Syn-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.

Synthesis, crystal structure and magneto-structural studies of 2D copper(II) coordination polymer containing l-alanine amino acid

A 2D coordination polymer of Cu(II) was synthesized by the reaction of CuCl2·2H2O with l-alanine and characterized by elemental analysis, spectroscopic methods and single crystal X-ray studies. X-ray analysis indicated that the compound is a 2D coordination polymer which the carboxylate group of amino acid ligands acts as bridging ligand between Cu(II) ions. The crystal structure of compound is stabilized by intermolecular hydrogen bond interactions. Magnetic susceptibility data of powdered sample between 2 and 300 K were interpreted in terms of a 2D-spin model, with weak antiferromagnetic exchange-coupling through syn-anti carboxylate bridges, with coupling constant J = −0.2 cm−1 between nearest-neighbor Cu(II) ions. The results are compared with those obtained from similar studies in other copper amino acid complexes. DFT studies showed that overlap of magnetic dx2−y2 orbitals of the neighboring Cu(II) ions and the molecular orbitals of bridging carboxylate groups is negligible what makes only weak antiferromagnetic interaction between them. Thermal gravimetric analysis (TGA) indicated that the compound is stable up to 240 °C and it converts to CuO at about 800 °C. Cyclic voltammetry studies showed a quasi-reversible redox and an irreversible peaks which can be attributed to Cu(I)/Cu(II) and Cu(II)/Cu(III) couples, respectively.

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.

Slow magnetic relaxation in a carboxylate-bridged CoII complex

A new Co(II) complex, {[Co(MPA)(4,4′-bpy)(H2O)]·2H2O}n (1) (H2MPA = 4-methylphthalic acid, 4,4′-bpy = 4,4′-bipyridine), has been prepared under solvothermal condition and fully characterized. The X-ray crystallography test demonstrates that 1 exhibits two-dimensional (2D) layer structure in which the helical Co(II) chains linked by syn-anti carboxylate bridges are connected by 4,4′-bpy ligands. Weak ferromagnetism was observed on direct-current (dc) susceptibility due to the collective effects of the helical chain structure and antiferromagnetic couplings between Co(II) ions transmitted by μ2-1,3-carboxylate groups. Interestingly, slow magnetic relaxation was observed in 1 at liquid helium temperatures without an external dc field.

Magneto-structural and theoretical study of the weak interactions in a Mn(II) complex with a very unusual N,O-chelating coordination mode of 2-aminoterephthalate

The Mn(II) complex {[Mn(atpa)(H2O)2]·H2O}n (1),with the dicarboxylate ligand 2-aminoterephthalic acid (H2atpa), has been synthesized and crystallographically, spectroscopically and magnetically characterized. Complex 1 shows a very unusual 1κ2N,O coordination mode of the aminoterephthalate dianion with the Mn(II) ion. One of the carboxylate groups shows a syn-anti-μ2-η1:η1 binding mode to form a 2D square grid. The magnetic properties of this compound can be very well reproduced with a regular S=5/2 chain model with a very weak antiferromagnetic coupling constant of J=−0.2cm−1 through the single syn-anti carboxylate bridges. EPR measurement also supports the experimental data obtained from the magnetic study. The influence of the torsion angle between the carboxylate groups on the various interaction energies of 1 is calculated by means of DFT study.

Catena-[bis(o-aminobenzoato-κ3 N,O:O′)Mn(II)

In the title complex, [C14H12MnN2O4]n, the Mn(II) cation octahedrally coordinated by two N and two O atoms from two o-aminobenzoate ligands and two O atoms from another two o-aminobenzoate ligands. The carboxylate groups of two o-aminobenzoate anions coordinate to the Mn(II) cation in a monodentate manner, whereas the other two o-aminobenzoate anions chelate the Mn(II) cations through the O-atom of the carboxylate group and the N-atom of the amino group. This complex adopts the syn-anti carboxylate bridging mode with the conformation syn(eq)-anti(eq). The title complex is a two-dimensional coordination polymer based on an infinite MnOCOMn chain. There is hydrogen bond interaction within the two dimensional network. The adjacent two-dimensional network is packed only by Van der Waals interactions.

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.

O-Phenylenedioxydiacetate complexes of Gd(III) and Ce(III): syntheses, crystal structures, and magnetic properties

{[Ln2(PDOA)3(H2O)6]∙2H2O}n (Ln = Gd, 1; Ln = Ce, 2; H2PDOA = o-phenylenedioxydiacetic acid) has been synthesized and characterized by chemical analyses, IR spectroscopy, and thermal analyses. Single-crystal X-ray structure analyses revealed that both 1 and 2 are polymeric and built up of a ladder-like arrangement of Ln(III) ions linked by short syn-anti carboxylate bridges and long bridges (legs of the ladder) formed by a second crystallographically independent PDOA. Ln(III) in both 1 and 2 is nine-coordinate with an O9 donor set formed by one chelating/bridging and one bridging PDOA, and an additional three waters. In the asymmetric unit, there is one crystallographically independent water of crystallization, which is involved in a rich system of hydrogen bonds of the O–H···O type. The identities of the bulk and single crystal phases were corroborated by powder X-ray diffraction. Variable temperature (2–300 K) magnetic studies indicate the presence of only weak antiferromagnetic interactions between pairs of paramagnetic Ln(III) ions with J/hc = −0.004 and −0.13 cm−1, for 1 and 2.

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.

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).

Dehydration induced 2D-to-3D crystal-to-crystal network re-assembly and ferromagnetism tuning within two chiral copper(ii)–tartrate coordination polymers

The synthesis of two homochiral l-tartrate-copper(II) coordination polymers, [Cu2(C4H4O6)2(H2O)2·xH2O]n (1), and [Cu(C4H4O6)]n (2), under hydrothermal conditions, is reported. Compound 1 adopts a 2D layered network structure with a space group of P21, while compound 2 features a 3D network structure with a space group P21212. Interestingly, the 2D layered structure of compound 1 can undergo a crystal-to-crystal network reassembly, with the formation of the 3D network structure of compound 2 under dehydration conditions. Variable temperature and field magnetic studies reveal the existence of a distinct ferromagnetic interaction between Cu(2+) ions as the result of distinct syn-anti carboxylate bridging coordination modes.

Synthesis, crystal structures, and magnetic properties of two heterobinuclear complexes with a dissymmetrical oxamidate ligand

Two heterobimetallic compounds {[CuLMn(H2O)3 · 1.75H2O]2} n (I) and {[CuLCo(H2O)3 · 2H2O]2} n (II) (H4L = N-(2,5-dicarboxyl phenyl)-N′-(2-amino propyl)oxamide) have been synthesized and characterized by IR, elemental analysis, single-crystal X-ray diffraction, and magnetic properties. They crystallize in the triclinic system with space group \(P\bar 1\). The structures of the complexes consist of neutral tetranuclear units formed through syn-anti carboxylate bridges in ladder-like chains. The magnetic properties of complexes I and II indicated antiferromagnetic interaction between the metal ions.

N-(sulfoethyl) iminodiacetic acid-based lanthanide coordination polymers: Synthesis, magnetism and quantum Monte Carlo studies

A series of lanthanide coordination polymers have been obtained through the hydrothermal reaction of N-(sulfoethyl) iminodiacetic acid (H3SIDA) and Ln(NO3)3 (Ln=La, 1; Pr, 2; Nd, 3; Gd, 4). Crystal structure analysis exhibits that lanthanide ions affect the coordination number, bond length and dimension of compounds 1–4, which reveal that their structure diversity can be attributed to the effect of lanthanide contraction. Furthermore, the combination of magnetic measure with quantum Monte Carlo(QMC) studies exhibits that the coupling parameters between two adjacent Gd3+ ions for anti–anti and syn-anti carboxylate bridges are −1.0×10−3 and −5.0×10−3cm−1, respectively, which reveals weak antiferromagnetic interaction in 4.

Coordination Assemblies of CoII/NiII/ ZnII/CdII with Succinic Acid and Bent Connectors: Structural Diversity and Spin-Canted Antiferromagnetism

Four bent ligands, (i) 4,4′-abpt, (ii) 4,4′-Hbpt, (iii) 3,4′-Hbpt, and (iv) 3,3′-Hbpt, as well as H2suc (succinic acid) have been utilized to construct seven coordination polymers: [Co(suc)(4,4′-abpt)(H2O)2]·H2O (1), [M(suc)(4,4′-Hbpt)(H2O)]·2H2O (M = Co for 2, Ni for 3), [Cd(suc)(4,4′-Hbpt)2(H2O)2] (4), [Co(suc)(3,4′-Hbpt)(H2O)3]·H2O (5), [Zn(suc)(3,4′-Hbpt)] (6), and [Zn(suc)0.5(3,3′-bpt)(H2O)] (7) (4,4′-abpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole, 4,4′-Hbpt = 1H-3,5-bis(4-pyridyl)-1,2,4-triazole, 3,4'-Hbpt = 1H-3-(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole, and 3,3′-Hbpt = 1H-3,5-bis(3-pyridyl)-1,2,4-triazole). The crystal structure analysis reveals that 1–3 form similar two-dimensional (2D) layer structures, where the adjacent metal centers are connected by a syn–anti carboxylate bridge from suc ligands to furnish a succinate-metal chain, which is further interlinked by bent ligands. 4–7 form different 1D chains via suc anions, and bpt isomers display versatile coordination modes. The magnetic behav...

Two 3D metal–organic frameworks with different topologies, thermal stabilities and magnetic properties

Two novel 3D metal–organic frameworks, [ML]n (M = Co, 1; Mn, 2) were successfully prepared in solvothermal conditions using 3,3′-dimethoxy-4,4′-biphenyldicarboxylic acid (H2L) as the ligand. X-Ray crystallography analysis reveals that MOF 1 crystallizes in the monoclinic system, space group P21/c in contrast to MOF 2 in the tetragonal system, space group I. MOF 1 contains an elongated [CoO6] octahedron with two bound methoxy groups in the trans position, whereas MOF 2 has a compressed [MnO6] octahedron with two coordinated methoxy groups in the cis arrangement. The ligand L shows a novel bis(tridentate) bridging coordination mode. MOF 1 exhibits a 3D framework with CdSO4 (cds) topology consisting of two different nodes and good thermal stability (313 °C). MOF 2 is a doubly interpenetrated 3D α-Po framework with a higher thermal stability (368 °C). The study of magnetic properties in the temperature range of 1.8–300 K shows the occurrence of weak ferromagnetic interactions (J = 0.15 K) between the high-spin Co(II) ions in 1, but a weak antiferromagnetic coupling (J = −0.15 cm−1) between Mn(II) ions in 2 due to the syn-anti carboxylate bridge.

A New 1D Coordination Polymer Constructed From a Dissymmetrical Oxamidate Ligand: Structure and Magnetic Properties

A new complex {{[Cu(oxbe)]Cu(tmen)}2・2ClO4}n (H3oxbe = N-benzoato-Nʹ-(2-aminoethyl)- oxamido, tmen = N,N,Nʹ,Nʹ-tetramethylethylenediamine) has been synthesized and characterized by IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction, and by its magnetic properties. It crystallizes in the triclinic system, space group P¯1, with a = 1.364(2), b = 1.379(2), c = 1.516(3) nm, α = 64.402(3), β = 66.098(3), γ = 89.604(3)°, V = 2.301(7) nm3, Z = 2, Dcalcd. = 1.71 g cm−3. The structure of 1 consists of tetranuclear units. Through syn-anti carboxylate bridges, the complex features a chain structure.

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.