Lanthanide Photoluminescence in Heterometallic Polycyanidometallate-Based Coordination Networks

Abstract

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.

Keywords: coordination networks; crystal engineering; functional materials; lanthanides; photoluminescence; poly-cyanidometallates.

Figure 1

Crystal structure and optical properties of three-dimensional [Ln^III(H₂O)₃][M^I(CN)₂]₃ (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy; M = Ag, Au) cyanido-bridged coordination polymers: (a) the views of the representative fragment of the structure together with the views of the whole network along a and c crystallographic directions, (b) the low-temperature (T = 20 K, λ_exc = 364 nm) pressure-dependent emission spectra of EuAu network, and the temperature-dependent emission spectra of TbAu compound (λ_exc = 350 nm). Colours for the structural diagrams: Ln, red; Ag/Au, dark blue; CN⁻, blue; H₂O, grey [57,58,60]. Reprinted with permission from Inorg. Chem. 1998, 37, 3209–3316. Copyright 1998 American Chemical Society. Reprinted with permission from Inorg. Chem. 2000, 39, 4527–4534. Copyright 2000 American Chemical Society.

Figure 2

Crystal structure and optical properties of cyanido-bridged (ⁿBu₄N)₂[Ln^III(NO₃)₄][Au^I(CN)₂] (Ln = Ce, Nd, Sm, Gd, Eu, Tb, Dy) chains: (a) the views of the single coordination chain, and the arrangement of chains, (b) the multi-coloured lanthanide-dependent emission of LnAu chains together with the related photos under UV light (top), and the multi-coloured temperature- and excitation-dependent emission of Ce_0.33Eu_0.17Tb_0.5Au chains together with the photo under UV light, all presented on the CIE 1931 chromaticity diagram. Colours for the structural diagrams: Ln, red; Au, dark blue; CN⁻, blue; NO₃⁻ and ⁿBu₄N⁺, orange [67,69]. Reprinted with permission from Inorg. Chem. 2017, 56, 7948–7959. Copyright 2017 American Chemical Society.

Figure 3

Crystal structure and optical properties of [Ln^III(H₂O)₆]₂[Pt^II(CN)₄]·2{Pt^II(CN)₄}·9H₂O (Ln = La–Lu) layered cyanido-bridged networks: (a) the views of the single coordination layer, and the arrangement of the layers and the interlayer [Pt^II(CN)₄]²⁻ counterions, (b) the polarization- and lanthanide-dependent emission spectra of SmPt, EuPt and the related reference BaPt networks (T = 80 K, λ_exc = 364 nm). Colours for the structural diagrams: Ln, red; Pt, dark blue; CN⁻, blue; H₂O, grey; Pt-Pt interaction, dark blue stick [74,77]. Adapted from J. Chem. Phys. 1978, 68, 4707–4713, with the permission of AIP Publishing.

Figure 4

Crystal structure and optical properties of [Ln^III(terpy)(H₂O)₂(NO₃)][Pt^II(CN)₄]·n(solvent) (Ln = Eu, Tb; terpy = 2,2’:6’2”-terpyridine) cyanido-bridged chains: (a) the views of the single coordination chain, and the arrangement of chains, (b) the low temperature (T = 77 K) excitation-variable emission spectra for EuPt and TbPt compounds, with the related excitation spectra shown for TbPt. Colours for the structural diagram: Ln, red; Pt, dark blue; CN⁻, blue; terpy, orange; NO₃⁻ and H₂O, grey. [81,87] Reprinted with permission from Inorg. Chem. 2008, 47, 1895–1897. Copyright 2008 American Chemical Society. Reprinted with permission from Inorg. Chem. 2012, 51, 12230–12241. Copyright 2012 American Chemical Society.

Figure 5

Crystal structure and optical properties of [Ln^III(3-OHpy)₂(H₂O)₄][Co^III(CN)₆]·H₂O (Ln = Eu, Tb, Dy; 3-OHpy = 3-hydroxypyridine) cyanido-bridged chains: (a) the views of the coordination chain, and the arrangement of chains; (b) the white light emission of DyCo chains and the related photo (top), the multi-coloured composition-dependent emission of Eu_xTb_1-Co (bottom), all shown on the CIE 1931 chromaticity diagram. Colours for the structural diagram: Ln, red; W, dark blue; CN⁻, blue; 3-OHpy, orange; H₂O, grey [96,97].

Figure 6

Crystal structure and optical properties of near-infrared (NIR)-emitting cyanido-bridged [Nd^III(pmmo)₂ (H₂O)₃][Cr^III(CN)₆] (a) (pmmo = pyrimidine N-oxide) and [Yb^III(3-pyone)₂(H₂O)₂][Co^III(CN)₆] (b) (3-pyone = 3-pyridone) coordination polymers. The top part of the figure shows the respective coordination skeletons of square grid layers (a) and nearly linear chains (b), while the bottom part presents the room temperature excitation and NIR-emission spectra under the indicated wavelength conditions. Colours for the structural diagrams: Nd/Yb, red; Co/Cr, dark blue; CN⁻, blue; pmmo/3-pyone, orange; H₂O, grey [99,100].

Figure 7

Crystal structure and optical properties of chiral [Eu^III(RR-iPr-pybox)(dmf)₄][W^V(CN)₈]·dmf·8H₂O (RR-iPr-pybox = RR-2,2’-(2,6-pyridinediyl)bis(4-isopropyl-2-oxazoline)) cyanido-bridged chains: (a) the views of the single chiral helical chain, and the arrangement of chains, (b) the temperature-dependent emission spectra collected under the UV light excitation of 340 nm. Colours for the structural diagram: Eu, red; W, dark blue; CN⁻, blue; RR-iPr-pybox, orange; dmf, grey [107].

Figure 8

Crystal structure and optical properties of two-dimensional [Tb^III(box)₂(dmf)₂] [W^V(CN)₈]·H₂O (box = 2,2’-bis(2-oxazoline)) coordination polymers: (a) the views of the single cyanido-bridged layer, and the arrangement of layers, (b) the excitation-dependent emission spectra collected at T = 77 K. Colours for the structural diagram: Tb, red; W, dark blue; CN⁻, blue; box, orange; dmf, grey [109].

Figure 9

Crystal structure and optical properties of two-dimensional [Ln^III(phen)(H₂O)₃]₂ [Ru^II(phen)(CN)₄]·14H₂O (Ln = Nd, Gd, Er, Yb; phen = 1,10-phenanthroline) coordination polymers: (a) the views of the cyanido-bridged layer, and the arrangement of layers, (b) the lanthanide- dependent room temperature emission spectra in the visible range together with the related energy level diagram. Colours for the structural diagram: Ln, red; Ru, dark blue; CN⁻, blue; phen, orange; H₂O, grey. Adapted from Ref. [114] with permission from The Royal Society of Chemistry.

Figure 10

Crystal structure and optical properties of three-dimensional [Ln^III(H₂O)₄]₂ [{Ru^II(CN)₄}₃(HAT)]·13H₂O⁴ (Ln = Nd, Gd, Yb; HAT = hexaazatriphenylene) coordination networks: (a) the view of the whole network along the b crystallographic direction, and the detailed view of the layered fragment of the 3D network situated within the (101) plane, (b) the lanthanide-dependent room temperature emission spectra in the visible range. Colours for the structural diagram: Ln, red; Ru, dark blue; CN⁻, blue; HAT, orange; H₂O, grey [116]. Reprinted with permission from J. Am. Chem. Soc. 2007, 129, 11491–11504. Copyright 2007 American Chemical Society.

Figure 11

Crystal structure and optical properties of supramolecular [Er^IIICu^II₂(L1)₂(Cl)₂][Cu^I₄(CN)₅(MeCN)₄] (L1 = N,N’-ethylene bis[4-(ethylamino)salicylideneimine anion) network: (a) the structural views of two main components, including the fragment of the cyanido-bridged CuI-based layer and the {ErIIICuI2} molecule, and their arrangement in the supramolecular network, (b) the room temperature excitation and emission spectra of the reference cyanide-free {ErIII2(H2L)4} molecule (black and purple lines), and the presented supramolecular network (red and light purple lines). Colours for the structural diagram: Er, red; Cu, dark blue; CN−, blue; L1, orange; Cl−, light green. Adapted from Ref. [120] with permission from The Royal Society of Chemistry.

Figure 12

Crystal structure and optical properties of two-dimensional [Ln^III{C₂F₅B(CN)₃}₃(H₂O)₃](Ln = La, Eu, Ho) coordination polymer (a,c), and the related anhydrous three-dimensional [Ln^III{C₂F₅B(CN)₃] (Ln = La, Eu, Ho) coordination network (b,c): (a) the views of the single layer, and the arrangement of layers, (b) the views of the 3D cyanido-bridged network along c and b crystallographic axes, (c) the room temperature excitation and emission spectra of the 2D LnB layer (solid lines), and 3D LnB network (dotted lines). Colours for the structural diagram: Ln, red; B, dark blue; CN⁻, blue; C₂F₅⁻, orange; H₂O, grey [123]. Reprinted with permission from Inorg. Chem. 2017, 56, 2278–2286. Copyright 2017 American Chemical Society.