Coordination Polymers Of Formula Research Articles

Isostructural Oxamate Complexes with Visible Luminescence (Eu3+) and Field-Induced Single-Molecule Magnet (Nd3+).

The search for new metal-organic compounds as candidates for quantum information processing technologies is in the spotlight. Several metal ions and organic linkers have been used to obtain such compounds. Herein, we describe the synthesis, crystal structures, and cryomagnetic properties of two air-stable isostructural neodymium(III) and europium(III) one-dimensional (1D) coordination polymers of formula [Nd(Hmpa)3(DMSO)2]n (1) and [Eu(Hmpa)3(DMSO)2]n (2) [Hmpa=N-(4-methylphenyl)oxamate, and DMSO=dimethylsulfoxide]. These complexes were prepared by reacting n-Bu4N(Hmpa) proligand [n-Bu4N+=tetra-n-butylammonium] and the correspondent LnCl3 ⋅ 6H2O salt (Ln=Nd or Eu) in the open air and mild conditions. The crystal structures of 1 and 2 reveal the Ln3+ ion surrounded by two DMSO molecules and three oxamate ligands, one of them connecting to adjacent mononuclear entities through carboxylate bridges featuring a homometallic chain, while the other two establishing double N-H ⋅ ⋅ ⋅ O hydrogen bonds among adjacent polymers to give a resultant supramolecular 2D network. Cryomagnetic measurements in the static (dc) and dynamic current (ac) regimes reveal that 1 behaves as a field-induced single-molecule magnet below 8.8 K. A photoluminescence study shows that Hmpa ligands efficiently sensitize the luminescence of Eu3+ complex in the visible region in the solid state at room temperature.

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer.

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

X-ray Structure and Magnetic Properties of Heterobimetallic Chains Based on the Use of an Octacyanidodicobalt(III) Complex as Metalloligand

The assembly of [Co2III(μ-2,5-dpp)(CN)8]2− anions and [MII(CH3OH)2(DMSO)2]2+ cations resulted into the formation of two heterobimetallic 1D coordination polymers of formula [MII(CH3OH)2(DMSO)2(μ-NC)2Co2III(μ-2,5-dpp)(CN)6]n·4nCH3OH [M = CoII (1)/FeII (2) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine. The [Co2III(μ-2,5-dpp)(CN)8]2− metalloligand coordinates the paramagnetic [MII(CH3OH)2(DMSO)2]2+ complex cations, in a bis-monodentate fashion, to give rise to neutral heterobimetallic chains. Cryomagnetic dc (1.9–300 K) and ac (2.0–13 K) magnetic measurements for 1 and 2 show the presence of Co(II)HS (1) and Fe(II)HS (2) ions (HS – high-spin), respectively, with D values of +53.7(5) (1) and −5.1(3) cm−1 (2) and slow magnetic relaxation for 1, this compound being a new example of SIM with transversal magnetic anisotropy. Low-temperature Q-band EPR study of 1 confirms that D value is positive, which reveals the occurrence of a strong asymmetry in the g-tensors and allows a rough estimation of the E/D ratio, whereas 2 is EPR silent. Theoretical calculations by CASSCF/NEVPT2 on 1 and 2 support the results from magnetometry and EPR. The analysis of the ac magnetic measurements of 1 shows that the relaxation of M takes place in the ground state under external magnetic dc fields through dominant Raman and direct spin-phonon processes.

Cu(i)-I coordination polymers as the possible substitutes of lanthanides as downshifters for increasing the conversion efficiency of solar cells.

This study tries to provide new solutions to increase the efficiency of conversion of photons in solar cells, using photoluminescent Cu(i) coordination polymers (CPs) as possible alternative materials of lower cost, than those used today, based on lanthanides. The selected CP of chemical formula [Cu(NH2MeIN)I]n (NH2MeIN = methyl, 2-amino isonicotinate) absorbs in the utraviolet and emits in the visible region, being also easily nanoprocessable, by a simple and one-pot bottom-up approach. Nanofibers of this CP can be embedded in organic matrices such as ethyl vinyl acetate (EVA), forming transparent and homogenous films, with a thermal stability of up to approximately 150 °C. These new materials maintain the optical properties of the CP used as a dopant, ([Cu(NH2MeIN)I]n), with emission in yellow (570 nm) at 300 K, which is intensified when the working temperature is lowered. In addition, these materials can be prepared with varying thicknesses, from a few microns to a few hundred nanometers, depending on the deposition method used (drop casting or spin coating respectively). The study of their external quantum efficiency (EQE) found an increase in the UV range, which translates into an increase in the conversion efficiency. The optimal CP concentration is 5% by weight in order to not diminish the transparency of the composite material. The calculated cost on the possible incorporation of this material into solar cells shows a 50% decrease over the cost reported in similar studies based on the use of lanthanides.

Magnetic order in a CuII–DyIII oxamato-based two-dimensional coordination polymer

We report the synthesis, crystal structure, and magnetic characterization of a novel two-dimensional copper(II)–dysprosium(III) coordination polymer of formula [Li I (OH 2 ) 4 ] 2 [Dy III Cu II 2 (Me 2 pma) 4 Cl(H 2 O)] . 4H 2 O ( 1 ) [Me 2 pma = N -2,6-dimethylphenyloxamate]. Compound 1 was obtained using the mononuclear anionic complex [Cu II (Me 2 pma) 2 ] 2– , as a bis(bidentate) metalloligand toward solvated dysprosium(III) cations, and it shows a square [Dy III Cu II 2 ] layered structure of (4 4. 6 2 ) net topology. Interestingly, the combination of two factors, the well-known efficiency of oxamato ligands to transmit strong magnetic couplings between neighboring atoms and such structural topology, is responsible for the observation of a ferromagnetic interaction between copper(II) and dysprosium(III) cations and a magnetic ordering ( T C = 7.5 K), paving the way for the obtention of novel future examples of the still very scarce magnetically ordered lanthanide-based coordination polymers.

Synthesis and characterisation of a novel ferrimagnetic chain based on copper(II) and rhenium(IV)

A novel one-dimensional copper(II)–rhenium(IV) coordination polymer of formula {[Re IV Br 4 (μ-ox)Cu II (pyim) 2 ]·MeCN} n ( 1 ) [ox = oxalate anion, pyim = 2-(2′-pyridyl)imidazole] has been prepared and characterised. Powder X-ray diffraction measurements on a sample of 1 support the purity of the bulk sample, whereas single-crystal X-ray diffraction shows that 1 crystallises in the orthorhombic system with space group Pbca . The crystal structure of 1 is made up of [Cu II (pyim) 2 ] 2+ cations and [ReBr 4 (ox)] 2− anions linked through bridging bromide and oxalate groups, which generate alternating Cu II and Re IV chains. Variable-temperature magnetic susceptibility measurements performed on 1 reveal an antiferromagnetic coupling between the Cu II and Re IV ions; at lower temperatures, this interaction leads to the occurrence of ferrimagnetic behaviour in 1 . Compound 1 is the first ferrimagnetic compound obtained with the [ReBr 4 (ox)] 2− precursor. Un nouveau polymère de coordination unidimensionnel à base de cuivre(II) et de rhénium(IV), de formule {[Re IV Br 4 (μ-ox)Cu II (pyim) 2 ]·MeCN} n ( 1 ) [ox = anion oxalate, pyim = 2-(2′-pyridyl)imidazole], a été préparé et caractérisé. Les mesures de diffraction des rayons X sur poudre ont confirmé la pureté de l’échantillon, alors que la diffraction des rayons X sur monocristal montre que 1 cristallise dans le système orthorhombique et le groupe d'espace Pbca . La structure du composé 1 contient des cations [Cu II (pyim) 2 ] 2+ et anions [ReBr 4 (ox)] 2− , lesquels sont connectés par des groupes bromure et oxalate, générant des chaînes de Cu II et Re IV alternés. La susceptibilité magnétique dc de 1 révèle un couplage antiferromagnétique entre ions Cu II et Re IV , mais aussi un comportement typique d'une chaîne ferrimagnétique. 1 est le premier composé ferromagnétique obtenu avec le précurseur [ReBr 4 (ox)] 2− .

Coordination polymers based on µ2η1:η1 and µ2η2:η2 bridging mode of pyridyl carboxylate: ionic liquid-induced hydrothermal synthesis, structural and thermogravimetric analysis

Two coordination polymers of formula [Cu(2-picolinate)(nicotinate)]n (1), [Mn(2-picolinate)2]n (2), using pyridine-2/3-carboxylic acid and metal salt acetate, have been synthesized hydrothermally at 120 °C for 48 h in presence of ionic liquid tetraethylammonium hydroxide (25% aqueous solution). Although all reported complexes were synthesized in same experimental conditions, they show diversity in their structural features, 2 crystallize in monoclinic crystal system where as 1 shows higher symmetry space group, orthorhombic. The 3D structure in 1 is based on anti-syn Cu–O–C–O–Cu chain with µ2η1:η1 coordinative mode of carboxylate ion and ligand bridging through carboxylate oxygen and pyridyl nitrogen of nicotinate ion while 2D sheet structure in 2 is due to Mn–O–Mn chain involving µ2η2:η2 coordinative mode together with syn-anti Mn–O–C–O–Mn chain via µ2η1:η1 coordinative mode of carboxylate ion of picolinate ion only. It is observed that these chains are the structure factors for dimensionality of reported CPs. Both coordination polymers are insoluble in almost all organic solvents as well as in water and show good thermal stability between 280 and 450 °C.

An azide-bridged copper(II) 1D-chain with ferromagnetic interactions: synthesis, structure and magnetic studies

A coordination polymer of formula [Cu(μ 1,3-N3)2(imH)2] n (1) has been synthesized by reaction of Cu(NO3)2 with imidazole and sodium azide in CH3OH/CH3CN. The complex was characterized by FTIR, elemental analysis, powder diffraction, thermogravimetric analysis, magnetic measurements, and single-crystal X-ray diffraction. The X-ray crystal structure shows that the Cu(II) centers have a distorted octahedral coordination geometry, being coordinated by two imidazole ligands at the trans positions. Each azide links two [Cu(imH)2]2+ units to form 1D zigzag chains. Variable-temperature magnetic susceptibility studies at low field reveal dominant intrachain ferromagnetic/antiferromagnetic interactions. Using a model with n = 10, the coupling parameters J AF = −2.95 and J F = 17.99 with g = 2.12 have been determined.

Synthesis and Crystal Structures of Various Phases of the Microporous Three-Dimensional Coordination Polymer [Zr(OH)2(C2O4)]n

A homometallic Zr(IV)-oxalate three-dimensional (3-D) coordination polymer of formula [Zr(OH)2(C2O4)·0.5H2O] is reported. This compound was found to be a microporous solid with reversible sorption abilities. Upon guest release and sorption, the crystalline material undergoes single crystal to single crystal transitions. The crystal structures for three phases have been solved from single crystal diffraction studies. They consist of the guest containing frameworks [Zr(OH)2(C2O4)·0.5H2O], 1, 3, and the guest-free porous phase [Zr(OH)2(C2O4)], 2; all are found with tetragonal space group I4/m. Phase 1 has been obtained by controlled diffusion of the reagents (ZrO(NO3)2 and H2C2O4) in a silica gel medium; the other phases have been formed from 1 by thermal activation (2) and re-adsorption of H2O (3).

Synthesis, Characterization, Luminescent and Thermal Properties of a Hybrid Inorganic–Organic Polymeric Framework Formed by Lead (II) Pyridinecarboxylate

A coordination polymer of formula [Pb0.5(pyc)] n , 1, where Hpyc = pyridine-3-carboxylic acid, has been synthesized and structurally characterized by X-ray single crystal diffraction analysis. Every Pb(II) centre demonstrate trigonal dodecahedron geometry. The ligand i.e. pyridine-3-carboxylate offers μ 3 - η 2 : η 1 coordination pattern using its hetero donor centres. The complex initially forms an infinite 1D chain (c-axis) which is turned to 2D sheet and finally a 3D network is recognized through ligand connectivity. Stabilization of 3D structure is further reinforced by π–π stacking interaction. An open channel is identified along c-axis. TG analysis has been performed for the complex. Emission study demonstrates the existence of intraligand and metal-to-ligand charge transfer transition in 1. A 3D coordination polymer of Pb(II) has been synthesized using pyridine-3-carboxylic acid. X-ray structure analysis shows octahedral coordination around Pb(II) leading to a trigonal dodecahedron geometry. Fluorescence study reveals that the intraligand CT and metal-to-ligand CT transitions are responsible for the emission in the complex.

Self assembly of a Fe III(L) complex with octacyano metallates [M IV(CN) 8] 4− (L = pentadentate macrocyclic ligand, M = Mo, W): Crystal structure and magnetic properties

The self assembly of [Fe III(L)]Cl 2ClO 4 (L = pentadentate macrocyclic ligand) with octacyano metallates [M IV(CN) 8] 4− (M = Mo, W) leads to bimetallic cyano-bridged 2-D coordination polymers of formula [{Fe(L)} 3{M(CN) 8} 2]Cl· xH 2O with M = Mo ( 2), or W ( 3). The structure of the tungsten analogue has been established by single crystal X-ray diffraction. The magnetic properties for both Mo and W derivative are reported.

A Copper(II)-Cytidine Complex as a Building Unit for the Construction of an Unusual Three-Dimensional Coordination Polymer

The chiral [Cu(cyd) 4 ] 6- anion acts as a multiarmed complex-ligand toward auxiliary copper(II) centers leading to the first example of cytidinate-bridged three-dimensional (3D) coordination polymer of formula [Cu 6 (H 2 O) 7 (ClO 4 ) 3 Cu(cyd) 4 ]-(ClO 4 ) 3 (1). Single crystal X-ray analysis of 1 shows a unique 3D covalent network supported by the exclusive hypercoordination of the cytidinate ligand that bridges four crystallographically independent copper(II) ions via the N3, O2, O2', O3', and O5' set of atoms. Magnetic susceptibility measurements in the temperature range 1.9-295 K reveal the coexistence of ferro- and antiferromagnetic interactions within the hexacopper(II) core of 1, the exchange pathways being the di-μ-aqua and the single-and double-alkoxo bridges.

A hexacarboxylic open-shell building block: synthesis, structure and magnetism of a three-dimensional metal–radical framework

An octahedral hexacarboxylic polychlorotriphenylmethyl radical (PTMHC) and its hydrogenated precursor (αH-PTMHC) have been reacted with Cu(II) and 4,4′-bipyridine to prepare two isomorphic three-dimensional (3-D) coordination polymers of formula [Cu6(PTMHC)2(4,4′-bipy)3(H2O)12]n (1) and [Cu6(αH-PTMHC)2(4,4′-bipy)3(EtOH)6(H2O)6]n (2). Both 3-D structures can be described as two interpenetrating primitive cubic nets connected through bipyridine linkers, which defines an unusual topology with Schlafi symbol of (62·81)·(66·89). Magnetic properties of both metal–organic frameworks have been studied in detail. 2 shows weak antiferromagnetic interactions between Cu(II) ions at low temperature. In contrast, 1 reveals unexpected metal–radical ferromagnetic interactions (θ = 2.1 (2) K). Information on the existence of magnetic ordering and the nature of the ordered phase for 1 has been investigated via very low temperature magnetic susceptibility measurements. Surprisingly, the experimental data indicate the occurrence of 3-D antiferromagnetic ordering below 0.5 K. This latter phenomenon has been explained with specific heat measurements. Experimental results reveal the coexistence of relatively strong ferromagnetic interactions with weaker antiferromagnetic ones, mediated through the bipyridine linkers, which finally determine the low temperature magnetic structure. A deeper study of the data allows the analysis of the magnetic behavior of 1 as a 3-D antiferromagnet, with TC = 0.39 K, with ferromagnetic exchange interactions that do not propagate with equal strength along the three crystallographic directions above this temperature.

Two-dimensional oxalate-bridged heterometallic coordination polymer: Crystal structure and thermal behavior of [NaCr(pyim)(ox) 2(H 2O)] · 2H 2O (pyim = 2-(2′-pyridyl)imidazole)

A new coordination polymer of formula [NaCr(pyim)(ox) 2(H 2O)] · 2H 2O (pyim = 2-(2′-pyridyl)imidazole, ox = oxalate) has been prepared and it revealed a novel two-dimensional framework generating from the oxalate-bridged heterometallic Cr III–Na I helical chains with alternative P/M arrangement. Within the 2-D layer, a regular alternation of the metal centers is interconnected by two types of oxalate dianions in common bis(bidentate) ligand and an unusual asymmetric monodentate bonding mode towards a sodium atom of a neighboring chain. The thermal behavior of the complex showed that the lattice and coordinated water molecules to Na + were lost at low temperature, and that the resulting anhydrous [NaCr(pyim)(ox) 2] is thermally stable at 633 K.

Two Novel Diamagnetic-metal Coordination Polymers of Nitronyl Nitroxide Radical Incorporating Isophthalate Bridges

Two novel coordination polymers of formula [Zn(NIT4py)2(ip)]n (1) and [Cd(NIT4py)2(ip)(H2O)]n (2) (NIT4py=2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and ip=isophthalate dianion), have been synthesized and determined by X-ray diffraction. The crystal structures of the complexes are both neutral 1-D chains. The Zn(II) ion adopts a distorted tetrahedral geometry and the Cd(II) ion adopts a distorted pentagonal bipyramidal geometry. Each isophthalate dianion binds two metal ions in bis-monodentate mode for complex (1) and in bis-bidentate mode for complex (2) leading to the 1-D chains. In complex (2) the 1-D chains develop into two-dimensional network via the hydrogen bond interactions. The magnetic studies show a weak antiferromagnetic coupling between two radicals through the diamagnetic Zn(II) in complex (1).

One- and two-dimensional metal–dicyanamido complexes with a flexible bridging co-ligand: structural and magnetic propertiesElectronic supplementary information (ESI) available: a scheme of the different bridging network topologies of dca complexes. See http://www.rsc.org/suppdata/dt/b2/b212886a/

Five coordination-polymers of formula [M(dca)2(bpp)]∞ [bpp is the flexible 1,3-bis(4′-pyridyl)propane ligand, dca = dicyanamido anion, M = Mn (1), Co (2), Zn (3), and Cd (4a and 4b)] have been synthesized and structurally characterized. Compounds 1, 2, 3 and 4a are isomorphous and consist of uniform chains in which adjacent metal ions are triply linked by two 1,5-dca and one bpp bridges and each metal ion is octahedrally coordinated with a trans geometry. The M(dca)2 chain motif adopts a sinusoidal topology with the M(dca)2M rings in a boat conformation, to adapt to the arc-shaped bpp ligand, which here acts as an intrachain bridge and takes an unusual GG conformation. Compound 4b is thermodynamically more stable than 4a. The structure of 4b consists of extended 2D coordination layers in which neighboring metal ions are linked by a bpp or two 1,5-dca bridges and the metal ion is in a cis-octahedral environment. The M(dca)2 chain motif adopts a zigzag topology with the M(dca)2M rings in the usual flat conformation, and the bpp ligand takes a TT conformation and acts as an “arch bridge” between adjacent chains to yield a corrugated (4,4) layer. Each layer is interpenetrated with two adjacent layers, generating an interesting 3D polycatenane. The temperature dependence of the magnetic susceptibility has been investigated for the Mn(II) and Co(II) species. 1 behaves as a 1D Heisenberg Mn(II) chain with a rather weak intrachain antiferromagnetic interaction, and 2 exhibits the complicated behavior characteristic of polynuclear Co(II) species with an octahedral coordination geometry.

Hydrothermal synthesis and characterisation of lead(II) benzene-1,3,5-tricarboxylate [Pb 3BTC 2]·H 2O: a lead(II) carboxylate polymer

The coordination polymer of formula [Pb 3BTC 2]·H 2O (BTC=1,3,5-benzenetricarboxylate) contains 2 different BTC trianions, 3 different Pb cations and 3 different carboxylate coordination modes.

Hydrothermal synthesis and characterisation of lead(II) benzene-1,3,5-tricarboxylate [Pb 3BTC 2]·H 2O: a lead(II) carboxylate polymer

The coordination polymer of formula [Pb 3BTC 2]·H 2O (BTC=1,3,5-benzenetricarboxylate) contains 2 different BTC trianions, 3 different Pb cations and 3 different carboxylate coordination modes.

Metamagnetic Behavior in [M (tvp) (NCS)2] Coordination Polymers (M = Fe(II) and Co(II); tvp = 1,2-di-(4-pyridyl)-ethylene)

We report the synthesis and magnetic properties of two new coordination polymers of formula [M(tvp)(NCS)2] (M = Fe(II) and Co(II)). The magnetic data reveal the occurrence of metamagnetic behavior. Switching from bulk antiferromagnetic to ferromagnetic behavior occurs for magnetic fields greater than 1300 G (Fe(II)) and 450 G (Co(II)) at temperatures lower than 4 K. Both compounds are isomorphous. A molecular structure is suggested in the light of the magnetic properties and precedent data on related systems.

Co-ordination engineering: when can one speak of an “understanding”? Case study of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine †

The mode of co-ordination of the multidentate ligand 2,2′-dimethyl-4,4′-bipyrimidine (L) was found to depend on the metal ion, the crystallization conditions, the metal-to-ligand ratio, and the anion. With nickel a chelating co-ordination through the endo-dentate nitrogen donor set is observed in the molecular complex [NiCl2(L)(H2O)]·CH3NO2, derived from hot CH3NO2. With Cu(NO3)2 and CuI–CH3CN one- and two-dimensional (1-D and 2-D) co-ordination polymers of formula ∞ 1[Cu(NO3)2(µ-L)] and ∞ 2[Cu2(µ3-I)2(µ-L)] are obtained, where the bipyrimidine ligand is solely bridging through the two exo-dentate nitrogen atoms. On the other hand, a synthesis from CuI and crystallization from hot dimethyl sulfoxide leads to a 1-D iodide-bridged co-ordination polymer ∞ 1[Cu(µ-I)(L)] with a chelating ligand. With AgNO3 two different types of co-ordination polymers were found, depending on the silver-to-ligand ratio. At a 1∶1 ratio in the presence of a co-ordinating anion a 2-D network, ∞ 2[Ag(µ-NO3)2(µ-L)], with only bridging bipyrimidine ligands is observed. At a metal excess, a 3-D framework, ∞ 3[Ag3(µ3-NO3)3(µ3-L)2], forms where L functions both as a chelating and as bridging ligand. A tetradentate co-ordination mode of L towards silver is also found with non-co-ordinating anions, such as BF4– and PF6–, and gives rise to the isostructural 2-D co-ordination polymers of formula ∞ 2[Ag3(CH3CN)3(µ3-L)2]X3 (X = BF4 or PF6).