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

Abstract

We report an efficient pathway toward sensitization of red room temperature EuIII emission by the charge-transfer (CT) states related to d8–d10 heterometallophilic interactions achieved by the simultaneous application of tetracyanidometallates of PtII/PdII and dicyanidometallates of AuI/AgI in the construction of a trimetallic d–d–f assembly. The combination of Eu3+, [MII(CN)4]2– (M = Pt, Pd), and [MI(CN)2]− (M = Au, Ag) ions along with 4,4′-bipyridine N,N′-dioxide (4,4′-bpdo) results in four novel isostructural 2D {[EuIII(4,4′-bpdo)­(H2O)2]­[MII(CN)4]}·[MI(CN)2]·H2O (MII/MI = 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 {EuIII[MII(CN)4]} n square grids coexisting with metal–organic {EuIII(4,4′-bpdo)} n chains, with the further attachment of [MI(CN)2]− ions through metallophilic {MII–MI} interactions. This results in dinuclear {MIIMI} 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 EuIII photoluminescence enhanced by energy transfer from {MIIMI} 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 EuIII-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 EuIII 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 PtII/AuI cyanide metal complexes is proven to be the best candidate for the sensitization of room temperature EuIII luminescence.

Holmium(iii) molecular nanomagnets for optical thermometry exploring the luminescence re-absorption effect

“…This is in line with the recent ndings on the critical role of cyanido stretching vibrations in the [M(CN) x ]dependent tuning of optical properties of f-block metal complexes. 88,93 In addition to the above characterization of optical thermometry, we have also performed three thermal heating-cooling cycling experiments checking the thermometric parameters at three different temperatures (Fig. 5a).…”

Solvent- and Temperature-Driven Photoluminescence Modulation in Porous Hofmann-Type SrII–ReVMetal–Organic Frameworks

“…49−57 This specific type of coordination compounds combines the advantages of the MOF materials, such as rich and tunable porosity and high stability under treatment by chemical and physical stimuli, with a great functional potential of heterometallic cyanido-bridged frameworks, broadly utilized in the generation of diverse magnetic and optical properties, 58−63 including tunable vis-tonear-IR (NIR) photoluminescence. 62,63 The conjunction of cyanido and organic bridges provides attractive porosity governing their magnetic 49−52 and sorption properties. 53−55 Although the Hofmann-type CPs can be emissive because of the insertion of luminescent guest molecules, this combination leads to the loss of porosity.…”

“…This is a difficult task because the 3d metal ions are often emission quenchers and the commonly used [M′(CN) 4 ] 2− ions are spatially separated, which hampers their emission originating from metallophilic interactions. 63,64 However, similar but rarely explored cyanidonitrido [Re V (CN) 4 (N)(L)] 2− (N 3− = nitrido and L = organic ligand) complexes are intrinsically emissive because of their d−d or metal-to-ligand charge-transfer (MLCT) transitions. 65−69 At the same time, they are good candidates for the construction of Hofmann-type CPs thanks to the nearly square-planar alignment of cyanido ligands.…”

Highly Efficient DCL, UCL, and TPEF in Hybridized Ln-Complexes from Ir-Metalloligand

“…The third problem could be resolved through the assembly of hybridized metal species (including f-block and d-block types) into one integrated coordination system, which might result in multiple ET and photon conversion pathways in different directions. 17,[20][21][22][23][24][25] This is likely to provoke unique UCL/DCL combinations in one integrated molecular system.…”