rare earth coordination chemistry

In the latter part of the last century, scientists began to focus on the applications of rare earth elements. A book specializing in rare earth coordination chemistry entitled "Coordination Chemistry of Rare Earths" was written by myself in 1997 (in Chinese, Science Press).

Electronic Configuration of Lanthanide Atoms in the Ground State

Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the resulting effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1–5].

Lanthanide Contraction

This results in chemical properties of yttrium that are very similar to those of the lanthanide elements. Due to lanthanide contraction, the radius of the lanthanide ion gradually decreases with increasing atomic number, resulting in regular changes in the properties of the lanthanide elements with increasing atomic number.

Specificity of the Photophysical Properties of Rare Earth Compounds

Spectral Terms
Selection Rules for Atomic Spectra
Lifetime
The Emission Spectra of Rare Earth Compounds

For the first group, emissions originate due to the transition of 4f electrons from the lowest excited states to the ground states, and the emissions are in the visible range. In the case of Figure 1.8c, the ligands of the complex are excited from S0 to S1 and then the energy.

Specificities of Rare Earth Coordination Chemistry

Chemical Bonding of Rare Earth Elements

Some low-valence lanthanide elements can form chemical bonds in organometallic or atomic cluster compounds. On the other hand, only 46 complexes contain RE–S bonds, 7 complexes contain RE–Se bonds, and 10 complexes contain RE–Te bonds.

Coordination Numbers of Rare Earth Complexes

Definition of Coordination Number
Large and Variable Coordination Number
Coordination Number and Effective Ionic Radius

All coordination numbers are between 3 and 12, and the most common coordination number is eight (37%). Therefore, the coordinating bonds of lanthanide complexes are non-directional and the coordination number varies from 3 to 12.

Tetrad Effect of Lanthanide Elements – Changing Gradation Rules in Lanthanide Coordination Chemistry

This explains why the tetrad effect was discovered so much later than the refracted gadolinium effect. The tetrad effect is not only related to the electronic configurations of lanthanide elements, but is also influenced by the surrounding conditions.

Coordination Chemistry of Inorganic Compounds .1 Rare Earth Hydroxides

Rare Earth Halide and Perchlorate Compounds
Rare Earth Cyanide and Thiocyanate Compounds
Rare Earth Carbonate Compounds
Rare Earth Oxalate Compounds
Rare Earth Nitrate Compounds
Rare Earth Phosphate Compounds
Rare Earth Sulfate Compounds

Structure: In rare-earth nitrates, the nitrate groups usually have one of the coordination modes shown in Figure 1.26 when coordinated with the central ions. For the lighter rare earth elements (lanthanum to gadolinium), REPO4 belongs to the monoclinic system.

Outlook

The lighter rare earth elements, lanthanum, cerium, praseodymium or neodymium, preferably form Ln[B5O8(OH)2] or Ln[B8O11(OH)5]. The borate network is shown in stick style and the balls represent the rare earth cations [27].

Introduction

A simple example is the keto-enol tautomerism equilibrium of acetylacetone (HL1) as shown in Figure 2.1. The positions of keto-enol tautomerism equilibria are determined by the solvent polarities and substituents.

Types of β -Diketones Used for Lanthanide Complexes .1 Mono( β -Diketone) Ligands

Bis( β -Diketones) Ligands
Dendritic β -Diketones Ligands

The next category of β-diketones are 4-acyl-1-phenyl-3-methyl-5-pyrazolones (see Figure 2.5) and their analogues 3-phenyl-4-acyl-5-isoxazolones (see Figure 2.6). Therefore, some dendritic β-diketonates (see Figure 2.9) and their corresponding lanthanide complexes have been synthesized [62–65].

Mononuclear Lanthanide Complexes with β -Diketones

Six-Coordinated Lanthanide Complexes with β-Diketones
Seven-Coordinated Lanthanide Complexes with β-Diketones
Eight-Coordinated Lanthanide Complexes with β-Diketones
Nine-Coordinated Lanthanide Complexes with β -Diketones
Ten-Coordinated Lanthanide Complexes with β-Diketones

Polynuclear β -Diketonate Lanthanide Complexes

d–f Polynuclear β-Diketonate Lanthanide Complexes

A comparative study of the optical and electroluminescent properties of EuIII complexes with TTA and 2-(2-pyridyl)azoles: the crystal structure of [Eu(TTA)3(PBO)]', European Journal of Inorganic Chemistry. Zhang et al. have recently developed xerogel-bound Ln-complex (Ln = Er, Nd, Yb, Sm) materials and structurally constructed the NIR-luminescent model complexes Ln(L8)3phen (Ln=Er, Nd, Yb, Sm and phen=1 ) characterized ,10-phenanthroline) (see Figure 2.19 for the molecular structure of the Nd complex) [35]. The replacement of the solvent molecules in Eu(L42)3(C2H5OH)(H2O) with a chelating phosphine oxide leads to an impressive improvement in both the overall quantum yield (from 2 to 30%) and the 5D0 lifetime (from 250 to 1060◦µs ).

72] recently reported two new neodymium metal organic chemical vapor deposition precursors, Nd(L3)3·monoglyme·H2O and Nd(L3)3·diglyme [monoglyme=(dimethoxyethane) and diglyme=(bis( 2-methoxyethyl )ether)] with the crystal structures of the former shown in Figure 2.33. Kotova et al., "The role of the auxiliary ligand N, N-dimethylaminoethanol in luminescence sensitization of EuIII and TbIII in dimericβ-diketonate," Journal of Physical Chemistry A. Kotova et al., "The role of the auxiliary ligand N, N-N- dimethylaminoethanol in luminescence sensitization EuIII and TbIII in dimericβ-diketonates,'' The Journal of Physical Chemistry A.

Summary and Outlook

Reprinted from Journal of Alloys and Compounds,451, S.V. Eliseeva, O.V. Kotova, V.G. Kessler, F. Gumy, J.C.G. Bünzli and N.P. Kuzmina, "Dimeric lanthanide hexafluoroacetylacetonate adductions with 4-cyanopyridine-n-oxide with permission from Elsevier.). They interestingly found that a strong Eu(III) luminescence with a lifetime of 868 µs and a luminescence quantum yield of 38%, regardless of the presence of oxygen, was established by a quantitative energy transfer from visible light radiation up to 460 nm. Liu et al., "Highly efficient sensitized red emission from europium(III) in bimetallic Ir-Eu complexes by transfer of energy 3MLCT,".

Philouze, “Highly efficient blue photoexcitation of europium in a bimetallic Pt-Eu complex”, Chemistry – An Asian Journal. The outlook for poly-β-diketones in supramolecular chemistry has been bright in recent years, even if they are relatively poorly researched and still in their infancy. Current challenges are the synthesis and structural characterization of the β-diketonate lanthanides by modifying their properties not only at the molecular level, but also at the nanometer-dimensional level, such as the supramolecular assemblies in nanomaterials or other underlying levels, enabling smart and controllable functionalities for high-tech applications at the frontiers of chemistry, materials chemistry, chemical biology and medicine.

Acknowledgments

Introduction

The coordination chemistry of rare earth elements (RE) started late compared to that of the transition metals. In fact, interest in the coordination chemistry of rare earths with carboxylic acids and polyaminopolycarboxylic acids has increased with the development of the rare earth chemistry since the very beginning, when citrate and polyaminopolycarboxylates were used as the initial eluents for separating rare earths using cations. exchange resins [1, 2]. So far, much work has been done on the solution chemistry of rare earth amino acid complexes, and about 100 complexes obtained at pH 1-4 or pH 6-7 have been structurally characterized by single crystal X-ray analysis [9, 10].

This particular aspect of rare earth-amino acid coordination will be discussed in Chapter 4. This chapter will cover the synthetic, structural and solution chemistry of rare earth complexes with carboxylic acids, polyaminopolycarboxylic acids and amino acids, with an emphasis on - sis on their structural chemistry. Since the carboxylate groups play key roles in the metal-ligand coordination bond in these complexes, we will begin the chapter with the coordination chemistry of rare earth-carboxylic acid complexes, followed by rare earth-polyaminopolycarboxylic acid and rare earth-amino . acid coordination chemistry.

Rare Earth Complexes with Carboxylic Acids

Preparation of Rare Earth Complexes with Carboxylic Acids

Synthesis Starting with Rare Earth Oxides 1
Synthesis Starting with Rare Earth Salts
Hydro(solvo)thermal Synthesis
Gel Synthesis – Crystal Growth in Gel

Structural Chemistry of Rare Earth Complexes with Carboxylic Acids

Coordination Modes and Types of Connectivity
Control of the Polymerization of the Complexes
Structures of the Rare Earth Complexes with Monocarboxylic Acids
Structures of the Rare Earth Complexes with Polycarboxylic Acids
Structures of Rare Earth Complexes with Carboxylic Acids Bearing Other Donor Atoms
Structures of d–f Heteronuclear Complexes with Carboxylic Acids

Solution Chemistry of Rare Earth Complexes with Carboxylic Acids

Each of the two RE(III) ions is coordinated by one unidentified pivalate and three unidentified pivalic acid molecules with CN=8 [31]. The carboxylate/RE ratio in the complex is 3, but the structure of [ErL3L3] is very similar to [LaL6]3− (HL=acetic acid). Each of the RE(III) ions is further coordinated by two chelating (η2) carboxylates and four terminal waters, CN=9 (Figure 3.7b).

Each of the two terminal Y(III) is then coordinated by two chelating (η2) ligands and two water, and each of the two internal Y(III) is coordinated by one chelating (η2) ligand and two water, CN= 8 ( Figure 3.10a). Three of the four types of triply bridging polymeric structures are found with the RE(III) complexes with acetates. Each of the Sc(III) ions is thus coordinated by six oxygen atoms from six different acetates, CN=6 [58].

Rare Earth Complexes with Polyaminopolycarboxylic Acids

Preparation of Rare Earth Complexes with Polyaminopolycarboxylic Acids
Structural Chemistry of Rare Earth Complexes with Polyaminopolycarboxylic Acids

Structures of Rare Earth Complexes with EDTA, DTPA, and TTHA

Solution Chemistry of Rare Earth Complexes with Polyaminopolycarboxylic Acids

There have been several interpretations of these trends, and the most widely accepted one is the change in the number of hydration water molecules [98, 99]. The structures and the coordination modes of the complexes appear to be dominated by two factors, namely the size of the RE(III) and the property of the counter cation [104]. The dinuclear complex, [Gd2(BT-DO3A)2], is centrosymmetric, and only half of the molecule is unique.

For IDA, NTA, EDTA and DTPA, the stability of the complexes (logβ1) changes linearly with pKa of the ligands due to the ionic nature of the RE(III)–O and RE(III)–N interactions, similar to the RE (III) complexes of carboxylic acids (Section 3.2.3). This is believed to be a result of a change in the chelating ability of the ligands. The trends are believed to reflect changes in the number of hydration water molecules [98, 99].

Rare Earth Complexes with Amino Acids

Preparation of Rare Earth Complexes with Amino Acids
Structural Chemistry of Rare Earth Complexes with Amino Acids

Structures of 1 : 3 (RE : L) Complexes
Structures of 1 : 2(RE : L) Complexes
Structures of 1 : 1 and 2 : 3(RE : L) Complexes

Solution Chemistry of Rare Earth Complexes with Amino Acids

Thus, the coordination numbers of the RE(III) in the three structures are ten, nine, and eight. Although most RE(III)-carboxylic acid dimeric complexes are centrosymmetric, with amino acids as ligands, similarly structured complexes are only available when the racemic form of the ligands is used for synthesis [127]. Each of the metal centers is surrounded by four oxygen atoms, one from each ligand.

Mononuclear species with 1 : 1 and 1 : 2 stoichiometry (RE : L) have been reported for all amino acids. Most studies show that they form both [RE(L)]1+ and [RE(L)2]1− species in solution with logβ1 and logβ2. This is a sign of similar chelation modes between RE–amino acid complexes and the β- or γ-carboxy oxygen in Asp or Glu may not be involved in the chelation of the α-carboxy oxygen and amino nitrogen by RE(III) ).

Summary and Outlook

1999) Crystal structure of isomorphic tetraaquabis(2,6-dihydroxy-benzoato-O)(2,6-dihydroxy-benzoato-O,O)terbium(III) and holmium(III) dihydrate complexes. Journal of Coordination Chemistry . 2006) Crystal structures and magnetic and luminescent properties of a series of homodinuclear lanthanide complexes with 4-cyanobenzoic ligand. 2002) Synthesis, structure and luminescence properties of ternary and quaternary complexes of europium with furoic acid. Journal of Molecular Structure. 1993) Synthesis, characterization and crystal structures of rare earth complexes with m-methylbenzoic acid.Huaxue Xuebao.

2005) Lanthanide complexes for second-order nonlinear optics: evidence for the direct contribution of electrons to quadratic hyperpolarizability. Journal of the American Chemical Society. 1970) Rare earth metal ions as probes of calcium ion binding sites in proteins: neodunium(III) acceleration of trypsinogen activation. Journal of Biological Chemistry. 1979) Affinity of lanthanoid(III) ions for nitrogen donor ligands in aqueous solution. Journal of the Chemical Society, Dalton Transactions.

Based Rare Earth Complexes

Introduction
Rare Earth Complexes with Amide Type Ligands

Rare Earth Complexes with Aliphatic Amide Type Ligands
Rare Earth Complexes with Silyl Amide Type Ligands

Rare Earth Complexes with N-Heterocyclic Type Ligands

Rare Earth Complexes with Pyridine Type Ligands
Rare Earth Complexes with Imidazole Type Ligands
Rare Earth Complexes with Porphyrin Type Ligands
Rare Earth Complexes with Phthalocyanine Type Ligands

Rare Earth Complexes with Schiff Base Type Ligands

Rare Earth Complexes with Imine Type Ligands
Rare Earth Complexes with H 2 Salen (30) Type Ligands

In addition, the small bite angle of the N–CH2–N group promotes a high coordination number around the rare earth metal. Due to the relatively greater steric hindrance, the rare-earth metal complexes with silylamide-type ligands often show low coordination numbers. The first preparation of the simple rare earth silylamide complexes Ln(4)3 was reported by Bradley et al.

The number of 12 was determined by the rare earth salts used for the preparation of the corresponding complexes. It is also useful to stabilize their rare earth complexes by prohibiting the coordination of the solvent molecule. The replacement of some or all of the hydrogen atom(s) of the porphin ring leads to the formation of so-called porprin derivatives, porphyrin (Por) (Figure 4.22).

Furthermore, it is well known that the development of rare earth coordination chemistry originates from the separation and extraction of rare earth ions. In this case, only the oxygen atom of H2salen is coordinated with the rare earth metal without the participation of nitrogen atoms from its C=N groups.