Synthesis, crystal structure and thermal behavior of tetra-kis-(3-cyano-pyridine N-oxide-κO)bis-(thio-cyanato-κN)cobalt(II), which shows strong pseudo-symmetry

The title compound, [Co(SCN)2(C6H4N2O)4], was prepared by the reaction of cobalt(II)thio-cyanate with 3-cyano-pyridine N-oxide in ethanol. In the crystal, the cobalt(II) cations are octa-hedrally coordinated by two terminal N-bonded thio-cyanate anions and four O-bonded 3-cyano-pyridine N-oxide coligands, forming discrete complexes that are located on centers of inversion, hence forming trans-CoN2O4 octa-hedra. The structure refinement was performed in the monoclinic space group P21/n, for which a potential lattice translation and new symmetry elements with a fit of 100% is suggested. The structure can easily be refined in the space group I2/m, where the complexes have 2/m symmetry. However, nearly all of the reflections that violate the centering are observed with significant intensity and the refinement in P21/n leads to significantly lower R(F) values (0.027 versus 0.033). Moreover, in I2/m much larger components of the anisotropic displacement parameters are observed and therefore, the crystal structure is presented in the primitive unit cell. IR investigations confirm that the anionic ligands are only terminally bonded and that the cyano group is not involved in the metal coordination. PXRD investigations show that a pure crystalline phase has been obtained and measurements using simultaneously thermogravimetry and differential thermoanalysis reveal that the compound decomposes in an exothermic reaction upon heating, without the formation of a coligand-deficient inter-mediate phase.

3–(2–Pyridyl)pyrazole Based Luminescent 1D-Coordination Polymers and Polymorphic Complexes of Various Lanthanide Chlorides Including Orange-Emitting Cerium(III)

A series of 18 lanthanide-containing 1D-coordination polymers 1∞[Ln2(2–PyPzH)4Cl6], Ln = La, Nd, Sm, dinuclear polymorphic complexes α–, β–[Ln2(2–PyPzH)4Cl6], Ln = Sm, Eu, Gd, α–[Tb2(2–PyPzH)4Cl6], and [Gd2(2–PyPzH)3(2–PyPz)Cl5], mononuclear complexes [Ce(2–PyPzH)3Cl3], [Ln(2–PyPzH)2Cl3], Ln = Tb, Dy, Ho, and Er, and salt-like complexes [Gd3(2–PyPzH)8Cl8]Cl and [PyH][Tb(2–PyPzH)2Cl4] were obtained from the reaction of the respective lanthanide chloride with the 3–(2–pyridyl)pyrazole (2–PyPzH) ligand at different temperatures. An antenna effect through ligand-to-metal energy transfer was observed for several products, leading to the highest luminescence efficiency displayed by a quantum yield of 92% in [Tb(2–PyPzH)2Cl3]. The Ce3+ ion in the complex [Ce(2–PyPzH)3Cl3] exhibits a bright and orange 5d-based broadband emission with a maximum at around 600 nm, marking an example of a strong reduction of the 5d-excited states of Ce(III). The absorption spectroscopy shows ion-specific 4f–4f transitions, which can be assigned to Nd3+, Sm3+, Eu3+, Dy3+, Ho3+, and Er3+ in a wide spectral range from UV–VIS to the NIR region.

3D-Frameworks and 2D-networks of lanthanide coordination polymers with 3-pyridylpyrazole: photophysical and magnetic properties

A series of 15 lanthanide-containing coordination polymers, both 3D- and 2D-networks, as well as complexes of Ln-trichlorides with 3-(3-pyridyl)pyrazole (3-PyPzH), were synthesized. A large structural diversity is observed depending on the ligand content: 3∞[Ln(3-PyPzH)Cl₃], Ln = Eu and Gd, of sra topology, 2∞[Sm(3-PyPzH)Cl₃], 2∞[Ln₂(3-PyPzH)₃Cl₆]·2solv, Ln = Eu³⁺, Tb³⁺, Dy³⁺, Ho³⁺ and Er³⁺, solv = Tol and MeCN, of sql topology and 2∞[Ln(3-PyPzH₂)Cl₄], Ln = La and Nd, of hcb topology with salt like complexes of the formula [(3-PyPzH₂)][Ln(3-PyPzH)₂Cl₄], Ln = Eu, Tb, Dy and Ho. The products were characterized by single-crystal and powder X-ray diffraction, high-temperature X-ray diffraction, differential thermal analysis and thermogravimetry (DTA/TG) combined with mass spectrometry, differential scanning calorimetry (DSC), IR-spectroscopy, UV-visible spectrophotometry, photoluminescence spectroscopy, and magnetic susceptibility. Absorption spectroscopy shows ion-specific 4f-4f transitions that can be assigned to Sm³⁺, Eu³⁺, Dy³⁺, Ho³⁺ and Er³⁺ in a wide range from the UV-VIS to NIR region. An excellent antenna effect through ligand-metal energy transfer was observed in 2∞[Tb₂(3-PyPzH)₃Cl₆]·2solv, leading to high efficiency of the luminescence indicated by a quantum yield up to 76%. Direct current magnetic susceptibility studies reveal the absence of interatomic interaction for Dy³⁺ and Er³⁺ and weak ferromagnetic interaction for Ho³⁺. Thermal analysis shows good stability up to 365 °C for 2∞[Ho₂(3-PyPzH)₃Cl₆]·2MeCN.

Structural diversity of salts of terpyridine derivatives with europium(III) located in both, cation and anion, in comparison to molecular complexes

Three salts of the common composition [EuCl2(X-tpy)2][EuCl4(X-tpy)]·nMeCN were obtained from EuCl3·6H2O and the respective organic ligands (X-tpy = 4′-phenyl-2,2′:6′,2″-terpyridine ptpy, 4′-(pyridin-4-yl)-2,2′:6′,2″-terpyridine 4-pytpy, and 4′-(pyridin-3-yl)-2,2′:6′,2″-terpyridine 3-pytpy). These ionic complexes are examples of salts, in which both cation and anion contain Eu3+ with the same organic ligands and chlorine atoms coordinated. As side reaction, acetonitrile transforms into acetamide resulting in the crystallization of the complex [EuCl3(ptpy)(acetamide)] (4). Salts [EuCl2(ptpy)2][EuCl4(ptpy)]·2.34MeCN (1), [EuCl2(4-pytpy)2][EuCl4(4-pytpy)]·0.11MeCN (2), and [EuCl2(3-pytpy)2][EuCl4(3-pytpy)]·MeCN (3) crystallize in different structures (varying in space group and crystal packing) due to variation of the rear atom of the ligand to a coordinative site. Additionally, we show and compare structural variability through the dimeric complexes [Eu2Cl6(ptpy)2(N,N′-spacer)]·N,N′-spacer (5, 6, 7) obtained from [EuCl3(ptpy)(py)] by exchanging the end-on ligand pyridine with several bipyridines (4,4′-bipyridine bipy, 1,2-bis(4-pyridyl)ethane bpa, and 1,2-bis(2-pyridyl)ethylene bpe). In addition, photophysical (photoluminescence) and thermal properties are presented.

Crystal structure, synthesis and thermal properties of bis-(4-benzoyl-pyridine-κN)bis-(iso-thio-cyanato-κN)bis-(methanol-κN)iron(II)

In the crystal structure of the title compound, [Fe(NCS)2(C12H9NO)2(CH4O)2], the FeII cations are octa-hedrally coordinated by two N atoms of 4-benzoyl-pyridine ligands, two N atoms of two terminal iso-thio-cyanate anions and two methanol mol-ecules into discrete complexes that are located on centres of inversion. These complexes are linked via inter-molecular O-H⋯O hydrogen bonds between the methanol O-H H atoms and the carbonyl O atoms of the 4-benzoyl-pyridine ligands, forming layers parallel to (101). Powder X-ray diffraction proved that a pure sample was obtained but that this compound is unstable and transforms into an unknown crystalline phase within several weeks. However, the solvent mol-ecules can be removed by heating in a thermobalance, which for the aged sample as well as the title compound leads to the formation of a compound with the composition Fe(NCS)2(4-benzoyl-pyridine)2, which exhibits a powder pattern that is similar to that of Mn(NCS)2(4-benzoyl-pyridine)2.

Bismuth as a versatile cation for luminescence in coordination polymers from BiX3/4,4'-bipy: understanding of photophysics by quantum chemical calculations and structural parallels to lanthanides

Coordination polymers (CPs) with bismuth(iii) as a connectivity centre have been prepared from BiX3 (X = Cl-I) and 4,4'-bipyridine (bipy) in order to implement Bi-based luminescence. The products were obtained via different synthetic routes such as solution chemistry, melt syntheses or mechanochemical reactions. Five neutral and anionic 1D-CPs are presented that show a chemical parallel to trivalent lanthanides forming isostructural or closely related 1D-CPs, of which five additional compounds are described. Bi3+ proves to be a versatile cation for luminescence resulting from energy transfer processes between a metal and a ligand in the presented CPs. Quantum chemical calculations were carried out to investigate Bi3+-participation in the luminescence processes. The calculated results allow an assignment of the bright transitions composed of mainly metal-to-ligand-charge transfer (MLCT) character. These results show that Bi3+ can form strongly luminescent coordination compounds with N-donor ligands.

Superparamagnetic Luminescent MOF@Fe₃O₄/SiO₂ Composite Particles for Signal Augmentation by Magnetic Harvesting as Potential Water Detectors

Herein, we present the generation of a novel complex particle system consisting of superparamagnetic Fe3O4/SiO2 composite microparticle cores, coated with luminescent metal-organic frameworks (MOFs) of the constitution (∞)(2)[Ln2Cl6(bipy)3]·2bipy (bipy = 4,4′-bipyridine) that was achieved by intriguing reaction conditions including mechanochemistry. The novel composites combine the properties of both constituents: superparamagnetism and luminescence. The magnetic properties can be exploited to magnetically collect the particles from dispersions in fluids and, by gathering them at one spot, to augment the luminescence originating from the MOF modification on the particles. The luminescence can be influenced by chemical compounds, e.g., by quenching observed for low concentrations of water. Thus, the new composite systems present an innovative concept of property combination that can be potentially used for the detection of water traces in organic solvents as a magnetically augmentable, luminescent water detector.

Luminescent coordination polymers for the VIS and NIR range constituting LnCl3 and 1,2-bis(4-pyridyl)ethane

Variable luminescence of lanthanide coordination polymers with bis-pyridylethane and thiazole.

Metallosupramolecular Materials for Energy Applications: Light Harvesting

Excitation energy transfer, a key process in natural light harvesting systems, has been extensively investigated with the help of synthetic molecular and supramolecular systems. The knowledge gathered from these studies has contributed to the development of novel energy harvesting materials that could find applications in nano-electronics and photonics, of which metallosupramolecular assemblies are one such class. In this chapter, the exciting developments in the use of metallosupramolecular materials in energy applications such as light harvesting are described. Emphasis is given to the state-of-the-art summary in the design and properties of metal–organic frameworks, self-assembled coordination polymers and metallogels, which all have prospects for light harvesting applications.

Post-Synthetic Shaping of Porosity and Crystal Structure of Ln-Bipy-MOFs by Thermal Treatment

The reaction of anhydrous lanthanide chlorides together with 4,4′-bipyridine yields the MOFs ∞2[Ln₂Cl₆(bipy)₃]·2bipy, with Ln = Pr − Yb, bipy = 4,4′-bipyridine, and ∞3[La₂Cl₆(bipy)₅]·4bipy. Post-synthetic thermal treatment in combination with different vacuum conditions was successfully used to shape the porosity of the MOFs. In addition to the MOFs microporosity, a tuneable mesoporosity can be implemented depending on the treatment conditions as a surface morphological modification. Furthermore, thermal treatment without vacuum results in several identifiable crystalline high-temperature phases. Instead of collapse of the frameworks upon heating, further aggregation under release of bipy is observed. ∞3[LaCl₃(bipy)] and ∞2[Ln₃Cl₉(bipy)₃], with Ln = La, Pr, Sm, and ∞1[Ho₂Cl₆(bipy)₂] were identified and characterized, which can also exhibit luminescence. Besides being released upon heating, the linker 4,4′-bipyridine can undergo activation of C-C bonding in ortho-position leading to the in-situ formation of 4,4′:2′,2′′:4′′,4′′′-quaterpyridine (qtpy). qtpy can thereby function as linker itself, as shown for the formation of the network ∞2[Gd₂Cl₆(qtpy)₂(bipy)₂]·bipy. Altogether, the manuscript elaborates the influence of thermal treatment beyond the usual activation procedures reported for MOFs.

Structural features and near infra-red (NIR) luminescence of isomeric Yb(iii) bipyridyl-N,N′-dioxide coordination polymers

The synthesis and structural characterization of a series of lanthanide complexes formed from YbX₃ salts (X = NO₃⁻ or CF₃SO₃⁻) and the isomeric 4,4′-bipyridine-N,N′-dioxide (4,4′-bpdo) or 3,3′-bipyridine-N,N′-dioxide (3,3′-bpdo) ligands has been undertaken by X-ray crystallography.

Highly luminescent thin films of the dense framework ∞(3)[EuIm2] with switchable transparency formed by scanning femtosecond-pulse laser deposition

Highly luminescent switchable thin films of the dense framework ∞(3)[EuIm2] were deposited by a scanning laser ablation technique using a femtosecond laser. The films can be controlled in terms of film thickness and amount of material deposited such that the material properties of the bulk material are retained on the nanometer scale. Polycrystalline films are formed that can be switched between transparent at visible light and nontransparent at UV light due to the intrinsic luminescence of the hybrid material, expanding the concept of smart films. The new femtosecond pulsed laser deposition method also provides a novel approach for coatings with framework compounds and coordination polymers.

Seven novel Sr(II)-Sm(III) and Sr(II)-Dy(III) coordination polymers: construction of five classes of structural topologies using different amounts of imidazole

The employment of pyridine-2,6-dicarboxylic acid (H2pda) and imidazole (im) in the synthesis of Sr(II)-Sm(III) and Sr(II)-Dy(III) coordination polymers has been reported. Seven novel heterometallic coordination polymers of compositions, [Dy3Sr3(pda)7(Hpda)(H2O)9]·6H2O (1), [LnSr(pda)3(H2O)5]·Him·H2O (Ln = Sm(2), Dy(3)), [Ln2Sr(pda)6(H2O)5]·4Him·C2H5OH·nH2O (Ln = Sm(4), n = 4; Dy(5), n = 5), [Sm2Sr2(pda)5(H2O)9]·2H2O (6) and [DySr(pda)3(H2O)4]·Him·3H2O (7), have been prepared and characterized. Complexes 1, 2-3, and 6 display three varieties of 2-D structures. 4-5 and 7 exhibit two types of 1-D chain structures. The structures of the complexes could be controlled via choosing appropriate starting materials and tuning the amount of imidazole. The photo-luminescent properties of these complexes have been investigated. The results show the exclusive luminescence emission bands being characteristic of Sm(III) and Dy(III).