Structural and Photophysical Properties of Coordination Networks Combining [Ru(Bpym)(CN)4]2- or [{Ru(CN)4}2(μ-bpym)]4- Anions (bpym = 2,2‘-Bipyrimidine) with Lanthanide(III) Cations: Sensitized Near-Infrared Luminescence from Yb(III), Nd(III), and Er(III) Following Ru-to-Lanthanide Energy Transfer

Europium(III) Photoluminescence Governed by d8-d10 Heterometallophilic Interactions in Trimetallic Cyanido-Bridged Coordination Frameworks

We report an efficient pathway toward sensitization of red room temperature Eu^III emission by the charge-transfer (CT) states related to d⁸-d¹⁰ heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of Pt^II/Pd^II and dicyanidometallates of Au^I/Ag^I in the construction of a trimetallic d-d-f assembly. The combination of Eu³⁺, [M^II(CN)₄]^2- (M = Pt, Pd), and [M^I(CN)₂]^- (M = Au, Ag) ions along with 4,4'-bipyridine N,N'-dioxide (4,4'-bpdo) results in four novel isostructural 2D {[Eu^III(4,4'-bpdo)(H₂O)₂][M^II(CN)₄]}·[M^I(CN)₂]·H₂O (M^II/M^I = Pt/Au, 1; Pt/Ag, 2; Pd/Au, 3; Pd/Ag, 4) coordination networks. They are built of hybrid coordination layers, based on cyanido-bridged {Eu^III[M^II(CN)₄]}_n square grids coexisting with metal-organic {Eu^III(4,4'-bpdo)}_n chains, with the further attachment of [M^I(CN)₂]^- ions through metallophilic {M^II-M^I} interactions. This results in dinuclear {M^IIM^I} units generating an orange emissive metal-to-metal-to-ligand charge-transfer (MMLCT) state, whose energy is tuned by the applied d⁸-d¹⁰ metal centers. Thanks to these CT states, 1-4 exhibit room temperature red Eu^III photoluminescence enhanced by energy transfer from {M^IIM^I} units, with the additional role of 4,4'-bpdo also transferring the energy to lanthanides. These donor CT states lying in the visible range successfully broaden the available efficient excitation range up to 500 nm. The overall emission quantum yield ranges from 8(1)% for 4 to 15(2)% for 1, with the intermediate values for 2 and 3 relatively high among the reported Eu^III-based compounds with tetracyanido- and dicyanidometallates. We found that the sensitization efficiency is equally high for all compounds because of the similar energies of the CT states, while the main differences are related to the observed emission lifetimes ranging from ca. 80 μs for 4 to 120-130 μs for 2 and 3 to ca. 180 μs for 1. This phenomenon was correlated with the energies of the vibrational states, e.g., cyanide stretching vibrations, responsible for nonradiative deactivation of Eu^III excited states, which are the highest for the Pd/Ag pair of 4 and the lowest for the Pt/Au pair in 1. Thus, the heaviest pair of Pt^II/Au^I cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature Eu^III luminescence.

Near-infrared emissive Er(iii) and Yb(iii) molecular nanomagnets in metal–organic chains functionalized by octacyanidometallates(iv)

Photoluminescent single-molecule magnets are formed in lanthanide(pyrazine N,N′-dioxide) chains with octacyanidometallate(iv) coordination branches playing a crucial role in sensitized NIR emission.

Multi-colour uranyl emission efficiently tuned by hexacyanidometallates within hybrid coordination frameworks

Hexacyanidometallates of transition metal ions govern the topology and the photoluminescence of bimetallic d–f hybrid coordination networks incorporating uranyl cations.

Sensitized near infrared emission through supramolecular d → f energy transfer within an ionic Ru(ii)-Er(iii) pair

The newly synthesized ionic triple salt Ru-Er, {[Ru^II(bpy)₂(dbim)][Er^III(hfac)₄][CF₃COO]·H₂O} (bpy = 2,2'-bipyridine; hfac^- = hexafluoroacetylacetonate; dbim = 2,2'-dibenzimidazole) exhibits near-infrared (NIR) emission at 1535 nm by intermolecular Ru → Er (d → f) energy transfer across supramolecular interactions when pumped within the Ru(ii) ³MLCT band. It is the first such observation for a transition metal-lanthanide ionic pair.

Incorporation of hexacyanidoferrate(iii) ion in photoluminescent trimetallic Eu(3-pyridone)[Co1−xFex(CN)6] chains exhibiting tunable visible light absorption and emission properties

Tuning of absorption and photoluminescence is achieved in trimetallic EuCoFe cyanido-bridged frameworks through the gradual replacement of [Co^III(CN)₆]³⁻ with [Fe^III(CN)₆]³⁻.

Lanthanide Photoluminescence in Heterometallic Polycyanidometallate-Based Coordination Networks

Solid-state functional luminescent materials arouse an enormous scientific interest due to their diverse applications in lighting, display devices, photonics, optical communication, low energy scintillation, optical storage, light conversion, or photovoltaics. Among all types of solid luminophors, the emissive coordination polymers, especially those based on luminescent trivalent lanthanide ions, exhibit a particularly large scope of light-emitting functionalities, fruitfully investigated in the aspects of chemical sensing, display devices, and bioimaging. Here, we present the complete overview of one of the promising families of photoluminescent coordination compounds, that are heterometallic d–f cyanido-bridged networks composed of lanthanide(3+) ions connected through cyanide bridges with polycyanidometallates of d-block metal ions. We are showing that the combination of cationic lanthanide complexes of selected inorganic and organic ligands with anionic homoligand [M(CN)_x]ⁿ⁻ (x = 2, 4, 6 and 8) or heteroligand [M(L)(CN)₄]²⁻ (L = bidentate organic ligand, M = transition metal ions) anions is the efficient route towards the emissive coordination networks revealing important optical properties, including 4f-metal-centred visible and near-infrared emission sensitized through metal-to-metal and/or ligand-to-metal energy transfer processes, and multi-coloured photoluminescence switchable by external stimuli such as excitation wavelength, temperature, or pressure.

Development of Ion-Conductive and Vapoluminescent Porous Coordination Polymers Composed of Ruthenium(II) Metalloligand

We synthesized two new porous coordination polymers (PCPs) {Ln₇(OH)₅[Ru(dcbpy)₃]₄·4nH₂O} (Ln₇-Ru₄; Ln = Ce, Nd) composed of the luminescent ruthenium(II) metalloligand [Ru(4,4'-dcbpy)₃]^4- ([4Ru]; 4,4'-dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and lanthanide ions Ln³⁺ (Ln = Ce, Nd). These two PCPs Ln₇-Ru₄ are isomorphous with the previously reported PCP La₇-Ru₄, and the lattice constants (a, c, and unit cell volume V) changed systematically according to the lanthanide contraction. All three Ln₇-Ru₄ compounds have OH^- anion containing porous structures and a large number of hydrate water molecules within the pores, resulting in moderate ion conductivities (10^-6-10^-7 S cm^-1) at 90% relative humidity (RH) and 298 K. In contrast, the structural transformation of Ln₇-Ru₄ associated with water-vapor adsorption/desorption strongly depends on the lanthanide ion; the Ln₇-Ru₄ compounds with larger Ln³⁺ ions recover the original porous structure at lower relative humidities (RH). A similar trend was observed for the ion conduction activation energy, suggesting that the bridging Ln³⁺ ion plays an important role in the formation of the ion-conductive pathways. La₇-Ru₄ and Ce₇-Ru₄ exhibit vapochromic luminescence associated with water vapor adsorption/desorption, arising from the ³MLCT emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln³⁺ ion; the vapochromic shift of Ce₇-Ru₄ was observed at RH values (near 100% RH) higher than that of La₇-Ru₄. ³MLCT emissions of the [4Ru] metalloligand in Nd₇-Ru₄ were barely observable in the visible region, but sharp emission bands characteristic of 4f-4f transitions of the Nd³⁺ ion were observed in the near-infrared (NIR) region (arising from the ¹MLCT transition of [4Ru]), suggesting the transfer of energy from the [4Ru] ³MLCT excited state to the 4f-4f transition state of the Nd³⁺ ions.

Octahedral Yb(iii) complexes embedded in [CoIII(CN)6]-bridged coordination chains: combining sensitized near-infrared fluorescence with slow magnetic relaxation

The rare octahedral Yb^III complexes formed in the bimetallic Yb–Co chains reveal significant magnetic anisotropy and photoluminescence activity in the near-infrared range.

Tetranuclear Heterometallic {Zn2Eu2} Complexes With 1-Naphthoate Anions: Synthesis, Structure and Photoluminescence Properties

A series of new tetranuclear heterometallic Zn(II) -Eu(III) complexes have been synthesized, that is, (bpy)2 Zn2Eu2 (naph)10 (1), (bpy)2 Zn2Eu2 (naph)8 (NO3)2 (2), and (phen)2 Zn2Eu2 (naph)8 (NO3)2 (3), and other ones, where naph(-) is the 1-naphthoate anion, bpy=2,2'-bipyridyl, and phen=1,10-phenanthroline. The solid-phase complexes consist of large supramolecular ensembles due to stacking interactions between the aromatic ligands. Photoluminescence (PL) measurements were carried out to study PL spectra, lifetimes and quantum yields (QY) of the synthesized complexes at different temperatures. The external QY for the solid phases of complexes under UV excitation was found to exceed 20 %. It has been shown that partial replacement of naphthoate ligands in the coordination environment of Eu(3+) by NO3(-) anions influences the PL properties. To investigate the behavior of these complexes in solvent, we dissolved complex 3 in MeCN, put it on a transparent glass as a substrate, and studied the PL properties at room temperature.

Single-molecule magnet behavior in 2,2'-bipyrimidine-bridged dilanthanide complexes

A series of 2,2'-bipyrimidine-bridged dinuclear lanthanide complexes with the general formula [Ln(tmhd)3]2bpm (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedionate, bpm = 2,2'-bipyrimidine, Ln = Gd(III), 1; Tb(III), 2; Dy(III), 3; Ho(III), 4 and Er(III), 5) has been synthesized and characterized. Sublimation of [Tb(tmhd)3]2bpm onto a Au(111) surface leads to the formation of a homogeneous film with hexagonal pattern, which was studied by scanning tunneling microscopy (STM). The bulk magnetic properties of all complexes have been studied comprehensively. The dynamic magnetic behavior of the Dy(III) and Er(III) compounds clearly exhibits single molecule magnet (SMM) characteristics with an energy barrier of 97 and 25 K, respectively. Moreover, micro-SQUID measurements on single crystals confirm their SMM behavior with the presence of hysteresis loops.

Crystal structures and luminescent properties of new lanthanide(iii) complexes derived from 2-phenyl-4-pyrimidinecarboxylate

Five novel lanthanide complexes with diverse structural motifs are constructed under different reaction conditions and their photoluminescence properties are studied.

Engineering metal-based luminescence in coordination polymers and metal-organic frameworks

The rapidly growing number of luminescent coordination polymers (CPs) and metal-organic frameworks (MOFs) illustrates high interest as well as accessibility of such materials. The interplay between inorganic and organic components in these materials offers a large number of viable luminescence processes. The enormous variability of available ligand-metal combinations opens the possibility of creating luminescence "by design", based on a proper understanding of the processes involved. Together with the multifunctionality of MOFs (e.g. porosity) further options like sensing become accessible. This tutorial review covers the main luminescence processes and focuses especially on metal-based luminescence of coordination polymers and MOFs.

The Utility of 2,2′-Bipyrimidine in Lanthanide Chemistry: From Materials Synthesis to Structural and Physical Properties

This paper reviews the recent investigations undertaken on the use of 2,2′-bipyrimidine (bpm) as a ligand for designing molecular complexes as well as polymeric lanthanide materials. A special emphasis is put on the ability of this polydentate neutral ligand to yield compounds of various dimensionalities, to act as a connector between these large ions, and influence their emissive and magnetic properties. This ligand can adopt a terminal or a bridging coordination mode with lanthanide ions, thus generating a wealth of frameworks of various topologies with the 4f elements. The main focus of this review is to show the originality brought by bpm in lanthanide structural chemistry and solid-state photophysics and magnetism.

Luminescent multifunctional lanthanides-based metal-organic frameworks

Metal-organic frameworks based on trivalent lanthanides (LnMOFs) are a very promising class of materials for addressing the challenges in engineering of luminescent centres. Lanthanide-bearing phosphors find numerous applications in lighting, optical communications, photonics and biomedical devices. In this critical review we discuss the potential of LnMOFs as multifunctional systems, which combine light emission with properties such as microporosity, magnetism, chirality, molecule and ion sensing, catalysis and activity as multimodal imaging contrast agents. We argue that these materials present a unique chance of observing synergy between several of these properties, such as the coupling between photoluminescence and magnetism. Moreover, an integrated approach towards the design of efficient, stable, cheap, environmentally-friendly and multifunctional luminescent LnMOFs is still missing. Although research into LnMOFs is at its early stage and much basic knowledge is still needed, the field is ripe for new ideas, which will enable sensor devices and photonic prototypes to become a commercial reality (81 references).