Single-molecule magnet behavior in heterometallic M(II)-Mn(III)(2)-M(II) tetramers (M(II) = Cu, Ni) containing Mn(III) salen-type dinuclear core

The linear-type heterometallic tetramers, [Mn(III)(2)(5-MeOsaltmen)(2)M(II)(2)(L)(2)](CF(3)SO(3))(2) x 2H(2)O (MII = Cu, 1a; Ni, 2a), where 5-MeOsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene) bis(5-methoxysalicylideneiminate), and H(2)L = 3-{2-[(2-hydroxy-benzylidene)-amino]-2-methyl-propylimino}-butan-2-one oxime, have been synthesized and characterized from structural and magnetic points of view. These two compounds are isostructural and crystallize in the same monoclinic P2(1)/n space group. The structure has a [M(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-M(II)] skeleton, where -NO- is a linking oximato group derived from the non-symmetrical Schiff-base complex [M(II)(L)] and -(O)(2)- is a biphenolato bridge in the out-of-plane [Mn(2)(5-MeOsaltmen)(2)](2+) dimer. The solvent-free compounds, 1b and 2b, have also been prepared by drying of the parent compounds, 1a and 2a, respectively, at 100 degrees C under dried nitrogen. After this treatment, the crystallinity is preserved, and 1b and 2b crystallize in a monoclinic P2(1)/c space group without significant changes in their structures in comparison to 1a and 2a. Magnetic measurements on 1a and 1b revealed antiferromagnetic Mn(III)---Cu(II) interactions via the oximato group and weak ferromagnetic Mn(III)---Mn(III) interactions via the biphenolato bridge leading to an S(T) = 3 ground state. On the other hand, the diamagnetic nature of the square planar Ni(II) center generates an S(T) = 4 ground state for 2a and 2b. At low temperature, these solvated (a) and desolvated (b) compounds display single-molecule magnet behavior modulated by their spin ground state.     

Crystal structures and magnetic properties of two low-dimensional materials constructed from [Mn(III)(salen)H2O]+ and [M(CN)8](3-/4-) (M = Mo or W) precursors

The syntheses, X-ray structures, and magnetic behaviors of two new cyano-bridged assemblies, the molecular [Mn(III)(salen)H2O]3[W(V)(CN)8].H2O (1) and one-dimensional [Mn(salen)(H2O)2]2[[Mn(salen)(H2O)][Mn(salen)]2[Mo(CN)(8)]].0.5ClO4.0.5OH.4.5H2O (2), are presented. Compound 1 crystallizes in the monoclinic system, has space group P2(1)/c, and has unit cell constants a = 13.7210(2) A, b = 20.6840(4) A, c = 20.6370(2) A, and Z = 4. Compound 2 crystallizes in the triclinic system, has space group P, and has unit cell dimensions a = 18.428(4) A, b = 18.521(3) A, c = 18.567(4) A, and Z = 2. The structure of 1 consists of the asymmetric V-shaped Mn-NC-W-NC-Mn-O(phenolate)-Mn molecules, where W(V) coordinates with [Mn(salen)H2O] and singly phenolate-bridged [Mn(salen)H2O]2 moieties through the neighboring cyano bridges. The [W(V)(CN)8]3- ion displays distorted square-antiprism geometry. The structure of 2 consists of the cyano-bridged [Mn3(III)Mo(IV)]n- repeating units linked by double phenolate bridges into one-dimensional zigzag chains. The Mn(III) centers are bound to Mo(IV) of square-antiprism geometry through the neighboring cyano bridges. The magnetic studies of 1 reveal the antiferromagnetic intramolecular interactions through the CN and phenolate bridges and the relatively weak intermolecular interactions. Compound 1 becomes antiferromagnetically ordered below TN = 4.6 K. The presence of the magnetic anisotropy is documented with the MH measurements carried out for both polycrystalline and single-crystal samples. At T = 1.9 K, the spin-flop transition is observed in the field of 18 kOe applied parallel to the bc plane, which is the easy plane of magnetization. Field dependence of magnetization of 1 shows field-induced metamagnetic behavior from the antiferromagnetic ground state of ST = 3/2 to the state of ST = 5/2. The magnetic properties of 2 indicate a weak antiferromagnetic interaction between Mn(III) centers in double-phenolate-bridged [Mn(III)(salen)]2 dinuclear subunits and a very weak ferromagnetic interaction between them through the diamagnetic [Mo(IV)(CN)8]4- spacer.     

Manganese(II/II/II) and Manganese(III/II/III) Trinuclear Compounds. Structure and Solid and Solution Behavior

Two mixed-valence Mn(III)Mn(II) complexes and a homo-valence Mn(II) trinuclear manganese complex of stoichiometry Mn(III)Mn(II)Mn(III)(5-Cl-Hsaladhp)(2)(AcO)(4)(MeOH)(2).4CH(3)OH (1a), Mn(III)Mn(II)Mn(III) (Hsaladhp)(2)(AcO)(2)(5-Cl-Sal)(2)(thf)(2) (3a) and Mn(II)Mn(II)Mn(II) (AcO)(6)(pybim)(2) (1b) where H(3)saladhp is a tridentate Schiff base ligand and pybim a neutral bidentate donor ligand, have been structurally characterized by using X-ray crystallography. The structurally characterized mixed-valence complexes have strictly 180 degrees Mn(III)-Mn(II)-Mn(III) angles as required by crystallographic inversion symmetry. The complexes are valence trapped with two terminal Mn(III) ions showing Jahn-Teller distortion along the acetate or salicylate-Mn(III)-X axis. The Mn.Mn separation is 3.511 ? and 3.507 ? respectively. The mixed-valence complexes have S = (3)/(2) ground state and the homovalence complex S = (5)/(2), with small antiferromagnetic exchange J couplings, -5.6 and -1.8 cm(-1), respectively, while the powder ESR spectra at 4 K show a broad low field signal with g approximately 4.3 for Mn(III)Mn(II)Mn(III) and a broad temperature-dependent signal at g = 2 for Mn(II)Mn(II)Mn(II). Crystal data for 1a: [C(36)H(60)O(20)N(2)Cl(2)Mn(3)], triclinic, space group P&onemacr;, a = 9.272(7) ?, b = 11.046(8) ?, c = 12.635(9) ?, alpha = 76.78(2) degrees, beta = 81.84(2) degrees, gamma = 85.90(2) degrees, Z = 1. Crystal data for 3a: [C(48)H(56)O(18)N(2)Cl(2)Mn(3)], monoclinic, space group P2(1)/n, a = 8.776(3) ?, b = 22.182(7) ?, c = 13.575(4) ?, beta = 94.44(1) degrees, Z = 2. Crystal data for 1b: [C(36)H(36)O(12)N(6)Mn(3)], triclinic, space group P&onemacr;, a = 13.345(6) ?, b = 8.514(4) ?, c = 9.494(4) ?, alpha = 75.48(1) degrees, beta = 75.83(1) degrees, gamma = 76.42(1) degrees, Z = 1.     

Mn(dca)2(pym)2 and Mn(dca)2(pym)(H2O) {dca = dicyanamide; pym = pyrimidine}: New coordination polymers exhibiting 1- and 2-D topologies

Two new coordination polymers comprised of Mn(2+), N(CN)(2)(-) (dicyanamide, herein denoted dca) and pyrimidine (pym) have been synthesized and structurally and magnetically characterized. Mn(dca)(2)(pym)(2), , crystallizes in the orthorhombic space group Pbcn and forms trans bi-bridged Mn-(micro(1,5)-dca)(2)-Mn ribbons that extend along the b-axis of the unit cell. Two terminally bonded pym ligands are trans-coordinated to the Mn center. Adjacent chains interdigitate in an undulating fashion presumably due to a templating effect imposed by the pym ligands where N-atoms of consecutive pym rings stack parallel to the chain axis. Mn(dca)(2)(pym)(H(2)O), , which crystallizes in the monoclinic space group P2(1)/c, has a unique interdigitated 2D network that consists of double-bridged [Mn(2)(dca)(2)(pym)(2)(H(2)O)(2)](2+)"dimers" that are connected via single-bridging dca ligands. Each MnN(5)O octahedron is comprised of a coordinated H(2)O, a monodentate pym ligand, and four micro(1,5)-bridging dca anions. The magnetic data for were fitted to a uniform antiferromagnetic chain model which yielded J/k(B) = -0.34(1) K. In contrast, is best described as an alternating chain owing to the presence of both single- and double-bridging dca anions; a least-squares fit afforded J(a) = -0.43(1) and J(b) = -0.20(2) K, respectively. A transition to long-range magnetic ordering was observed for below approximately 2.4 K in addition to a field-induced spin flop transition at 15.6 kOe (1.7 K).     

A canted antiferromagnetic ordered phase of cyanido-bridged Mn(III)(2)Re(IV) single-chain magnets

A new cyanido-bridged Re(IV)-Mn(III) heterometallic 1D system, [Mn(III)(5-Me-saltmen)](2)[Re(IV)Cl(4)(CN)(2)]·3CH(3)CN (), was designed and structurally characterized. Interchain interactions stabilize a canted antiferromagnetic ordered state below 6.2 K that does not prevent slow relaxation of the magnetization reminiscent of the single-chain magnet properties of the individual chains.     

Cyanido-bridged Fe(III)-Mn(III) heterobimetallic materials built from Mn(III) Schiff base complexes and di- or tri-cyanido Fe(III) precursors

The reaction of [Fe(III)L(CN)(3)](-) (L being bpca = bis(2-pyridylcarbonyl)amidate, pcq = 8-(pyridine-2-carboxamido)quinoline) or [Fe(III)(bpb)(CN)(2)](-) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate) ferric complexes with Mn(III) salen type complexes afforded seven new bimetallic cyanido-bridged Mn(III)-Fe(III) systems: [Fe(pcq)(CN)(3)Mn(saltmen)(CH(3)OH)]·CH(3)OH (1), [Fe(bpca)(CN)(3)Mn(3-MeO-salen)(OH(2))]·CH(3)OH·H(2)O (2), [Fe(bpca)(CN)(3)Mn(salpen)] (3), [Fe(bpca)(CN)(3)Mn(saltmen)] (4), [Fe(bpca)(CN)(3)Mn(5-Me-saltmen)]·2CHCl(3) (5), [Fe(pcq)(CN)(3)Mn(5-Me-saltmen)]·2CH(3)OH·0.75H(2)O (6), and [Fe(bpb)(CN)(2)Mn(saltmen)]·2CH(3)OH (7) (with saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion, salpen(2-) = N,N'-propylenebis(salicylideneiminato) dianion, salen(2-) = N,N'-ethylenebis(salicylideneiminato) dianion). Single crystal X-ray diffraction studies were carried out for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe(III)-CN-Mn(III)] complexes while systems 3-7 are heterometallic chains with {-NC-Fe(III)-CN-Mn(III)} repeating units. These chains are connected through π-π and short contact interactions to form extended supramolecular networks. Investigation of the magnetic properties revealed the occurrence of antiferromagnetic Mn(III)···Fe(III) interactions in 1-4 while ferromagnetic Mn(III)···Fe(III) interactions were detected in 5-7. The nature of these Mn(III)···Fe(III) magnetic interactions mediated by a CN bridge appeared to be dependent on the Schiff base substituent. The packing is also strongly affected by the nature of the substituent and the presence of solvent molecules, resulting in additional antiferromagnetic interdinuclear/interchain interactions. Thus the crystal packing and the supramolecular interactions induce different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic S(T) = 3/2 ground state, interact antiferromagnetically in their crystal packing. At high temperature, the complexes 3-7 exhibit a one-dimensional magnetic behavior, but at low temperature their magnetic properties are modulated by the supramolecular arrangement: a three-dimensional antiferromagnetic order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties are detected for 5 and 6.     

Two novel cyanide-bridged bimetallic magnetic chains derived from manganese(III) Schiff bases and hexacyanochromate(III) building blocks

Two novel complexes, [{Mn(salen)}(2){Mn(salen)(CH(3)OH)}{Cr(CN)(6)}](n)·2nCH(3)CN·nCH(3)OH (1) and [Mn(5-Clsalmen)(CH(3)OH)(H(2)O)](2n)[{Mn(5-Clsalmen)(μ-CN)}Cr(CN)(5)](n)·5.5nH(2)O (2) (salen(2-) = N,N'-ethylene-bis(salicylideneiminato) dianion; 5-Clsalmen(2-) = N,N'-(1-methylethylene)-bis(5-chlorosalicylideneiminato) dianion), were synthesized and structurally characterized by X-ray single-crystal diffraction. The structural analyses show that complex 1 consists of one-dimensional (1D) alternating chains formed by the [{Cr(CN)(6)}{Mn(salen)}(4){Mn(salen)(CH(3)OH)}(2)](3+) heptanuclear cations and [Cr(CN)(6)](3-) anions. While in complex 2, the hexacyanochromate(III) anion acts as a bis-monodentate ligand through two trans-cyano groups to bridge two [Mn(5-Clsalmen)](+) cations to form a straight chain. The magnetic analysis indicates that complex 1 shows three-dimensional (3D) antiferromagnetic ordering with the Ne?el temperature of 5.0 K, and it is a metamagnet displaying antiferromagnetic to ferromagnetic transition at a critical field of about 2.6 kOe at 2 K. Complex 2 behaves as a molecular magnet with Tc = 3.0 K.     

Cyanide-bridged Fe(III)-Mn(III) chain with metamagnetic properties and significant magnetic anisotropy

The assembling of [Mn(5-MeOsalen)(H2O)]+ and [(Tp)Fe(CN)3]- affords the one-dimensional zigzag chain [(Tp)Fe(CN)3Mn(5-MeOsalen).2CH3OH]n [1; Tp- = hydrotris(pyrazolyl)borate and 5-MeOsalen2- = N,N'-ethylenebis(5-methoxysalicylideneiminate)]. The corroborated experimental and ab initio data indicate ferromagnetic Fe(III)-Mn(III) couplings and D < 0 anisotropy on Mn(III). The field-induced metamagnetic behavior is due to interchain effects.     

Coulombic aggregations of Mn(III) salen-type complexes and Keggin-type polyoxometalates: isolation of Mn2 single-molecule magnets

The reaction of Mn(III) salen-type complexes with di- and tetraanionic α-Keggin-type polyoxometalates (POMs) was performed, and three types of Coulombic aggregations containing Mn(III) out-of-plane dimeric units (abbreviated as [Mn(2)](2+)) that are potentially single-molecule magnets (SMMs) with an S(T) = 4 ground state were synthesized: [Mn(2)(5-MeOsaltmen)(2)(acetone)(2)][SW(12)O(40)] (1), [Mn(2)(salen)(2)(H(2)O)(2)](2)[SiW(12)O(40)] (2), and [Mn(5-Brsaltmen)(H(2)O)(acetone)](2)[{Mn(2)(5-Brsaltmen)(2)}(SiW(12)O(40))] (3), where 5-Rsaltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(5-R-salicylideneiminate) with R = MeO (methoxy), Br (bromo) and salen(2-) = N,N'-ethylenebis(salicylideneiminate). Compound 1 with a dianionic POM, [SW(12)O(40)](2-), is composed of a 1:1 aggregating set of [Mn(2)](2+)/POM, and 2, with a tetraanionic POM, [SiW(12)O(40)](4-), is a 2:1 set. Compound 3 with [SiW(12)O(40)](4-) forms a unique 1D coordinating chain with a [-{Mn(2)}-POM-](2-) repeating unit, for which a hydrogen-bonded dimeric unit ([Mn(5-Brsaltmen)(H(2)O)(acetone)](2)(2+)) is present as a countercation. Independent of the formula ratio of [Mn(2)](2+)/POM, Mn(III) dimers and POM units in 1-3 form respective segregated columns along a direction of the unit cell, which make an alternate packing to separate evenly identical species in a crystal. The nearest intermolecular Mn···Mn distance is found in the order 2 < 3 < 1. The segregation of the [Mn(2)](2+) dimer resulted in interdimer distances long enough to effectively reduce the intermolecular magnetic interaction, in particular in 1 and 3. Consequently, an intrinsic property, SMM behavior, of Mn(III) dimers has been characterized in this system, even though the interdimer interactions are still crucial in the case of 2, where a long-range magnetic order competitively affects slow relaxation of the magnetization at low ac frequencies.     

Slow relaxation in a one-dimensional rational assembly of antiferromagnetically coupled [Mn4] single-molecule magnets

Four discrete Mn(III)/Mn(II) tetranuclear complexes with a double-cuboidal core, [Mn(4)(hmp)(6)(CH(3)CN)(2)(H(2)O)(4)](ClO(4))(4).2CH(3)CN (1), [Mn(4)(hmp)(6)(H(2)O)(4)](ClO(4))(4).2H(2)O (2), [Mn(4)(hmp)(6)(H(2)O)(2)(NO(3))(2)](ClO(4))(2).4H(2)O (3), and [Mn(4)(hmp)(6)(Hhmp)(2)](ClO(4))(4).2CH(3)CN (4), were synthesized by reaction of Hhmp (2-hydroxymethylpyridine) with Mn(ClO(4))(2).6H(2)O in the presence of tetraethylammonium hydroxide and subsequent addition of NaNO(3) (3) or an excess of Hhmp (4). Direct current (dc) magnetic measurements show that both Mn(2+)-Mn(3+) and Mn(3+)-Mn(3+) magnetic interactions are ferromagnetic in 1-3 leading to an S(T) = 9 ground state for the Mn(4) unit. Furthermore, these complexes are single-molecule magnets (SMMs) clearly showing both thermally activated and ground-state tunneling regimes. Slight changes in the [Mn(4)] core geometry result in an S(T) = 1 ground state in 4. A one-dimensional assembly of [Mn(4)] units, catena-{[Mn(4)(hmp)(6)(N(3))(2)](ClO(4))(2)} (5), was obtained in the same synthetic conditions with the subsequent addition of NaN(3). Double chairlike N(3)(-) bridges connect identical [Mn(4)] units into a chain arrangement. This material behaves as an Ising assembly of S(T) = 9 tetramers weakly antiferromagnetically coupled. Slow relaxation of the magnetization is observed at low temperature for the first time in an antiferromagnetic chain, following an activated behavior with Delta(tau)/k(B) = 47 K and tau(0) = 7 x 10(-)(11) s. The observation of this original thermally activated relaxation process is induced by finite-size effects and in particular by the noncompensation of spins in segments of odd-number units. Generalizing the known theories on the dynamic properties of polydisperse finite segments of antiferromagnetically coupled Ising spins, the theoretical expressions of the characteristic energy gaps Delta(xi) and Delta(tau) were estimated and successfully compared to the experimental values.     

Assembly of azido- or cyano-bridged binuclear complexes containing the bulky [Mn(phen)2]2+ building block: syntheses, crystal structures, and magnetic properties

Two new cyano-bridged heterobinuclear complexes, [Mn(II)(phen)2Cl][Fe(III)(bpb)(CN)2] x 0.5CH3CH2OH x 1.5H2O (1) and [Mn(II)(phen)2Cl][Cr(III)(bpb)(CN)2] x 2H2O (2) [phen = 1,10-phenanthroline; bpb(2-) = 1,2-bis(pyridine-2-carboxamido)benzenate], and four novel azido-bridged Mn(II) dimeric complexes, [Mn2(phen)4(mu(1,1)-N3)2][M(III)(bpb)(CN)2]2 x H2O [M = Fe (3), Cr (4), Co (5)] and [Mn2(phen)4(mu(1,3)-N3)(N3)2]BPh4 x 0.5H2O (6), have been synthesized and characterized by single-crystal X-ray diffraction analysis and magnetic studies. Complexes 1 and 2 comprise [Mn(phen)2Cl]+ and [M(bpb)(CN)2]- units connected by one cyano ligand of [M(bpb)(CN)2]-. Complexes 3-5 are doubly end-on (EO) azido-bridged Mn(II) binuclear complexes with two [M(bpb)(CN)2]- molecules acting as charge-compensating anions. However, the Mn(II) ions in complex 6 are linked by a single end-to-end (EE) azido bridging ligand with one large free BPh4(-) group as the charge-balancing anion. The magnetic coupling between Mn(II) and Fe(III) or Cr(III) in complexes 1 and 2 was found to be antiferromagnetic with J(MnFe) = -2.68(3) cm(-1) and J(MnCr) = -4.55(1) cm(-1) on the basis of the Hamiltonian H = -JS(Mn)S(M) (M = Fe or Cr). The magnetic interactions between two Mn(II) ions in 3-5 are ferromagnetic in nature with the magnetic coupling constants of 1.15(3), 1.05(2), and 1.27(2) cm(-1) (H = -JS(Mn1)S(Mn2)), respectively. The single EE azido-bridged dimeric complex 6 manifests antiferromagnetic interaction with J = -2.29(4) cm(-1) (H = -JS(Mn1)S(Mn2)). Magneto-structural correlationship on the EO azido-bridged Mn(II) dimers has been investigated.     

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.     

Heterometallic MIIRuIII2 compounds constructed from trans-[Ru(Salen)(CN)2]- and trans-[Ru(Acac)2(CN)2]-. Synthesis, structures, magnetic properties, and density functional theoretical study

The synthesis, structures, and magnetic properties of four cyano-bridged M(II)Ru(III)2 compounds prepared from the paramagnetic Ru(III) building blocks, trans-[Ru(salen)(CN)2]- 1 [H2salen = N,N'-ethylenebis(salicylideneimine)] and trans-[Ru(acac)2(CN)2]- (Hacac = acetylacetone), are described. Compound 2, {Mn(CH3OH)4[Ru(salen)(CN)2]2}.6CH3OH.2H2O, is a trinuclear complex that exhibits antiferromagnetic coupling between Mn(II) and Ru(III) centers. Compound 3, {Mn(H2O)2[Ru(salen)(CN)2]2.H2O}n, has a 2-D sheetlike structure that exhibits antiferromagnetic coupling between Mn and Ru, leading to ferrimagnetic-like behavior. Compound 4, {Ni(cyclam)[Ru(acac)2(CN)2]2}.2CH3OH.2H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane), is a trinuclear complex that exhibits ferromagnetic coupling. Compound 5, {Co[Ru(acac)2(CN)2]2}n, has a 3-D diamond-like interpenetrating network that exhibits ferromagnetic ordering below 4.6 K. The density functional theory (DFT) method was used to calculate the molecular magnetic orbitals and the magnetic exchange interaction between Ru(III) and M(II) (Mn(II), Ni(II)) ions.     

Linear NiII-MnIII2-NiII tetramers: an oligomeric component of the MnIII2NiII single-chain magnets

Heterometallic linear tetramers [Mn(5-R-saltmen)Ni(pao)(bpy)(2)](2)(ClO(4))(4) (5-R-saltmen(2-) = N,N'-1,1,2,2-tetramethylethylene bis(5-R-salicylideneiminate); pao(-) = pyridine-2-aldoximate; bpy = 2,2'-bipyridine, R = H, 1; Cl, 2; Br, 3; MeO, 4) have been synthesized and structurally characterized. These compounds exhibit a [Ni(II)-NO-Mn(III)-(O)(2)-Mn(III)-ON-Ni(II)] skeleton where -ON- is an oximate bridge between Mn(III) and Ni(II) ions and -(O)(2)- is a bi-phenolate bridge between Mn(III) ions. These tetramers can be seen as oligomeric units of the heterometallic Mn(III)(2)-Ni(II) chain observed in a family of single-chain magnets (Clérac, R.; Miyasaka, H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837. Miyasaka, H.; Clérac, R.; Mizushima, K.; Sugiura, K.; Yamashita, M.; Wernsdorfer, W.; Coulon, C. Inorg. Chem. 2003, 42, 8203.). Magnetic measurements on these tetramers confirm the nature of the magnetic interactions reported for the Mn(III)(2)-Ni(II) chains: a strong antiferromagnetic Mn(III)/Ni(II) coupling via the oximate bridge (J(Ni-Mn) ranges from -23.7 to -26.1 K) and a weak ferromagnetic Mn(III)/Mn(III) coupling through the bi-phenolate bridge (J(Mn-Mn) ranges from +0.4 to +0.9 K). These magnetic interactions lead to tetramers with an S = 2 ground state.     

Two WV-MnIII bimetallic assemblies built by octacyanotungstate(v) and MnIII Schiff bases: molecular structures and a spin-flop transition

Two W(V)-Mn(III) bimetallic compounds, [Mn(Cl-salmen)(H(2)O)2]{[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8].2H(2)O (1.2H(2)O) [5-Clsalmen = N,N'-(1-methylethylene)bis(5-chlorosalicylideneiminato) dianion], which contains trinuclear Mn(2)W and isolated Mn(III) moieties, and [Mn(3-MeOsalcy)(H(2)O)2]3[W(CN)(8)].2H(2)O (2.2H(2)O) [3-MeOsalcy = N,N'-(trans-1,2-cyclohexanediylethylene)bis(3-methoxysalicylideneiminato) dianion] molecules were prepared in redox processes and characterized using X-ray analysis and magnetic measurements. Compound 1 is composed of the {[Mn(5-Clsalmen)(H(2)O)]2[W(CN)8]}- trimer, in which two CN groups among eight in [W(CN)8](3-) bridge W(5+) and two Mn(3+) ions and the remaining CN ligands are hydrogen-bonded to water molecules or unbound, and the [Mn(Cl-salmen)(H(2)O)2]+ cation. Subsequently, two water molecules of the isolated cation are subject to hydrogen bonds. For 2, there are no covalent bonds among the subunits and six serial stacks of [Mn(3-MeOsalcy)(H(2)O)2]+ units are all hydrogen-bonded. The many hydrogen bonds found in both complexes eventually lead to three-dimensional networks. The magnetic studies for 1 reveal that antiferromagnetic interactions (J = -5.4 cm(-1)) between W(V) and Mn(III) centers within the trimer are transmitted via the bridging CN groups. Intermolecular antiferromagnetic couplings (zJ' = -0.2 cm(-1)) are also observed. The static and dynamic magnetic data of 1 demonstrate the existence of a field-induced spin-flop transition occurring among the clusters and monomeric molecules.     

Dodecanuclear manganese(III) phosphonates with cage structures

Treatments of Mn(O(2)CR)(2) (R = Me, Ph) with NBu(4)MnO(4) in CH(3)CN or CH(3)CN/CH(2)Cl(2) in the presence of acetic acid, delta(1)-cyclohexenephosphonic acid (C(6)H(9)PO(3)H(2)), and 2,2'-bipyridine or 1,10-phenanthroline result in three novel dodecamanganese(III) clusters [Mn(12)O(8)(O(2)CMe)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (1), [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(bipy)(3)] (2), and [Mn(12)O(8)(O(2)CPh)(6)(O(3)PC(6)H(9))(7)(phen)(3)] (3). They have a similar Mn(12) core of [Mn(III)(12)(mu(4)-O)(3)(mu(3)-O)(5)(mu-O(3)P)(3)] with a new type of topologic structure. Solid-state dc magnetic susceptibility measurements of complexes 1-3 reveal that dominant antiferromagnetic interactions are propagated between the magnetic centers. The ac magnetic measurements suggest an S = 2 ground state for compounds 1 and 3 and an S = 3 ground state for compound 2.     

Tris(chloranilato)ferrate(III) anionic building block containing the (Dihydroxo)oxodiiron(III) dimer cation: synthesis and characterization of [(TPA)(OH)FeIIIOFeIII(OH)(TPA)][Fe(CA)3]0.5(BF4)0.5.1.5MeOH.H2O [TPA = tris(2-pyridylmethyl)amine; CA = chloranilate

[(TPA)(OH)FeIIIOFeIII(OH)(TPA)][Fe(CA)3]0.5(BF4)0.5.1.5MeOH.H2O (1) which possesses both the [FeIII(CA)3]3- (CA= chloranilate) and hydroxooxoiron(III) ions has had its structure determined by single-crystal X-ray diffraction. The 2-300 K magnetic susceptibility of 1 provides the magnetic parameters, g = 2.07, J/kB = -165 K (115 cm-1), theta = -1 K, and the spin impurity, rho = 0.05, which indicates a strong antiferromagnetic interaction between iron(III) ions via the oxo anion.     

Heterometallic Cr-Mn complexes containing cyanide and oxalate bridges

Three heterometallic Cr-Mn compounds, {Mn(mu-ox)0.5(H2O) [Cr(phen)(CN)4]}n.n H2O.2n CH3OH, (1), {Mn(mu-ox)0.5(H2O)[Cr(bpy)(CN)4]}n.2n H2O x n CH3OH, (2), and {Mn(mu-ox)0.5(bpy)[Cr(bpy)(CN)4]}n, (3) (ox = oxalate), containing cyanide and oxalate bridges based on building blocks [Cr(L)(CN)4]- (L = phen and 2,2'-bipyridine) have been prepared. A new approach was first employed to synthesize ox-bridged compounds via facile oxidation-hydrolysis reactions of diaminomaleonitrile. X-ray crystallography revealed that the structures of 1 and 2 are similar, where cyano-bridged corrugated ladderlike chains are further connected through bis-bidentate oxalato bridges to unique two-dimensional layered structures. Of note is that the introduction of 2,2'-bipyridine led to an interesting cluster-based chainlike compound (3) with cyano-bridged squares [Mn2Cr2] extended by ox bridges. Magnetic studies show antiferromagnetic (AF) interaction between cyano-bridged Cr(III)-Mn(II) and ox-bridged Mn(II)-Mn(II) ions, with the result that 1 and 2 exhibit AF ordering with spin-flop behaviors below 18 and 19 K, respectively.     

Synthesis, structure, and magnetic ordering of layered (2-D) V-based tris(oxalato)metalates

The reaction of K3[M(III)(ox)3].3H2O [M = V (1), Cr; ox = oxalate], Mn(II)/V(II), and [N(n-Bu)4]Br in water leads to the isolation of 2-D V-based coordination polymers, [[N(n-Bu)4][Mn(II)V(III)(ox)3]]n (2), [[N(n-Bu)4][V(II)Cr(III)(ox)3]]n (3), [[N(n-Bu)4][V(II)V(III)(ox)3]]n (4), and an intermediate in the formation of 4, [[N(n-Bu)4][V(II)V(III)(ox)3(H2O)2]]n.2.5H2O (4a), while 1-D [V(II)(ox)(H2O)2]n (5) is obtained by using Na2ox and [V(OH2)6]SO4 in water. The structures of 1-5 have been investigated by single crystal and/or powder X-ray crystallography. In 1, V(III) is coordinated with three oxalate dianions as an approximately D3 symmetric, trigonally distorted octahedron. 1 is paramagnetic [mu(eff) = 2.68 mu(B) at 300 K, D = 3.84 cm(-1) (D/k(B) = 5.53 K), theta = -1.11 K, and g = 1.895], indicating an S = 1 ground state. 2 exhibits intralayer ferromagnetic coupling below 20 K, but does not magnetically order above 2 K, and 3 shows a strong antiferromagnetic interaction between V(II), S = 3/2 and Cr(III), S = 3/2 ions (theta = -116 K) within the 2-D layers. 4 and 4a magnetically order as ferrimagnets at T(c)'s, taken as the onset of magnetization, of 11 and 30 K, respectively. The 2 K remanent magnetizations are 2440 and 2230 emu.Oe mol(-1) and the coercive fields are 1460 and 4060 Oe for 4 and 4a, respectively. Both 4 and 4a clearly show frequency dependence, indicative of spin-glass-like behavior. The glass transition temperatures were at 6.3 and 27 K, respectively, for 4 and 4a. 1-D 5 exhibits antiferromagnetic coupling of -4.94 cm(-1) (H = -2Jsigma(i=1)n.S(i-1) - gmu(B)sigma(i=0)(n)H.S(i)) between the V(II) ions.     

Theoretical insights into the ferromagnetic coupling in oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear complexes with aromatic diimine ligands

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.