Anti Carboxylate Bridges Research Articles

Syntheses, structures and magnetic properties of two CoII/NiII isostructural coordination polymers based on an asymmetric semirigid tricarboxylate ligand.

Two new isostructural complexes, namely, poly[aqua[μ3-2-(4-carboxyphenoxy)terephthalato-κ3O1:O4:O4'](1,10-phenanthroline-κ2N,N')cobalt(II)], [Co(C15H8O7)(C12H8N2)(H2O)]n or [Co(μ3-Hcpota)(phen)(H2O)]n, I, and poly[aqua[μ3-2-(4-carboxyphenoxy)terephthalato-κ3O1:O4:O4'](1,10-phenanthroline-κ2N,N')nickel(II)], [Ni(C15H8O7)(C12H8N2)(H2O)]n or [Ni(μ3-Hcpota)(phen)(H2O)]n, II, have been synthesized by solvothermal reactions. Complexes I and II were fully characterized by IR spectroscopy, elemental analyses, thermogravimetric analyses, and powder and single-crystal X-ray diffraction. They both present two-dimensional structures based on [M2(μ-COO)2]2+ (M= CoII or NiII) dinuclear metal units with a fes topology and a vertex symbol (4·82). Interestingly, the positions of the two dimeric metal motifs and the two partially deprotonated Hcpota2- ligands reproduce regular flying butterfly arrangements flipped upside down and sharing wings in the ab plane. Magnetic studies indicate antiferromagnetic interactions (J= -5.21 cm-1 for I and -11.53 cm-1 for II) in the dimeric units, with Co...Co and Ni...Ni distances of 4.397 (1) and 4.358 (1) Å, respectively, that are related to double syn-anti carboxylate bridges.

Synthesis, crystal structure and magnetic properties of poly[[diaqua{μ6-2-[bis-(carboxyl-atometh-yl)amino]-terephthalato}-dicobalt(II)] 1.6-hydrate

The asymmetric unit of the polymeric title compound {[Co2(C12H7NO8)(H2O)2]·1.6H2O} n comprises two CoII ions, which are coordinated by fully deprotonated 2-aminodi-acetic terephthalic acid (adtp4-) and terminal water mol-ecules in distorted octa-hedral N1O5 and O6 coordination environments. The title compound features tetra-nuclear CoII units bridged by κ 3 O:O:O'- and κ 3 O:O,O'-carboxyl-ate groups, which are joined into ribbons via syn-anti carboxyl-ate bridges. The parallel adtp4- ligands with an alternately reversed arrangement further link adjacent CoII ribbons into (010) layers, which are assembled into a three-dimensional supra-molecular network via inter-molecular hydrogen bonds. The disordered water solvent mol-ecules are situated in channels parallel to [100]. Magnetic measurements and analyses reveal that the title compound displays anti-ferromagnetic behaviour. The purity of the title compound was characterized by X-ray powder diffraction.

Temperature-Controlled Assembly/Reassembly of Two Dicarboxylate-Based Three-Dimensional Co(II) Coordination Polymers with an Antiferromagnetic Metallic Layer and a Ferromagnetic Metallic Chain.

Two new dicarboxylate-based three-dimensional cobalt coordination polymers, [Co(Me2mal)(bpe)0.5(H2O)]n (1) and [Co(Me2mal)(bpe)0.5]n (2), were synthesized from dimethylmalonic acid (H2-Me2mal) in temperature-controlled solvothermal reactions. Lower temperatures (60–80 °C) favored the formation of 1, while higher temperatures (120 °C) favored the production of 2. Compound 1 is comprised of Co(II) corrugated layers linked by syn–anti carboxylate bridges from the Me2mal2− ligands and pillared through bis-monodentate bpe groups. Compound 2 is comprised of a three-dimensional network involving one-dimensional Co–carboxylate chains bonded by antisymmetric µ4-Me2mal2− ligands and aligned parallel to the [001] direction. The solvothermal retreatment of crystalline samples of 1 in a DMF/H2O solvent at 120 °C allowed the structural reassembly, with complete conversion within 2 over 48 h. Magnetic analyses revealed that compound 1 exhibits both spin-orbital coupling and antiferromagnetic interactions through a syn–anti carboxylate (Me2mal2−) bridge exchange pathway [Co–Co separation of 5.478 Å] and compound 2 showed a ferromagnetic interaction resulting from the short Co–Co separation (3.150 Å) and the small Co–O–Co bridging angles (98.5° and 95.3°) exchange pathway which was provided by µ4-Me2mal2− bridging ligand.

Syntheses, structures, magnetic properties and luminescence of four coordination polymers based on an asymmetric semirigid tricarboxylate ligand

In this work, four new complexes, [Mn(μ3-Hcpoia)(phen)(H2O)]n1, [Mn2(μ4-Hcpoia)2(μ2-bib)(H2O)2]n2, [Zn(μ2-Hcpoia)(phen)(H2O)]n3, and [Zn2(μ2-Hcpoia)2(μ2–4,4′-bpy)(H2O)2]n·2nH2O 4 (H3cpoia = 4-(4-carboxyphenoxy)isophthalic acid, phen = phenanthroline, bib = 1,4-di(1H-imidazol-1-yl)benzene, 4,4′-bpy = 4,4′-bipyridine) have been synthesized by solvothermal reactions. Complexes 1–4 were fully characterized by IR spectroscopy, elemental analyses, thermogravimetric analyses, powder and single-crystal X-ray diffraction. Complexes 1 and 2 present two-dimensional (2D) structures based on the dinuclear Mn(II) secondary building units with the vertex symbols of (4.82) and (32.44)(34.46.64.7), respectively. Complex 3 possesses one-dimensional (1D) structure and reveals a uninodal 2-connected chain with the 2C1 topology. Complex 4 exhibits a 1D ladder-like double chain, containing a 1D metal–organic chain interconnected by the 4,4′-bpy ligand with the vertex symbol of (42.6). Such a rich structural diversity of 1–4 is driven by various factors, including the type of the metal(II) ions and the ancillary ligands, as well as the coordination mode of ligand. Complexes 1 and 2 show antiferromagnetic interactions (J = −0.719 cm−1 for 1, and J = −6.981 cm−1 for 2) in dimeric units with the Mn-Mn distances of 4.451(1) and 3.151(5) Å, respectively, that are related to double syn−anti carboxylate bridges and four bis-bidentate carboxylate groups with syn−syn and μ–oxo modes. The solid-state luminescent behaviors of 3, 4 were also investigated systematically.

Four 3D coordination polymers based on layers with single syn-anti carboxylate bridges: synthesis, structures, and magnetic properties.

Four novel coordination polymers (CPs) based on a new 4-(3,5-dicarboxylphenyl) picolinic acid ligands (H3L), [M3(L)2(H2O)6]·4H2O (M3 = Mn3, 1; Co3, 2; Ni3, 3, Co1.01Ni1.99, 4), have been hydrothermally synthesized, and structurally and magnetically characterized. In these isomorphous CPs, octahedrally coordinated metal ions are linked by the single syn–anti carboxylate bridge (μ-COO) to give linear trinuclear motifs. The motifs are connected through the other single syn–anti carboxylate bridge (μ-COO) to give a 2D (4,4) layer, and the layers are interlinked by the L ligands into 3D frameworks. Magnetic measurement indicates that antiferromagnetic interactions between metal ions are mediated through the single syn–anti carboxylate bridges in 1 and 2, while the same carboxylate bridges in 3 transmit ferromagnetic couplings. The bimetallic CP 4 shows interesting complicated magnetic behaviors due to the competition effect of Co(ii) and Ni(ii) ions.

Two novel coordination polymers in the family of lanthanide complexes with o-phenylenedioxydiacetato as ligand

Two novel coordination polymers [Ce(PDOA)(NO3)(H2O)2]n (1) and {[Ce(PDOA)(NO3)(H2O)3]·H2O}n (2) (PDOA=o-phenylenedioxydiacetato) have been prepared using hydrothermal conditions and have been structurally characterized. In both crystal structures 1 and 2 the Ce(III) atoms are decacoordinated by oxygen atoms from PDOA ligands with chelating and bridging functions, chelating nitrato ligands and aqua ligands. While in 1 the PDOA ligand presents a hexadentate coordination mode, in 2 it is coordinated in a pentadentate manner; this difference leads to different types of one-dimensional structural motifs: in 2 there are zig–zag chains of the –Ce–O–C–O–Ce– type with syn–anti carboxylate bridges and in 1 these chains are additionally interlinked by further syn–anti carboxylate bridges leading to a strip- or ribbon-like arrangement formed of {Ce3} fused triangles. The endothermic dehydration of 1 within the temperature range 69–199°C is at least a two-step process as suggested by TG and DTA methods. A variable temperature (2–300K) magnetic study reveals Curie–Weiss behavior for 1 with θ=−35.5K observed above 50K. The origin of the observed behavior is discussed.

Synthesis, structures and magnetic properties in 3d-electron-rich isostructural complexes based on chains with sole syn-anti carboxylate bridges.

To evaluate magnetic properties of isostructural compounds, a series of 3D carboxylate coordination polymers [M(H2bpta)]n, (H4bpta = 2,2',4,4'-biphenyltetracarboxylic acid, M = Fe(II) (1), Ni(II) (2), Cu(II) (3) and Zn(II) (4)), was synthesized in H2O-CH3CN or H2O solvents, respectively. Structurally, complexes 1-4 have isostructural features with (5,5)-connected 3D framework, wherein the M(II) centre takes an octahedral coordination environment consisting of six oxygen atoms from carboxylates of ligands. The M(II) sites are linked by syn-anti carboxylates to form chains with an M···M separation of 4.880(2) (M = Fe), 4.784(2) (M = Ni), 4.541(2) (M = Cu), and 4.607(2) Å (M = Zn), respectively. The shortest M···M distances between interchains locate 9.122(4), 9.077(3), 9.361(3), and 8.767(2) Å, respectively. Magnetically, the isostructural polymers show different magnetic behaviors due to different spins of central ions. Theoretical analysis indicates that couplings between magnetic ions obey uniform chain models. The magnetic susceptibility of 1 and 2 are perfectly fitted by the modified Fisher model to yield an effective intra-chain exchange coupling constant of -0.81(1) and 3.67(2) cm(-1), respectively. For 3, a Heisenberg ferromagnetic S = 1/2 chain included the intra-chain magnetic exchange interaction (J = 9.28(1) cm(-1), and zj' = -0.068(3) cm(-1)), weak ferromagnetic interactions in intra-chains, and weak antiferromagnetic interactions between interchains. The phenomena of 1-3 accord with the common view that the exchange interaction between two magnetic M(II) ions bridged by the syn-anti carboxylate bridge is dominantly weak ferro- or anti-ferromagnetic interactions. In addition, the M-O-C-O-M spin exchange interactions |J| of M2(CO2)2 (M = Mn(3d(5))(20), Fe(3d(6)), Co(3d(7))(20), Ni(3d(8)), Cu(3d(9))) decrease in strength with Cu2(CO2)2 > Ni2(CO2)2 > Co2(CO2)2 > Fe2(CO2)2 > Mn2(CO2)2, consistent with orbit order.

Luminescent lanthanide-2-phenylpyrimidine-carboxylate frameworks: structure and luminescence tuning

Six novel luminescent lanthanide-2-phenylpyrimidine-carboxylate frameworks, namely, [Ln(ppmc)3(phen)] (Ln = Eu (1), Tb (2)), [Ln(ppmc)2(C2O4)0.5(H2O)] (Ln = Eu (3), Tb (4)), {[Eu(ppmdc)(phen)(C2O4)0.5]·0.5H2O} (5) and [Tb(ppmdc)(benzoate)(phen)] (6) (Hppmc = 2-phenylpyrimidine-4-carboxylic acid, H2ppmdc = 2-phenylpyrimidine-4,6-dicarboxylic acid) have been synthesized. The X-ray structure analyses reveal that all of the compounds contain carboxylate-bridged dimer units; however, coordination environments of Ln3+ ions, bridging modes of carboxylate, and the linkage between them are different. In the isostructural compounds 1 and 2, extensive π–π stacking exists between the anti–anti carboxylate bridged dimer. However, syn–anti carboxylate bridges are found in compounds 3 and 4 in which oxalate connects the dimers to form 1D chains. Compound 5 has a 2D structure connected by both μ4-ppmdc2− and oxalate in which the carboxylates adopt both anti–anti and chelate-bridging modes. Compound 6 featuring 1D chains also contains anti–anti carboxylate-bridged dimers that are linked by the μ3-ppmdc2− ligand. All six compounds show characteristic red or green emission attributed to Eu3+ and Tb3+. The luminescence lifetime and quantum yield are presented and discussed in detail. The use of different ligands and reaction conditions has led to distinct coordination environments of lanthanide ions and the aggregation of dimeric units, which are considered as the dominating factors for the resulting photoluminescence behaviour of solid samples.

Syntheses, crystal structures and magnetic properties of five new manganese(ii) complexes: influence of the conformation of different alkyl/aryl substituted malonate ligands on the crystal packing

Five new manganese(II)-based complexes of general formula [Mn(Rmal)(H2O)]n with Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me2mal) (2), diethylmalonate (Et2mal) (3), butylmalonate (Butmal) (4) and benzylmalonate (Bzmal) (5) were synthesized and their structures characterized by single crystal X-ray diffraction. 1 and 2 are three-dimensional compounds whereas 3–5 exhibit two-dimensional networks. The structure of 1 consists of chains of μ-κO:κO bridged aquamanganese(II) ions which are interlinked through anti–anti carboxylate bridges. The structure of 2 is built by double μ-κO:κO bridged bis[aquamanganese(II)] entities which are linked to six other dimanganese(II) units through oxo- and anti–syn carboxylate bridges. These dinuclear entities also occur in 4 and 5. They are interconnected by anti–anti and anti–syn carboxylate bridges to four other units, leading to neutral layered structures. Finally, compound 3 consists of aqua-bridged chains of manganese(II) ions connected through tetrakis(monodentate) Et2mal ligands leading to a sheet-like structure. The topological representation of the crystal structures shows the of four different nets: (10,3)-d utp (1), 6-connected crs (2), gek2 (3) and the square-grid sql topology (4–5). The magnetic properties of 1–5 were investigated in the temperature range 2.0–300 K. Overall antiferromagnetic behavior occurs in 1, 2, 4 and 5 with susceptibility maxima in the range 3.6–17.0 K. Compound 3 exhibits an overall antiferromagnetic behaviour in the high temperature range with a weak spin canting in the low temperature domain and magnetic ordering below ca. 32 K.

The synthesis, structure, and magnetic properties of two novel manganese(ii) azido/formate coordination polymers with isonicotinic acid N-oxide as a coligand

Two novel azide/formate manganese(II) coordination polymers, based on isonicotinic acid N-oxide, [Mn2L2(N3)2(CH3OH)]n (1), and [MnL(HCO2)]n (2) [HL = isonicotinic acid N-oxide (INO)] have been synthesized under solvothermal conditions and characterized by elemental analysis, IR and single-crystal X-ray diffraction. The structure of 1 consists of unprecedented 1D chains built by double syn,anti carboxylate bridges, double EE azide and mixed bridges of syn,syn carboxylate and the N-oxide group, which are further linked through azido (EE) and INO to generate a unique 3D framework. Complex 2 is a 2-fold interpenetrating pcu net based on hexanuclear Mn6 clusters, which are formed by the linkage of six MnII ions with six syn,syn,anti formate anions and six syn,syn carboxylate groups. Magnetic susceptibility measurements reveal that dominant antiferromagnetic coupling exists between the MnII ions in 1 and 2.

Synthesis, structures, and magnetic properties of carboxylate-bridged trinuclear complexes based on low-spin manganese(III)/iron(III) building blocks

Four linear trinuclear transition metal complexes have been prepared and characterized. The complexes [MII(MeOH)4][FeIII(L)2]2·2MeOH (M = Fe (1) or Ni (2)), [CoII(EtOH)2(H2O)2][FeIII(L)2]2·2EtOH (3), and [MnII(phen)2][MnIII(L)2]2·4MeOH (4) (H2L = ((2-carboxyphenyl)azo)-benzaldoxime, phen = 1,10-phenanthroline) possesses a similar syn–anti carboxylate-bridged structure. The terminal Fe(III) or Mn(III) ions are low spin, and the central M(II) ions are high spin. Magnetic measurements show that antiferromagnetic interactions were present between the adjacent metal ions via the syn–anti carboxylate bridges. The antiferromagnetic coupling between low-spin Fe(III) and Ni(II) is unusual, which has been tentatively assigned to the structural distortion of Fe(III).

Pillaring Role of 4,4′-Azobis(pyridine) in Substituted Malonate-Containing Manganese(II) Complexes: Syntheses, Crystal Structures, and Magnetic Properties

Six new manganese(II) complexes of formulas [Mn2(Rmal)2(H2O)2(azpy)]n (1–3), [Mn(Phmal)(H2O)(azpy)]n (4), [Mn2(Et2mal)2(H2O)4(azpy)2]n (5), and [Mn(Bzmal)(H2O)3(azpy)] (6) [azpy = 4,4′-azobispyridine (1–6), Rmal = methylmalonate (Memal) (1), dimethylmalonate (Me2mal) (2), and butylmalonate (Butmal) (3), Phmal = phenylmalonate (4), Et2mal = diethylmalonate (5), and Bzmal = benzylmalonate (6)] were synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes 1–3 are three-dimensional compounds whose structure consists of corrugated layers of manganese(II) linked through syn–anti carboxylate (Rmal) bridges, which are pillared through the bis-monodentate azpy molecule. Complex 4 has a layered structure of manganese(II) ions connected by carboxylate (Phmal) bridges in the syn–anti coordination mode as in 1–3, the azpy group acting here as a terminally bound monodentate ligand. The structure of 5 consists of Et2mal–Mn(II) neutral chains linked through the azpy ligand, giving rise to a complex three-dimensional network. Complex 6 is constituted by neutral [Mn(Bzmal)(H2O)3(azpy)] mononuclear units, which are interlinked through O–H···O, O–H···N, and π–π type intermolecular interactions to afford a three-dimensional supramolecular structure. The topological analysis of these crystallographic structures shows the occurrence of four different nets: a (3,4)-connected InS-type (1–3), a binodal layered hcb (4), a uninodal CdS-type (5), and a (4,5)-connected tcs topology (6). The magnetic properties of 1–5 were investigated in the 2.0–300 K temperature range. Overall antiferromagnetic behavior occurs in 1–4 with susceptibility maxima in the range 2.8–5.5 K, the exchange pathway being provided by the syn–anti carboxylate (substituted malonate) bridge [manganese–manganese separation in the range 5.4365(3)–5.5274(1) Å]. Very weak antiferromagnetic interactions are observed in 5 through the trans-bis-monodentate Et2mal ligand, the intrachain manganese–manganese separation being 7.328(3) Å. The much larger manganese–manganese separation through the bis-monodentate azpy ligand in 1–5 (values greater than 13.5 Å) accounts for the lack of any significant magnetic interaction though this extended bridge.

Carboxylate-bridged helical chains based on an azo carboxylate oximate ligand

Two helical one-dimensional complexes [Mn Ⅱ (MeOH) 4 ][Mn IV (L · ) 2 ]·2MeOH ( 1 ) and [Mn Ⅲ (salen)][Mn Ⅲ (L) 2 ] ( 2 ) (H 2 L = HON=C(Ph)N=NC 6 H 4 CO 2 H) contain the noninnocent ligand [Mn(L · ) 2 ] 2- and innocent low-spin [Mn(L) 2 ] - . Intrachain antiferromagnetic interaction between adjacent manganese ions via the syn - anti carboxylate bridges in complex 1 . Alternate syn - anti and anti - anti carboxylate bridges have been found to transmit ferro- and antiferromagnetic coupling between high-spin and low-spin Mn(Ⅲ) ions in complex 2 .

A new three-dimensional cobalt(II) coordination polymer based on biphenyl-2,2′,6,6′-tetracarboxylic acid and 1,2,4-triazole: Synthesis, crystal structure and magnetic properties

Abstract A new three-dimensional coordination polymer with the formula [Co(bta)0.5(Htz)(H2O)]n ( 1 ) (H4bta = biphenyl-2,2′,6,6′-tetracarboxylic acid and Htz = 1,2,4-triazole), has been hydrothermally synthesized and structurally characterized. The structure of 1 can be considered as two-dimensional [Co(bta)(H2O)]n layers, consisting of one-dimensional [Co(COO)]n chains, which are separated by bta ligands, and neutral Htz pillars. The variable temperature magnetic property study indicates that there is a weak antiferromagnetic coupling interaction between Co(II) ions, which mainly arises from the antiferromagnetic coupling interaction in the one-dimensional [Co(COO)]n chains through syn–anti carboxylate bridges.

Synthesis, structures and magnetic properties of four new oxamidato-bridged heterobimetallic complexes

Four new heterobimetallic coordination polymers, namely, {[Cu(aeoe)M(H 2O) 3 · 2H 2O] 2} n (M = Mn(II) ( 1), Co(II) ( 2), Ni(II) ( 3)) and [Cu(aeoe)Ni(H 2O) 3] 2 ( 4) (H 4aeoe = N′-(2-aminoterephthalic acid)- N′′-(ethylenediamine)oxamidato) have been synthesized and characterized structurally. Complexes 1– 3 are allomerism and feature 1-D ladder-like chain structure constructed from neutral tetranuclear complex units through the syn– anti carboxylate bridges, whereas complex 4 is a cyclic neutral tetranuclear complex unit. Their magnetic properties are also investigated based on their structures.

Structure and magnetic properties of polynuclear copper(II) compounds with syn– anti carboxylato- and bromo-bridges

Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) ( 1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) ( 2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn– anti carboxylate bridges and additionally on linear monobromo- (in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8–300 K. They reveal the occurrence of strong antiferromagnetic coupling ( J 1 = −102.5 cm −1) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge ( J = −57.0 cm −1). Very weak ferromagnetic interaction through the syn– anti carboxylate bridge J 2 is expected as it was observed in isomorphous Cu(2-qic)Cl ( J = 0.37 cm −1). For 2 a weak ferromagnetic couplings through the syn– anti carboxylate ( zJ′ = 1.35 cm −1) and dibromo-bridges ( J = 8.31 cm −1) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog ( J = 15.0 cm −1). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.

Synthesis, structure and magnetic properties of 5-(4-Sulfophenylazo) salicylate-bridged 1D coordination polymers containing linear trinuclear metal clusters

Three new trinuclear metal complexes with an azobenzene-containing ligand [M 3(Sasa) 2(Py) 2(H 2O) 8] (Na 2HSasa = 5-(4-Sulfophenylazo) salicylic acid disodium salt; Py = pyridine; M = Cu, Co, Zn), are synthesized through the interface diffusion and structurally characterized by single crystal X-ray diffraction, XRPD analysis and spectral methods. The metal ions in distorted octahedral coordination environments are connected by Sasa ligands to form 1D coordination polymer chain containing the linear trinuclear units with single syn–anti carboxylate bridges. The extensive hydrogen bonding interactions hold these chains together into 3D supramolecular network. Weak antiferromagnetic interactions between adjacent metal ions with J = −1.85 cm −1 and J = −2.81 cm −1 dominate the magnetic properties of Cu(II) and Co(II) complexes, separately.

Diversity of carboxylate coordination in two novel zinc(II) cinnamate complexes

Two novel mixed-ligand zinc(II) complex compounds [Zn(cinn)2(mpcm)]n (1) and [Zn(p-HO-cinn)2(nia)(H2O)2]·H2O (2) (cinn=cinnamato, mpcm=methyl-3-pyridylcarbamate, nia=nicotinamide) were prepared and characterized by elemental analysis, infrared spectroscopy, single crystal X-ray diffraction and thermal analysis. Diverse modes of carboxylate coordination were found in the complexes. In 1 the cinnamate ligands coordinate as monodentate and bridging (syn–anti), respectively. The syn–anti carboxylate bridges connect the molecules of 1 to infinite polymeric helical chains. The structure of 2 is monomeric. One of the carboxylate oxygens of p-hydroxycinnamate is semi-coordinated (Zn–O=2.549(2)Å).

Chiral Molecular Magnets: Synthesis, Structure, and Magnetic Behavior of the Series [M(L‐tart)] (M = MnII, FeII, CoII, NiII; L‐tart = (2R,3R)‐(+)‐tartrate)

A new series of layered magnets with the formula [M(L-tartrate)] (M = Mn(II), Co(II), Fe(II), Ni(II); L-tartrate = (2R,3R)-(+)-tartrate) has been prepared. All of these compounds are isostructural and crystallize in the chiral orthorhombic space group I222, as found by X-ray structure analysis. Their structure consists of a three-dimensional polymeric network in which each metal shows distorted octahedral coordination bound to four L-tartrate ligands, two of which chelate through an alcohol and a carboxylate group and the other two bind terminally through a monodentate carboxylate group. The chirality of the ligand imposes a Delta conformation on all metal centers. Magnetically, the paramagnetic metal centers form pseudotetragonal layers in which each metal is surrounded by four other metals, with syn,anti carboxylate bridges. These salts show intralayer antiferromagnetic or ferromagnetic interactions, depending on the electronic configuration of the metal, and weak interlayer antiferromagnetic interaction. In all cases the magnetic properties are strongly affected by the anisotropy of the system, and the presence of magnetic canting has been found. The Mn derivative behaves as a weak ferromagnet with a critical temperature of 3.3 K. The Ni derivative shows very unusual magnetic behavior in that it exhibits antiferromagnetic ordering below 6 K, the onset of spontaneous magnetization arising from spin reorientation into a canted phase below 4.5 K, and a field-induced ferromagnetic state above 0.3 T at 2 K, behavior typical of metamagnets. The Fe and Co derivatives show antiferromagnetic interactions between spin carriers, but do not order above 2 K.

A quasi-tetrahedral Cu4 cluster and a helical-chain copper (II) complex with single syn-anti carboxylate bridges: crystal structure and magnetic properties.

A tridentate Schiff base carboxylate ligand, derived from the condensation of pyridine 2-carboxaldehyde with anthranilic acid, reacts with copper trifluoroacetate salt to give rise to the helical chain complex [Cu(C(13)H(9)N(2)O(2))(F(3)CCO(2))](n)() (1) and with copper nitrate to give rise to the tetranuclear complex [[Cu(4)(C(13)H(9)N(2)O(2))(4)(H(2)O)(4)].3.5NO(3).0.5N(3)] (2) with the addition of azide salt. The structures of these complexes have been solved by X-ray crystallography. The Cu(II) ions are in a distorted square-pyramidal environment in complex 1. They are sequentially bridged by carboxylate groups in the syn-anti conformation, resulting in the formation of an infinite helix like chain along the crystallographic c-axis. The crystal structure of complex 2 consists of tetranuclear [Cu(4)(L)(4)(H(2)O)(4)](4+) (L = C(13)H(9)N(2)O(2)(-)) cations and isolated NO(3)(-) and N(3)(-) anions in the ratio 1:3.5:0.5, respectively, involving bridging carboxylate groups in the syn-anti conformation. For 1 the carboxylato-Cu(II) coordination is apical-basal, while for 2 it is basal-basal. From the magnetic susceptibility measurements the complex 1 is found to exhibit very weak antiferromagnetic interaction whereas a weak ferromagnetic coupling has been established for complex 2. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.