Structure polynuclear lanthanide complexes

Two-Step Approach for the Calculation of Electronic Structure of Polynuclear Lanthanide Complexes... 

Alternatively, hydrolysis of presumably not so soluble lanthanide carboxylate complexes may be possible by carrying out the hydrolysis under hydrothermal conditions. It appears that such conditions (high temperature and high pressure) are particularly conducive to the formation of polynuclear lanthanide complexes, often with unpredictable but nevertheless interesting structure. Under ambient pressure, analogous synthesis generally produces complexes with carboxylate coordination only and without any involvement of hydroxo groups. 

The synthesis, structures, and luminescence properties of polynuclear lanthanide complexes and lanthanide coordination polymers, which are formed from multidentate oxygen and nitrogen-containing Schiff-base ligands, are described in this chapter. 

Two kinds of salen-type Schiff-base ligands, conjugated and flexible, have been used in the synthesis of polynuclear lanthanide complexes and lanthanide coordination polymers Lanthanides Coordination Chemistry, Rare Earth Metal Cluster Complexes. The stoichiometry and structures of these complexes are dependent on the Schiff-base... 

In the first part of this chapter, we have tried to demonstrate that the lanthanide ions can give rise to the formation of a variety of mononuclear supramolecular systems that can be employed for sensing and imaging, and in the formation of novel self-assembly structures that can be further exploited for use in materials-based systems. The next part of this chapter demonstrates that such supramolecular structures can be expanded to polynuclear lanthanide complexes and self-assemblies. 

As mentioned above, design of coordination structures of lanthanide complexes enable precise manipulations of the electron transitions in f orbitals. The geometrical, vibrational, and steric structures of lanthanide complexes are directly linked to luminescence properties such as emission quantum yield, radiative, and nonradiative rate constants. The control of the coordination structures of lanthanide complexes is expected to provide desirable emission properties. Lanthanide polynuclear complexes and coordination polymers have been also studied from the viewpoint of thermostability of complexes. However, the correlation between coordination structures and photophysical properties of lanthanide complexes has been scarcely investigated, and the optimum coordination environment for strong-luminescent properties has been still unclear. Additionally, lanthanide coordination polymer with both high thermostability and strong-luminescent properties has not been previously reported. 

We can see so many lanthanide clusters behave as efficient SMMs in those p -O-fixed complexes. Especially, the energy barrier record (530 K) for polynuclear lanthanide SMMs, held by the p5-0-fixed Dy5 with a square-based pyramid, has not been broken by the end of 2013. Such a structural characteristic should support the isolation of a robust SMM to a great extent, which provides a change to explore new methods for achieving SMMs with high barriers. 

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

Carbonate has proved to be a versatile ligand. Its coordination mode expands from 1 to 6, the last one is visualized when each atom binds two metal ions simultaneously. In recent years, significant progress has been made in the synthesis, structure, and magnetic properties of polynuclear carbonato complexes of transition metal ions. Such studies have also been extended to lanthanides and actinides. The speciation studies of these metal ions in aquatic environments in the presence of carbonate have resulted in significant... 

Reduction of dinitrogen molecule by divalent lanthanide complexes has been a popular subject in coordination and organometallic chemistry of the lanthanide elements. In the course of these studies, a large number of polynuclear lanthanide clusters featuring a core of lanthanide atoms organized around a dinitrogen unit have been obtained and structurally characterized. 

Interestingly, the mathematical treatment leading to Eq. (44) is very general and any paramagnetic system, for which Bleaney s approach requires two independent crystal-field parameters may benefit from its use for testing isostructurality, as demonstrated with the structural analyses of rhombic mononuclear (Terazzi et al., 2006) and polynuclear (Ouali et al., 2004) lanthanide complexes. 

Several studies of the circular dichroism (CD) spectra of aqueous solutions of the lanthanides in the presence of optically active ligands have been made (Katzin, 1970 Misumi et al., 1974 Prados et al., 1974). The CD spectra are highly structured in the region of the intra-4f transitions and are very sensitive to change in the pH of the solution particularly at values for which polynuclear hydroxo complexes could be formed. 

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