In this work, we report on the structural and physicochemical characterization and an in-depth photophysical study of a family of isostructural coordination polymers (CPs) with the general formula {[M2(mu 3-2onic)4(H2O)4](ClO4)2 & centerdot;2H2O}n (where M(iii) = Y (1Y), Nd (2Nd), Eu (3Eu), Gd (4Gd), Tb (5Tb), Dy (6Dy), Er (7Er) and Yb (8Yb) and 2onic = 2-oxonicotinate). They consist of a cationic 2D layered structure in which two eight-coordinated rare-earth centres are interconnected by means of 2onic ligands, which demonstrates great flexibility with respect to changes in temperature and pressure (vacuum) derived from partial dehydration implying both lattice and coordination water molecules, which in turn promotes the rearrangement of the hydrogen-bonded network. Similar structural breathing effects are observed under variable gas-pressurization conditions, leading to some metastable phases while vacuum conditions are maintained. Periodic density functional theory (PDFT) calculations performed on 1Y with variable amounts of water successfully reproduced the structural evolution during dehydration. The fact that the vacuum-/pressure-induced effect is fully reversible in addition to the significantly improved photoluminescence (PL) shown by the vacuum-/pressure-activated compounds shifts the attention towards these compounds as potential pressure and humidity sensors. 2Nd and 8Yb, in addition to acting as emitters in the visible range, behave as near-infrared (NIR) emitters, with the former displaying characteristic emission even at room temperature. A thorough analysis of the excitations and energy-transfers by means of semi-empirical methods and multi-configurational calculations on suitable fragment models, and further confirmation by density of states (DOS) theory on the PDFT-optimized structure, allows elucidating the PL mechanism operating in the variable emission in the solid state. The water solubility of the compounds allows the study of the PL properties of the complexes, which surprisingly present quantum efficiencies exceeding those of the solid state especially in the solution of 5Tb (with the quantum yield (QY) increased from 1.6 to 21.5%).

The coordination polymer (CP) of [Mn(3-ampy)2(N(CN)2)2]n formula (ampy = aminopyridine) known for its good magnetic properties has surprisingly shown promising performance for electrocatalysis of oxygen reduction reaction (ORR). Mn-based metal-organic compounds are mostly considered as inferior materials for such electrocatalytic reactions in alkaline solutions. In contrast, in the present study, above mentioned Mn CP supported with Vulcan Carbon XC72R showed an exceptionally efficient oxygen reduction via a pseudo 4-electron pathway with maximum n electron transfer (n) = 3.79 at 0.8 V. The concentration of material supported has been studied to optimize its electrocatalytic properties, finding that best ratio of the CP on supporting material is 1:1 (w/w). The resulting hybrid exhibitis an onset potential of 0.85 V vs RHE, a value which is consistent with the working potential range of a fuel cell. This result indicated that this Mn-based CP is not only good for the magnetic applications, but also for electrocatalytic applications.

Abstract In this work, we present four metal-organic compounds based on Zn(II) ion and 3-aminoisonicotinic acid (H3isoani). Upon different synthetic conditions, three open 3D metal-organic frameworks of {[Zn(μ-3isoani)2]·4H2O}n (1), {[Zn(μ-3isoani)2]·2DMF}n (2) and {[Zn(μ-3isoani)2]·DMF}n (3) formulae and a fourth discrete coordination complex with [Zn(3isoani)2(H2O)4] (4) composition are obtained. All compounds can be interchanged with one another by adequate treatment of the samples under specific conditions. Furthermore, each compound showcases distinguished photoluminescent emission upon UV excitation, in such a way that the Zn-3isoani system exhibits variable emission along the composition. This variability in emission was measured at both room and low temperatures to assess the nuances of their photophysical behavior. Moreover, the emission properties are further elucidated by means of density functional theory (DFT) calculations, which provide insight into the underlying mechanisms governing their luminescent characteristics.

Five new bis(ZnDy) complexes with the general formula [Zn2(μ-H2L)2(μ-dicarb)Dy2(L')2(L'')2]X2·solv were synthesized using Mannich bis(compartmental) ligand H4L (highly phenoxido-containing macrocycle). Tetrafluorosuccinate (1, 3) and succinate (2, 4, 5) were used as dicarboxylates; ancillary ligands L' = NO3- (1), hfac (2 and 3), CF3CO2-/tfac (4), dbm (5); L'' = MeOH (4); and counterions X = NO3- (1) or OTf- (2-5). All complexes have a similar axial environment defined by three phenoxido donors, while the equatorial ligand set was systematically tuned to control the electron density around DyIII. Magnetic measurements and ab initio calculations reveal a clear structure-property correlation: ligands that reduce the equatorial electron density stabilize the ground doublet MJ = ± 15/2 and provide enhanced SMM behavior and wider hysteresis loops (tetrafluorosuccinate and nitrate in 1 with UOrbach = 370 ± 30 K). More electron-donating ligands compress the Dy-O distances and reduce magnetic anisotropy, leading to weaker or absent SMM behavior. DyIII-centered emission was detected in all compounds, and analysis of the 482 nm band enabled the estimation of the splitting of the 6H15/2 ground term, which matches ab initio results. This confirms the internal consistency between spectroscopic and theoretical descriptions and reinforces the structure-magnetism correlation for these compounds.

In recent years, CO2 emission has become an important issue due to its possible effects on climate change or the extinction of species. Therefore, there is an urgent necessity to find materials able to capture and store high amounts of CO2 to reverse this situation. In this sense, nanomaterials are attractive materials from the carbon capture and storage point of view thanks to their unique chemical and physical properties. Their surface can be easily functionalized to enhance the gas uptake capacity and their nanosize leads to the high surface area to volume ratios. In this chapter, different nanomaterials for carbon capture are evaluated, from carbon-based nanomaterials to the most advanced nanoporous materials, for which various synthetic processes will be described, as well as modification techniques to further improve their absorption performance and a comparison of different nanomaterials used for CO2 storage.

This work comprises the characterization of a 3D metal-organic framework (MOF), namely, {[Zn(mu-3isoani)2]4H2O}n, synthesized through the coordination of 3-aminoisonicotinic acid (H3isoani) with Zn2+ ions. The assembly of the building blocks resulted in a doubly interpenetrated open 3D crystalline structure with a quartz-like topology that possessed solvent-accessible voids occupied with water molecules. The compound exhibited excellent photoluminescence properties with a dual fluorescent emission arising from the organic molecule as corroborated by calculations using the time-dependent density functional theory (TD-DFT). The independent nature of each emission band with temperature inspired us to study the compound as a ratiometric luminescent thermometer. Notably, it showed the best performance in the 200-300 K range. In addition, the MOF was dispersed in polymethylmethacrylate (PMMA) for the construction of an easy-handled membrane via the solution-casting method for detecting aqueous Fe3+ ions with a competitive KSV value of 3.7 x 103 M-1 and a limit of detection (LOD) of 2.8 x 10-5 M.

Here, the synthesis by a soft solvothermal route of two novel isoreticular compounds based on the in situ generated (by a nucleophilic aromatic substitution) 2-hydroxi-5-(trifluoromethyl)-pyrimidine (H1L) ligand and Zn-(II) and Cd-(II) as metallic centers (with the general formula [ML2]n and labeled as GR-MOF-30 for M = Zn and GR-MOF-31 for M = Cd) is reported, together with their detailed structural and photoluminescent characterization. These metal-organic frameworks are the first examples of coordination compounds based on Zn-(II) and Cd-(II) constructed with this novel ligand. Structures show remarkable intermolecular interactions, including C-F···π and π···π stacking, which not only stabilize the structure but also improve the luminescent properties of the materials. DFT calculations were employed to unequivocally assign the bands observed in UV-vis solid-state spectroscopy. A photophysical study of the materials revealed that GR-MOF-30 and GR-MOF-31present fluorescence band maxima at 394 and 388 nm, respectively, with phosphorescence band maxima and emission lifetimes of 500 and 48.1 ms for GR-MOF-30 and 450 and 69.2 ms for GR-MOF-31. Interestingly, the photoluminescence properties of compound GR-MOF-30 are hardly affected by the change of temperature; meanwhile, GR-MOF-31 shows a transition from a dominating fluorescent emission at room temperature to a phosphorescent emission at 25 K.

We have prepared a bis(compartmental) Mannich base ligand H4L (1,4,8,11-tetraaza-1,4,8,11-tetrakis(2-hydroxy-3-methoxy-5-methylbenzyl)cyclotetradecane) specifically designed to obtain bis(TMIILnIII) tetranuclear complexes (TM = transition metal). In this regard, we have succeeded in obtaining three new complexes of the formula [Zn2(mu-L)(mu-OAc)Dy2(NO3)2]center dot[Zn2(mu-L)(mu-OAc)Dy2(NO3)(OAc)]center dot 4CHCl3 center dot 2MeOH (1) and [TM2(mu-H2L)2(mu-succinate)Ln2(NO3)2] (NO3)2 center dot 2H2O center dot 6MeOH (TMII = Zn, LnIII = Dy (2); TMII = Co, LnIII = Dy (3)). Compound 1 contains two different bis(ZnDy) tetranuclear molecules that cocrystallize in the structure, in which acetato bridging ligands connect the ZnII and DyIII ions within each ZnDy subunit. This compound does not exhibit slow magnetic relaxation at zero field, but it is activated in the presence of an applied dc magnetic field and/or by Dy/Y magnetic dilution, showing two relaxation processes corresponding to each of the two different bis(ZnDy) units found in the structure. As revealed by the theoretical calculations, magnetic relaxation in 1 is single-ion in origin and takes place through the first excited state of each DyIII ion. When using the succinato dicarboxylate bridging ligand instead of acetate, compounds 2 and 3 were serendipitously formed, which have a closed structure with the succinate anion bridging two ZnDy subunits belonging to two different ligands. It should be noted that only compound 2 exhibits slow relaxation of magnetization in the absence of an external magnetic field. According to experimental and theoretical data, 2 relaxes through the second excited Kramers doublet (Ueff = 342 K). In contrast, 3 displays field-induced SMM behaviour (Ueff = 203 K). However, the Co/Zn diluted version of this compound 3Zn shows slow relaxation at zero field (Ueff = 347 K). Ab initio theoretical calculations clearly show that the weak ferromagnetic coupling between CoII and DyIII ions is at the origin of the lack of slow relaxation of this compound at zero field. Compound 2 and its diluted analogues 2Y and 3Zn show hysteresis loops at very low temperature, thus confirming their SMM behaviour. Finally, compounds 1 and 2 show DyIII based emission even at room temperature that, in the case of 2, allows us to extract the splitting of the ground 6H15/2 term, which matches reasonably well with theoretical calculations. Introducing a dicarboxylate linker in a linear tetranuclear bis(ZnDy) complex enables the serendipitous formation of a cyclic version of the system with a Ueff = 342 K.

This study presents the development of zirconium polycarboxylate gel systems as substrates for advanced fluorescence sensing devices. Zirconium-based metal–organic gels (MOGs) offer a promising alternative due to the robustness of the Zr–O bond, which provides enhanced chemical stability. In this work, zirconium polycarboxylate gels were synthesized using green solvents in a rapid room temperature method. Fluorescein, naphthalene-2,6-dicarboxylic acid, and 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakisbenzoic acid were incorporated as fluorophores to give the gel luminescent properties, enabling it to be used as a sensor. These fluorophores produce specific changes in the perceived color and intensity of the fluorescence emission upon interaction with different analytes in a solution, allowing a qualitative identification of different solvents and compounds. However, the fragile structure of neat gels hinders reproducible quantitative analysis of fluorescence emission. Therefore, to increase their mechanical stability during manipulation, a composite material was developed by combining the MOGs with quartz microcrystals, which proved to be a more reliable fluorescent system. The results show that the material can identify univocally different solvents and analytes in aqueous solutions by the quantitative analysis of the emission intensities. This work presents an innovative approach to create advanced fluorescence sensors with improved mechanical properties and stability using zirconium polycarboxylate gels and multiple fluorophores.

Two novel Ce(III) metal organic frameworks (MOFs) with formulas [Ce(5Meip)(H-5Meip)]nGR-MOF-17 and [CeCl(5Meip)(DMF)]nGR-MOF-18 (5Meip = 5-methylisophthalate, DMF = N,N-dimethylformamide) have been synthesized, forming 3-dimensional frameworks. Magnetic measurements show that both compounds present field-induced slow magnetic relaxation under a small applied dc field. For GR-MOF-17, the temperature dependence of relaxation times is best described by a Raman mechanism, whereas for GR-MOF-18, relaxation occurs through a combination of Raman and local-mode pathways. Moreover, when avoiding short Ce⋯Ce interactions by magnetic dilution in GR-MOF-17@La and GR-MOF-18@La, only the local-mode mechanism is responsible for magnetic relaxation. Photophysical studies show the occurrence of ligand-centred luminescence in both compounds and phosphorescence emission at low temperature for GR-MOF-17.

The aim to access linked tetravanadate [V 4 O 12 ] 4− anion with mixed copper(II) complexes, using α -amino acids and phenanthroline-derived ligands, resulted in the formation of four copper(II) complexes [Cu(dmb)(Gly)(OH 2 )] 2 [Cu(dmb)(Gly)] 2 [V 4 O 12 ]·9H 2 O ( 1 ) [Cu(dmb)(Lys)] 2 [V 4 O 12 ]·8H 2 O ( 2 ), [Cu(dmp) 2 ][V 4 O 12 ]·C 2 H 5 OH·11H 2 O ( 3 ), and [Cu(dmp)(Gly)Cl]·2H 2 O ( 4 ), where dmb = 4,4′-dimethioxy-2,2′-bipyridine; Gly = glycine; Lys = lysine; and dmp = 2,9-dimethyl-1,10-phenanthroline. The [V 4 O 12 ] 4− anion is functionalized with mixed copper(II) units in 1 and 2 ; while in 3 , it acts as a counterion of two [Cu(dmp)] 2+ units. Compound 4 crystallized as a unit that did not incorporate the vanadium cluster. All compounds present magnetic couplings arising from Cu⋯O/Cu⋯Cu bridges. Stability studies of water-soluble 3 and 4 by UV–Vis spectroscopy in cell culture medium confirmed the robustness of 3 , while 4 appears to undergo ligand scrambling over time, resulting partially in the stable species [Cu(dmp) 2 ] + that was also identified by electrospray ionization mass spectrometry at m / z = 479. The in vitro cytotoxicity activity of 3 and 4 was determined in six cancer cell lines; the healthy cell line COS-7 was also included for comparative purposes. MCF-7 cells were more sensitive to compound 3 with an IC 50 value of 12 ± 1.2 nmol. The tested compounds did not show lipid peroxidation in the TBARS assay, ruling out a mechanism of action via reactive oxygen species formation. Both compounds inhibited cell migration at 5 µM in wound-healing assays using MCF-7, PC-3, and SKLU-1 cell lines, opening a new window to study the anti-metastatic effect of mixed vanadium–copper(II) systems. Graphical abstract

The preparation of highly efficient photoluminescent rare-earth based coordination compounds, characterized by photoluminescence quantum yield (PLQY) over 90% and thermal/chemical stability that allows their processing in various media (aqueous solutions, polymeric films, etc.) holds enormous significance in their applicability. Herein, a family of isostructural coordination polymers (CPs) with 6-methyl-2-oxonicotinate (6m2onic) ligand, chemically and structurally characterized as {[M(6m2onic)4Na(H2O)3]8H2O}n [where M(III) = Eu (1Eu), Tb (2Tb), Gd (3Gd), Y (4Y) and Eu0.5Tb0.5 (5Eu-Tb)], are reported. Their peculiar crystal structure, based on a hydrogen-bonded framework of 1D arrays in which octacoordinated metal centers (established by four chelating 6m2onic ligands) and Na centers are sequentially linked, gives rise to an excellent metal-organic system benefitting from not only bright PL emissions in solid state but also enough chemical and thermal stability as to yield PL water-soluble complexes and photostable thin-films. In particular, the terbium(III)-based counterpart highlights for its first-in-class PLQY and versatility, which imbues the compound with efficiencies of 97% in bulk state, 35% in aqueous solution, 85% in polymer-based thin-films and 15% after its calcination at 250 degrees C. The experimental photophysical characterization in those media, involving also pH-responsive behavior, is well supported by a solid theoretical analysis of their intramolecular transfers and electronic transitions.

In this work a family of multidimensional (2-(1H-tetrazol-5-yl)ethyl) amino acid coordination compounds have been synthesized and thoroughly characterized. For this purpose, glycine, valine, phenylalanine and tyrosine have been selected as starting amino acids and Mn2+, Zn2+ and Cd2+ as metallic nodes. From one side, for Mn2+ based dimer magnetic resonance imaging studies have been conducted, prompted by the number and disposition of the coordinated water molecules and taking into consideration the promising future of manganese-based coordination compounds as bio-compatible substitutes to conventional Gd based contrast agents. From another side, d10 block metal-based complexes allowed exploring photoluminescence properties derived by in situ synthesized ligands. Finally, amino acid preserved structural chirality allowed us to examine chiroptical properties, particularly focusing on circularly polarized luminescence. A family of multidimensional coordination compounds have been synthesized based on glycine, valine, phenylalanine and tyrosine. Magnetic resonance imaging studies and chiroptical properties have been explored. image

The work presented herein reports on the synthesis, structural and physicochemical characterization and luminescence properties of a family of isostructural coordination polymers (CPs) with a general formula {[Ln(6m2onic)4Na(H2O)3]8H2O}n (where Ln(iii) = Nd (1Nd), Sm (2Sm), Dy (3Dy), Er (4Er), Tm (5Tm), Yb (6Yb) and Dy0.77Eu0.12Y0.11 for the multi-metal compound (7DyEuY) and 6m2onic = 6-methyl-2-oxonicotinate). The crystal structures consist of one-dimensional heterometallic arrays where octacoordinated lanthanide and hexacoordinated sodium centres are sequentially linked and which are held together into a 3D architecture by an extensive hydrogen bonding network formed by the crystallisation water molecules. Photoluminescence measurements in the solid state at variable temperature reveal good properties based on the capacity of the 6m2onic ligand to provide ligand-centred excitation, as suggested by time-dependent density functional theory (TDDFT), and promote efficient energy transfers to the lanthanide(iii) ions, to eventually present intense emissions in both the visible and near-infrared (NIR) regions. On the one hand, compound 4Er displays characteristic lanthanide-centred bands in the NIR region even at room temperature, meaning that the framework is able to isolate the excitons from the vibrational quenching component. On the other hand, regarding the compounds emitting in the visible region, the almost white light emitted by compound 3Dy with a quantum yield (QY) of 6.2% should be noted. Both a purer white emission and an improved QY (up to 15.8%) may be achieved by means of a doping strategy of europium and yttrium ions into the Dy counterpart. Finally, taking advantage of white light emitted by compound 3Dy, the chemical and optical stabilities in water have been confirmed by the photophysical study performed in solution.

Five novel coordination polymers based on 6-aminopicolinate and bipyridine-type spacers are reported, showing fluorescent and phosphorescent emissions and good sensing capacity for Fe3+ and Zn2+ in water when processed as paper analytical devices.

Herein, we report the synthesis and photoluminescence properties of a new 1,3-dioxo-2-(1H-tetrazol-5-yl)-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic (H3L) ligand and three coordination polymers (CPs). Compound [Zn(ntca)DMF]n center dot DMF (1) (ntca2- = 1,4,5,8-naphthalenetetracarboxylate 1,8-monoanhydride, DMF = N,N-dimethylformamide) formed 1D coordination polymer chains packed by hydrogen bonding interactions. On its part, compounds namely [(CH3)2NH2](Zn2(mu-OH)(L)(5-NH2-tetrazolate)n center dot 2H2O (2) and [(CH3)2NH2](ZnL)n (3) (where H3L stands for 1,3-dioxo-2-(1H-tetrazol-5-yl)-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid) crystallize as 2D-layered and 3D anionic frameworks containing dimethylammonium cations occupying the voids. Photoluminescence (PL) measurements have been performed in the solid state on all CPs and ligands to characterize their emission properties, including variable-temperature spectra, lifetime and efficiency. Moreover, the photophysical properties have been studied from the theoretical viewpoint by means of time dependent density functional theory (TD-DFT) in order to elucidate the mechanisms and electronic transitions governing the process. Compounds 1 and 3 present an intense blue luminescence which was originated in the electronic transitions of the ntca2- and the L3- ligands. Compound 2 displays a lower quantum yield which could be tentatively attributed to the weak pi-pi interactions of the aromatic clouds of L3- or the molecular vibrations and/or possible rotational motions of the 5-amino-tetrazolate co-ligand. Herein, we report the synthesis and photoluminescence properties of a new 1,3-dioxo-2-(1H-tetrazol-5-yl)-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic (H3L) ligand and three coordination polymers (CPs).

Co( ii ) and sulfadiazine based compounds with variable anisotropy and metal–metal distances are reported to exhibit SMM behavior and spin-canted antiferromagnetism.

Herein, a flexible system composed of two Ni(II)-based coordination compounds: a 3D framework of {[Ni(mu-3isoani)2]& sdot;DMF}n (1) formula and a 0D monomeric [Ni(3isoani)2(H2O)4] (2) complex (where 3isoani = 3-aminoisonicotinato and DMF = dimethylformamide) which show mutual solvent-induced reversible trans-formations into each other is reported. The system shows reversible 1 <-> 2 transformations upon the exposure of one compound to the solvent present in the other, that is, the MOF (1) in water and the monomer (2) in DMF. The process is easily followed by the naked eye because it involves a colour change from green (1)-to-brownish green (2), making the process traceable as previously observed for the Co(II)-based system. Moreover, these com-pounds present very different magnetic properties since 1 shows field-induced single-molecule magnet (SMM) behaviour, which corresponds to one of the few Ni(II)-based compounds showing single-ion behaviour (being Ni(II) the unique spin carrier), whereas 2 behaves as a regular paramagnet, all of which is explained according to a careful study of the magnetic properties by means of experimental direct-current (dc) and alternating-current (ac) measurements. Obtained experimental results are well supported by active space self -consistent field (CASSCF) calculations that allow understanding the slow relaxation occurring in the Ni(II) ion.

Electrocatalytic activities of three MOFs based on two similar benzoate derivative ligands and transition metal or lanthanide ions, namely {[Co(3a4obenz)]center dot 0.5DMF center dot H2O}(n) (1(Co)), {[Cu-3(3o4obenz)(2)(DMF)(2)]center dot 3H(2)O}(n) (2(Cu)) and {[Tb-5(3a4obenz)(6)(OH)(3)(DMF)(3)]center dot 5H(2)O}(n) (3(Tb)), where 3a4obenz = 3-amino-4-oxobenzoato and 3o4obenz = 3,4dioxobenzoato have been investigated. In addition to their properties in bulk state, these MOFs have been also supported on reduced graphene oxide (rGO). The deposited MOFs present improved electrocatalytic performance than bulk samples, among which 1(Co)@rGO presents the best electrocatalytic activity and also exhibits a high selectivity and superior tolerance towards methanol crossover effects. The ratio of MOF supported on rGO has been concisely studied to optimize the performance of the oxygen reduction reaction (ORR), finding that 1(Co)/rGO in a 3:7 ratio (w/w) shows the best results with 3.73 electrons transferred (n) at 0.7 V (maximum of n = 3.83 at 0.8 V), Tafel slope of 118 mV/dec, onset potential of 0.93 V vs RHE, and the best stability among other compositions.

As a starting point, a new 3D porous framework with the {[CoL]·0.5DMF·H2O}n chemical formula (where L = 3-amino-4-hydroxybenzoate) is described. Its performance as a single molecule magnet was explored. The study of magnetic properties reveals that Co-MOF shows no frequency-fdependant alternating current (ac) signals under zero direct current (dc) magnetic field, whereas single-molecule magnet behaviour is achieved when CoII ions are diluted in a ZnII based matrix. Interestingly, this strategy renders a bifunctional [CoxZn1-xL]n material that is also characterized by a strong photoluminescent emitting capacity.