The chemistry of the less familiar elements is a fascinating topic especially for the inorganic minded. The lanthanides, or rare earths, comprise the 5d block of the periodic table and represent a huge array of applications from catalysis to lasers, and of course, imaging agents.1

Recent advances in luminescence and magnetic resonance microscopy have, in part, been stimulated by extraordinary success in the development of new lanthanide probes. The unique properties of the lanthanides provide for a deep tool chest for the chemist, biologist and the imaging scientist to exploit, and that exploitation is in full swing.

In this review we focus on two classes of lanthanide probes that are subsets of the larger area of metalloimaging: luminescent and magnetic lanthanides. In Section 2 we discuss the general design and photophysical properties of lanthanides and how these parameters are tuned to develop bioresponsive probes for optical imaging. In Section 3 we provide a brief description of how MR images are acquired and the how MRI contrast agents are engineered to respond to biological events of interest. These guiding principles have driven research that has produced a truly diverse number of new agents that are target specific and bioresponsive (or bioactivatable). While other imaging modalities utilize lanthanide-based probes, these topics are beyond the scope of this review. We direct the reader to explore some excellent reviews in the important areas of radiometals and multimodal imaging.2–5

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Lanthanide probes for bioresponsive imaging.

The magnet-like behavior can beobserved by slow relaxation of the magnetization below theblocking temperature. Since the discovery of SMMs in theearly 1990s, this assumption has formed the basis for theunderstanding of the origin of the anisotropic barrier.However, in recent years the development of novel lantha-nide-only SMMs that challenge and defy this theory pose anumber of questions:

A Polynuclear Lanthanide Single-Molecule Magnet with a Record

Recent developments in luminescent coordination polymers: Designing strategies, sensing application and theoretical evidences

A series of five unique d–f heteronuclear luminescent metal–organic frameworks (MOFs) in an entangled polyrotaxane array and the light-harvesting block homonuclear zinc compound have been isolated successfully and characterized. The series of isostructural polymers feature 3,4-connected (4.82)(4.83.92)(6.8.9)2(6.92)(83) topology and high stability, exhibiting diverse void spaces. By taking advantage of the isostructural MOFs 2 and 3, the intensities of red and green emissions can be modulated by adjusting the ratios of EuIII and TbIII ions correspondingly, and white-light emission can be generated by a combination of different doped TbIII and EuIII concentrations. The Tb–Zn-based framework {[Tb3Zn6(bipy2)2(Hmimda)7 (H2O)3]·5H2O}n (3; H3mimda = 2-methyl-1-H-imidazole-4,5-dicarboxylic acid and bipy = 4,4′-bipyridine) can detect trace MgII ion with relatively high sensitivity and selectivity. Dehydrated MOF 3a shows a remarkable emission quenching effect through the introduction of I2 solids. Further investi...

Series d-f Heteronuclear Metal-Organic Frameworks: Color Tunability and Luminescent Probe with Switchable Properties.

In the past 30 years, metal-organic frameworks (MOFs) have garnered widespread attention owing to their diverse chemical structures, and tunable properties. As a result, MOFs are of interest for a wide variety of potential applications spanning multiple scientific and engineering disciplines. MOFs have been synthesized using several elements from the periodic table, including those with metal nodes containing s-, p-, d-, and f-block elements. MOFs synthesized with rare-earth (RE) elements, which include scandium, yttrium and the series of fifteen lanthanides are an intriguing family of MOFs from the standpoint of both structure and function. While RE-MOFs can possess many of the same properties common to all MOF families (i.e., permanent porosity, tunable pore size/shape, accessible Lewis acidic sites), they can also display unique structures and properties owing to the high coordination numbers and distinct optical properties of RE-elements. In this review, we present the progress, and highlight several discoveries from research conducted on the topic of RE-MOFs. First, diverse structures of RE-MOFs are presented, divided into classes based on the composition of the RE-metal node being RE(iii)-ions, RE(iii)-chains, or RE(iii)-clusters. Then, several potential applications of RE-MOFs are presented, highlighting examples in the areas of chemical sensing, white light emission, biological imaging, drug delivery, near infrared emission, catalysis, gas adsorption, and chemical separations.

Rare-earth metal-organic frameworks: from structure to applications.

A new zinc compound, together with a corresponding series of Zn-4f heterometallic coordination polymers, namely, [Zn(H2PBDA)(PBDA)]n (1), {[Ln2(PBDA)2·2H2O] [Zn2(PBDA)2Cl2]}n [H2PBDA = 3-(pyridin-3-yl-oxy) benzene-1,2-dicarboxylic acid, and Ln = Pr(2), Nd(3), Eu(4), Gd(5), Dy(6), Ho(7), Er(8)] have been hydrothermally synthesized and characterized systematically. Polymers 2–8 feature two-dimensional (2D) 4,4 networks, containing the original 1D heterometallic double stranded chains composed of [Ln2Zn2(PBDA)2] entities. The extensive hydrogen bonding and π–π stacking interactions were observed to stabilize the extended architectures. The luminescence emission spectra of the polymers vary depending on the lanthanide(III) ion present. Informative magnetic susceptibility measurements show that the same carboxylate bridging fashion of the PBDA ligand results in the different magnetic properties occurring within the heterometallic coordination polymers. In addition, polymer 6 exhibits an interesting slow magnetic relaxation behavior at lower temperatures.

A series of Zn-4f heterometallic coordination polymers and a zinc complex containing a flexible mixed donor dicarboxylate ligand.

Reactions of lanthanide(III) nitrates with multi-donor carboxylate ligand in the presence of oxalate anion afforded four new lanthanide coordination polymers with three dimensional (3D) frameworks, namely, {[Ln2(DPPA)2(μ2-C2O4)(H2O)2]·2H2O}n (Ln = Nd (1), Sm (2)) and [Ln2(HDPPA)2(DPPA)2]n (Ln = Tb (3), Yb (4)), (H3DPPA = 3-(4-hydroxyl pyridinium-1-yl) phthalic acid and H2C2O4 = oxalic acid). Compounds 1 and 2 are isostructural and isomorphous, featuring oxalate pillared binodal (4,5)-connected porous 3D framework with intersected 1D channels, in which the coordinated and lattice waters are accommodated. The complexes 3 and 4 are also isostructural, but featuring a (4,6)-connected 3D network based on a rectangular window composed of {Ln(HDPPA)}(+) extended anion chains, further interlinked by DPPA. The Tb(III) analogue exhibits intense characteristic green photoluminescence employing DPPA as an antenna. While Sm(III) compound 2 mainly involves ligand-to-ligand charge transfer. Variable-temperature susceptibility analyses of complexes 1 (Nd), 2 (Sm) and 3 (Tb) revealed that depopulation of the Stark levels together with weak antiferromagnetic interactions between the lanthanide ions lead to a continuous decrease in χ(M)T when the samples are cooled from 300 to 2 K.

https://www.rsc.org/suppdata/dt/c3/c3dt50810b/c3dt50810b.pdf

A series of 3D lanthanide frameworks constructed from aromatic multi-carboxylate ligand: structural diversity, luminescence and magnetic properties.

The combination of lanthanide and zinc nitrates reaction with a rigid 1-H-2-methyl-4,5-imidazole-dicarboxylic acid yields a new zinc complex of Zn(Hmimda)2·2H2O (1) and a family of heteronuclear polymers, namely, {[Ln2Zn2(μ3-Hmimda)2 (μ3-mimda)2·4H2O]·mH2O}n, Ln = Sm, m = 2 (2), Ln = Eu, m = 3 (3), Ln = Gd, m = 2 (4), Ln = Tb, m = 3 (5), Ln = Dy, m = 3 (6) (H3mimda = 1H-2-methyl-4,5-imidazole-dicarboxylic acid). Structural analysis shows that complexes 2–6 are isostructural and all crystallize in the monoclinic system, except for a slight disparity for 2. They have an extended nonporous structure constructed from tetraheteronuclear edifices with new framework topology, in which the Ln(III)–Zn square tetranuclear complexes act as the second building unit, which are further interconnected by the Hmimda to afford a two-dimensional corrugated layer. Both compounds 5 and 6 exhibit characteristic fluorescence in the visible region. The variable temperature magnetic investigations indicate that the magnetic inte...

A Series of Heterometallic Three-Dimensional Frameworks Constructed from Imidazole–Dicarboxylate: Structures, Luminescence, and Magnetic Properties

Lanthanide coordination polymers based on multi-donor ligand containing pyridine and phthalate moieties: Structures, luminescence and magnetic properties

Hong-Liang Song

Papers

A series of Zn-4f heterometallic coordination polymers and a zinc complex containing a flexible mixed donor dicarboxylate ligand.

A series of 3D lanthanide frameworks constructed from aromatic multi-carboxylate ligand: structural diversity, luminescence and magnetic properties.

A Series of Heterometallic Three-Dimensional Frameworks Constructed from Imidazole–Dicarboxylate: Structures, Luminescence, and Magnetic Properties

Lanthanide coordination polymers based on multi-donor ligand containing pyridine and phthalate moieties: Structures, luminescence and magnetic properties

Zn-Tb coordination polymer luminescent material based on like-amino acid ligand and preparation method thereof