Variable-temperature Magnetic Measurements Research Articles

Structural Diversity due to Amino Alcohol Ligands Leading to Rare μ4-Hydroxo-Bridged Tetranuclear and “Bicapped Cubane” Cores in Copper(II) Complexes: A Theoretical and Experimental Magnetostructural Study

The μ4-hydroxo- and alkoxo-bridged tetranuclear copper(II) complexes, [Cu4(μ4-OH)(dmae)4][Ag(NO3)4] (1), [Cu4(μ4-OH)(dmae)4][Na(NO3)4] (2), [Cu4(μ4-OH)(dmae)4][K(NO3)4] (3), and hexanuclear alkoxo-bridged "bicapped cubane" copper(II) complex [Cu6(ae)8(ClO4)2](ClO4)2·MeOH (8) (dmae = N,N-dimethylaminoethanolato and ae = 2-aminoethanolato) were synthesized via self-assembly from chelating amino alcohols and copper(II), silver (1), sodium (2), and potassium (3) nitrates or copper(II) perchlorate (8). The complexes are characterized by elemental analyses, single-crystal X-ray diffraction, and variable temperature magnetic measurements. The crystal structures of complexes 1-3 consist of almost planar tetranuclear [Cu4(μ4-OH)(dmae)4](3+) units, in which Cu(II) ions are also weakly bonded to nitrate anions. The adjacent tetranuclear units of 1-3 are connected by ionic interactions between nitrate anions and sodium, potassium, or silver cations resulting in the formation of 1D polymers. The crystal structure of 8 consists of hexanuclear [Cu6(ae)8](4+) "bicapped cubane" units, in which the capping Cu(II) ions are weakly bonded to perchlorate anions. The adjacent hexanuclear units of 8 are connected by hydrogen bonds resulting in the formation of 3D hydrogen bonded networks. Also the results from the synthetic studies leading to the formation of new copper(II) and silver(I) complexes (4-7) using Hae, 3-aminopropanol (Hap), and N,N-dimethylaminopropanol (Hdmap) in similar reactions, which gave tetra- and hexanuclear complexes, are presented. Experimental magnetic studies showed that complexes 1 and 2 exhibit dominant antiferromagnetic coupling leading to an S = 0 ground state, whereas 8 exhibits a large dominant antiferromagnetic interaction between the capping copper atoms and the copper atoms of the top and bottom faces of the cubane unit that define two isosceles triangles. This interaction leads to an S = 1/2 ground state for each triangle. The weak ferromagnetic interaction between these doublet states through the cubane unit leads to a triplet S = 1 ground state for 8. The values of the magnetic exchange coupling constant were the following: J = +1.8 (1) and +2.9 cm(-1) (2) between adjacent copper atoms; J' = -29.2 (1) and -32.2 cm(-1) (2) between opposite copper atoms; J = -297.6 cm(-1) and zJ' = +0.07 cm(-1) (8). Magnetic coupling constants calculated for 2 and 8 by DFT methods are in general of the same nature and magnitude as the experimental ones.

Preparation, Crystal Structure and Magnetic Properties of Two 1,2-Di(4-pyridyl)ethylene-Bridged Manganese(II) Complexes

Two polymeric carboxylato-bridged manganese(II) complexes, \( {}_{\infty }^{1} \)[Mn(bpe)(NBA)2] (1) and \( {}_{\infty }^{1} \)[Mn(bpe)(MBA)2] (2) (bpe = 1,2-di(4-pyridyl)ethylene; HNBA = m-nitrobenzoic acid; HMBA = m-methyl-benzoic acid), were synthesized and characterized. Compounds 1 and 2 are isostructural. X-ray diffraction studies show that the title compounds possess a double chain structure. The chains in 1 and 2 are assembled into 2-D layers via C–H···O hydrogen bonds interactions. Furthermore, owing to the offset face-to-face π–π stacking interactions, the adjacent 2-D layers embed into each other to form a 3-D supramolecular framework. Variable-temperature (2–300 K) magnetic susceptibility measurements show the presence of weak antiferromagnetic interactions between the high-spin Mn(II) (S = 5/2) ions through a carboxylato bridge with the best fit parameters for 1 being J = −0.13 cm−1, zJ′ = −0.098 cm−1 and for 2, J = −0.33 cm−1, zJ′ = −0.001 cm−1.

Scalene-tricopper(II) bridged by 5-(1H-benzo[d]imidazol-2-yl-1H-imidazole-4-carboxylic acid: Synthesis, crystal structure and magnetic properties

New scalene tricopper complex [CuII3(HImbm)(bipy)6](ClO4)4 · 3CH3OH · 4H2O (1) (H3Imbm = 5-(1H-benzo[d]imidazol-2-yl)-1H-imidazole-4-carboxylic acid, bipy = 2,2′-bipyridine) was synthesized. X-ray analysis reveals that 1 crystallizes in monoclinic P2(1)/c. Complex 1 can be described as three terminal [Cu(bpy)2]2 + units bridged by one asymmetric H3Imbm ligand with its peripheral three chelating pockets to capture three Cu atoms in a scalene-triangular geometry. The variable-temperature magnetic measurement was recorded for the crystallographically characterized 1, and the magnetic response was analyzed very well using a scalene triangle Cu3 model, indicating a dominant antiferromagnetic coupling with J12 = − 44.3 cm− 1, J23 = − 27.3 cm− 1, and g = 2.08, given J13 = 0.

Mn<sup>III</sup> <sub>2</sub>Ln<sup>III</sup> <sub>2</sub> (Ln = Gd, Dy, Ho) Complexes From The Initial Employment of 1,3-Propanediol In Mixed 3d/4f Metal Cluster Chemistry

The initial employment of 1,3-propanediol (pdH2) in the synthesis of 3d/4f metal clusters has afforded a new family of tetranuclear [Mn2Ln2O2{(CH3)3CCO2}8{(CH3)3CCO2H}2(pdH2)2] (Ln = Dy, 1; Gd, 2; Ho, 3) complexes. Compounds 1-3 represent new additions to the small family of MnIII 2Ln2 clusters possessing planar or diamond-like cores. Variable-temperature, dc and ac magnetization measurements were performed on compounds 1-3 and revealed the existence of very weak antiferromagnetic exchange interactions between the metal centers leading to a ground state spin value S = 5 in case of 2·2(CH3)3CCO2H·2H2O. Keywords: 1, 3-propanediol, 3d/4f clusters, crystal structures, magnetic properties.

Structure and magnetism of heptanuclear complex encapsulated the octacyanomolybdate(IV) core

Abstract A new heptanuclear complex [{Cu(TPA)CN}6Mo(CN)2][ClO4]8 (1) (TPA = tris(2-pyridylmethyl)amine) was formed by the reaction of [Cu(TPA)]2 + cations and K4Mo(CN)8. The octacyanomolybdate core is encapsulated by six mononuclear copper cations via cyano bridges. 1 Crystallizes in monoclinic space group P21/n with a = 22.30(2) A, b = 27.13(3) A, c = 24.35(2) A, β = 94.10(2)°, and Z = 4. Variable temperature magnetic measurements have demonstrated that very weak antimagnetic interaction between the nearest paramagnetic CuII centers at low temperature is exhibited, transferred by ―NC―Mo―CN― bridging units.

Oligonuclear homo- and mixed-valence manganese complexes based on thiophene- or aryl-carboxylate ligation: Synthesis, characterization and magnetic studies

Mixed-valence trinuclear manganese compounds [Mn3O(O2CTh)6(L)x(H2O)y]·n(solvent) (Th=thiophene, 1·CH3CN: L=pyridine (py), x=3, y=0, n=1, solvent=CH3CN; 1·∼H2O: L=py, x=3, y=0, n=∼1, solvent=H2O; 2: L=py, x=2, y=1, n=0.25, solvent=CH3CN; 3: L=3-Mepy, x=2, y=1, n=0) containing a [MnIIMn2III(μ3-O)]6+ core have been prepared. Homo-valence tetranuclear manganese complexes (NBun4)[Mn4O2(O2CAr)9(L)] (4·ThCO2H·CH2Cl2: Ar=–Th, L=EtOH; 6: Ar=–Ph, L=H2O; 7: Ar=–Ph-p-Me, L=H2O; 8·CH2Cl2: –Ph-3,5-Me2, no L) with a [MnIII4(μ3-O)2]8+ core and [MnIIMnIII3O2(O2CTh)7(bpy)2] (5) were synthesized, structurally and magnetically characterized. Compounds 1–3 were obtained by comproportionation of MnII(O2CMe)2·4H2O with (NBun4)MnVIIO4 in aprotic pyridine (1) or aprotic/protic py/EtOH (2) or Mepy/EtOH (3) solvent mixtures. Clusters 4–8 were synthesized by comproportionation of MnII(O2CAr)2·xH2O/ArCOOH with (NBun4)MnVIIO4 in EtOH/CH3CN. X-ray structural characterization of the 2-thiophenecarboxylate (ThCO2−) containing compounds 1·CH3CN, 1·∼2H2O and 4·ThCO2H·CH2Cl2 revealed a thiophene ring disorder about the (O2)C–C(Th) bond so that the S atom and opposite (5–)CH group are distributed over two ring positions each. The MnII atom in the approximately isosceles triangular [MnIIMn2III(μ3-O)]6+ cores in 1 could be clearly assigned from bond valence sum calculations and bond distances. The [Mn4(μ3-O)2]8+ core in the anionic complexes in the structures of 4·ThCO2H·CH2Cl2 and 8·CH2Cl2 has an all MnIII oxidation level and “butterfly-like” arrangement. The magnetic properties of 4–8 were investigated by variable temperature magnetic susceptibility and magnetization measurements. Similar magnetic behavior was observed for the [MnIII4(μ3-O)2]8+ butterfly-core compounds 4, 6–8, with antiferromagnetic interactions between pairs of manganese ions with amplitude of ∼14.5cm−1 and ∼4.6cm−1 for the Mnb⋯Mnb and Mnb⋯Mnw coupling, respectively (b=body, w=wing). Changing the Ar-ligand size in [Mn4O2(O2CAr)9(L)]− does not have a significant effect on the magnetic properties of these butterfly clusters.

Synthesis, X-ray structural and magnetic characterizations, and epoxidation activity of a new bis(μ-acetato)(μ-alkoxo)dinuclear iron(III) complex

The synthesis, crystal structure and variable temperature magnetic measurements of a new dinuclear Fe(III) complex, [Fe2(μ1,3-O2Cfn)(OH2)(MeOH)Cl2L] (1) [fn=furan, L=N,N′-bis(salicyaldehydene)-1,3-diaminopropan-2-ol], is reported. From X-ray diffractometry, it is shown that each Fe(III) centre in 1 is in a distorted octahedral environment. A variable temperature magnetic study reveals strong antiferromagnetic behaviour of 1 with J=−22.2±0.1cm−1. Use of 1 as an alkene epoxidation catalyst towards (E)-stilbene and styrene with tert-butyl hydrogen peroxide (TBHP) and iodosylbenzene (PhIO) reveals that TBHP is the better oxidant in terms of the yield of the reaction.

Coordination Polymers Containing Manganese(II)-Azido Layers Connected by Dipyridyl-tetrazine and 4,4′-Azobis(pyridine) Linkers

Two new polynuclear manganese(II) complexes [Mn(dptz)(N(3))(2)](n) (1) and [Mn(azpy)(N(3))(2)](n) (2) (where dptz = dipyridyl-tetrazine and azpy = 4,4'-azobis(pyridine)) have been synthesized by self-assembly of the ligand azide, together with dptz and azpy as secondary spacers. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that in complex 1, which is the first reported Mn(II) complex with the ligand dptz, two μ(1,3) bridging azides connect neighboring manganese ions in a zigzag manner to generate a neutral two-dimensional (2D) sheet which is further connected by the dptz ligands to form a three-dimensional (3D) framework. By contrast, complex 2 contains dimeric [Mn(2)(μ(1,1)-N(3))(2)](2+) fragments linked to four identical motifs by means of four single μ(1,3)-N(3) bridges, that generates a neutral 2D Mn(II)-azide sheet which is further interconnected by azpy ligands to neighboring manganese ions forming an unprecedented 3D network. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of predominantly antiferromagnetic coupling for both complexes that has been reproduced with a regular antiferromagnetic S = 5/2 chain (J) with interchain interactions (j) modeled with the molecular field approximation with J = -7.1 cm(-1) and j' = -0.8 cm(-1) for 1 and J = -4.2 cm(-1) and j' = 0.1 cm(-1) for 2.

Crown-linked dipyridylamino-triazine ligands and their spin-crossover iron(ii) derivatives: magnetism, photomagnetism and cooperativity

The syntheses, crystallography and magnetic properties of a series of compounds of formula trans-[Fe(II)(L(1))2(NCX)2] (X = S, Se, BH3 (1-3)), cis-[Fe(II)(L(2))(NCX)2]·CH2Cl2 (X = S, Se, BH3 (4-6)) and trans-[Fe(II)(L(3))(NCX)2]n (X = S, Se (7-8)) are described (L(1) = 6-chloro-N(2),N(2)-diethyl-N(4),N(4)-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L(2) = 6,6'-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N(2),N(2)-diethyl-N(4),N(4)-di(pyridin-2-yl)-1,3,5-triazine-2,4-diamine, L(3) = 6,6'-(1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diyl)bis(N(2),N(2),N(4),N(4)-tetra(pyridin-2-yl)-1,3,5-triazine-2,4-diamine)). The magnetostructural properties of 1-8 have been probed in detail by variable temperature magnetic measurements and crystallographic methods. 1-6 display mononuclear structures while 7 and 8 form 1-D chain structures. Complexes 4-6 have the potential to form 1D-chains via L(2) bridging, but instead form mononuclear complexes. Magnetic studies show that complexes 1, 2, and 4 remain in the high-spin (HS) state at all temperatures. An aged, dry, powdered sample of 3 gives an abrupt HS to LS transition (T1/2 = 200 K), while a freshly prepared, powdered sample of 3·1.5H2O displays thermal hysteresis (Δ = 7 K). Complexes 5, 6 and 7 undergo a gradual spin transition with T1/2 values of 100 K, 150 K and 130 K, respectively. Cooperativity parameters are compared, with 3 showing cooperativity (positive C) and 5 and 6 showing anticooperativity. Photomagnetic LIESST (light induced excited spin state trapping) studies were performed on complexes 5 and 6 and reveal T(LIESST) values lower than 60 K. An attempt has been made to understand the electronic structure of complex 3 and its cooperativity behaviour using density functional methods, the calculations reproducing the sign and, in part, the magnitude of the cooperativity.

Fingerprinting the oxidation state of U(iv) by emission spectroscopy

The solid-state structure of the known complex [Et4N][U(NCS)5(bipy)2] has been re-determined and a detailed spectroscopic and magnetic study has been performed in order to confirm the oxidation states of both metal and bipy ligand. Electronic absorption and infrared spectroscopy suggest that the uranium is in its +4 oxidation state and this has been corroborated by emission spectroscopy and variable temperature magnetic measurements, as well as theoretical calculations. Therefore the bipy ligands are neutral, innocent ligands and not, as would be inferred from just a solid state structure, radical anions.

Syntheses, Crystal Structures, Magnetic Behaviours, and Thermal Properties of Three Hydrogen‐Bonding Networks Containing Dicyanamide and 4‐Hydroxypyridine

Three new dicyanamide‐bridged polymeric complexes of {[Mn(dca)2(L)2] · 2H2O} n (1), {[Cd(dca)2(L)2] · 2H2O} n (2), and {[Co(dca)2(L)2]2(L)} n (3) (dca = dicyanamide, L = pyridinium‐4‐olate) have been synthesized and structurally characterized. In the three compounds, the protons of hydroxyl groups of 4‐hydroxypyridine transfer to pyridyl nitrogen atoms. Compounds 1 and 2 are isomorphous forming one‐dimensional chains where metals are connected by double dca anions. These one‐dimensional chains are extended into two‐dimensional layers through weak C–H⋯N hydrogen bonds. Further, these layers are assembled into a three‐dimensional supramolecular network through N–H⋯O, O–H⋯O hydrogen bonds. Complex 3 is a coordination layer of (4, 4) topology with octahedral metal centers linked by four single μ1,5‐bridges. These layers are interlocked by N–H⋯O, O–H⋯O hydrogen bonds from coordinated water molecules and free L molecules, which leads to a three‐dimensional supramolecular architecture. The variable temperature magnetic susceptibilities measurement of compounds 1 and 3 shows the existence of weak antiferromagnetic interactions between the metal centers. The thermogravimetric analyses of the compounds 1–3 are also discussed.

Fabrication of metal–organic hybrid architectures using bridging diphenyl phosphate: Syntheses, characterization, magnetic properties and the effect of weak interactions on their crystal packing

Ten different metal-organic hybrids of divalent metal ions have been synthesized using the diphenyl phosphate ligand and three different N,N donor spacers. All the complexes have been characterized by single crystal X-ray crystallography and other physico-chemical methods. For six complexes, the diphenyl phosphate (dpp) ligand acts as a bridge between the metal ions, whereas in four complexes dpp acts as a monodentate ligand. All nine complexes (1-9) show two dimensional coordination structures created by the N,N donor spacers, and, the remaining one (10) has a one dimensional ribbon-like structure. Here the aromatic rings present in the compounds viz. phenyl rings of dpp and the pyridyl rings of N,N donor spacers, have a key role to extend the dimensionality in their solid-state structures. In each instance, the aromatic rings of dpp and N,N donor spacers are nicely involved in the supramolecular structure generation by the help of π-π interactions. In all the cases, the role of weak interactions on the crystal packing and their effect in the generation of different supramolecular architectures has been thoroughly investigated. Variable temperature magnetic measurements of three relevant complexes have been carried out. Compounds 1 and 3 clearly indicate the existence of a weak antiferromagnetic interaction between the metal ions through the bridging dpp ligand. In 5, where dpp acts as a monodentate ligand; the metal ion may be considered as an isolated monomer.

Solvent-driven dimensionality control in molecular systems containing CuII, 2,2′-bipyridine and an oxamato-based ligand

A discrete dicopper(II) system, [Cu(bipy)(H2mpba)]2·2H2O (1), and its isomeric chain, [Cu(bipy)(H2mpba)]·dmso (2) [bipy = 2,2′-bipyridine and H4mpba = N,N′-1,3-phenylenebis(oxamic acid)], were obtained by modifying the ratio of the H2O–dmso solvent mixture, and their interconversion was also monitored by changing the solvents during the synthesis. The solvents play an essential role in the formation and crystallization of these complexes, presenting different dimensionalities and connectivities. The double deprotonated H2mpba2− adopts the bidentate/monodentate (1) and bis-bidentate (2) bridging modes toward the (2,2′-bipyridyl)copper(II) units affording a dinuclear compound (1) and a linear chain (2), respectively. Variable-temperature magnetic measurements show the occurrence of weak intradinuclear (1) and intrachain (2) antiferromagnetic interactions.

Synthesis, spectroscopic, and crystallographic characterizations of an antiferromagnetically coupled, oxobridged trinuclear manganese(IV) cluster [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O [phen = 1,10-phenanthroline

Design and synthesis of a triangular manganese compound, [Mn3O4(H2O)2(phen)4](NO3)4 · 3H2O (1) with mono-µ-oxo and di-µ-oxo, is described. The complex has been characterized by elemental analysis, spectroscopy, single crystal and powder diffraction measurements, thermogravimetric analysis, etc. Bond Valence Sum calculations and X-ray photoelectron spectroscopy reveal that each manganese at each vertex of the triangle is +IV oxidation state. Variable temperature magnetic measurements show strong antiferromagnetic coupling between metal ions with the following set of parameters: g = 1.99, J 1 = −50.0 cm−1, and J 2 = −90.2 cm−1 (where J 1 describes the interaction across the two mono-µ-oxo bridges and J 2 is the exchange coupling across the di-µ-oxo bridge). The compound breaks down in three steps when heated from room temperature to 900°C. The final ash of the compound is confirmed by infrared spectrum with standard MnO2.

Synthesis and characterization of four novel manganese(II) chains formed by 4,4′-azobis(pyridine) and benzoate or nitrobenzoates: Stabilization of unusual ladder structures

Four new manganese(II) coordination polymers: [Mn(4,4′-azpy)(C6H5COO)2](4,4′-azpy)0.5 (1), [Mn(4,4′-azpy)(p-(NO2)C6H4COO)2] (2), [Mn(4,4′-azpy)(m-(NO2)C6H4COO)2] (3) and [Mn(4,4′-azpy)(o-(NO2)C6H4COO)2(H2O)2] (4), where 4,4′-azpy=4,4′-azobis(pyridine), have been synthesized by self-assembly of MnX2 (X=benzoate, p-, m-, or o-nitrobenzoates) together with 4,4′-azpy. All four complexes were characterized by elemental analyses, IR spectroscopy, thermal analyses, single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that complexes 1, 2 and 3 feature a 1D molecular ladder formed by syn–syn (complex 1) or syn–anti (complexes 2 and 3) carboxylate-bridged dimeric Mn(II) units which are joined together by 4,4′-azpy ligands. In complex 1, these ladders assemble with the help of π–π and C–H⋯π interactions to form a nanoporous framework that incorporates non coordinated 4,4′-azpy molecules by exploiting host–guest C–H⋯π and hydrogen bonding interactions. Complex 2 presents a 3D supramolecular framework by π–π and CH⋯π interactions, whereas, complex 3 having a similar ladder structure to 1 and 2, forms a 2D grid through π–π interactions. On the other hand, complex 4 is a 4,4′-azpy bridged fish-bone chain of carboxylate-coordinated mononuclear manganese(II) units, which are linked together by strong hydrogen bonds to form a 2D structure. Variable-temperature (2–300K) magnetic susceptibility measurements show the presence of weak antiferromagnetic interactions within the discrete Mn–(OCO)2–Mn dimers for complexes 1, 2 and 3 that have been fitted with a S=5/2 dimer model (J=−0.8, −0.5 and −0.4cm−1 respectively). The magnetic data of complex 4 can be reproduced with a S=5/2 monomer model including a Zero Field Splitting (|D|=1.7cm−1).

Polynuclear nickel(II) complexes with salicylaldimine derivative ligands

The reaction of pentadentate salicylaldimine ligand 2-((2-(2-(2-hydroxybenzylideneamino)ethylthio)ethylimino)methyl)phenol (H2L) and its related hydrogenated derivative 2-((2-(2-(2-hydroxybenzylamino)ethylthio)ethylamino)methyl)phenol (H4L1) with hydrated nitrate and perchlorate nickel(II) salts afforded polynuclear metal complexes. These complexes were characterized by elemental analysis, IR and UV–Vis spectroscopy, molar conductance and variable temperature magnetic measurements. Single crystal X-ray diffraction of [(NiL)2]·CH3OH·4H2O (1) and [Ni3(H2L1)2(NO3)2] (3) complexes has revealed the presence of an octahedral coordination geometry around the nickel ion. The magnetic data indicate that a moderate antiferromagnetic interaction is present in complexes 1 and 3.

(Naphthalene-2,3-diolato-κ2O,O′)[tris(pyridin-2-ylmethyl)amine-κ4N]cobalt(III) tetraphenylborate acetone monosolvate hemihydrate

In the title salt, [Co(C10H6O2)(C18H18N4)](C24H20B)·C3H6O·0.5H2O, the CoIII ion in the complex cation is six-coordinated in a rigid octa­hedral N4O2 geometry. The asymmetric unit contains one complete [Co(C10H6O2)(C18H18N4)]+ unit, one tetraphenylborate counter-anion and one acetone and one water mol­ecule that is located on an inversion centre. All the features of the CoIII ion are fully consistent with the formulation of the cation as a Co3+–catecholate complex. Variable-temperature magnetic measurements in the region 2–380 K show a obvious diamagnetism over the observed temperature range.

Solvothermal synthesis, crystal structure and magnetic properties of homometallic Co(II) and Cu(II) chains with double di(4-pyridyl)sulfide as bridges

Two new coordination polymers {[Co(μ-4,4′-dps)2(H2O)2](NO3)2·2(4,4′-dps)·4H2O}n (1) and {[Cu(μ-4,4′-dps)2(H2O)2](NO3)2·2H2O}n (2) [4,4′-dps=di(4-pyridyl)sulfide] have been synthesized by solvothermal reactions between the nitrate salts of cobalt(II) (1) and copper(II) (2) and the 4,4′-dps molecule. Compounds 1 and 2 have been characterized by elemental analysis, thermal analysis (TG/DTA), vibrational spectroscopy, single crystal X-ray diffraction analysis and variable-temperature magnetic measurements. Compounds 1 and 2 are cationic chain compounds of formula {[M(μ-4,4′-dps)2(H2O)2]n2n+ [M=Co(II) (1) and Cu(II) (2)] with double 4,4′-dps bridges, uncoordinated nitrate anions, and crystallization water (1 and 2) and 4,4′-dps (1) molecules. Each metal ion in 1 and 2 is six-coordinated with two coordinated water molecules in trans position and four pyridyl-nitrogen atoms from four 4,4′-dps ligands building a distorted octahedral environment. The values of the intrachain metal–metal separation are 9.940(4) and 9.702(4)Å for 1 and 2, respectively. The magnetic properties of 1 and 2 correspond to those of magnetically isolated copper(II) and high-spin cobalt(II) centers, the extended 4,4′-dps bridge being a poor mediator of magnetic interactions.

A binuclear Cu(II) complex of a Schiff-base type polyhydroxyl ligand with asymmetrical phenoxo and methoxo bridges: crystal structure and magnetic properties

[Cu2(H4L)(OCH3)(H2O)] · 2MeOH (1) has been synthesized from the reaction of 2-hydroxy-5-methylisophthalaldehyde, tris(hydroxymethyl)aminomethane and copper(II) perchlorate in methanol with the Schiff-base polyhydroxyl ligand (H4L)3− formed in situ. Single-crystal X-ray structure analysis of 1 reveals a binuclear structure with Cu(II) asymmetrically bridged by a methoxo and a phenoxo group with Cu–O–Cu bridging angles of 102.93(7)° and 100.17(7)°, respectively. The binuclear Cu(II) moieties utilize the coordinated and noncoordinated alkoxyl groups for formation of intermolecular hydrogen bonds, thus affording a 3-D supramolecular structure. Variable temperature magnetic measurements reveal strong antiferromagnetic coupling in 1 with the 2J-value of −729 cm−1, which was mediated cooperatively by the methoxo and phenoxo bridges. Magneto-structural correlations are discussed based on the crystal structure.

Structure and magnetism of heptanuclear complex constructed by the encapsulation of octacyanotungstate(IV) with copper(II) cations of tripodal ligands

Abstract A new heptanuclear compound [{Cu(TPA)CN}6W(CN)2][ClO4]8·14H2O (1) (TPA = tris(2-pyridylmethyl)amine) was synthesized by the reaction of [Cu(TPA)]2 + unit and K4W(CN)8. The cyanometalate core is encapsulated by mononuclear copper moieties via cyano bridges. 1 crystallizes in monoclinic space group P21/c with a = 22.01(2) A, b = 26.87(3) A, c = 31.64(2) A, β = 128.87(2)°, and Z = 4. Variable temperature magnetic measurements have demonstrated that very weak ferromagnetic interaction between the nearest paramagnetic CuII centers is exhibited. Thus weak ferromagnetic coupling might be transferred by NC W CN bridging units.