Lutetium structure

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

The metallophthalocyanines which have found application as elecfiochromes are mainly the rare earth derivatives, especially lutetium, and second row fiansition metals such as zirconium and molybdenum. Synthesis of these molecules follows the fiaditional routes, e.g. condensation of 1,2-dicyanobenzene with a metal acetate in a high boiling solvent (see Chapter 2). These compounds have structures in which the rare earth element is sandwiched between two phthalocyanine rings, e.g. zirconium bisphthalocyanine (1.92 M = Zr) and lutetium bisphthalocyanine (192 M = Lu), the latter protonated on one of the meso N atoms to balance the charge. 

Mono- and bimetallic lanthanide complexes of the tren-based macrobicyclic Schiff base ligand [L58]3- have been synthesized and structurally characterized (Fig. 15), and their photophysical properties studied (90,91). The bimetallic cryptates only form with the lanthanides from gadolinium to lutetium due to the lanthanide contraction. The triplet energy of the ligand (ca. 16,500 cm-1) is too low to populate the terbium excited state. The aqueous lifetime of the emission from the europium complex is less than 0.5 ms, due in part to the coordination of a solvent molecule in solution. A recent development is the study of d-f heterobimetallic complexes of this ligand (92) the Zn-Ln complexes show improved photophysical properties over the homobinuclear and mononuclear complexes, although only data in acetonitrile have been reported to date. 

Many other organic materials have been deposited by evaporation in vacuo but usually form either a polycrystalline or an amorphous structure. However, Hoshi et al. [424] have made some progress in depositing epitaxial films of lutetium diphthalocyanine on to single crystals of potassium bromide. Here again the temperature of the substrate is critical but only relatively small areas of continuous crystal have been obtained. 

Table 1 lists the lattice parameters of the RxTyPbz plumbides in the order of the periodic table, i.e. from the yttrium to the lutetium compounds. For each compound also the structure type is listed. 

FIGURE 17 Projection of the LuAgPb structure onto the ab plane. Lutetium, silver, and lead atoms are drawn as medium gray, black filled, and open circles, respectively. All atoms lie on mirror planes atz = 0 (thin lines) and z = 1/2 (thick lines). The trigonal prismatic coordination of the two crystallographically independent tin atoms is emphasized. 

A more elegant pathway starts from homoleptic LnR3 (R = CH(SiMe3)2, OC6H3fBu2-2,6) [244]. The molecular structure of (OEP)Lu[CH(SiMe3)2] displays a square pyramidal coordination geometry at lutetium with a terminal Lu-C distance of 2.374(8) A (Fig. 24, Table 19). 

Monocationic Schiff base complexes of gadolinium and lutetium were obtained by employing a highly aminofunctionalized Schiff base ligand as shown in Eq. (15) [170], An X-ray structure analysis of the lutetium complex revealed discrete cations and a distorted square antiprismatic coordination polyhedron. 

The complex has a tetrahedral configuration with Lu-C bonds of 2.42-2.50 A bond length. The bulky 2,6-dimethylphenyl group provides steric limitations in the complex. Ytterbium complex isomorphous with lutetium is also known. The electronic structure and the nature of chemical bonding of the lutetium complex was studied by the INDO method [26]. The MO s of Lu(CgH9)4 ion and the charge distribution are shown in Figs 5.4 and 5.5, respectively. 

All the hexaisothiocynato complexes of praseodymium to lutetium and yttrium are isostructural. The formula of the lanthanum complex is (GtH LafNCS) but its structure is not known. Since lanthanum is large it may adopt six-coordination less readily. Another example of six-coordination is hexakis antipyrene yttrium(III) iodide whose structure is shown in Fig. 5.7. The antipyrene ligand is large and the six oxygen atoms coordinated to yttrium form an octahedron with S6 molecular symmetry. 

The lutetium complex [253] has a structure characterized by a tetrahedral metal core of Lu atoms bound by bridging hydrogens, and tri-A H4 and tetradentate (AIH4 Et20) groups. 

Hart and co-workers have demonstrated that the nine-coordinate cations [M(terpy)3] may be prepared in the absence of coordinating counterions in the cases of europium, samarium, lanthanum, and lutetium 175, 201, 202). The most widely investigated compound in this series is [Eu(terpy)3][C104]3, which has been structurally characterized. The metal is in a nine-coordinate tricapped trigonal-prismatic arrangement (Fig. 25) 201). The distortion from Dj symmetry to is explained by the nonplanarity of the terpy ligands, and is predicted from spectroscopic observations. It is not clear how the above observations may be correlated with a report that... 

---