in 9 and 11 compared to 8, 12 and 13.

Crystal structures of discrete, one-dimensional and cocrystalline copper(ii)–uranyl(vi) systems: the influence of the reactant ratio in the competition between hydrogen bonds and coordinate bonds

This paper presents the syntheses and crystal structures of four copper(II)–uranyl(VI) compounds [{CuIILOEt–en}2·{(UVIO2)(NO3)2(H2O)2}] (1), [CuII(MeCN)LOEt–pn(UVIO2)(NO3)2] (2), [(UVIO2)2(μ-H2O)2(NO3)4]∙4[CuIILOEt–py(H2O)]∙2MeCN (3) and {[CuIILOMe–en(UVIO2)(NO3)]2[(UVIO2)2(μ-HO)2(NO3)4]}n (4), where H2LOEt–en, H2LOEt–pn, H2LOEt–py and H2LOMe–en are 3-ethoxysalicylaldehyde-diamine (H2LOEt) or 3-methoxysalicylaldehyde-diamine (H2LOMe) ligands in which the diamine functionality are ethylenediamine, 1,3-diaminopropane, 2,3-diaminopyridine and ethylenediamine, respectively. Compound 1 is a [1 × 2 + 1 × 1] trinuclear cocrystal containing two mononuclear [CuIILOEt–en] and one mononuclear [(UVIO2)(NO3)2(H2O)2] moiety; two coordinated water molecules interact with two O4 compartments by forming hydrogen bonds. Compound 2 is a dinuclear system in which two phenoxo oxygen atoms coordinate with the uranium(VI) centre. Compound 3 is a [2 × 1 + 1 × 4] hexanuclear cocrystal of four mononuclear [CuIILOEt–py(H2O)] units and one dinuclear [(UVIO2)2(μ-H2O)2(NO3)4] moiety; O–H⋯O and C–H⋯O interactions interlink the five units here. In 4, there are two dinuclear [CuIILOMe–en(UVIO2)(NO3)]+ cations and one dinuclear [(UVIO2)2(μ-HO)2(NO3)4]2− anion, which are self-assembled to generate a one-dimensional topology. Interesting structural aspects including the weak interaction directed self-assemblies and most importantly, the competition between hydrogen bond and coordinate bond formation and the influence of the reactant ratio in governing that competition are discussed. The diffuse reflectance or solution transmission spectra (for the d–d band) of 1–4 and the corresponding mononuclear copper(II) precursors are also described.

A novel thermally stable hydroperoxo–copper(ii) complex in a Cu(N2O2) chromophore of a potential N4O2 donor Schiff base ligand: synthesis, structure and catalytic studies

The generation and study of metal-hydroperoxo/metal-peroxo (LCu(II)-OOH or LCu(II)-OO˙) complexes is a fascinating area of research of many chemical and biochemical researchers, because of their involvement as active intermediates in many biological and industrial catalytic oxidation processes. For this purpose we have designed a bulky hexa-coordinating ligand with potential N4O2 donor atoms which could provide an opportunity to synthesize a mononuclear Cu(II) complex with an aim to utilize it in the catalytic oxidation of aromatic hydrocarbons by an environmentally benign oxidant, H2O2. The Cu(II) complex (1) was structurally characterized and found to have square-planar geometry with the two pyrazolyl groups remaining in dangling mode. A novel mononuclear complex [Et3NH][LCu(II)-OOH] (2) was found to form in the reaction between 1 and H2O2 in the presence of Et3N. The presence of this dangling groups favours the stability of hydroperoxo species, [LCu-OOH](-) (2) through H-bonding with the coordinated phenoxo oxygen atom, which was confirmed by ESI-MS(+) and MS(-) (m/z) mass analysis and DFT calculations. This complex was found to be thermally stable at room temperature [k(d) = (5.67 ± 0.03) × 10(-5) s(-1) at 25 °C] and may be due to the formation of O-O-H···O(phenoxo) H-bonding as delineated by the DFT calculations. Complex 1 was found to be an efficient catalyst for the oxidation of aromatic hydrocarbons to the corresponding aldehyde and alcohol in 2:1 mole ratio with TON ~300.

Synthesis, crystal structure and DFT analysis of a phenoxo bridged Cu(II) complex and an azide and μ3-O mixed bridged trinuclear Cu(II) complex

One binuclear Cu(II) complex, [Cu2(L1)2(N3)2] (1), and a trinuclear Cu(II) complex, [Cu3(L2)3(μ1,1N3)2](ClO4) (2), of two potentially tridentate NNO-donor Schiff base ligands, [2-(1-(2-(4,6-dimethylpyrimidin-2-yl)hydrazono)ethyl)phenol] (HL1) and [2-((2-(4,6-dimethyl pyrimidin-2-yl) hydrazono) methyl) phenol] (HL2), have been synthesized and characterized by elemental analyses, UV–Vis IR spectroscopy, DFT and single crystal X-ray crystallography. The ligands HL1 and HL2 are [1+1] condensation products of 2-hydrazino-4,6-dimethylpyrimidine with 2-hydroxy acetophenone and salicylaldehyde respectively. In 1, the two Cu(II) centers are bridged by μ-phenoxo groups. In 2, the three Cu(II) centers are held together by two μ1,1 bridging azide ions and a phenoxo oxygen atom which binds the three metal centers and behaves as a μ3-O atom. The geometries of the complexes have been optimized using the UB3LYP level of theory. The calculation confirms that all the copper centers are five coordinate with distorted square pyramidal geometries, which is consistent with the experimental data.

A hexanuclear copper(II) Schiff base complex incorporating rare “bicapped cubane” core: Structural aspects, magnetic properties and EPR study

The reaction of Cu2(CH3COO)4·2H2O with the Schiff base ligand, H4L [(OH)2C6H3CHN–C(CH3)(CH2OH)2], yields a novel hexanuclear copper (II) cluster {[Cu6(HL)4]·CH3OH·0.5CH3CN·6.5H2O} (1) with a rare “bicapped cubane” core. Title complex has been characterized by different physico-chemical techniques. Single-crystal X-ray structure reveals that the “bicapped cubane” core was formed by a cubane-like Cu4O4 subcore capped by two copper(II) atoms over opposite faces. The cubane copper(II) atoms are in distorted square pyramidal geometry and connected each other via μ3-alkoxo oxygens while two apical copper(II) atoms are in distorted square planar environments and connected to the main cubane subcore by doubly phenoxo bridged oxygen atoms. EPR spectra of the complex reveals overall strong antiferromagnetic behavior, well supported by cryomagnetic susceptibility measurements in the range 2–300K under the magnetic field of 0.1T leading different coupling constants: J1=+60cm−1, J2=−45.5±1cm−1; J3=−140±1cm−1, using the general Hamiltonian H=−J(Si·Sj). A plausible magneto-structural correlation has also been established.

A new tetraiminodiphenol macrocyclic ligand and its two dicopper(II) complexes: Syntheses, crystal structures, electrochemistry and magnetochemistry

This paper deals with the diprotonated salt, [H4L](ClO4)2 (1), of the tetraiminodiphenolate macrocyclic ligand, H2L which is the [2+2] condensation product of 4-ethyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane, and two diphenoxo-bridged dicopper(II) complexes [Cu2L(ClO4)2] (2) and [Cu2L(ClO4)](ClO4) (3). The syntheses, characterization and crystal structures of 1–3 and the magnetic and electrochemical properties of the metal complexes 2 and 3 are presented. The cationic macrocycle [H4L]2+ is stabilized by four intramolecular and symmetric NH…O…HN hydrogen bonds involving phenoxo oxygen and imino nitrogen atoms. One metal center in 3 is tetracoordinated and in a square planar geometry. The second metal ion of 3 and both the metal ions in 2 are pentacoordinated and in a square pyramidal geometry; one perchlorate oxygen atom occupies the apical position in each case. Both 2 and 3 exhibit quasireversible two-step one-electron couples in the reduction window. The E½ (ΔEp) values (in mV) for the CuIICuII/CuIICuI couple is −0.466V (0.067V) for 2 and −0.490V (0.076V) for 3, while the E½ (ΔEp) values (in mV) for the CuIICuI/CuICuI couple is −0.953V (0.060V) for 2 and −0.985V (0.069V) for 3. Variable-temperature (2–300K) magnetic susceptibility measurements of the two compounds reveal that the metal centers in both of the complexes are coupled by strong antiferromagnetic interactions with 2J values (H=−JS1·S2) of −780 and −820cm−1 for 2 and 3, respectively.

Pentacoordinate NiII Complexes: Preparation, Magnetic Measurements, and Ab Initio Calculations of the Magnetic Anisotropy Terms

Two novel mononuclear five-coordinate nickel complexes with distorted square-pyramidal geometries are presented. They result from association of a tridentate "half-unit" ligand and 6,6'-dimethyl-2,2'-bipyridine according to a stepwise process that highlights the advantage of coordination chemistry in isolating an unstable tridentate ligand by nickel chelation. Their zero-field splittings (ZFS) were studied by means of magnetic data and state-of-the-art ab initio calculations. Good agreement between the experimental and theoretical axial D parameters confirms that large single-ion nickel anisotropies are accessible. The synthetic process can also yield dinuclear nickel complexes in which the nickel ions are hexacoordinate. This possibility is facilitated by the presence of phenoxo oxygen atoms in the tridentate ligand that can introduce a bridge between the two nickel ions. Two different double bridges are characterized, with the bridging oxygen atoms coming from each nickel ion or from the same nickel ion. This coordination change introduces a difference in the antiferromagnetic interaction parameter J. Although the magnetic data confirm the presence of single-ion anisotropies in these complexes, these terms cannot be determined in a straightforward way from experiment due to the mismatch between the principal axes of the local anisotropies and the presence of intersite anisotropies.

Rational design of ferromagnetic coupled diphenoxocarboxylate triply bridged dinuclear nickel(ii) complexes: orbital countercomplementarity of the bridging ligands

Four new dinuclear complexes [Ni(μ-L)(μ-OAc)Ni(H2O)2]NO3 (1), Ni(μ-L)(μ-OBz)Ni(H2O)(MeOH)]NO3·3MeOH (2), [Ni(μ-L)(μ-9-An)Ni(H2O)(MeOH)]NO3 (3) and [Ni(μ-L)(μ-OAc)Ni(H2O)(N3)]·CH3OH (4) have been prepared from the compartmental ligand N,N′,N′′-trimethyl-N,N′′-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H2L) and different carboxylate ligands (OBz = benzoate and 9-An = 9-anthracenecarboxylate), and then magnetically and structurally characterized. The X-ray structures of these complexes reveal that the Ni2+ ions are bridged by two phenoxo groups belonging to the L2− ligand and one syn–syn carboxylate group, giving rise to diphenoxocarboxylate triply bridged dinuclear nickel(II) complexes. The syn–syn carboxylate bridging group folds the structure with hinge angles (β) in the range 32–36°. The folding of the structure takes place with a concomitant decrease of the O–Ni–O bridging angle (θ) and an increase of the shift carbon atom directly linked to the phenoxo oxygen atom with respect to the Ni–Ni–O plane in the bridging region (τ angle). All the complexes exhibit ferromagnetic interactions between the slightly distorted octahedral Ni2+ ions. A comparative analysis of the magneto-structural data for 1–4 and other diphenoxocarboxylate bridged complexes clearly show that not only the θ angle, but also the τ and β angles play a significant role in determining the sign and magnitude of the magnetic exchange coupling in these complexes. The ferromagnetic behaviour observed for 1–4 has been justified on the basis of their relatively low θ and high β and τ values, all of them decreasing the antiferromagnetic contribution in complexes 1–4, as well as the countercomplementarity effects between the diphenoxo and carboxylate bridging ligands. DFT theoretical calculations unequivocally demonstrate that the countercomplementarity mechanism is operative in compounds 1–4.