Synthesis, structure and magnetic properties of two new azido-Co(II) coordination architectures: from ferromagnetic coupling to single-chain-magnets

Two new azido-Co(II) complexes with pyrazine carboxylato ligands, [Co(N(3))(L)·H(2)O](n) (L = pyrazine-2-carboxylato) (1) and [CoNa(N(3))(2)(L)](n) (2), have been obtained by carefully tuning the Co(II):N(3)(-) ratio. Here we present the structural and magnetic characterization of these new species. Modulation of the coordination environment of Co(II) leads to a variation of the magnetic properties of the obtained compounds. Complex 1 exhibits ferromagnetically coupled [Co(2)] units that form the rungs of the ladder with a nearly negligible coupling between these units, while complex 2 is a 2D arrangement of 1D Co(II) single-chain magnets.     

Complexed bridging ligand,Cu(bptap)2, as a ferromagnetic coupler

A novel complexed bridging ligand [Cu(bptap)2] which acts as a ferromagnetic coupler forms one dimensional chain consisting of tri-copper(II) [Cu2(Cu(bptap)2)]4+ units in which adjoining copper(II) ions are ferromagnetically coupled.     

Magnetic circular dichroism study of a dicobalt(II) methionine aminopeptidase/fumagillin complex and dicobalt II-II and II-III model complexes

The dicobalt form of the metallohydrolase methionine aminopeptidase from Escherichia coli (CoCo EcMetAP) has an active site with one 5-coordinate Co (II) and a more weakly bound 6-coordinate Co (II). These metal ions are bridged by two carboxylate amino acid side chains and water or hydroxide, potentially enabling magnetic exchange coupling between the metals. We used variable-temperature, variable-field magnetic circular dichroism to determine whether such coupling occurs. CoCo EcMetAP's MCD spectrum shows distinct d-d transitions at 495 and 567 nm caused by 6- and 5-coordinate Co (II), respectively. The magnetization curves for 5- and 6-coordinate Co (II) are very different, indicating that their electronic ground states vary considerably, ruling out any coupling. When the fungal metabolite fumagillin binds to the CoCoEcMetAP, the qualitative MCD spectrum is unchanged; however, VTVH MCD data show that 5- and 6-coordinate Co (II) ions have similarly shaped magnetization curves, indicating that the Co (II) ions now share the same electronic ground state. Fitting the VTVH MCD data to a model in which dimer wave functions are calculated using a spin Hamiltonian with zero-field splitting showed the Co (II) ions to be weakly ferromagnetically coupled, with J = 2.9 cm (-1). Ferromagnetic coupling is unusual for dinuclear Co (II); therefore, to support the CoCoEcMetAP/fumagillin complex results, we also analyzed VTVH MCD data from a matched pair of dinuclear cobalt complexes, 1 and 2. Complex 1 shares the carboxylate and hydroxide-bridged dicobalt(II) structural motif with the active site of CoCo EcMetAP. Complex 2 contains a nearly isostructural Co (II) ion, but the Co (III) is diamagnetic, so any magnetic coupling is switched off, while the spectral features of the Co (II) ion remain. Magnetization data for 1, fitted to the dimer model, showed that the Co (II) ions were weakly ferromagnetically coupled, with J = 1.7 cm (-1). Magnetization data for Co (II) ions in 2, however, reflect loss of magnetic exchange coupling.     

Solid-state dinuclear-to-trinuclear conversion in an oxalato-bridged chromium(III)-cobalt(II) complex as a new route toward single-molecule magnets

A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)-cobalt(II) complex of formula [CrL(ox)(2)CoL'(H(2)O)(2)][CrL(ox)(2)]·4H(2)O (1) has been self-assembled in solution using different aromatic α,α'-diimines as blocking ligands, such as 2,2'-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L' = Me(2)phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 Cr(III) anions and the S = 3 Cr(III)Co(II) cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)-cobalt(II) complex of formula {[CrL(ox)(2)](2)CoL'} (2). Complex 2 possesses a moderately anisotropic S = 9/2 Cr(III)(2)Co(II) ground state, and it exhibits slow magnetic relaxation behavior at very low temperatures (T(B) < 2.0 K).     

A novel nonanuclear CuII carboxylate-bridged cluster aggregate with an S= 7/2 ground spin state

The Cu(II) aggregate in [Cu(9)(cpida)(6)(MeOH)(6)].6(MeOH)[H(3)cpida = 2-(carboxyphenyl)iminodiacetic acid] is made up of two weakly ferromagnetically coupled carboxylate-bridged Cu(4) units that are antiferromagnetically linked through a central Cu(II) to give a Cu(9) core with an S= 7/2 spin ground state.     

Tuning the spin ground state in heterononanuclear nickel(II)-copper(II) cylinders with a triangular metallacyclophane core

Two new heterometallic Ni(II)(n)Cu(II)((9-n)) complexes [n = 1 (2) and 2 (3)] have been synthesized following a multicomponent self-assembly process from a n:(3 - n):2:6 stoichiometric mixture of Ni(2+), Cu(2+), L(6-), and [CuL'](2+), where L and L' are the bridging and blocking ligands 1,3,5-benzenetris(oxamate) and N,N,N',N',N'-pentamethyldiethylenetriamine, respectively. Complexes 2 and 3 possess a unique cyclindrical architecture formed by three oxamato-bridged trinuclear linear units connected through two 1,3,5-substituted benzenetris(amidate) bridges, giving a triangular metallacyclophane core. They behave as a ferromagnetically coupled trimer of two (2)/one (3) S = (1)/(2) Cu(II)(3) plus one (2)/two (3) S = 0 Ni(II)Cu(II)(2) linear units with overall S = 1 Ni(II)Cu(II)(8) (2) and S = (1)/(2) Ni(II)(2)Cu(II)(7) (3) ground states.     

Valence Tautomerism in Octahedral and Square‐Planar Phenoxyl–Nickel(II) Complexes: Are Imino Nitrogen Atoms Good Friends?

The two tetradentate ligands H(2)L and H(2)L(Me) afford the slightly distorted square-planar low-spin Ni(II) complexes 1 and 2, which comprise two coordinated phenolate groups. Complex 1 has been electrochemically oxidized into 1(+), which contains a coordinated phenoxyl radical, with a contribution from the nickel orbital. In the presence of pyridine, 1(+) is converted into 1(Py) (+), an octahedral phenolate nickel(III) complex with two pyridines axially coordinated: An intramolecular electron transfer (valence tautomerism) is promoted by the geometrical changes, from square planar to octahedral, around the metal center. The tetradentate ligand H(2)L(Me), in the presence of pyridine, and the hexadentate ligand H(2)L(Py) in CH(2)Cl(2) afford, respectively, the octahedral high-spin Ni(II) complexes 2(Py) and 3, which involve two equatorial phenolates and two axially coordinated pyridines. At 100 K, the one-electron-oxidized product 2(Py) (+) comprises a phenoxyl radical ferromagnetically coupled to the high-spin Ni(II) ion, with large zero-field splitting parameters, while 3(+) involves a phenoxyl radical antiferromagnetically coupled to the high-spin Ni(II) ion.     

Synthesis and characterization of a Mn22 single-molecule magnet and a [Mn22]n single-chain magnet

The reactions of [Mn12O12(O2CEt)16(H2O)4] with phenylphosphinic acid (PhHPO2H) in MeCN and MeCN/CH2Cl2 have led to isolation of [Mn22O12(O2CEt)22(O3PPh)8(H2O)8] (2) and [Mn22O12(O2CEt)20(O3PPh)8(O2PPhH)2(H2O)8]n (3), respectively, both containing PhPO3(2-) groups from in situ oxidation of PhHPO(2)(-). Complex 2 is molecular and consists of two Mn9 subunits linked by four additional Mn atoms. Complex 3 contains almost identical Mn22 units as 2, but they are linked into a one-dimensional chain structure. The Mn22 unit in both compounds is mixed-valence Mn(III)18, Mn(II)4. Solid-state, variable-temperature dc magnetic susceptibility and magnetization measurements were performed on vacuum-dried samples of 2 and 3, indicating dominant antiferromagnetic interactions. A good fit of low-temperature magnetization data for 2 could not be obtained because of problems associated with low-lying excited states, as expected for a high nuclearity complex containing Mn(II) atoms. An approximate fit using only data collected in small applied fields indicated an S = 7 or 8 ground state for 2. Solid-state ac susceptibility data established that the true ground state of 2 is S = 7 and that the connected Mn22 units of 3 are ferromagnetically coupled. Both 2 and 3 displayed weak out-of-phase ac signals indicative of slow magnetization relaxation. Single-crystal magnetization versus applied dc field scans exhibited hysteresis loops for both compounds, establishing them as new single-molecule and single-chain magnets, respectively. Complex 2 also showed steps in its hysteresis loops characteristic of quantum tunneling of magnetization, the highest nuclearity molecule to show such QTM steps. Arrhenius plots constructed from dc magnetization versus time decay plots gave effective barriers to magnetization relaxation (U(eff)) of 6 and 11 cm(-1) for 2 and 3, respectively.     

Ferromagnetic spin coupling between endohedral metallofullerene La@C82 and a cyclodimeric copper porphyrin upon inclusion

The cyclic host cyclo-[P(Cu)](2) carrying two covalently connected Cu(II) porphyrin units can accommodate La@C(82), a paramagnetic endohedral metallofullerene, in its cavity to form the inclusion complex cyclo-[P(Cu)](2)?La@C(82), which can be transformed into the caged complex cage-[P(Cu)](2)?La@C(82) by ring-closing olefin metathesis of its side-chain olefinic termini. On the basis of electron spin resonance (ESR) and electron spin transient nutation (ESTN) studies, cyclo-[P(Cu)](2)?La@C(82) is the first ferromagnetically coupled inclusion complex featuring La@C(82), whereas cage-[P(Cu)](2)?La@C(82) is ferrimagnetic.     

Ferromagnetism in malonato-bridged copper(II) complexes. Synthesis,crystal structures,and magnetic properties of [[Cu(H2O)3][Cu(mal)2(H2O)]]n and [[Cu(H2O)4]2[Cu(mal)2(H2O)]][Cu(mal)2(H2O)2][[Cu(H2O)4][Cu(mal)2(H2O)2][(H2mal = malonic acid)

Three malonato-bridged copper(II) complexes of the formulas [[Cu(H2O)3][Cu(C3H2O4)2(H2O)]]n (1), [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]] [Cu(C3H2O4)2(H2O)2][[Cu(H2O)4][Cu(C3H2O4)2(H2O)2]] (2), and [Cu(H2O)4][Cu(C3H2O4)2(H2O)2] (3) (C3H2O4 = malonate dianion) have been prepared, and the structures of the two former have been solved by X-ray diffraction methods. The structure of compound 3 was already known. Complex 1 crystallizes in the orthorhombic space group Pcab, Z = 8, with unit cell parameters of a = 10.339(1) A, b = 13.222(2) A, and c = 17.394(4) A. Complex 2 crystallizes in the monoclinic space group P2/c, Z = 4, with unit cell parameters of a = 21.100(4) A, b = 21.088(4) A, c = 14.007(2) A, and beta = 115.93(2) degrees. Complex 1 is a chain compound with a regular alternation of aquabis(malonato)copper(II) and triaquacopper(II) units developing along the z axis. The aquabis(malonato)copper(II) unit acts as a bridging ligand through two slightly different trans-carboxylato groups exhibiting an anti-syn coordination mode. The four carboxylate oxygens, in the basal plane, and the one water molecule, in the apical position, describe a distorted square pyramid around Cu1, whereas the same metal surroundings are observed around Cu2 but with three water molecules and one carboxylate oxygen building the equatorial plane and a carboxylate oxygen from another malonato filling the apical site. Complex 2 is made up of discrete mono-, di-, and trinuclear copper(II) complexes of the formulas [Cu(C3H2O4)2(H2O)2]2-, [[Cu(H2O)4] [Cu(C3H2O4)2(H2O)2]], and [[Cu(H2O)4]2[Cu(C3H2O4)2(H2O)]]2+, respectively, which coexist in a single crystal. The copper environment in the mononuclear unit is that of an elongated octahedron with four carboxylate oxygens building the equatorial plane and two water molecules assuming the axial positions. The neutral dinuclear unit contains two types of copper atoms, one that is six-coordinated, as in the mononuclear entity, and another that is distorted square pyramidal with four water molecules building the basal plane and a carboxylate oxygen in the apical position. The overall structure of this dinuclear entity is nearly identical to that of compound 3. Finally, the cationic trimer consists of an aquabis(malonato)copper(II) complex that acts as a bismonodentate ligand through two cis-carboxylato groups (anti-syn coordination mode) toward two tetraaqua-copper(II) terminal units. The environment of the copper atoms is distorted square pyramidal with four carboxylate oxygens (four water molecules) building the basal plane of the central (terminal) copper atom and a water molecule (a carboxylate oxygen) filling the axial position. The magnetic properties of 1-3 have been investigated in the temperature range 1.9-290 K. Overall, ferromagnetic behavior is observed in the three cases: two weak, alternating intrachain ferromagnetic interactions (J = 3.0 cm-1 and alpha J = 1.9 cm-1 with H = -J sigma i[S2i.S2i-1 + alpha S2i.S2i+1]) occur in 1, whereas the magnetic behavior of 2 is the sum of a magnetically isolated spin doublet and ferromagnetically coupled di- (J3 = 1.8 cm-1 from the magnetic study of the model complex 3) and trinuclear (J = 1.2 cm-1 with H = -J (S1.S2 + S1.S3) copper(II) units. The exchange pathway that accounts for the ferromagnetic coupling, through an anti-syn carboxylato bridge, is discussed in the light of the available magneto-structural data.     

Self-assembly and magnetic properties of a double-propeller octanuclear copper(II) complex with a meso-helicate-type metallacryptand core

An octanuclear copper(II) complex possessing a dimer-of-tetramers structure self-assembles from a binuclear oxamatocopper(II) metallacryptand of the meso-helicate type; its magnetic behaviour is consistent with its unique double-propeller molecular topology.     

A nonanuclear copper(II) polyoxometalate assembled around a mu-1,1,1,3,3,3-azido ligand and its parent tetranuclear complex

Reaction of Cu(II), [gamma-SiW10O36]8-, and N3- affords three azido polyoxotungstate complexes. Two of them have been characterized by single-crystal X-ray diffraction. Complex KNaCs10[{gamma-SiW10O36Cu2(H2O)(N3)2}2].26H2O (1) is obtained as crystals in few hours after addition of CsCl. This linear tetranuclear Cu(II) complex consists in two [gamma-SiW10O36Cu2(H2O)(N3)2]6- units connected through two W=O bridges. When the filtrate is left to stand for one night, a new complex is obtained. From both elemental analysis and IR spectroscopy, it has been postulated that this compound could be formulated K(1.5)Cs(5.5)[SiW10O37Cu2(H2O)2(N3)].14 H2O (1 a), showing the loss of one azido ligand per polyoxometalate unit. Finally, when no cesium salt is added to the reaction medium, the nonanuclear complex K12Na7[{SiW8O31Cu3(OH)(H2O)2(N3)}3(N3)].24 H2O (2) is obtained after three days. Compound 2 crystallizes in the R3c space group and consists in three {Cu3} units related by a C3 axis passing through the exceptional mu-1,1,1,3,3,3-azido bridging ligand. Each trinuclear Cu(II) unit is embedded in the [gamma-SiW8O31]10- ligand, an unprecedented tetravacant polyoxometalate, showing that partial decomposition of the [gamma-SiW10O36]8- precursor occurs with time in such experimental conditions. Magnetically, complex 1 behaves as two isolated {Cu2(mu(1,1)-N3)2} pairs in which the metal centers are strongly ferromagnetically coupled (J = +224 cm(-1), g = 2.20), the coupling through the W=O bridges being negligible. The magnetic behavior of complex 2 has also been studied. Relatively weak ferromagnetic couplings (J1 = +1.0 cm(-1), J2 = +20.0 cm(-1), g=2.17) have been found inside the {Cu3} units, while the intertrimeric magnetic interactions occurring through the hexadentate azido ligand have been found to be antiferromagnetic (J3 = -5.4 cm(-1)) and ferromagnetic (J4 = +1.3 cm(-1)) with respect to the end-to-end and end-on azido-bridged Cu(II) pairs, respectively.     

Trinuclear, antiferromagnetically coupled Cu(II) complex with an EPR spectrum of mononuclear Cu(II): effect of alcoholic solvents

A rigid trinuclear copper pyrazolato framework supports the solvolytic exchange of mu3-X by mu3-OR ligands (X = Cl and Br; R = alkyl group), converting the trinuclear ferromagnetically coupled S = 3/2 system to antiferromagnetically coupled S = 1/2 in the solid state. In contrast, we propose that, in alcoholic solutions, solvolysis results in unsymmetrical coordination of the Cu3 cluster, magnetically decoupling one Cu center from the other two. This disguises the intact triangular Cu(II)3 system as a mononuclear Cu(II) complex in its electron paramagnetic resonance spectrum.     

Crystal structures and magnetic properties of two octacyanotungstate(IV) and (V)-cobalt(II) three-dimensional bimetallic frameworks

The synthesis, X-ray structures, and magnetic behavior of two new, three-dimensional compounds [W(IV)[(mu-CN)(4)Co(II)(H(2)O)(2)](2).4H(2)O](n) (1) and [[W(V)(CN)(2)](2)[(mu-CN)(4)Co(II)(H(2)O)(2)](3).4H(2)O](n) (2) are presented. Compound 1 crystallizes in the tetragonal system, space group I4/m with cell constants a = b = 11.710(3) A, c = 13.003(2) A, and Z = 4, whereas 2 crystallizes in the orthorhombic system, space group Cmca with cell constants a = 13.543(5) A, b = 16.054(6) A, c = 15.6301(9) A, and Z = 4. The structure of 1 shows alternating eight-coordinated W(IV) and six-coordinated Co(II) ions bridged by single cyanides in a three-dimensional network. The geometry of each [W(IV)(CN)(8)](4-) entity in 1 is close to a square antiprism. Its eight cyanide groups are coordinated to Co(II) ions which have two coordinated water molecules in trans position. The structure of 2 consists of alternating eight-coordinated W(V) and six-coordinated Co(II) ions linked by single cyanide bridges in a three-dimensional network. Each [W(V)(CN)(8)](3-) unit shows a geometry close to a square antiprism. Only six of its eight cyanide groups are coordinated to Co(II) ions while the other two are terminal. The Co(II) ion in 2 has the same CoN(4)O(2) environment as in 1. The magnetic behavior of 1 is that of magnetically isolated high spin Co(II) ions (S(Co) = 3/2), bridged by the diamagnetic [W(IV)(CN)(8)](3-) units (S(W(IV)) = 0). The magnetic behavior of 2, where the high spin Co(II) ions are bridged by the paramagnetic [W(V)(CN)(8)](3-) units [S(W(V)) = 1/2], is that of ferromagnetically coupled Co(II) and W(V) giving rise to an ordered ferromagnetic phase below 18 K. The magnetic properties of 1 are used as a blank to extract the parameters that are useful to analyze the magnetic data of compound 2.     

Models for the lower S states of photosystem II: a trinuclear mixed-valent MnII/MnIV/MnII complex

The trinuclear complex Mn(3)(pko)(4)(CH(3)O)(2)(SCN)(2).CH(3)OH, 1, where Hpko is 2,2'-dipyridylketonoxime, is a rare example of a complex simultaneously containing Mn(II) and Mn(IV). X-ray crystallography and XANES spectroscopy clearly distinguish the Mn(II)(2)Mn(IV) valence isomer from the more commonly observed Mn(III)(2)Mn(II) formulation. Fits to variable-temperature magnetic susceptibility data indicate that the Mn(II) and Mn(IV) are ferromagnetically coupled (J = +6.13 cm(-1)) and that 1 has an S = (13)/(2) ground state.     

Synthesis, structure, and magnetism of bimetallic manganese or nickel complexes of a bridging verdazyl radical

Two binuclear metal-radical complexes, formed by the reaction of M(hfac)(2) x 2H(2)O (M = Mn or Ni; hfac = hexafluoroacetylacetonate) with the 1,5-dimethyl-3-(4,6-dimethylpyrimidin-2-yl)-6-oxoverdazyl radical (3), were synthesized. The binuclear Mn complex 5 (i.e., 3[Mn(hfac)(2)](2)) crystallizes in the monoclinic space group C2/c: C(30)H(17)N(6)O(9)F(24)Mn(2), a = 29.947(3), b = 17.143(3), c = 16.276(3) A, beta = 123.748(3)*, Z = 4. The compound consists of two pseudo-octahedral Mn(II) ions, both bearing two hfac ancillary ligands, bridged by the bis(bidentate) radical 3. The temperature dependence of the magnetic susceptibility of 5 reveals moderate antiferromagnetic exchange between each of the Mn(II) ions and the verdazyl radical (J = -48 cm(-1)). The S = 9/2 ground spin state of the complex was corroborated by low-temperature magnetization versus field measurements. In contrast, the magnetic susceptibility versus temperature behavior of 6 (whose molecular structure is presumed to be analogous to that of 5) indicates that the two Ni(II) ions are strongly ferromagnetically coupled to the verdazyl radical (J = +220 cm(-1)). The magnetization versus field behavior of 5 is consistent with an S = 5/2 ground-state species.     

Isolation of a pentadentate ligand and stepwise synthesis, structures, and magnetic properties of a new family of homo- and heterotrinuclear complexes

A neutral pentadentate ligand, di(pyrazolecarbimido)amine (Hdcadpz), and its adduct with HClO4, [H2dcadpz]+[ClO4]-, were for the first time isolated from our previously reported [Cu3(dcadpz)2(Hpz)2(ClO4)2](ClO4)2.H2O by the use of (NH4)2S to remove the CuII ions and characterized by IR, EA, UV, NMR, MS, and X-ray crystallography. Reactions of copper(II) or nickel(II) nitrate with Hdcadpz in a 1:2 molar ratio generated two mononuclear precursors of [Cu(dcadpz)2] (1) and [Ni(dcadpz)2].2/3DMF (2). Furthermore, three new linear homo- and heterotrinuclear complexes of the same motif [M{M'(dcadpz)2}M] (M=CoII, NiII, M'=CuII, NiII), [{Co(pdm)}2{Cu(dcadpz)2}](NO3)4 (3), [{Ni(pdm)}2{Cu(dcadpz)2}](NO3)4 (4), and [{Ni(MeOH)(H2O)2}2{Ni(dcadpz)2}](NO3)4 (5), were synthesized from these two precursors (pdm=2,6-pyridinedimethanol) and characterized by X-ray crystallography. Magnetic studies show that the central Cu(dcadpz)2 motif is antiferromagnetically coupled with both the terminal Co(II) atoms via the dcadpz- ligand in 3 with a J value of -5.27 cm(-1) and ferromagnetically coupled with both the terminal Ni(II) atoms in 4 with a J value of 2.50 cm(-1), while 5 behaves only as a Curie paramagnet between 2 and 300 K due to the diamagnetic character of the central square-planar Ni(II) atom.     

Triangular,ferromagnetically-coupled CuII 3-pyrazolato complexes as possible models of particulate methane monooxygenase (pMMO)

Magnetic susceptibility and EPR studies show that trinuclear Cu(II)-pyrazolato complexes with a Cu(3)(mu3-X)2 core (X = Cl, Br) are ferromagnetically coupled: J(Cu-Cu) = +28.6 cm(-1) (X = Cl), +3.1 cm(-1) (X = Br). The orderly transition from an antiferromagnetic to a ferromagnetic exchange among the Cu centers of Cu(3)(mu3-X) complexes, X = O, OH, Cl, Br, follows the change of the Cu-X-Cu angle from 120 degrees to approximately 80 degrees. The crystal structures of [Bu4N]2"[Cu3(mu3-Br)2(mu-pz*)3Br3] (pz* = pz (1a) or 4-O2N-pz (1b), pz = pyrazolato anion, C(3)H(3)N(2)(1-)) are presented.     

The first unequivocally ferromagnetically coupled squarato complex: origin of the ferromagnetism in an interlocked 3D Fe(II) system

An unprecedented interlocked 3D Fe(II) system, [Fe(squarate)(bpy)(2H2O)] x 3H2O, 1 (bpy = 4,4'-bipyridine), the first unequivocally ferromagnetically coupled squarato complex to be reported, has been synthesised and magnetically characterized.     

Ferromagnetic vs antiferromagnetic coupling in bis(mu-phenoxo)dicopper(II) complexes. Tuning of the nature of exchange coupling by remote ligand substituents

Two bis(mu-phenoxo)dicopper(II) complexes, [(L(CH3))(2)Cu(2)] (1) and [(L(t-Bu))(2)Cu(2)] (2), where L(CH3) and L(t-Bu) represent the dianions of (methylamino)-N,N-bis(2-methylene-4,6-dimethylphenol) and of (methylamino)-N,N-bis(2-methylene-4,6-di-tert-butylphenol), respectively, are reported to demonstrate the effect of remote substituents on the nature of exchange coupling interactions between the copper(II) centers. In contrast to 1, which is as usual antiferromagnetically coupled, complex 2 is a rare example of a ferromagnetically coupled diphenoxodicopper(II) complex.