Clusters lanthanides

Monomeric lanthanide alkoxides are generally imstable, unless they are stabilized by bulky substituents (20). Spassky and co-workers have shown that clustered lanthanide alkoxides Ln5(/i-0)(0-i-C3H7)i3 can initiate ROP of DL-lactide in dichloromethane (56). The following order of reactivity (La Sm Yb) has been reported. Low polydispersity is seen even at high conversion and long reaction time, except in case of lanthane because of exceedingly high reactivity and low selectivity. ROP of -CL is more complex, and transesterification reactions can occur before the monomer conversion is complete. 

Unlike the di-f dihalides, such compounds differ little in energy from both the equivalent quantity of metal and trihalide, and from other combinations with a similar distribution of metal-metal and metal-halide bonding. So the reduced halide chemistry of the five elements shows considerable variety, and thermodynamics is ill-equipped to account for it. All four elements form di-iodides with strong metal-metal interaction, Prl2 occurring in five different crystalline forms. Lanthanum yields Lai, and for La, Ce and Pr there are hahdes M2X5 where X=Br or I. The rich variety of the chemistry of these tri-f compounds is greatly increased by the incorporahon of other elements that occupy interstitial positions in the lanthanide metal clusters [3 b, 21, 22]. 

One of the distinctive aspects of transition-metal and lanthanide chemistry is cluster formation via metal-metal bonding that is characteristic of many of these elements in low oxidation states [1]. The unique structural, chemical, and... 

Kornienko A, Emge TJ, Kumar GA, Riman RE, Brennan JG (2005) Lanthanide clusters with internal Ln ions Highly emissive molecules with sohd-state cores. J Am Chem Soc 127 3501-3505... 

Kornienko AY, Emge TJ, Brennan JG (2001) Chalcogen-rich lanthanide clusters Cluster reactivity and the influence of andllary ligands on structure. J Am Chem Soc 123 11933-... 

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. 

A deeper analysis [80] on this Cu - Dy chain showed that NN and NNN interactions are efficient above Tc and that inter spin-ladder ferromagnetic interaction is observed in this family of compounds [79-82]. Attempts were made to use the 3d tectons with other lanthanide precursors, such as hexanuclear lanthanide clusters. Regular chains were obtained with Dy-Cu ferromagnetic interaction but their close packing prevents observation of SCM behaviour [83]. 

Controllable Assembly, Structures, and Properties of Lanthanide-Transition Metal-Amino Acid Clusters... 

Abstract Amino acids are the basic building blocks in the chemistry of life. This chapter describes the controllable assembly, structures and properties of lathanide(III)-transition metal-amino acid clusters developed recently by our group. The effects on the assembly of several factors of influence, such as presence of a secondary ligand, lanthanides, crystallization conditions, the ratio of metal ions to amino acids, and transition metal ions have been expounded. The dynamic balance of metalloligands and the substitution of weak coordination bonds account for the occurrence of diverse structures in this series of compounds. 

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. 

For mixed lanthanide-transition metal clusters, Yukawa et al. have synthesized an octahedral [SmNi6] cluster by the reaction of Sm3+ and [Ni(pro)2] in nonaque-ous medium [66-68]. The six [Ni(pro)2] ligands use 12 carboxylate oxygen atoms to coordinate to the Sm3+ ion, which is located at the center of an octahedral cage formed by six nickel atoms. The coordination polyhedron of the central Sm3+ ion may be best described as an icosahedron. The [SmNir, core is stable in solution but the crystal is unstable in air. The cyclic voltammogram shows one reduction step from Sm3+ to Sm2+ and six oxidation steps due to the Ni2+ ions. Later, similar [LaNis] and CjdNif> clusters were also prepared. 

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