Magnetic coupling in EE and EO azido-bridged binuclear copper complexes: Synthesis,structure and magnetic studies

Four azide bridged dinuclear copper(II) complexes, [Cu₂(L^X)₂(N₃)₂](ClO₄)₂, with L^X = substituted N,N-bis[(3,5-dimethylpyrazole-1-yl)-methyl]benzylamine, [X = H (1), OMe (2), Me (3) and Cl (4)] have been synthesized, out of which complexes 1 and 2 have been characterized structurally. In Complex 1 the two bridging azide ligands have connected the two metal centers in an end-on (EO) fashion with aSP (asymmetric Square Pyramidal) geometry and showed an weak antiferromagnetic interaction (J = −3.34 cm⁻¹). On the contrary, in complex 2, the two metal centers have been connected in end-to-end (EE) fashion exhibiting moderately strong ferromagnetic interaction (J = +19.7 cm⁻¹). Cyclic voltammetric studies performed on all the four complexes show a reasonably good correlations when E_1/2 for Cu^IICu^II → Cu^IICu^III and Cu^IICu^III → Cu^IIICu^III oxidations are plotted against σ (substituent constants) with ρ = −0.182 (R² = 0.92) and −0.684 (R² = 0.99) respectively.     

Assembly of cyano-bridged Cu(II)/Cu(II) and Cu(I)/Cu(II) compounds obtained by controlled ration of cyanide

One reaction system of Cu²⁺, dipn, and CN⁻ with two different molar ratio sets of 1:1:5, and 2:1:8 produced two compounds 1 [Cu^II(dipn)][Cu^II(CN)₄], and 2, respectively (dipn = dipropylenetriamine). Their structures were determined by X-ray crystallography. Compound 2 is built from Cu(I) and Cu(II) centers, which are bridged by cyanide groups and metal-metal bonds. The magnetic properties of 1 and 2 were investigated in 2-300 K. Compound 1 exhibits an antiferromagnetic exchange interaction between copper(II) ions mediated by cyano-bridges.     

Novel copper complexes based on the thiocyanate bridge - Synthesis, X-ray studies and magnetic properties

Three novel compounds {[Cu(bpzm)(SCN)][Cu(bpzm)(MeOH)][Cu(SCN)₄]}_n (1a), {[Cu₂(bpzm)₂(μ-SCN)(SCN)₃]}_n (1b) and [Cu₂(μ-SCN)₂(SCN)₂(dpa)₂] (2) have been obtained in one-step self-assembly reaction of copper dichloride, a suitable N-N ligand (bis(pyrazol-1-yl)methane and 2,2′-dipyridylamine) and ammonium thiocyanate. For the reaction involving bis(pyrazol-1-yl)methane, an unprecedented in situ reduction of some Cu(II) ions to Cu(I) has been observed. The compound {[Cu(bpzm)(SCN)][Cu(bpzm)(MeOH)][Cu(SCN)₄]}_n (1a) belongs to a relatively scarce group of mixed-valence Cu^II/Cu^I coordination polymers with interesting polymeric architecture. It creates infinite two-dimensional structure consisting of layers extending along crystallographic plane (0 0 1), in which the cations [Cu^II(bpzm)(SCN)]⁺ and [Cu^II(bpzm)(MeOH)]²⁺ are connected by ions [Cu^I(SCN)₄]³⁻ through single end-to-end thiocyanato bridges. Structure 1b consists two crystallographically independent chains. The chain A has a zig-zag form and extends along the crystallographic direction [0 0 1], whereas the second chain is linear and runs along the crystallographic direction [0 1 0]. The structure 2 consists of dinuclear [Cu₂(dpa)₂(μ-SCN)₂(SCN)₂] units. Variable-temperature magnetic susceptibility measurements show very weak antiferromagnetic interactions between the paramagnetic centres Cu(II) centers inside the crystal lattices of three novel compounds.     

Structural and magnetic properties of metal complexes with pyridine-2,6-dicarboxylate and 5-(4-bromophenyl)-2,4′-bipyridine

A series of complexes has been synthesized based on pyridine-2,6-dicarboxylate (L1) as the bridging ligand and 5-(4-bromophenyl)-2,4′-bipyridine (L2) as the pendant with different metal ions such as Ni^II, Co^II, and Cu^II, under hydrothermal conditions. In nickel and cobalt complexes [M(L1)(L2)₂ · H₂O]_n (M = Ni²⁺ or Co²⁺), the metal ions are bridged by L1 to form 1D coordination zigzag polymeric chains with L2 pendants possessing hexa-coordinated distorted octahedral geometries. While the copper ions are penta-coordinated by L1 and L2 with distorted square pyramidal geometries forming the tetranuclear cluster with the formula [Cu₄(L1)₄(L2)₄] · 2H₂O. It has been found that both the structure and magnetic property of these complexes are metal ions dependent. Intramolecular antiferromagnetic interactions were observed in the nickel and cobalt 1D coordination polymers, while ferromagnetic coupling was found in the tetranuclear copper cluster. Density functional theory calculations suggested that the O–C–O bridges of L1 in a basal–apical mode are responsible for intracluster intermetallic ferromagnetic exchange for the tetranuclear copper cluster.     

Synthesis, crystal structure, spectroscopy and magnetic properties of a dinuclear Cu complex with 3,5-bis(2-pyridyl)pyrazole bridging ligand

A dinuclear Cu^II complex [Cu₂(bpp)₂(H₂O)₂](ClO₄)₂ (1) with 3,5-bis(2-pyridyl)pyrazole (Hbpp), has been synthesized and characterized by elemental analyses, thermal analysis, conductance, UV-vis and IR spectra. The crystal structure of 1, determined by X-ray diffraction technique, reveals that two centrosymmetric Cu^II centers are bridged by a pair of tetradentate anionic bpp ligands, adopting a square-pyramidal environment with the water ligand occupying the axial site. An interesting feature of this structure is the formation of a two-dimensional supramolecular network through O-H?O hydrogen bonds between the water moieties of the cationic [Cu₂(bpp)₂(H₂O)₂]²⁺ subunits and perchlorate anions. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility and EPR measurements. Very strong antiferromagnetic interaction between the Cu^II centers (with H=−JS₁S₂, J=−368.3 cm⁻¹) has been observed, and the magneto-structural correlations was analyzed.     

Weak ferromagnetism in 1D coordination polymers: Syntheses,crystal structures,spectroscopic and magnetic properties of [Cu(L)(Memal)]n (Memal = the dianion of methylmalonic acid,L = 1,10-phenanthroline, 2,2′-bipyridine)

Investigation of the CuCl₂/H₂Memal/L (H₂Memal = methylmalonic acid, L = 1,10-phenanthroline or 2,2′-bipyridine) reaction system in MeOH and various molar ratios has lead to the isolation of two one-dimensional coordination polymers presenting the [Cu(L)(Memal)] repeating unit (1, L = 1,10-phen; 2, L = 2,2′-bpy). The Memal²⁻ ligand adopts the bidentate [chelating] + unidentate coordination mode between the Cu^II ions. Magnetic susceptibility measurements on 1 and 2 indicated the existence of weak ferromagnetic intrachain interactions and X-band EPR spectra from powdered samples of 1 and 2 are consistent with the stereochemistry of the Cu^II ions and with the presence of weak exchange interactions.     

Ferromagnetic exchange coupling in a new bis(μ-chloro)-bridged copper(II) Schiff base complex: Synthesis,structure, magnetic properties and catalytic oxidation of cycloalkanes

A new (μ-chloro)-bridged complex [Cu(HL)Cl]₂ · H₂O (1) with the Schiff base ligand H₂L, [2-((E)-(2-hydroxyethylimino)methyl)-4-bromophenol], has been synthesized and characterized by elemental analysis, IR, UV–Vis and EPR spectroscopic studies. X-ray diffraction studies show that 1 is a binuclear Cu^II complex with a pair of chlorine atoms bridging the copper atoms in a central Cu₂Cl₂ core. Each copper atom in 1 adopts a distorted square-pyramidal geometry with the imine nitrogen atom, alkoxy and phenoxy oxygen atoms from the Schiff base ligand and a bridging chlorine atom constructing the basal plane, while the apical position of the pyramid is occupied by the other bridging chlorine atom. Variable temperature susceptibility measurements show that complex 1 presents the highest ferromagnetic coupling [J = +43.2(5) cm⁻¹] reported till date in any doubly chloro-bridged Cu^II dimer, and a weak interdimer antiferromagnetic coupling [J′ = -0.276(8) cm⁻¹]. The complex also exhibits high catalytic activity towards the oxidation of hydrocarbons using H₂O₂ as terminal oxidant.     

DFT-BS study on the magnetic coupling interaction in a series of (R-Bpmp)Mn2(μ-OAc)2 complexes

The magnetic properties of a series of dinuclear Mn^II systems are investigated by the calculations based on density functional theory combined with broken-symmetry approach (DEF-BS). It is found that there are weak antiferromagnetic interactions in these systems with different bridging ligands. The changing trend of the magnetic coupling constants J indicates that with the electronegativity of the increasing bridging ligands, the antiferromagnetic coupling interaction is weakened. The analyses of the magnetic orbitals and the spin densities show that the weakly antiferromagnetic couplings in these systems are due to the vertical magnetic d orbitals and the weak spin delocalization. These results should be instructive for the design of new molecular magnetic materials.     

Double End‐On Azido Copper(II) Dinuclear Complex with Oxazoline Ligand: Synthesis,Structure, Magnetic Properties and Theoretical Study

A double azido‐bridged Cu^II dinuclear complex with the chelating chiral ligand, [Cu₂(L)₂(N₃)₄] ( 1 ) [L = (+)‐2, 2′‐isopropylidene‐bis((4R)‐4‐benzyl‐2‐oxazoline)] was synthesized and characterized by single‐crystal X‐ray diffraction, IR spectroscopy, magnetic measurements, and theoretical studies. The asymmetric double end‐on azido bridges in complex 1 lead to a weak antiferromagnetic behavior with J = –7.4 cm^–1. The exchange interactions in complex 1 were investigated by DFT calculations, and the calculated exchange interaction (J = –8.0 cm^–1) is in good agreement with the experimental value.     

A linear Cu-Gd-Cu-Gd complex derived from the assembly reaction of [NaCuH3L] and [Gd(thd)3(H2O)2] (H3L = meso-1,2-diphenyl-1-(2-oxybenzamido)-2-(2-oxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetra-methyl-3,5-heptanedione)

A linear tetranuclear Cu^II-Gd^III-Cu^II-Gd^III complex [Cu^IIL^dpen(meso)Gd^III(thd)₂(H₂O)]₂ was synthesized from the reaction of [NaCu^IIL^dpen(meso)(DMF)] with [Gd^III(thd)₃(H₂O)₂], and the structures and magnetic properties were investigated, where H₃L^dpen(meso) = meso-1,2-diphenyl-1-(2-hydroxybenzamido)-2-(2-hydroxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione. The Cu^II complex component [NaCu^IIL^dpen(meso)(DMF)] has a one-dimensional (1D) chain structure, in which the Na⁺ ion is coordinated by two phenoxo and an ethoxy oxygen atoms of a Cu^II complex and an amido oxygen atom of the adjacent Cu^II unit to produce the 1D structure, in which the diphenylethylenediamine moieties have the array of {(1R,2S)-Na-(1S,2R)}_1∞. The assembly reaction of the Cu^II and Gd^III components gave a linear complex with the array of Cu(1)-Gd(1)-Cu(2)-Gd(2), in which two diphenylethylenediamine moieties have the same chirality of (1R,2S)-(1R,2S) or (1S,2R)-(1S,2R). Two linear Cu(1)-Gd(1)-Cu(2)-Gd(2) units are linked by hydrogen bonds through two water molecules to give a cyclic structure with a center of symmetry. The temperature dependence of the magnetic susceptibilities and field-dependent magnetization revealed the ferromagnetic interaction between the Cu^II and Gd^III ions within the linear chain.     

2D Compound Constructed by Cu3 Units with Mixed Azido and Tetrazole Double Bridges: Synthesis,Structure, and Theoretical Study on Magnetic Properties

The two‐dimensional (2D) layer Cu^II compound [Cu₃(L)₂(N₃)₄] ( 1 ) [L = 2‐amino‐3‐(5‐tetrazole)‐methyate‐N‐pyridine] was synthesized by in‐situ hydrothermal reaction of CuCl₂ · 2H₂O, NaN₃, and 3‐(5‐tetrazole)‐methyate‐N‐pyridine. The central Cu1 and Cu2 atoms are located in five‐coordinate and six‐coordinate arrangements, respectively. Three Cu^II ions are linked by mixed double EO (end‐on)‐azido‐tetrazole bridges to give trinuclear Cu^II clusters, which are further extended by EE (end‐to‐end) azido bridges to form 2D metal‐organic layers. The magnetic exchange interactions in complex 1 were investigated by DFT calculations, and the calculated exchange interaction (J = –849 cm^–1) revealed that the double EO‐azido‐tetrazole bridges transmit antiferromagnetic coupling between Cu^II ions.     

High-dimensional mixed-valence copper cyanide complexes: Syntheses,structural characterizations and magnetism

Reactions of CuCl₂ with different CN complexes in presence of a neutral ancillary ligand lead to two novel mixed-valence Cu complexes [Cu^II(bpy)Cu^I(CN)₃]_n, 1 (bpy = 2,2′-bipyridine) and {[Cu^II(tn)₂][Cu^I₄(CN)₆]}_n2 (tn = 1,3-diaminopropane). For compound 1, the asymmetric unit involves two Cu ions Cu1 and Cu2 (Cu^I and Cu^II centres, respectively) which strongly differ in their environments. The Cu1 ion presents a CuC₄ pseudo-tetrahedral geometry, while the Cu2 ion presents a CuN₅ slightly distorted square-pyramidal geometry. The extended structure of 1 is generated by three cyano ligands which differ in their coordination modes. One CN group has a μ₃ coordination mode and bridges two Cu^I and one Cu^II ion, while the two other CN groups act as μ₂ bridges leading to a sophisticated 3-D structure. As for 1, the asymmetric unit of 2 involves three crystallographically different Cu ions (Cu1A and Cu1B, presumably Cu^I centres, and Cu2 presumably Cu^II centres). The Cu2 ion presents centrosymmetric CuN₄ coordination environments involving four nitrogen atoms from two bidentate tn ligands; while the Cu1A and Cu1B ions are three coordinated to cyano groups. The structure can be described as formed by 18-membered “[Cu^I(CN)]₆” planar metallocycles that are connected to their six neighbors to generate 2-D sheets; these sheets stack forming infinite hexagonal channels in which the [Cu(tn)₂]²⁺ units are located. Magnetic measurements show an unexpected weak ferromagnetic coupling (θ = 0.239(1) K) of the Cu^II ions through the long and “a priori diamagnetic” –NC–Cu^I–CN– bridges in compound 1 and an essentially paramagnetic behavior in compound 2.     

Rhenium(IV)–copper(II) heterobimetallic complexes: Synthesis,crystal structure and magnetic properties

Two Re(IV)–Cu(II) heterometallic complexes {(CuL_α)[ReCl₄(ox)]}_n (where L_α = N-meso-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄), 1, and (CuL_β)[ReCl₄(ox)] (L_β = N-rac-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄N-rac-5,12-Me₂-7,14-Et₂-[14]-4,11-dieneN₄), 2, were synthesized. The [CuL²⁺] macrocyclic cation is coordinated from above and below by [ReCl₄(ox)]²⁻ units through the chloro-ligands and creates a chloro-bridged heterometallic Re^IV–Cu^II one-dimensional zig-zag chain. Compound 2 can be viewed as a heterobimetallic dinuclear unit, in which the Re(IV)-Cu(II) centers are linked by an oxalato bridge. The magnetic behavior of 1 and 2 has been investigated over the temperature range 1.8–300 K. Compound 1 behaves like a ferrimagnetic {Re(IV)–Cu(II)} bimetallic, one-dimensional chain with intrachain antiferromagnetic coupling. Compound 2 shows a weak antiferromagnetic interaction within the [Re(IV)–Cu(II)] unit along with a strong single-ion anisotropy, D(Re) = −63 cm⁻¹.     

Syntheses, structures, and properties of metal complexes involving π-conjugated tetrathiafulvalene-pyridine ligand

Four metal complexes based on the phenyl-bridged pyridine ligand with tetrathiafulvalene unit (TTF-Ph-Py, L), Ni^II(acac)₂(L)₂ (1, acac = acetylacetonate), M(hfac)₂(L)₂ (M = Ni^II, 2; M = Cu^II, 3; hfac = hexafluoroacetylacetonato) and [Co^II(Tp^Ph2)(OAc)(L)]·H₂O (4, Tp^Ph2 = hydridotri(3,5-diphenylpyrazol-1-yl) borate), have been synthesized and structurally characterized. The absorption spectra and redox behaviors of these new compounds have been studied. Optimized conformation and molecular orbital diagram of L has been calculated with density functional theory (DFT).     

Synthesis,crystal structures and magnetic properties of five new metal(II) compounds constructed with isomers of aminobenzonitrile and dicyanamide ligands

Five new compounds formulated as [Ni^II(dca)₂(para-ABN)₂(H₂O)₂] (1), [Cu^II(dca)₂(para-ABN)₂(H₂O)₂] (2), [Cu^II(dca)₂(para-ABN)₂]_n, (3), [Cu^II(dca)₂(ortho-ABN)₂]_n, (4) and [Cd^II(dca)₂(meta-ABN)₂]_n (5), where dca = dicyanamide and ABN = aminobenzonitrile, have been synthesized and characterized by single crystal X-ray diffraction studies and low temperature (300–2 K) magnetic measurements. The structural analyses revealed that 1 and 2 are isomorphous where dca and para-ABN both act as monodentate ligands. 3 consists of infinite double stranded chains of Cu(II) ions connected through the para-ABN bridges whereas 4 and 5 consist of infinite double stranded chains of Cu(II) and Cd(II) respectively, connected through μ_1,5-dca bridges. The compounds extend their geometries to three-dimensional for 1–3 and 5 and two-dimensional for 4 through hydrogen bonding interactions. All the metal ions Ni²⁺, Cu²⁺ and Cd²⁺ are located on inversion centres and have distorted octahedral coordination geometries. The variable temperature magnetic susceptibility measurements show that the global feature of the χ_MT versus T curves for 3 and 4 is characteristic of very weak antiferromagnetic interactions and between 300 and 2 K the best fit parameters were determined as J = −2.35 and −5.1 cm⁻¹, respectively.     

Magnetostructural correlations in the antiferromagnetic Co2−x Cux(OH)AsO4 (x=0 and 0.3) phases

The Co_2−xCu_x(OH)AsO₄ (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2) Å, b=8.559(2) Å, c=6.039(1) Å and a=8.316(1) Å, b=8.523(2) Å, c=6.047(1) Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O₅-trigonal bipyramid dimers and M(2)O₆-octahedral chains (M=Co and Cu) are present. Co₂(OH)AsO₄ shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21 K within the presence of a ferromagnetic component below the ordering temperature. When Co²⁺ is partially substituted by Cu²⁺ions, Co_1.7Cu_0.3(OH)AsO₄, the ferromagnetic component observed in Co₂(OH)AsO₄ disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx²−y² orbital and the absence of overlap between neighbour ions.     

Synthesis,structure, and magnetic properties of two dimer paddle-wheel CuII toluate complexes with nitronyl nitroxide radicals

Two new paddle-wheel dimeric copper complexes, [Cu₂(4-MePhCOO)₄(NITmPy)₂] (1) and [Cu₂(3-MePhCOO)₄(NITmPy)₂] (2) (NITmPy?=?2-(3-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro1H-imidazolyl-1-oxyl-3-oxide), were synthesized by reaction of copper toluate and NITmPy. Single crystal X-ray analyses revealed that both complexes are symmetrical dimers. Cu with four deprotonated methyl-benzoate bridging ligands form a paddle-wheel core and pyridyl nitrogen of radical ligands at the apical position. Based on the Cu–Cu axis of 1 and 2, we exploited the steric constraints of the methyl groups and induced the paddle-wheel. Two magnetic exchange pathways with strong antiferromagnetic interaction between dimeric Cu^II ions and weak antiferromagnetic interaction between NITmPy ligands exist in the complexes. IR and powder X-ray diffraction of the complexes were also studied.     

Intermolecular Interaction and Magnetic Coupling Mechanism of a Mononuclear Nickel(II) Complex

The mononuclear complex [Ni(HOphen)(OSO₃)(H₂O)₃] · 5H₂O (HOphen = 1, 10‐phenanthrolin‐2‐ol) was prepared and its single structure was determined by X‐ray crystallography. In this complex, the Ni^II ion has a distorted octahedral arrangement. Crystal structure analysis shows that two kinds of π–π stacking interactions and C–H ··· O short contact intermolecular interactions exist among the adjacent complexes. Fitting to the variable‐temperature magnetic susceptibility data gave the magnetic coupling constant, 2J = –0.98 cm^–1. Theoretical calculations, based on density functional theory (DFT) coupling with the broken‐symmetry approach (BS), revealed that the π–π stacking magnetic coupling pathways resulted in weak ferromagnetic interactions with 2J = 4.86 cm^–1 and 2J = 4.16 cm^–1, respectively, for the adjacent Ni^II ions with separations of 8.568(19) Å and 8.749(32) Å, respectively; whereas the magnetic coupling pathway of the C–H ··· O short contact intermolecular interaction led to a weak antiferromagnetic interaction with 2J = –17.62 cm^–1 for the adjacent Ni^II ions with a separation of 10.291(26) Å. The ferromagnetic coupling sign can be explained by the McConnell I spin‐polarization mechanism.     

聚合物{[CuII(Hpb) (mal)]H2O}n :单体的量子化学计算和磁性研究

{[Cu^Ⅱ（Hpb）（mal）]H=O}n （Hpb=2-2＇-pyridylbenzimidazole, mal=maleic acid） is a helical chain-like polymer complex. In order to investigate the electronic structure of the complex, the monomer Cu^Ⅱ（Hpb）（mal） was obturated with different functional groups respectively. For these selective segments, the geometry optimizations were conducted by using hybrid DFT （B3LYP）methods to find that the structure obturated with H2O was better consistent with the experiment, and then this model would be used to latter calculations, such as the frontier molecular orbital and the NBO charge population analysis. In addition the magnetic behaviors of this complex were analyzed by experiments and the weak antiferromagnetic couple between copper（Ⅱ） ions was observed. The exchange coupling constant was calculated by DFT based on the spin broken symmetry formalism. The calculated coupling constants were in good agreement with the experimental data.     

Theoretical study on photoinduced magnetization process: Possible meta-stable molecular structure for a photomagnetic high-spin molecule [MoIV(CN)2(CN-CuL)6]8+

An intermediate in photoinduced magnetization process for the photomagnetic high-spin molecule [Mo^IV(CN)₂(CN-CuL)₆]⁸⁺ is studied with quantum chemistry calculations of the density functional theory and the ab initio multireference configuration interaction methods. It is found that the intramolecular electronic transfer from Mo^IV to Cu^II leads one trigonal-bipyamid coordinated Cu^II to be changed to the tetrahedral coordinated Cu^I with the light irradiation. The calculated magnetic properties show that the paramagnetic system [Mo^IV(CN)₂(CN-Cu^IIL)₆]⁸⁺ with six isolated spin 1/2 Cu ions is changed to ferromagnetic coupling high-spin system [Mo^V(CN)₂(CN-Cu^IIL)₅(CN-Cu^IL)]⁸⁺. These calculations will help to understand photoinduced magnetization phenomenon and provide a clue for the synthesization of new reversible photoinduced magnetic compounds.