Synthesis and magnetism of a binuclear copper(II)–manganese(II) complex with N,N-bis(N-hydroxyethylaminoethyl)oxamido as a bridging ligand

The heterobinuclear complex, [CuMn(L)(phen)2](ClO4)2· H2O, [L = N,N-bis(N-hydroxyethyleneamine)oxamido, phen=1,10-phenanthroline], has been synthesized with N,N-bis(N-hydroxyethylaminoethyl)oxamido as the bridging ligand. The electronic reflectance spectrum indicates the presence of exchange-coupling interaction between bridging MnII and CuII ions. The variable-temperature magnetic susceptibility of the complex was measured over the 4–300K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange between the MnII ion and CuII ion and fits the data for a heterobinuclear CuII–MnII magnetic exchange model based on the Hamiltonian operator (H= –2JS1S2, S1=1/2, S2=5/2), giving the antiferromagnetic coupling parameter of 2J=–74.0cm–1.     

Synthesis and magnetism of binuclear cobalt(II) complexes with the tetraacetylethene dianion as a bridging ligand

Three novel binuclear CoIIcomplexes, [Co2(TAE)-(phen)4](ClO4)2·3H2O(1),[Co2(TAE)(Nphen)4](ClO4)2 ·4H2O(2) and [CO2(TAE)(bipy)4](ClO4)2·H2O(3) (TAE=tetraacetylethene dianion, phen=1,10–phenanthroline, Nphen=5–nitro·1,10–phenanthroline, bipy =2,2-bipyridy1), have been synthesized and characterized by elemental analysis, i.r., molar conductance and electronic reflection spectra. The complexes are proposed to contain tetraacetylethene dianion bridged structures and two CoII ions. The variable-temperature magnetic susceptibility of complex (1) was measured in the 4–300 K range. The magnetic coupling parameter is consistent with antiferromagnetic exchange between the two CoII centres and the data fit a binuclear magnetic exchange model based on the Hamiltonian operator ( = –2 J12, S1=S2=3/2), giving the antiferromagnetic coupling parameter of 2J=–1.55cm–1.     

Synthesis,Crystal Structure and Magnetism of A 1-D Polymeric Manganese(II) Complex with 2-Hydroxyl-2-Hydroxylate-Malonate as Bridging Ligand

A one-dimensional chain complex {Na[MnL(H₂O)₂]} _n (L = 2-hydroxyl-2-hydroxylate-malonate trivalent anion) has been synthesized and its crystal structure determined by X-ray crystallography. In the complex each Mn ion is located in a distorted octahedral environment with two oxygen atoms O(7) and O(8) from terminal ligands of two H₂O molecules, and four other coordinating oxygen atoms O(1), O(5), O(3A) and O(6A) from two bridging ligands, respectively. Each bridging ligand provides four coordinating oxygen atoms, in which O(6) comes from the hydroxylate, O(5) from the hydroxyl, and O(1) and O(3) from two carboxylate groups, respectively. The O(1) and O(5) atoms coordinate to one Mn ion and the O(3) and O(6) atoms coordinate to another Mn ion; a one-dimensional chain is thereby constructed. The variable-temperature magnetic susceptibility of the complex was measured in the 4–300 K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange and generates the antiferromagnetic coupling parameter, 2J=–0.0544 cm^–1.     

氰根桥联配合物GdFe(CN)6.4H2O的合成、结构及磁性研究

合成了一个氰根桥联Gd(III)离子Fe的三维网状配合物GdFe(CN)6.4H2O。使用元素分析、红外光谱对配合物进行了一般性表征。用X射线衍射法测定了配合物的单晶结构, 属单斜晶系,空间群为C2, 晶胞参数为: a=1.2759(6), b=0.7404(1),c=1.3654(5)nm, β=90.22(3)°, Z=4, 对该配合物进行了变温磁化率测定(4.2-300K)。并使用哈密顿算符(H=-2JS1S2,S1=1/2, S2=7/2)对所测数据进行了理论分析, 求得表征CN^-离子所桥联Gd(III)离子与Fe(III)离子间磁相互作用强弱的磁交换积分J=-69.1cm^-^1, 表明Gd(III)离子与Fe(III)离子间存在有中等强度的反铁磁相互作用。该相互作用是目前已见文献报道的桥联稀土离子和过渡金属离子间发现的最大的磁相互作用。     

Synthesis,crystal structure and magnetism of a 1-D polymeric manganese(II) complex with pyrazine-2-carboxylate as bridging ligand

A one-dimensional chain complex {[Mn(pyz)(SCN)(H₂O)₂] · H₂O} (pyz = pyrazine-2-carboxylic anion) has been synthesized and its crystal structure determined by X-ray crystallography. In the complex each Mn ion is located in a distorted octahedral environment with two oxygen atoms O(3), O(4) from terminal ligands of two water molecules, another oxygen atom O(1) from the carboxylate group of pyz, and three nitrogen atoms N(1), N(2A) from two different pyz units and N(3) from the terminal ligand thiocyanate anion, in which a chelated five-membered ring is formed by coordination of O(1) and N(1) to the Mn(1) atom. Thus, an infinite zigzag chain consisting of Mn and pyz is constructed and the chains are linked together by hydrogen bonding from coordinated and uncoordinated water molecules, the sulfur atom of thiocyanate and the carboxylate oxygen of pyz. The variable-temperature magnetic susceptibility of the complex was measured in the 4–300 K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange between the two manganese(II) centers and the data fit a binuclear magnetic exchange model based on the Hamiltonian operator (H = –2JS ₁ S ₂, S ₁ = S ₂ = 5/2), giving the antiferromagnetic coupling parameter of 2J = –0.17 cm^–1. This is the first pyrazine-2-carboxylic anion bridging complex dealing with the magnetic interaction study.     

The syntheses,crystal structure and magnetic behavior of μ-imidazolato-dicopper(II) complexes with the dinucleating hexaazamacrocycles

The synthesis, crystal structure and magnetic properties of the imidazolate-bridged dinuclear copper(II) complex [LCu2(Im)](ClO4)3(H2O) ·1/2(MeCN), (ImH=imidazole, L=bis-p-xylylBISDIEN) have been studied. Single crystal X-ray diffraction determination reveals the distorted square planar geometries of the imidazolate bridged dicopper(II) center are incorporated within the dinucleating macrocycle. The Cu—Cu separation in the complex is 6.005Å. Magnetic measurements reveal an antiferromagnetic exchange interaction with a coupling constant of J=–26.52cm–1. The enzymatic activity of the title complex is 5.9 percent of that of the protein.     

Antiferromagnetic complexes involving metal---metal bonds III. Synthesis, structure and magnetic properties of heterotrinuclear complexes of the type M(CO)5L (M = Cr, Mo and w) containing [(C5H5CrSCMe3)2S] as unusual antiferromagnetic ligand L

Isostructural heterotrinuclear complexes (C₅H₅CrSCMe₃)₂S · M(CO)₅ (II–IV) were isolated from photochemical reactions between the antiferromagnetic complex (C₅H₅CrSCMe₃)₂S (I) (with the Cr---Cr bond 2.689 Å long and with the exchange parameter −2J = 430 cm⁻¹) and metal hexacarbonyls, M(CO)₆, where M is Cr, Mo, or W. According to the X-ray structural data on III and IV, complex I plays the role of an unusual antiferromagnetic ligand L bound to M through the sulphide bridge (M–S 2.58(2) Å). Its geometry remains practically unaffected by the complex formation (the Cr---Cr bond length in III and IV is 2.73(1) Å). The exchange parameter, −2J (410, 440 and 440 cm⁻¹ in II to IV, respectively), also shifts only insignificantly from that of I, which probably means that indirect exchange via the sulphide bridge in I is of minor importance compared with the direct Cr---Cr exchange. The Cr---Cr bond length may thus be correlated with the observed overall exchange coupling.     

Synthesis,crystal structure and magnetism of a three-dimensional manganese(II) complex with carbamyldicyanomethanide anion (<Emphasis Type="Italic">cda</Emphasis>) as a bridging ligand

A three-dimensional complex {[Mn(cda)₂]·2MeOH}_n has been synthesized and its crystal structure determined by X-ray crystallography. In the complex each Mn ion is located in a distorted octahedral environment with two oxygen atoms O(1D) and O(1E) from two amide groups, and four nitrogen atoms N(2), N(2A), N(3B) and N(3C) from four nitrile groups of four cda anions, respectively; each cda anion as a ₃-bridging ligand provides two nitrile nitrogen atoms, and an amide oxygen atoms to coordinate three Mn ions. Thus, a three-dimensional network consisting of Mn ions and cda bridging ligands is constructed with solvent MeOH molecules trapped in the cavities. The variable-temperature magnetic susceptibility of the complex was measured in the 5–300K range. The magnetic coupling parameter is consistent with an antiferromagnetic exchange and generates the antiferromagnetic coupling parameter, 2J=–0.2cm^–1.     

Exchange coupling in Di-μ-hydroxo-bis{bis[(S)alaninato]chromium(III)} trihydrate

Summary Magnetic susceptibility data have been collected in the temperature range 1.8 to 290 K for the di--hydroxo-bridged bimetallic chromium complex di--hydroxo-bis{bis-[(S)alaninato]chromium(III)} trihydrate. The magnetic susceptibility data reflect antiferromagnetic exchange coupling interactions and may be fitted assuming bilinear and biquadratic exchange of the form –2JS₁·S₂–j(S₁·S₂)² using the Van Vleck equation. The best fit of the experimental data yields J=–6.45 cm^–1, j=0.65 cm^–1, and g=1.98. The magnetic parameters are discussed in terms of the structure of the compound and the correlation between the exchange coupling constant and structural features.     

Homo and heteronuclear complexes of dioxime ligands

The mononuclear fragments [Cu(HDopn)(OH)2]+ and [Cu(HPopn)(OH)2]+, [H2Dopn=3,3-(trimethylene- dinitrilo)-dibutan-2–one dioximate and H2Popn, = 3, 3-(phenylenedinitrilo)-dibutan-2–one dioximate] were used to prepare four binuclear complexes [(OH2)Cu (Dopn)Cu(ditn)]2+, [(OH2)Cu(Dopn)Ni(ditn)(H2O)]2+ (ditn=diethylenetriamine) and [(OH2)Cu(Popn)Cu(L) (H2O)]2+ (L=2,2-bipyridine or 1,10–phenanthroline). Two trinuclear complexes, [{Cu(Popn)(OH2)}2M (H2O)n]2+ (when M=CuII, n=1; M=ZnII, n= 2), have been synthesised and characterised by elemental analyses, f.a.b. mass, i.r., electronic, e.s.r. spectroscopy and variable temperature (5–300K) magnetic susceptibility measurements. A strong antiferromagnetic interaction (J=–545cm–1 to –700cm–1) has been found for the binuclear copper(II) complexes. The X-band e.s.r. spectra of these complexes at 300K and for trinuclear complexes at 120K indicate square-pyramidal geometry for the copper centres with a (dx2–y2)1 ground state. The binuclear complex of copper(II)–nickel(II) centres with antiferromagnetic interaction (J=–107 cm–1) is described, and moderately strong zero-field splitting within the quartet state leads to Kramers doublet, as indicated by X-band e.s.r. spectra of this complex. The trinuclear copper(II) complex with an antiferromagnetic interaction (J= –350cm–1) is also described. The heterometallic trinuclear copper(II)–zinc(II)–copper(II) system shows a very weak interaction (J–1cm–1).     

Synthesis and magnetic properties of nickel(II) complexes with the nitronyl nitroxides

Four novel complexes of nickel(II), Ni(tfac)2(NITPa)2 (1), Ni(tfac)2(NITPhNO2)2 (2), Ni(pfpr)2(NITPa)2 (3) and Ni(pfpr)2(NITPhNO2)2 (4), [tfac=trifluoro- acetato, NITPa=2-(3,4-methylenedioxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxy-3-oxid, NITPhNO2= 2-(3-nitrophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxid, pfpr=pentafluoropropionato], have been prepared and characterized by elemental analysis, i.r., and electronic spectra, and molar conductances. The temperature dependence of the magnetic susceptibility for complexes (1) and (3) was measured (4–300K). The observed data were successfully simulated giving the exchange integral J=–1.48cm–1 for (1) and J=–1.25cm–1 for (3). These results indicate a weak antiferromagnetic spin exchange interaction between nickel(II) ion and the radicals.     

Metal chelates of heterocyclic nitrogen containing ketones,Part IX. Magnetic and spectral studies of the dimeric copper(II) complex of 2-picolyl methyl ketone semicarbazone and its ligation by solvent molecules

Summary The preparation and characterization of [(PMKSC-H)Cu]₂Cl₂ by i.r. electronic and e.s.r. spectra as well as variable temperature magnetic susceptibility are described and a square planar geometry is assumed for the isolated complex. The magnetic susceptibility data indicates overall antiferromagnetic spin coupling. The variable temperature magnetic susceptibility in conjunction with the best fitting procedure yielded: 2J=–46cm^–1, g=2.15 and 6=–5 K. E.s.r. data confirm the existence of spin-spin coupling with D=0.0398 cm^–1. The g-values obtained from the e.s.r. studies were g₁₁=2.24, g=2.08 and g_av.=2.13. The results were used to estimate the Cu-Cu separation in the dimer. The problem of ligation of the dimeric copper(II) complex by various organic solvents was investigated. E.s.r., i.r. and electronic spectra together with the magnetic susceptibiliy studies indicate that [(PMKSC-H)Cu]₂Cl₂ dissociated in polar solvents to give the adducts [(PMKSC-H)CuL_s]Cl which were isolated and characterized.     

Magneto-structural xorrelations in 2D and 3D extended structures of manganese(II)-malonate systems

Two polymeric malonato-bridged manganese(II) complexes of formula [Mn(mal)(H(2)O)(2)](n)() (1) and [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) have been synthesized and characterized (mal = malonate dianion; 4,4'-bipy = 4,4'-bipyridine). The crystal structure of complex 1 was already known. Complex 2 crystallizes in monoclinic space group P2(1)/n, Z = 2, with unit cell parameters of a = 7.2974(10) A, b = 18.7715(10) A, c = 7.514(3) A, and beta = 91.743(12) degrees. The structure determination reveals that the complex [Mn(2)(mal)(2)(4,4'-bipy)(H(2)O)(2)](n)() (2) is a 3D network being composed of Mn-malonate sheets which are pillared by bidentate 4,4'-bipy spacer forming small voids. The Mn-Mn distances through Mn-mu-(O3-C8-O4)-Mn, Mn-mu(O1-C6-O2)-Mn, and Mn-mu-4,4'-bipy-Mn bridges are 5.561, 5.410, and 11.723 A, respectively. The magnetic behaviors of complexes 1 and 2 in the temperature range 300-2 K are very close, corresponding to a weak antiferromagnetic coupling. The magnetic pathways of complex 1 are through two Mn-O-C-O-Mn with anti-anti conformation and two Mn-O-C-O-Mn with syn-anti conformations and in complex 2 through all Mn-O-C-O-Mn with syn-anti conformations. Both syn-anti and anti-anti conformations create weak antiferromagnetic coupling, and the susceptibility data are fitted by the expansion series of Lines and the Curély formula for an S = 5/2 antiferromagnetic quadratic layer, based on the exchange Hamiltonian H = -Sigma(nn)()JS(i)()S(j)(). The best fit is given by the superexchange parameters J = -0.32 cm(-)(1) and g = 2.00 for complex 1 and J = -0.14 cm(-)(1), J(inter) = -0.031 cm(-)(1), and g = 2.00 for complex 2. Finally, in both the complexes there is a magnetic pathway Mn-O-C-C-C-O-Mn, and this pathway through the three carbon atoms of the malonato-bridging ligand could be considered negligible.     

Asymmetric azido-copper(II) bridges: ferro- or antiferromagnetic? experimental and theoretical magneto-structural studies

Reaction of NaN(3) with the [Cu(II)(tn)](2+) ion (tn = 1,3-diaminopropane) in basic aqueous solution yields the azido-bridged complex of formula [Cu(2)(tn)(2)(N(3))(4)] (1), which is characterized by X-ray crystallography. The structure of 1 is made up of dinuclear neutral complexes, of formula [Cu(2)(tn)(2)(N(3))(4)], resulting from the assembling of two mononuclear units through two equivalent end-on azide bridges connecting asymmetrically two Cu(tn)(N(3))(2) entities. These dinuclear units are connected through two asymmetric end-to-end N(3) bridges to form a chain of dimers. Magnetic measurements for compound 1 show weak antiferromagnetic exchange interactions between the Cu(II) ions. The magnetic data were modeled using the susceptibility expression derived for an alternating AF S = 1/2 chain. A very satisfactory fit over the whole temperature range was obtained with g = 2.1438(4), J(1) = -3.71(2) cm(-1), and J(2) = -3.10(2) cm(-1) (J(1) and J(2) are the singlet-triplet separations). This magnetic behavior differs from those observed for similar examples which were reported as having alternating ferro- and antiferromagnetic exchange interactions; thus, DFT calculations were done to understand the nature of the magnetic coupling in such asymmetric end-on and end-to-end N(3) bridges. Theoretical results show that the double asymmetric end-on bridges produce antiferromagnetic coupling while the end-to-end ones can present ferro- or antiferromagnetic coupling depending on the copper coordination sphere.     

Magnetic properties of diruthenium(II,III) carboxylate compounds with large zero-field splitting and strong antiferromagnetic coupling

The magnetic properties of mixed-valent compounds of general formula Ru2Cl(mu-O2CR)4 [R = CH2-CH3 (1), C(Me)=CHEt) (2)] have been studied in the 2-300 K temperature range. This magnetic study also includes a revision of the magnetic properties of the complex Ru2Cl(mu-O2CCMePh2)4 (3). Compounds 1-3 show a linear structure and a strong antiferromagnetic coupling between the diruthenium units through the chlorine atoms according to previous studies. Two fitting models to explain the magnetic properties of these complexes that incorporate a large zero-field splitting together with a strong antiferromagnetic coupling are described. These models consider that each diruthenium unit (S = 3/2) is magnetically coupled to the nearest diruthenium unit and ignores the longer distance magnetic coupling. The fitting models were found to be successful in fitting the magnetic data of the linear diruthenium(II,III) complexes. The zero-field splitting, D, and the antiferromagnetic coupling, zJ, vary from 37.8 to 48.0 cm-1 and from -7.43 to -13.30 cm-1, respectively, for complexes. The D values are similar to those calculated for the nonlinear diruthenium(II,III) compounds and confirm the validity of the proposed fitting models.     

New charge transfer salts based on bis(ethylenedithio)tetrathiafulvalene (ET) and ferro- or antiferromagnetic oxalato-bridged dinuclear anions: syntheses, structures and magnetism of ET5[MM'(C2O4)(NCS)8] with MM' = Cr(III)Fe(III), Cr(III)Cr(III)

Electrochemical combination of the magnetic dinuclear anion [MM'(C2O4)(NCS)8](4-) (MM' = Cr(III)Cr(III), Cr(III)Fe(III)) with the ET organic pi-donor (ET = BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene) gives rise to two new isostructural molecular hybrid salts ET5[MM'(C2O4)(NCS)8], with MM' = CrCr (1), CrFe (2). The molecular structure of compound 1 has been determined by single crystal X-ray diffraction. The particular arrangement of the organic units consists of an unprecedented two-dimensional organic sublattice nearly similar to that observed in kappa-phase structures. For both compounds, the magnetic susceptibility measurements indicate (i) the ET radicals do not contribute to the magnetic moment probably due to the presence of strong antiferromagnetic interaction between them, and (ii) in the anion, the magnetic coupling is antiferromagnetic for 1 (J = -3.65 cm(-1)) and ferromagnetic for 2 (J = 1.14 cm(-1), J being the parameter of the exchange Hamiltonian H = -2JS1S2). The field dependence of the magnetization of compound 2 at 2.0 K gives further evidence of the S = 4 ground-state arising from the interaction between S = 3/2 Cr(III) and S = 5/2 Fe(III). EPR measurements confirm the nature of the magnetic interactions and the absence of any contribution from the organic part, as observed from the static magnetic measurement. Conductivity measurements and electronic band structure calculations show that both salts are semiconductors with low activation energies.     

Structure distortion effects in the spectrum of tunnel-exchange states of tetrahedral mixed-valence tetramers

Tunnel-exchange states of a tetrameric mixed-valence (MV) d₁–d₁–d₁–d₂ cluster are considered. Energy levels of distorted pseudotetrahedral conjiprations with rhombic and trigonal symmetry are calculated. It is demonstrated that the correlation diagrams of planar systems are symmetric with respect to the sign of the double exchange parameter. A strong double exchange always results in the ferromagnetic ground state of planar systems. The following types of spectrum defamations of the d₁–d₁–d₁–d₂ tetramer from tetrahedral to planar systems have been found: a) with a weak positive double exchange, deformation of a tetrahedral system does not lead to any change of spin of the antiferromagnetic ground state of the cluster; b) with a strong positive double exchange, the defonnation alters the antiferromagnetic ground (S = 1/2) state of the tetrahedral system to the ferromagnetic (S = 5/2) state of the planar system, or to an intermediate (S = 3/2) state; c) with a negative double exchange, irrespective of its absolute value, the tetrahedral system deformation does not alter the spin of the ground state. With a weak double exchange, this ground state remains antiferromagnetic, and with a strong double exchange, it is ferromagnetic or intermediate.Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 33–46, September–October, 1993.Translated by L. Chernomorskaya     

Constructing single-chain magnets by supramolecular π-π stacking and spin canting: a case study on manganese(III) corroles

A single‐chain magnet (SCM) was constructed from manganese(III) 5,10,15‐tris(pentafluorophenyl)corrole complex [Mn^III(tpfc)] through supramolecular π–π stacking without bridging ligands. In the crystal structures, [Mn(tpfc)] molecules crystallized from different solvents, such as methanol, ethyl acetate, and ethanol, exhibit different molecular orientations and intermolecular π–π interaction or weak Mn ??? O interaction to form a supramolecular one‐dimensional motif or dimer. These three complexes show very different magnetic behaviors at low temperature. Methanol solvate 1 shows obvious frequency dependence of out‐of‐phase alternating‐current magnetic susceptibility below 2 K and a magnetization hysteresis loop with a coercive field of 400 Oe at 0.5 K. It is the first example of spin‐canted supramolecular single‐chain magnet due to weak π–π stacking interaction. By fitting the susceptibility data χ_MT (20–300 K) of 1 with the spin Hamiltonian expression ${\overrightarrow{H}}A single-chain magnet (SCM) was constructed from manganese(III) 5,10,15-tris(pentafluorophenyl)corrole complex [Mn(III) (tpfc)] through supramolecular π-π stacking without bridging ligands. In the crystal structures, [Mn(tpfc)] molecules crystallized from different solvents, such as methanol, ethyl acetate, and ethanol, exhibit different molecular orientations and intermolecular π-π interaction or weak Mn???O interaction to form a supramolecular one-dimensional motif or dimer. These three complexes show very different magnetic behaviors at low temperature. Methanol solvate 1 shows obvious frequency dependence of out-of-phase alternating-current magnetic susceptibility below 2?K and a magnetization hysteresis loop with a coercive field of 400?Oe at 0.5?K. It is the first example of spin-canted supramolecular single-chain magnet due to weak π-π stacking interaction. By fitting the susceptibility data χ(M) T (20-300?K) of 1 with the spin Hamiltonian expression H = -2J Σ(i=1)(n-1) S(Ai) S(Ai+1) + D Σ(i) S((iZ)(2)), the intrachain magnetic coupling parameter transmitted by π-π interaction of -0.31?cm(-1) and zero field splitting parameter D of -2.59?cm(-1) are obtained. Ethyl acetate solvate 2 behaves as an antiferromagnetic chain without ordering or slow magnetic relaxation down to 0.5?K. The magnetic susceptibility data χ(M) T (20-300?K) of 2 was fitted by assuming the spin Hamiltonian H = -2JΣ(i=1)(n-1) S(Ai) S(Ai+1), and the intrachain antiferromagnetic coupling constant of -0.07?cm(-1) is much weaker than that of 1. Ethanol solvate 3 with a dimer motif shows field-induced single-molecule magnet like behavior below 2.5?K. The exchange coupling constant J within the dimer propagated by π-π interaction is -0.14?cm(-1) by fitting the susceptibility data χ(M) T (20-300?K) with the spin Hamiltonian H = -2J S(A) S(B) + β(S((A)g(A)) + S((B)g(B)))H. The present studies open a new way to construct SCMs from anisotropic magnetic single-ion units through weak intermolecular interactions in the absence of bridging ligands.     

Synthesis,crystal structure and magnetic properties of the first dinuclear copper(II)–iron(II) complex [Cu(L)Fe(CN)5NO] based on nitroprusside

The nitrosyl cyanide [Cu(L)Fe(CN)₅NO] was prepared by the reaction of [Cu(L)]Cl₂ [L = 3, 10-bis(2-hydroxymethyl)-1,3,5,8,10,12-hexaazacyclotetradecane] with Na₂[Fe(CN)₅NO]·2H₂O in aqueous solution. Single-crystal analysis revealed that the title complex is the first structurally characterized dinuclear copper(II)–iron(II) complex based on the nitroprusside. Variable temperature magnetic susceptibility measurements (4.0–180.0 K) show the occurrence of very weak antiferromagnetic interactions between the copper(II) ions with zJ = –0.410 cm^–1.     

Structural and magnetic properties of Mn(III) and Cu(II) tetranuclear azido polyoxometalate complexes: multifrequency high-field EPR spectroscopy of Cu4 clusters with S = 1 and S = 2 ground states

Two new azido-bridged polyoxometalate compounds were synthesized in acetonitrile/methanol media and their molecular structures have been determined by X-ray crystallography. The [[(gamma-SiW10O36)Mn2(OH)2(N3)(0.5)(H2O)(0.5)]2(mu-1,3-N3)](10-) (1 a) tetranuclear Mn(III) complex, in which an end-to-end N3- ligand acts as a linker between two [(gamma-SiW10O36)Mn2(OH)2]4- units, represents the first manganese-azido polyoxometalate. The magnetic properties have been studied considering the spin Hamiltonian H = -J1(S1S2+S1*S2*)-J2(S1S1*), showing that antiferromagnetic interactions between the paramagnetic centers (g = 1.98) occur both through the di-(mu-OH) bridge (J1 = -25.5 cm(-1)) and the mu-1,3-azido bridge (J2 = -19.6 cm(-1)). The [(gamma-SiW10O36)2Cu4(mu-1,1,1-N3)2(mu-1,1-N3)2]12- (2 a) tetranuclear Cu(II) complex consists of two [gamma-SiW10O36Cu2(N3)2]6- subunits connected through the two mu-1,1,1-azido ligands, the four paramagnetic centers forming a lozenge. The magnetic susceptibility data have been fitted. This reveals ferromagnetic interactions between the four Cu(II) centers, leading to an S=2 ground state (H = -J1(S1S2+S1*S2*)-J2(S2S2*), J1 = +294.5 cm(-1), J2 = +1.6 cm(-1), g = 2.085). The ferromagnetic coupling between the Cu(II) centers in each subunit is the strongest ever observed either in a polyoxometalate compound or in a diazido-bridged Cu(II) complex. Considering complex 2 a and the previously reported basal-basal di-(mu-1,1-N3)-bridged Cu(II) complexes in which the metallic centers are not connected by other magnetically coupling ligands, the linear correlation J1 = 2639.5-24.95*theta(av) between the theta(av) bridging angle and the J1 coupling parameter has been proposed. The electronic structure of complex 2 a has also been investigated by using multifrequency high-field electron paramagnetic resonance (HF-EPR) spectroscopy between 95 and 285 GHz. The spin Hamiltonian parameters of the S = 2 ground state (D = -0.135(2) cm(-1), E = -0.003(2) cm(-1), g(x) = 2.290(5), g(y) = 2.135(10), g(z) = 2.158(5)) as well as of the first excited spin state S = 1 (D = -0.960(4) cm(-1), E = -0.080(5) cm(-1), g(x) = 2.042(5), g(y) = 2.335(5), g(z) = 2.095(5)) have been determined, since the energy gap between these two spin states is very small (1.6 cm(-1)).