Synthesis,crystal structure,and magnetic properties of a linear trinuclear Cu(II) complex

A new linear trinuclear Cu(II) complex, [Cu₃(NTA)₂(4,4′-bpt)₄(H₂O)₂]?·?10H₂O (H₃NTA?=?nitrilotriacetic acid, 4,4′-bpt?=?4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole) (1), was obtained from evaporation of an aqueous solution containing Cu(NO₃)₂?·?6H₂O, 4,4′-bpt, nitrilotriacetic acid (H₃NTA), and NaOH. 1 was characterized using single-crystal X-ray diffraction, IR, and elemental analysis. In the trimer, the three linear copper ions are bridged by two NTA carboxylate groups in a syn–anti conformation and connected by 4,4′-bpt to produce a 1-D array. Temperature-dependent magnetic susceptibilities reveal the presence of weak antiferromagnetic exchange between metal centers.     

Synthesis and characterization of a trinuclear Cu(II)3 complex bridged by an extended phloroglucinol-ligand: implications for a rational enhancement of ferromagnetic interactions

The synthesis and characterization of the extended phloroglucinol-ligand H(3)felden based on the trialdehyde 2,4,6-triformylphloroglucinol and its trinuclear Cu(II)(3) complex [(felden){Cu(bpy)}(3)](ClO(4))(3) is presented. This study is motivated to optimize analogous extended phloroglucinol-ligands based on the triketone 2,4,6-triacetylphloroglucinol, which transmit ferromagnetic interactions by the spin-polarization mechanism between three Cu(II) ions and have therefore been applied as the central ligand backbone for a class of heptanuclear single-molecule magnets in a supramolecular approach. A detailed NMR spectroscopic study reveals that the ligand H(3)felden is not in the usually anticipated enol-imine form but in the tautomeric keto-enamine form. The presence of a C(3h) and a C(s) symmetric isomer results in a set of four different signals for each proton. In conjunction with FTIR, electronic absorption spectroscopy, and bond length considerations, it also appears that the complex [(felden){Cu(bpy)}(3)](ClO(4))(3) must be considered as a resonance hybrid of an enolate-imine and a keto-enamine form. A strong contribution of the keto-enamine resonance structure with loss of the central π system explains the weak but ferromagnetic interactions between the Cu(II)S = 1/2 spins. This detailed analysis identifies the strong resonance with unsaturated groups in 2,4,6-position of phloroglucinol as the main source for the low ferromagnetic couplings by the spin-polarization mechanism in these ligands. This provides a synthetic handle to improve the spin-polarization mechanism in these ligands by replacing the imine with amine functions.     

Bright phosphorescence of a trinuclear copper(I) complex: luminescence thermochromism, solvatochromism, and "concentration luminochromism"

A photophysical study is reported for the trinuclear copper(I) complex {[3,5-(CF3)2Pz]Cu}3. The neutral compound exhibits multicolor bright phosphorescent emissions both in the solid state and in solution. The emission can be tuned to multiple visible colors by controlling the temperature, solvent, and {[3,5-(CF3)2Pz]Cu}3 concentration, giving rise to luminescence thermochromism, luminescence solvatochromism, and a new optical phenomenon called "concentration luminochromism", respectively.     

Synthesis and studies of a trinuclear Mn(II) carboxylate complex

We report a carboxylate triangle consisting of three manganese(II) centres which is made from manganese(II) carbonate and pivalic acid. The magnetic exchange within the triangle is extremely weak, and antiferromagnetic. Several models have been used to fit the magnetic data, and the best fit uses two weak antiferromagnetic coupling constants of J(1)=-0.588 cm(-1) and J(2)=-0.855 cm(-1). Exchange interactions between the metal centres has been calculated using DFT adopting all the three possible Heisenberg models for a trinuclear system and the results are compared with experimental values. Spin density distribution is used to analyse the nature of the coupling between the metal centres. EPR spectroscopy has been used to explore the nature of the ground state. Recrystallisation of the trinuclear compound from MeCN gives a polymer, while oxidation in air leads to a known compound--an edge-sharing bitetrahedral (MnIII2MnII4) cage.     

Syntheses and structures of isoindoline complexes of Zn(II) and Cu(II): an unexpected trinuclear Zn(II) complex

Deprotonation of the tridentate isoindoline ligand 1,3-bis[2-(4-methylpyridyl)imino]-isoindoline, 4'-MeLH, and reaction with hydrated zinc(II) perchlorate produces an unexpected trinuclear Zn(II) complex, [Zn(3)(4'-MeL)(4)](ClO(4))(2).5H(2)O (1), whereas reaction with hydrated copper(II) perchlorate in methanol produces the expected mononuclear product, [Cu(4'-MeL)(H(2)O)(2)]ClO(4) (2). X-ray diffraction shows that the trinuclear Zn(II) complex (1) contains a linear zinc backbone, and the arrangement of ligands about the outer chiral zinc(II) atoms is helical. The two terminal zinc ions exhibit approximate C(2) site symmetry, with tetrahedral coordination by two pyrrole and two pyridyl nitrogen atoms of the potentially tridentate isoindoline ligands. The central zinc ion exhibits approximate tetrahedral symmetry, with coordination by four pyridyl nitrogen atoms of four different isoindoline ligands. Pyridyl-pyrrole intramolecular pi-stacking interactions contribute to the stability of the trinuclear cation. The structure of the mononuclear copper(II) complex cation in 2 is best described as a distorted trigonal bipyramid. The isoindoline anion binds Cu(II) in both axial positions and one of the equatorial positions; water molecules occupy the other two equatorial positions.     

Hyperfine splittings in spin-frustrated trinuclear Cu(3) clusters

The hyperfine structures of the EPR spectra of the spin-frustrated and distorted Cu(II) trimers were calculated in the spin-coupling model. The correlations between the hyperfine structures of the EPR spectra and geometry of the Cu(3) clusters (equilateral, isosceles, and scalene triangles) were found. For the EPR spectrum of the spin-frustrated ground state 2(S = 1/2) of an equilateral triangle Cu(3) cluster (J(12) = J(13) = J(23) = J), the calculated hyperfine structure represents the complicated spectrum of the 24 hyperfine lines, of total length 5a, where a is the hyperfine constant of the mononuclear Cu center. For an isosceles Cu(3) cluster (J(12) not equal J(13) = J(23)), the hyperfine splittings of the EPR spectra of the two split S = 1/2 levels with intermediate spins S(12) = 0 and S(12) = 1 are essentially different. The EPR signal of the |(S(12) = 0)S = 1/2> level is characterized by the four equally spaced hyperfine lines (interval A = a) with the same relative spectral amplitudes 16:16:16:16 and total length 3a. For the |(S(12) = 1)S = 1/2> level, the calculated hyperfine structure represents the spectrum of the 16 hyperfine lines with equal spacing (interval A' = a/3), the spectral intensity distribution 1:1:3:3:5:5:7:7:7:7:5:5:3:3:1:1 and total length 5a. These hyperfine spectra differ from the hyperfine structure (10 lines with interval a/3) of the EPR signals of the excited S = 3/2 level of the Cu(3) cluster. The quartet hyperfine structure, characteristic of a single Cu(2+) nucleus, which was observed experimentally for the doublet ground state of the spin-frustrated Cu(3)(II) clusters, corresponds to the hyperfine structure of the EPR signal of the |(S(12) = 0)S = 1/2> level. This hyperfine structure is evidence of the lowering of the Cu(3) cluster symmetry from trigonal to orthorhombic and the small splitting of the spin-frustrated 2(S = 1/2) ground state.     

Pressure-induced phase transitions on a liquid crystalline europium(III) complex

The effect of pressure on the phase behavior of the liquid crystalline complex [Eu(bta)(3)L(2)] (bta is benzoyltrifluoroacetonate, and L is the Schiff base 2-hydroxy-N-octadecyl-4-tetradecyloxybenzaldimine) was studied by X-ray diffraction, Raman spectroscopy, and luminescence spectroscopy. The pressure was varied between ambient pressure and 8.0 GPa. [Eu(bta)(3)L(2)] exhibits a smectic A (SmA) phase at room temperature. The complex undergoes a transition from the SmA phase to a solid lamellar structure around 0.22 GPa and another transition from the solid lamellar phase to an amorphous state from 1.6 to 3.5 GPa. At low pressures, the smectic layer spacing increases, and the intermolecular distance decreases. Above 3.5 GPa, both the interlamellar and the intermolecular spacings hardly change, but the intensity of X-ray reflections exhibits a remarkable decrease and eventually vanishes. An interpretation of the changes in the molecular structure is given. It was found that less interdigitation of the alkyl chains situated in adjacent layers and/or a full extension of the alkyl chains occurred at low pressures and that the second phase transition was accompanied by a transfer of the hydrogen atom from the nitrogen atom of the imine group to the oxygen atom of the Schiff base ligand. The effect of applying pressure equals that of the lanthanide contraction on the phase behavior.     

Room temperature phosphorescence from a platinum(II) diimine bis(pyrenylacetylide) complex

Room temperature phosphorescence has been observed in a synthetically facile Pt(II) complex, Pt(dbbpy)(CtriplebondC-pyrene)(2) (dbbpy = 4,4'-di(tert-butyl)-2,2'-bipyridine; CtriplebondC-pyrene = 1-ethynylpyrene), in fluid solution. The static and time-resolved absorption and luminescence data are consistent with phosphorescence emerging from the appended CtriplebondC-pyrenyl units following excitation into the low energy dpi Pt --> pi* dbbpy metal-to-ligand charge transfer absorption bands.     

Aggregation-induced phosphorescence and mechanochromic luminescence of a tetraphenylethene-based gold(I) isocyanide complex

In this study, a new twisting gold(I) isocyanide complex based on tetraphenylethene (TPE), TPE-NC-Au, was designed and synthesized. It exhibits aggregation induced phosphorescence (AIP) characteristics, owing to the incorporation of Au moiety and conformation rigidification in the aggregated states. Moreover, the emission color of the crystalline solid of TPE-NC-Au changes from blue (454 nm) to green (500 nm) in response to mechanical grinding, due to the combined effects of conformation planarization, enhanced π…π stacking, as well as the emergence of aurophilic interactions in the ground amorphous state. Notably, the emission color can be restored upon solvent fuming, associating with the reconstruction of crystalline lattices. The AIP and switchable mechanochromism of TPE-NC-Au make it suitable for potential applications in bioimaging, sensing, and optoelectronic devices.     

Magnetic studied of a binuclear Cu(II) complex constructed from Cu(II) macrocyclic complex

A new binuclear copper(II) compound [(CuL)₂(Tpha)](ClO₄)₂ · 4H₂O (I), where L = 1,3,6,9,11,14-hexaazatricyclo[12.2.1.1^6,9]octadecane, Tpha = terephthalate dianion, has been constructed and structurally characterized by X-ray crystallography. Crystal analysis denotes that complex I crystallizes in the monoclinic system, space group P2₁/c with a = 11.115(2), b = 13.185(3), c = 16.184(3) Å and β = 105.68(3)°. Magnetic measurements confirm that I present an antiferromagnetic interaction between the paramagnetic ions.     

Magnetic properties of a manganese(II) trinuclear complex involving a tridentate Schiff-Base ligand

The Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol gave a tridentate ligand, abbreviated as Hpoxap. This ligand bears the functionality of a terminating group in a trinuclear complex [Mn(poxap)Mn(ac)4Mn(poxap)], where ac- is the acetate bridge. The magnetic data were treated simultaneously during the fitting procedure with the spin Hamiltonian containing isotropic exchange, the zero-field splitting parameters, and the molecular-field correction and resulted in JMn-Mn/hc = -4.73 cm-1, gMn(t) = 1.96, DMn(t)/hc = -0.45 cm-1, and zj/hc = +0.45 cm-1 with ground state S = 5/2, where t = terminal atom. At low temperature, the features of a ferromagnetic correlation become evident.     

Oxidative DNA strand scission induced by a trinuclear copper(II) complex

A novel trinuclear copper(II) complex, Cu3-L (L = N,N,N',N',N' ',N' '-hexakis(2-pyridyl)-1,3,5-tris(aminomethyl)benzene), exhibited efficient oxidative strand scission of plasmid DNA. The solution behavior of the complex has been studied by potentiometric titration, UV spectroscopy, and cyclic voltammetry. The data showed that there are three redox-active copper ions in the complex with three types of bound water. The complex demonstrated a moderate binding ability for DNA. Cu3-L readily cleaves plasmid DNA in the presence of ascorbate to give nicked (form II) and then linear (form III) products, while the cleavage efficiency using H2O2 is less than by ascorbate, suggesting that the cleavage mode of the trinuclear complex is somewhat different from the traditional Fenton-like catalysis. Meanwhile, Cu3-L is far more efficient than its mononuclear analogue Cu-DPA (DPA = 2,2'-dipyridylamine) at the same [Cu2+] concentration, which suggests a possible synergy between the three or at least two Cu(II) centers in Cu3-L that contributes to its relatively high nucleolytic efficiency. Furthermore, the presence of standard radical scavengers does not have clear effect on the cleavage efficiency, suggesting the reactive intermediates leading to DNA cleavage are not freely diffusible radicals.     

Structure of a new trinuclear nickel(II) complex with a salen-type bisoxime ligand

A new trinuclear Ni(II) complex {[NiL(DMF)]₂(OAc)₂Ni}·2DMF (H₂L = 4,4′-dichloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol) is synthesized and characterized by elemental analyses, IR spectra, UV-Vis spectra and X-ray crystallography. The results show that the Ni(II) complex consists of three Ni(II) ions, two tetradentate (μ-L)^2? units, two coordinated μ-acetate ions, two coordinated DMF molecules, and two crystallization DMF molecules. All hexacoordinated Ni(II) ions of the complex have a slightly distorted octahedral geometry. The crystal packing of the Ni(II) complex reveals a notable feature of this structure: the formation of an infinite supramolecular 2D layered structure by virtue of intermolecular C-H…O hydrogen bonding.     

Oxamato-bridged trinuclear Ni(II)Cu(II)Ni(II) complexes with irregular spin state structures and a binuclear Ni(II)Cu(II) complex with an unusual supramolecular structure: crystal structure and magnetic properties

Four oxamato-bridged heterotrinuclear Ni(II)Cu(II)Ni(II) complexes of formula ([Ni(bispictn)](2)Cu(pba))(ClO(4))(2).2.5H(2)O (1), ([Ni(bispictn)](2)Cu(pbaOH))(ClO(4))(2).H(2)O (2), ([Ni(cth)](2)Cu(pba))(ClO(4))(2) (3), and ([Ni(cth)](2)Cu(opba))(ClO(4))(2).H(2)O (4) and a binuclear Ni(II)Cu(II) complex of formula [Cu(opba)Ni(cth)].CH(3)OH (5) have been synthesized and characterized by means of elemental analysis, IR, ESR, and electronic spectra, where pba = 1,3-propylenebis(oxamato), pbaOH = 2-hydroxyl-1,3-propylenebis(oxamato), opba = o-phenylenebis(oxamato), bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine, and cth = rac-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane. The crystal structures of 1, 3, and 5 have been determined. The structures of complexes 1 and 3 consist of trinuclear cations and perchlorate anions, and that of 5 consists of neutral binuclear molecules which are connected by hydrogen bonds and pi-pi interactions to produce a unique supramolecular "double" sheet. In the three complexes, the copper atom in a square-planar or axially elongated octahedral environment and the nickel atom in a distorted octahedral environment are bridged by the oxamato groups, with Cu.Ni separations between 5.29 and 5.33 A. The magnetic properties of all five complexes have been investigated. The chi(M)T versus T plots for 1-4 exhibit the minimum characteristic of antiferromagnetically coupled NiCuNi species with an irregular spin state structure and a spin-quartet ground state. The chi(M)T versus T plot for 5 is typical of an antiferromagnetically coupled NiCu pair with a spin-doublet ground state. The Ni(II)-Cu(II) isotropic interaction parameters for the five complexes were evaluated and are between 102 and 108 cm(-)(1) (H = -JS(Cu).S(Ni)).     

Synthesis and crystal structure of a new oxamidato-bridged trinuclear Cu2 II MnII complex containing a macrocyclic ligand

A new oxamidato-bridged trinuclear complex [(CuL)₂Mn](ClO₄)₂ (H₂L = 2,3-dioxo-5,6,14,15-dibenzo-1,4, 8,12-tetraazacyclo-pentadeca-7,3-dien)] was prepared and its structure determined. The complex is monoclinic, space group P2₁/n, with a = 10.625(3), b = 11.602(3), c = 16.020(5)?Å, β = 91.031(5)°, Z = 2; it was refined to R1 = 0.0555. In the solid state, the structure consists of centrosymmetric [(CuL)₂Mn]²⁺ cations separated by perchlorate anions; the central manganese atom is four coordinated with square planar geometry.     

Rhenium complexes with 2-(diphenylphosphinomethyl)aniline: formation of a cyclic, trinuclear oxorhenium(V) core

Reactions of 2-(diphenylphosphinomethyl)aniline, H(2)L(2), with (NBu(4))[ReOCl(4)] yield different oxo rhenium(V) complexes depending on the conditions applied. This comprises monomeric compounds such as [ReOCl(3)(H(2)L(2))] (1), [ReOCl(2)(OMe)(H(2)L(2))] (2), or [ReO(2)(H(2)L(2))(2)]Cl (5) as well as the dimeric μ-oxo complex [{ReOCl(2)(H(2)L(2))}(2)]O] (3) and the oxo-bridged trimer [{ReOCl(H(2)L(2))}O](3) (4). The latter compound represents the first example of a hitherto unknown trinuclear, cyclic oxo(V) core. [{ReOCl(H(2)L(2))}O](3) contains a tensed 6-membered metallacycle, which readily undergoes rearrangements and reactions with additional ligands. Compounds of the compositions 5 and [ReO(2)(H(2)L(2))(H(2)L(1))]Cl (6) were isolated either from the decomposition of 4 in CH(2)Cl(2)/n-pentane or from reactions with 2-(diphenylphosphino)aniline, H(2)L(1).     

Vapochromic and mechanochromic phosphorescence materials based on a platinum(II) complex with 4-trifluoromethylphenylacetylide

Planar platinum(II) complex Pt(Me(3)SiC≡CbpyC≡CSiMe(3))(C≡CC(6)H(4)CF(3)-4)(2) (6) with 5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine and 4-trifluoromethylphenylacetylide exhibits remarkable luminescence vapochromic and mechanochromic properties and a thermo-triggered luminescence change. Solid-state 6 is selectively sensitive to vapors of oxygen-containing volatile compounds such as tetrahydrofuran (THF), dioxane, and tetrahydropyrane (THP) with phosphorescence vapochromic response red shifts from 561 and 608 nm to 698 nm (THF), 689 nm (dioxane), and 715 nm (THP), respectively. Upon being mechanically ground, desolvated 6, 6·CH(2)Cl(2), and 6·(1)/(2)CH(2)ClCH(2)Cl exhibit significant mechanoluminescence red shifts from 561 and 608 nm to 730 nm, while vapochromic crystalline species 6·THF, 6·dioxane, or 6·THP affords a mechanoluminescence blue shift from 698 nm (THF), 689 nm (dioxane), or 715 nm (THP) to 645 nm, respectively. When the compounds are heated, a thermo-triggered luminescence change occurs, in which bright yellow luminescence at 561 and 608 nm turns to red luminescence at 667 nm with a drastic red shift. The multi-stimulus-responsive luminescence switches have been monitored by the changes in emission spectra and X-ray diffraction patterns. Both X-ray crystallographic and density functional theory studies suggest that the variation in the intermolecular Pt-Pt interaction is the key factor in inducing an intriguing luminescence switch.     

Ground-state electronic and magnetic properties of a mu3-oxo-bridged trinuclear Cu(II) complex: correlation to the native intermediate of the multicopper oxidases

The ground-state electronic and magnetic properties of one of the possible structures of the trinuclear Cu(II) site in the native intermediate (NI) of the multicopper oxidases, the mu(3)-oxo-bridged structure, are evaluated using the C(3)-symmetric Cu(3)(II) complex, mu(3)O. mu(3)O is unique in that no ligand, other than the oxo, contributes to the exchange coupling. However, mu(3)O has a ferromagnetic ground state, inconsistent with that of NI. Therefore, two perturbations have been considered: protonation of the mu(3)-oxo ligand and relaxation of the mu(3)-oxo ligand into the Cu(3) plane. Notably, when the oxo ligand is sufficiently close to the Cu(3) plane (<0.3 Angstroms), the ground state of mu(3)O becomes antiferromagnetic and can be correlated to that of NI. In addition, the ferromagnetic (4)A ground state of mu(3)O is found from variable-temperature EPR to undergo a zero-field splitting (ZFS) of 2D = -5.0 cm(-1), which derives from the second-order anisotropic exchange. This allows evaluation of the sigma-to-pi excited-state exchange pathways and provides experimental evidence that the orbitally degenerate (2)E ground state of the antiferromagnetic mu(3)O would also undergo a ZFS by the first-order antisymmetric exchange that has the same physical origin as the anisotropic exchange. The important contribution of the mu(3)-oxo bridge to the ground-to-ground and ground-to-excited-state superexchange pathways that are responsible for the isotropic, antisymmetric, and anisotropic exchanges are discussed.