Phenoxo Oxygen Atoms Research Articles

Syntheses, Structures, and Magnetic Properties of Three One-Dimensional End-to-End Azide/Cyanate-Bridged Copper(II) Compounds Exhibiting Ferromagnetic Interaction: New Type of Solid State Isomerism

The work in this paper presents the syntheses, structures, and magnetic properties of three end-to-end (EE) azide/cyanate-bridged copper(II) compounds [Cu(II)L(1)(μ(1,3)-NCO)](n)·2nH(2)O (1), [Cu(II)L(1)(μ(1,3)-N(3))](n)·2nH(2)O (2), and [Cu(II)L(2)(μ(1,3)-N(3))](n) (3), where the ligands used to achieve these species, HL(1) and HL(2), are the tridentate Schiff base ligands obtained from [1 + 1] condensations of salicylaldehyde with 4-(2-aminoethyl)-morpholine and 3-methoxy salicylaldehyde with 1-(2-aminoethyl)-piperidine, respectively. Compounds 1 and 2 crystallize in the monoclinic P2(1)/c space group, while compound 3 crystallizes in the orthorhombic Pbca space group. The metal center in 1-3 is in all cases pentacoordinated. Three coordination positions of the metal center in 1, 2, or 3 are satisfied by the phenoxo oxygen atom, imine nitrogen atom, and morpholine (for 1 and 2) or piperidine (for 3) nitrogen atom of one deprotonated ligand, [L(1)](-) or [L(2)](-). The remaining two coordination positions are satisfied by two nitrogen atoms of two end-to-end bridging azide ligands for 2 and 3 and one nitrogen atom and one oxygen atom of two end-to-end bridging cyanate ligands for 1. The coordination geometry of the metal ion is distorted square pyramidal in which one EE azide/cyanate occupies the apical position. Variable-temperature (2-300 K) magnetic susceptibilities of 1-3 have been measured under magnetic fields of 0.05 (from 2 to 30 K) and 1.0 T (from 30 to 300 K). The simulation reveals a ferromagnetic interaction in all three compounds with J values of +0.19 ± 0.01, +0.79 ± 0.01, and +1.25 ± 0.007 cm(-1) for 1, 2, and 3, respectively. Compound 1 is the sole example of a ferromagnetically coupled EE cyanate-bridged 1-D copper(II) system. In addition, a rare example of supramolecular isomerism and a nice example of magnetic isomerism have been observed and most interestingly a new type of solid state isomerism has emerged as a result of the comparison of the structure and magnetic properties of 2 with a previously published compound (2A) having the same composition and even the same crystal system and space group (New J. Chem.2001, 25, 1203-1207).

Pure Trinuclear 4 f Single-Molecule Magnets: Synthesis, Structures, Magnetism and Ab Initio Investigation

A family of linear Dy(3) and Tb(3) clusters have been facilely synthesized from the reactions of DyCl(3), the polydentate 3-methyloxysalicylaldoxime (MeOsaloxH(2) ) ligand with auxiliary monoanionic ligands, such as trichloroacetate, NO(3)(-), OH(-), and Cl(-). Complexes 1-5 contain a nearly linear Ln(3) core, with similar Ln···Ln distances (3.6901(4)-3.7304(3) Å for the Dy(3) species, and 3.7273(3)-3.7485(5) Å for the Tb(3) species) and Ln···Ln···Ln angles of 157.036(8)-159.026(15)° for the Dy(3) species and 157.156(8)-160.926(15)° for the Tb(3) species. All three Ln centers are bridged by the two doubly-deprotonated [MeOsalox](2-) ligands and two of the four [MeOsaloxH](-) ligands through the N,O-η(2)-oximato groups and the phenoxo oxygen atoms (Dy-O-Dy angles=102.28(16)-106.85(13)°; Tb-O-Tb angles=102.00(11)-106.62(11)°). The remaining two [MeOsaloxH](-) ligands each chelate an outer Ln(III) center through their phenoxo oxygen and oxime nitrogen atoms. Magnetic studies reveal that both Dy(3) and Tb(3) clusters exhibit significant ferromagnetic interactions and that the Dy(3) species behave as single-molecule magnets, expanding upon the recent reports of the pure 4f type SMMs.

The importance of an additional water bridge in making the exchange coupling of bis(μ-phenoxo) dinickel(ii)complexes ferromagnetic

Two new nickel(II) complexes [Ni(2)L(2)(PhCOO)(2)(H(2)O)] (1), [Ni(2)L(2)(PhCH(2)COO)(2)(H(2)O)] (2) have been synthesized using a tridentate Schiff base ligand, HL (2-[(3-dimethylamino-propylimino)-methyl]-phenol) and the carboxylate monoanions, benzoate and phenylacetate, respectively. The complexes have been characterized by spectral analysis, variable temperature magnetic susceptibility measurement and crystal structure analysis. The structural analyses reveal that both complexes are dinuclear in which the distorted octahedral Ni(2+) ions share a face, bridged by one water molecule and two μ(2)-phenoxo oxygen atoms. A monodentate benzoate or phenylacetate anion and two nitrogen atoms of the chelating deprotonated Schiff base (L) complete the hexa-coordination around the metal ion. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complexes 1 and 2 with J values of 11.1(2) and 10.9(2) cm(-1) respectively. An attempt has been made to rationalize the observed magneto-structural behavior considering the importance of the additional water bridge in the present two complexes and also in other similar species.

Syntheses and crystal structures of dinuclear, trinuclear [2 × 1 + 1 × 1] and tetranuclear [2 × 1 + 1 × 2] copper(ii)–d10complexes (d10⇒ ZnII, CdII, HgIIand AgI) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine)

Syntheses, characterization and crystal structures of heterotetranuclear [2 × 1 + 1 × 2] co-crystals [{CuIILZnII(H2O)2}{CuIIL}2](ClO4)2 (1) and [{CuIILCdII(H2O)2(CH3CN)}{CuIIL}2](ClO4)2 (2), dinuclear compound [CuIILHgII(CH2COCH3)](ClO4) (3) and heterotrinuclear [2 × 1 + 1 × 1] co-crystal [{CuIILAgI(H2O)}{CuIIL}](ClO4) (4) derived from N,N′-ethylenebis(3-ethoxysalicylaldimine) (H2L) are reported herein. Compounds 3 and 4 crystallize in the orthorhombic Pbca and monoclinic P21/c systems, respectively, while the space group of compounds 1 and 2 is monoclinic C2/c. The structure of 3 consists of a monophenoxo-bridged CuIIHgII dinuclear core in which the mercury(II) centre is dicoordinated by the bridging phenoxo oxygen atom and the CH2 carbon atom of the mono-deprotonated acetone anion. The coordination environment of HgII in this compound is almost linear. In the CuII2AgI compound 4, one diphenoxo-bridged [CuIILAgI(H2O)]+ cation is co-crystallized with one mononuclear [CuIIL] moieties. On the other hand, the structures of the CuII3MII compounds 1 (M = Zn) and 2 (M = Cd) consist of one diphenoxo-bridged dinuclear CuIIMII unit and two mononuclear [CuIIL] moiety; the composition of the dinuclear unit being [CuIILZnII(H2O)2]2+ and [CuIILCdII(H2O)2(CH3CN)]2+ for 1 and 2, respectively. The AgI (in 4), ZnII (in 1) and CdII (in 2) ions in the diphenoxo-bridged dinuclear cores are tri-, tetra- and heptacoordinated, respectively. The metal ions are coordinated to two bridging phenoxo oxygen atoms, with the silver(I) and zinc(II) centres being additionally coordinated to one and two water molecules, respectively. While in the case of cadmium(II), the additional five coordination positions are occupied by two ethoxy oxygen atoms, two water oxygen atoms and one acetonitrile nitrogen atom. The coordination environment of silver(I) in 4 is pyramidal with a scalene O3 triangle as the base, whereas those of zinc(II) and cadmium(II) in 1 and 2 are distorted tetrahedral and distorted pentagonal bipyramidal, respectively. The coordinated water molecule in 4 and each of the two coordinated water molecules in 1 and 2 are encapsulated into the O4 compartment of a [CuIIL] moiety resulting in the [2 × 1 + 1 × 1] (for 4) or [2 × 1 + 1 × 2] (for 1 and 2) cocrystallization and self-assemblies. Clearly, the encapsulation of the coordinated water molecule(s) is the governing force for the formation of dinuclear-mononuclear co-crystals in 1, 2 and 4. In addition all four compounds 1–4 have π–π stacking interactions which form dimers between pairs of adjacent molecules in the structure of 3 consisting of CuIIHgII dimers, while one-dimensional stacks are formed in the CuII3ZnII (1), CuII3CdII (2) and CuII2AgI (4) complexes. The compositions of the title compounds are compared with the related systems derived from the same ligand. The [2 × 1 + 1 × 1] co-crystal, 4, is a new type of system in terms of the number of components. Again, in spite of the tri-, tetra- and hepta-coordinated nature of the second metal ion in the dinuclear cores, co-crystallization in 1, 2 and 4, respectively, are new observations. The accommodation/coordination of varieties of metal ions by the O4 compartment of H2L has also been highlighted in the present investigation.

Use of a Reduced Schiff-Base Ligand to Prepare Novel Chloro-Bridged Chains of Rare Cu(II) Trinuclear Complexes with Mixed Azido/Oxo and Chloro/Oxo Bridges

Two mixed bridged one-dimensional (1D) polynuclear complexes, [Cu(3)L(2)(mu(1,1)-N(3))(2)(mu-Cl)Cl](n) (1) and {[Cu(3)L(2)(mu-Cl)(3)Cl].0.46CH(3)OH}(n) (2), have been synthesized using the tridentate reduced Schiff-base ligand HL (2-[(2-dimethylamino-ethylamino)-methyl]-phenol). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. In both complexes the basic trinuclear angular units are joined together by weak chloro bridges to form a 1D chain. The trinuclear structure of 1 is composed of two terminal square planar [Cu(L)(mu(1,1)-N(3))] units connected by a central Cu(II) atom through bridging nitrogen atoms of end-on azido ligands and the phenoxo oxygen atom of the tridentate ligand. These four coordinating atoms along with a chloride ion form a distorted trigonal bipyramidal geometry around the central Cu(II). The structure of 2 is similar; the only difference being a Cl bridge replacing the mu(1,1)-N(3) bridge in the trinuclear unit. The magnetic properties of both trinuclear complexes can be very well reproduced with a simple linear symmetrical trimer model (H = -JS(i)S(i+1)) with only one intracluster exchange coupling (J) including a weak intertrimer interaction (j) reproduced with the molecular field approximation. This model provides very satisfactory fits for both complexes in the whole temperature range with the following parameters: g = 2.136(3), J = -93.9(3) cm(-1) and zj = -0.90(3) cm(-1) (z = 2) for 1 and g = 2.073(7), J = -44.9(4) cm(-1) and zJ' = -1.26(6) cm(-1) (z = 2) for 2.

A Unique Example of Structural and Magnetic Diversity in Four Interconvertible Copper(II)−Azide Complexes with the Same Schiff Base Ligand: A Monomer, a Dimer, a Chain, and a Layer

Four new Cu(II)-azido complexes of formula [CuL(N(3))] (1), [CuL(N(3))](2) (2), [Cu(7)L(2)(N(3))(12)](n) (3), and [Cu(2)L(dmen)(N(3))(3)](n) (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single mu-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu(II) ions are linked by phenoxo oxygen atoms and two different azide bridges (mu-1,1 and mu-1,1,3). The structure of complex 4 is a double helix in which two mu-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N(3)) and Cu(dmen)(N(3))(2) are joined together by weak mu-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand pi overlap (J = -1.77) and by an asymmetric 1,1-N(3) bridge (J = -1.97 cm(-1)), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J = -1.35 and -2.64 cm(-1)).

Mononuclear Cu and dinuclear Cu–Ln complexes of benzimidazole based ligands including N and O donors: Syntheses, characterization, X-ray molecular structures and magnetic properties

The synthesis of two mononuclear precursor copper complexes, [(HL 2) 2Cu], 1, and [(HL 3) 2Cu]·H 2O, 2, and three dinuclear Cu–Ln complexes, [(HL 1) 2Cu(CH 3CN) 2Gd(NO 3) 3], 3, [(HL 3) 2CuGd(NO 3) 3]·2(H 2O), 4, and [(HL 3) 2CuTb(NO 3) 3]·2(H 2O), 5, based on the ligands H 2L 1 (4-bromo-2-[1-(5-bromo-2-hydroxy-3-methoxybenzyl)-1 H-benzimidazol-2-yl]-6-methoxyphenol), H 2L 2 (2-(1 H-benzimidazol-2-yl)-4-bromo-6-methoxyphenol) and H 2L 3 (2-(1 H-benzimidazol-2-yl)-6-methoxyphenol) are described in this contribution. The X-ray crystal structures of H 2L 2, 1, 3, 4, and 5 have been solved. The novel ligand H 2L 2 crystallizes with two independent molecules in the asymmetric unit; several intermolecular hydrogen contacts connect alternate independent H 2L 2 molecules into chains developing along c. In complex 1, two (HL 2) − ligands chelate the copper ion through their imidazolyl nitrogen and phenoxo oxygen atoms, in a relative head to tail arrangement. The molecular structure of 3 is similar to those of the previously reported Cu–Ln complexes of H 2L 1. In the isostructural complexes 4 and 5, two HL 3 ligands sandwich one Cu 2+ ion through their N,O sites and one Ln 3+ ion through their O 2 site, implying a relative head to head arrangement, at variance with the relative head to tail arrangement of HL 2 in the mononuclear copper precursor 1. The magnetic properties of 1, 3, 4, and 5 have been investigated. Extended intermolecular antiferromagnetic interactions operate in complex 1 (( J Chain = −0.8(1) cm −1). Ferromagnetic interactions between Gd ( S = 7/2) and Cu ( S = 1/2) centers operate in complexes 3 and 4, leading to an S = 4 ground state ( J CuGd = 7.2(2) cm −1 for 3 and J CuGd = 6.5(2) cm −1 for 4). Depopulation of the Tb Stark levels, preclude obtaining reliable information on the presence and sign of the Cu–Tb interaction in 5. These new complexes are complementary to those previously reported: the Cu–O 2–Gd core is planar while deformations are borne by the ligands at variance with previous examples where the constraints were located at the Cu–O 2–Gd core. The presence of two independent ligands in the Cu,Gd coordination spheres confers a degree of freedom greater than that allowed by a unique tetradentate ligand. As a result, the strength of the magnetic interaction is not solely related to the dihedral angle between the CuOO and GdOO planes in the central core.

Synthesis, crystal structure and magnetic properties of three unprecedented tri-nuclear and one very rare tetra-nuclear copper(ii) Schiff-base complexes supported by mixed azido/phenoxo/nitrato or acetato bridges

Three novel mixed bridged trinuclear and one tetranuclear copper(II) complexes of tridentate NNO donor Schiff base ligands [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(CH(3)OH)(2)(BF(4))(2)] (1), [Cu(3)(L(1))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (2), [Cu(3)(L(2))(2)(mu(1,1)-N(3))(2)(mu-NO(3)-1kappaO:2kappaO')(2)] (3) and [Cu(4)(L(3))(2)(mu(1,1)-N(3))(4)(mu-CH(3)COO-1kappaO:2kappaO')(2)] (4) have been synthesized by reaction of the respective tridentate ligands (L(1) = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, L(2) = 2-[1-(2-diethylamino-ethylimino)-ethyl]-phenol, L(3) = 2-[1-(2-dimethylamino-ethylimino)-methyl]-phenol) with the corresponding copper(ii) salts in the presence of NaN(3). The complexes are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. Complex 1 is composed of two terminal [Cu(L(1))(mu(1,1)-N(3))] units connected by a central [Cu(BF(4))(2)] unit through nitrogen atoms of end-on azido ligands and a phenoxo oxygen atom of the tridentate ligand. The structures of 2 and 3 are very similar; the only difference is that the central unit is [Cu(NO(3))(2)] and the nitrate group forms an additional mu-NO(3)-1kappaO:2kappaO' bridge between the terminal and central copper atoms. In complex 4, the central unit is a di-mu(1,1)-N(3) bridged dicopper entity, [Cu(2)(mu(1,1)-N(3))(2)(CH(3)COO)(2)] that connects two terminal [Cu(L(3))(mu(1,1)-N(3))] units through end-on azido, phenoxo oxygen and mu-CH(3)COO-1kappaO:2kappaO' triple bridges to result in a tetranuclear unit. Analyses of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the copper(II) ions in complexes 1-3, with the exchange parameter J of -9.86, -11.6 and -19.98 cm(-1) for 1-3, respectively. In complex 4 theoretical calculations show the presence of an antiferromagnetic coupling in the triple bridging ligands (acetato, phenoxo and azido) while the interaction through the double end-on azido bridging ligand is strongly ferromagnetic.

Experimental Evidence for the Participation of 5d GdIIIOrbitals in the Magnetic Interaction in Ni−Gd Complexes

The syntheses, structural determinations, and magnetic studies of two trinuclear Ni-Gd-Ni complexes are described. The structural studies demonstrate that the two complexes present a linear arrangement of the Ni and Gd ions, with Ni ions in slightly distorted square-pyramidal or octahedral environments in complexes 1 and 2, respectively. The Ni and Gd ions are linked by two or three phenoxo bridges, so that complexes 1 and 2 present edge-sharing or face-sharing bridging cores. Ferromagnetic interactions operate in these complexes. While a unique J parameter is able to fit the magnetic data of complex 2, two very different J constants are needed for 1. This result is at first sight surprising, for the structural data of the two Ni-O(2)-Gd cores in complex 1 are quite similar (similar Ni-O and Gd-O bond lengths, similar angles, and dihedral angles), the only difference coming from the angle between the planes defined by the Gd ion and the two bridging phenoxo oxygen atoms of each Ni-O(2)-Gd half core. This latter magnetic behavior can be considered as a signature for the participation of 5d Gd(III) orbitals in the exchange interaction mechanism and can explain why edge-sharing complexes have larger J parameters than face-sharing complexes.

Syntheses and structures of a phenoxo-bridged copper(II) distorted cubane and related complexes with 2-hydroxy-N-(2-pyridylalkyl)benzamide ligands

Abstract Two new pyridylalkylamide ligands containing phenol groups appended to the amide, 2-hydroxy-N-(2-pyridylmethyl)benzamide (HLPhOH) and 2-hydroxy-N-(2-pyridylethyl)benzamide (HLPhOH′), were synthesized. Copper(II) complexes of these ligands were synthesized and characterized by X-ray crystallography, ESI-MS, FTIR, UV/Vis, and EPR spectroscopy. When basic Et3N was used to deprotonate the ligands, tetracopper(II) [Cu4(LPhO)4] (1) or dicopper(II) [Cu2(LPhO′)2(CH3OH)2] (3) were formed. When base was not used, mononuclear [Cu(HLPhOH)2Cl2] (2) resulted. Complex 1 possesses a distorted cubane-like structure, with the ligands bridging via the phenoxo oxygen atoms, and the copper atoms possessing a distorted square planar geometry. The ligands in dimeric complex 3 also bridge between copper(II) atoms via the phenoxo oxygen atoms, and the copper atoms are square pyramidal. Monomeric 2 is a tetragonally distorted six-coordinate species with pyridyl N atoms and chloride ligands in the equatorial plane, and long interactions with the amide carbonyl O atoms in the axial positions.

New coordination polymer based on salpn Schiff base and azide bridging ligands: Synthesis and structural characterization of {Na[Co III(μ-salpn)(μ 1,1-N 3) 2]} n (H 2salpn = N, N′-bis(salicylidene)-1,3-diaminopropane)

One-pot reaction of cobalt(II) nitrate hexahydrate Co(NO 3) 2 · 6H 2O with H 2salpn ( N, N′-bis(salicylidene)-1,3-diaminopropane) in presence of a large excess of sodium azide (NaN 3) gives the new Co(III) compound {Na[Co III(μ-salpn)(μ 1,1-N 3) 2]} n ( 1), which was characterized by single crystal X-ray diffraction analysis. The crystal structure shows polymeric 1D complex generated by the hexadentate Schiff base salpn 2− and two crystallographically different azide ligands. The two nitrogen atoms of the salpn ligand are bonded to the cobalt(III) ion while each phenoxo oxygen atom is bonded to the same Co(III) ion and to two equivalent sodium ions. Each azide ligand acts with the end-on bridging coordination mode between Co(III) and Na(I) ions. The Co(III) ion adopts a distorted octahedral geometry arising from two oxygen and two nitrogen atoms of the salpn ligand and from two nitrogen atoms of the two crystallographically different azide ligands in trans positions. Such [Co(salpn)(N 3) 2] entities are connected each other by sodium ions through four oxygen atoms of two equivalent Schiff base ligands and two nitrogen atom of the two different azide ligands to generate the 1D structure of 1.

A single molecule magnet (SMM) with a helicate structure

The X-ray structure determination of [L2Cu2Gd2(NO3)6(H2O)2](0.5H2O) (L = bis-[(2-hydroxy-3-ethoxyphenyl)methylene]-4,4′-methylenedianiline) confirms the existence of a tetranuclear double-stranded homotopic and unsaturated helicate. In each Cu–Gd pair, the reduced Cu⋯Gd distance allows ferromagnetic Cu–Gd superexchange interactions through two phenoxo oxygen atoms. Replacement of gadolinium ions by terbium ions yields the first example of a helicate behaving as a single molecule magnet (SMM).

Crystal Structure of a Dinuclear Sodium Complex with a Phenol-based Dinucleating Ligand with Four Methoxyethyl Chelating Arms

A pair of dinucleating ligands, 2,6-bis[bis(2-methoxyethyl)aminomethyl]-4-methylphenolate (bomp-), incorporates two sodium ions to form a dinuclear sodium complex, [Na2(bomp)2] (C42H74N4Na2O10). It crystallizes in the monoclinic space group P21/c with dimensions a = 19.9993(4)Å, b = 9.9700(2)Å, c = 24.3473(7)Å, β = 98.8492(7)°, and V = 4796.89(19)Å3 and with Z = 4. The two sodium ions are bridged by two phenoxo oxygen atoms of the bomp ligands to form a bis(μ-phenoxo)-dinuclear sodium(I) core structure. The Na…Na distance is 3.3261(6)Å, and each sodium ion has a distorted octahedral geometry.

Copper(II) Complexes with New Polypodal Ligands Presenting Axial−Equatorial Phenoxo Bridges {2-[(Bis(2-pyridylmethyl)amino)methyl]-4-methylphenol, 2-[(Bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol}: Examples of Ferromagnetically Coupled Bi- and Trinuclear Copper(II) Complexes

Two new ligands, 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (HL) and 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol (HSL), were synthesized and were used to prepare the trinuclear copper(II) complex {[CuSL(Cl)]2Cu}(PF6)2.H2O (1) and the corresponding binuclear complexes [Cu2(SL)2](PF6)2 (2) and [Cu2L2](PF6)2 (3). The crystal structure of 1 shows two different coordination environments: two square base pyramidal centers (Cu1 and Cu1a, related by a C2 axes), acting as ligands of a distorted square planar copper center (Cu2) by means of the sulfur atom of the SCH3 substituent and the bridging phenoxo oxygen atom of the ligand (Cu2-S = 2.294 A). Compounds 2 and 3 show two equivalent distorted square base pyramidal copper(II) centers, bridged in an axial-equatorial fashion by two phenoxo groups, thus defining an asymmetric Cu2O2 core. A long copper-sulfur distance measured in 2 (2.9261(18) A) suggests a weak bonding interaction. This interaction induces a torsion angle between the methylthio group and the phenoxo plane resulting in a dihedral angle of 41.4(5) degrees. A still larger distortion is observed in 1 with a dihedral angle of 74.0(6) degrees. DFT calculations for 1 gave a ferromagnetic exchange between first neighbors interaction, the calculated J value for this interaction being +11.7 cm-1. In addition, an antiferromagnetic exchange for 1 was obtained for the second neighbor interaction with a J value of -0.05 cm-1. The Bleaney-Bowers equation was used to fit the experimental magnetic susceptibility data for 2 and 3; the best fit was obtained with J values of +3.4 and -16.7 cm-1, respectively. DFT calculations for 2 and 3 confirm the nature and the values of the J constants obtained by the fit of the experimental data. ESR and magnetic studies on the reported compounds show a weak exchange interaction between the copper(II) centers. The low values obtained for the coupling constants can be explained in terms of a poor overlap between the magnetic orbitals, due to the axial-equatorial phenoxo bridging mode observed in these complexes.

Cyanide-Bridged Mn(III)−Fe(III) Bimetallic Complexes Based on the Pentacyano(1-methylimidazole)ferrate(III) Building Block: Structure and Magnetic Characterizations

Seven cyanide-bridged bimetallic complexes have been synthesized by the reaction of [Fe(1-CH3im)(CN)5]2- with Mn(III) Schiff base complexes. Their crystal structure and magnetic properties have been characterized. Five complexes, [Mn2(5-Brsalen)2Fe(CN)5(1-CH3im)] x H2O (1), [Mn2(5-Clsalen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (2), [Mn2(5-Clsaltn)2(H2O)2Fe(CN)5(1-CH3im)] (3), [Mn2(5-Clsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x H2O (4), and [Mn2(5-Brsaltmen)2(H2O)2Fe(CN)5(1-CH3im)] x CH3OH (5), are neutral and trinuclear with two [Mn(SB)]+ (SB2- = Schiff base ligands) and one [Fe(1-CH3im)(CN)5]2-. Complex {[Et4N][Mn(acacen)Fe(CN)5(1-CH3im)]}n x 6nH2O (6) is one-dimensional with alternate [Mn(acacen)]+ and [Fe(CN)5(1-CH3im)]2- units. The two-dimensional complex {[Mn4(saltmen)4Fe(CN)5(1-CH3im)]}n[ClO4]2n x 9nH2O (7) consists of Mn4Fe units which are further connected by the phenoxo oxygen atoms. Magnetic studies show the presence of ferromagnetic Mn(III)-Fe(III) coupling in the trinuclear compounds with the magnetic coupling constant (J) ranging from 4.5 to 6.0 cm-1, based on the Hamiltonian H = -2JSFe(SMn(1) + SMn(2)). Antiferromagnetic interaction has been observed in complex 6, whereas ferromagnetic coupling occurs in complex 7. Complexes 6 and 7 exhibit long-range magnetic ordering with a TN value of 4.0 K for 6 and Tc of 4.8 K for 7. Complex 6 shows metamagnetic behavior at 2 K, and complex 7 possesses a hysteresis loop with a coercive field of 500 Oe, typical of a soft ferromagnet.

Synthesis, characterisation and cryomagnetic studies of a novel homonuclear Nd(III) Schiff base dimer

A novel homodinuclear complex [NdIII(L)(NO3)]2 (1) has been synthesised [H2L=N1,N3- bis(salicylideneimino)diethylenetriamine, a pentadentate Schiff base with N3O2 donor set] and characterised with spectroscopic and micro-analytical techniques. Single crystal X-ray diffraction study reveals a centrosymmetric binuclear neutral entity [space group, P21/n; a=12.911(5); b=11.938(5); c=13.960(5)Å; Z=4] where Nd(III) metal centers are bridged together by two phenoxo oxygen atoms each coming from the two ligands. The most interesting fact is that two similar “salen” moieties of each ligand are behaving completely different in their coordination. In the doubly deprotonated ligand (L2−), one phenoxo oxygen is mono coordinated to the metal, whereas its immediate neighbour on the other end bridges the two Nd(III) centers. The distance between the Nd(III) centers is found to be 3.884(3)Å. Temperature dependence (2–300K) magnetic susceptibility study suggests the presence of an antiferromagnetic interaction operating via two phenoxo bridges.

Magneto-structural study on a tetracopper(II) Schiff base complex stabilizing a decanuclear water aggregate

A new tetranuclear copper(II) complex [Cu 4L 2(3-ppz) 2] ( 1) has been prepared from the reaction of [Cu 2LBr] and 3-phenylpyrazole (3-ppz), where H 3L is a pentadentate Schiff base N, N′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine). The complex as 1 · 6H 2O has been structurally characterized by X-ray crystallography. The structure shows the presence of a tetranuclear copper(II) complex with a core showing Cu⋯Cu distances in the range of 3.261(1)–3.492(1) Å. The tetrameric complex is formed from the self-assembly of two dimeric {Cu 2L} + units in the presence of two anionic 3-ppz ligands as linkers. The alkoxo oxygen atoms bind three copper(II) centers giving two equatorial and one axially elongated Cu–O bond. The variable temperature magnetic susceptibility data in the range 300–17 K show antiferromagnetic spin–spin coupling giving magnetic moments of 3.3 μ B at 300 K and 0.56 μ B at 17 K for the Cu 4 unit. A theoretical fitting to the magnetic data gives J values of −86.3, −47.32 and 11.13 cm −1 with a diamagnetic ground state. The crystal structure shows the presence of two complexes and 12 water molecules in the unit cell belonging to the triclinic space group P 1 ¯ . Among them, 10 water molecules form an aggregate in which six water molecules are in a chair conformation of the cyclohexane-type with two water dimers hydrogen bonded to the cyclic structure. The discrete decameric water assembly is anchored onto the metalloorganic host involving four phenoxo oxygen atoms of two Cu 4 units and four water molecules of the cyclic chair hexameric unit through hydrogen bonding interactions.

Self‐Assembly and Characterization of Homo‐ and Heterodinuclear Complexes of Zinc(II) and Lanthanide(III) Ions with a Tridentate Schiff‐Base Ligand

AbstractTridentate Schiff‐base ligand HL (L = C12H9N2O) reacts with lanthanide(III) nitrates to give complexes of formulae [M2L3(NO3)3], where M = Y3+ (1), La3+ (2), Nd3+ (3), Sm3+ (4), Eu3+ (5), Gd3+ (6), Tb3+ (7), Dy3+ (8), Ho3+ (9), Lu3+ (10), and [MM1L3(NO3)x], where M = Eu3+, and M1 = Dy3+ (11), Zn2+ (12); x = 3 for 11 and 2 for 12. The structures of the complexes have been assigned on the basis of the spectroscopic data (solution analysis) and microanalyses. In the case of complexes 3, 5, 8 and 12 the structures have been confirmed by X‐ray crystallography. The structural analysis of the dinuclear complexes showed the presence of two metal atoms [M(1) and M(2)] and three ligands, L. Each lanthanide atom is coordinated to by 9 donor atoms with typical Ln–N and Ln–O distances. Zinc(II) is coordinated to by two oxygen atoms and four nitrogen atoms from two ligands. The metal ions are bridged by the phenoxo oxygen atoms of the ligands. We have obtained a heterodinuclear complex by a rapid one‐step reaction. Quantum mechanical calculations indicated that the formation of heterodinuclear complex 12 is slightly favored energetically over the homodinuclear complex 5. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Tetranuclear Manganese(II) Complexes of Thiacalixarene Macrocycles with Trigonal Prismatic Six-Coordinate Geometries: Synthesis, Structure, and Magnetic Properties

Two tetranuclear manganese(II) complexes [Mn(II)4(thiaS)2] (1) and [Mn(II)4(thiaSO)2] (2) have been synthesized under solvothermal conditions in methanol with p-tert-butylthiacalix[4]arene (thiaS) and p-tert-butylsulfinylthiacalix[4]arene (thiaSO). For both complexes, the structure has been established from single-crystal X-ray diffraction. [Mn4(thiaS)2].H2O (1) crystallizes in the orthorhombic Immm (No. 71) space group with the following parameters: a = 18.213 (5) angstroms, b = 19.037 (5) angstroms, c = 29.159 (5) angstroms, V = 10110 (4) angstroms3, and Z = 4. [Mn4(thiaSO)2].H2O (2) crystallizes in the monoclinic C2/m (No. 12) space group with the following parameters: a = 33.046(1) angstroms, b = 19.5363 (8) angstroms, c = 15.7773 (9) angstroms, beta = 115.176 (2) degrees, V = 9218.3 (8) angstroms3, and Z = 4. The two complexes are neutral and are best described as manganese squares sandwiched between two thiacalixarene macrocycles. In both complexes, each manganese center is six-coordinated in a trigonal prismatic geometry with four phenoxo oxygen atoms plus two sulfur atoms for 1 or two oxygen atoms from SO groups for 2. The two tetranuclear complexes exhibit identical magnetic behaviors resulting from antiferromagnetic interactions between the four manganese centers. The simulation of the magnetic susceptibility was done considering a single exchange-coupling constant between the manganese(II) ions, J (H = -J(S1S2 + S2S3 + S3S4 + S1S4)). The best fits give the same result for the two complexes: g = 1.94 and J = -5.57 cm(-1).

The crystal structure and thermal stability of [bis-picrate(pentaethylene glycol)] praseodymium(III)picrate complex

[Bis-picrate(pentaethylene glycol)]praseodymium(III) picrate, [Pr(pic)2⋅(EO5]+[pic]−, was successfully obtained from the reaction of praseodymium nitrate hexahydrate, picric acid and pentaethylene glycol in acetonitrile–methanol as solvent. The crystal system is monoclinic with space group P21/c, a = 18.91419(11) A, b = 9.0470(6) A, c = 24.1209(14) A and α = γ = 90∘, β = 109.07(1)∘, V = 3880.3(4) A3 and Z = 4. The Pr atom is coordinated to the flexible and open EO5 ring via all the six oxygen atoms and two picrate ligands, one via phenoxo oxygen atom and the other one with both phenoxo and nitro oxygen atoms in a bidentate manner resulting a 9-coordinate tricapped trigonal prismatic geometry. The two picrate ligands coordinated to the Pr atom are at the opposite sides of the hexadentate EO5 ring with phenyl fragments almost perpendicular with dihedral angle of 89.7(3)∘. Thermal analysis results show that the complex is stable up to 100∘C when it began to slowly decompose and followed by an explosive decomposition at 290∘C.