Yttrium coordination number

Many factors affect coordination numbers and coordination polyhedra. It was recognized during 1962-1975 that the chemistry of yttrium and lanthanides is dominated by large coordination numbers. Although the structure of Nd(Br0.3>3 9H2O had been determined as early as 1939 by Helmholtz [6] and shown that the central neodymium ion was bound to nine water molecules in a face-centred trigonal prismatic structure, the commonly held opinion was that the rare earth ions formed six-coordinate, octahedral complexes [7]. This notion was based on the known octahedral, six-coordination known at that time for the most... 

Some 20 years ago, analysis of the coordination numbers for large numbers of coordination compounds of yttrium and the lanthanides indicated that coordination numbers of 8 and 9 are almost equally common, accounting for around 60% of the known structures, and it is unlikely that this distribution has changed significantly. As already pointed out, it is steric factors that determine the coordination number (and geometry) adopted by a lanthanide ion (see e.g. X.-Z. Feng, A.-L. Guo, Y.-T. Xu, X.-F. Li and P.-N. Sun, Polyhedron, 1987, 6, 1041 J. Margalo and A. Pires de Matos, Polyhedron, 1989, 8, 2431). Saturation in the coordination sphere of the metal can come about in one of two ways. 

Higher coordination numbers of 8 -F 1 are adopted in the LT-YF3 type by the trifluorides of the larger ions TP+, bP+ and the smaller rare-earth ions Sm to Ln. The tysonite or LaF3 type with CN 9 + 3 is found for the trifluorides of the larger 4f and the 5f elements (see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry). 

Hydrates of rare earth chlorides also have two different crystal systems a triclinic system for lanthanum, cerium, and praseodymium, as well as a monoclinic system for neodymium to lutetium and yttrium. CeCl3-7H20, as an example of the former system, is different from the above infinite polymer as two cerium atoms are connected by two [i2-bridges to form a dimer. The formula for this dimer is [(H20)7Ce([i2-Cl)2Ce(H20)7]Cl4 as shown in Figure 1.18. Therefore, the coordination number of cerium is nine and the polyhedron takes on a destroyed mono-capped square antiprism configuration. 

The REPO4 structure for the heavier rare earth elements (terbium to lutetium, yttrium, and scandium) belong to the tetragonal system. The coordination number of the central ions is... 

With this arrangement of ligands, each lanthanum is seven coordinate and each sodium is five coordinate. In general, a coordination number of 6 or less is the most common for yttrium, lanthanide alkoxide, and aryloxide complexes (4a, 6). A rare example of an alkoxide complex that contains seven-coordinate yttrium is the cyclic decamer [Y(OC2H4OMe)3]10 (see Section V.C.l Fig. 56). 

Coordination numbers from 3 to 12 have been observed in solid compounds of scandium and yttrium and some specific examples are given in Tables 1 and 2. Some discussion of these properties will be introduced in individual sections. The structural chemistry of scandium(III) has been reviewed with coordination numbers from 3 to 9 being highlighted.37... 

A combination of 89Y and 29Si has been used to observe the fluxionality of some yttrium alkoxides, siloxides, and adducts. Large 89Y chemical shift changes have been observed on changing the coordination number of the yttrium.79... 

Many of the early reports of complexes with bidentate oxygen ligands involved acac complexes and the /3-diketonate and related ligands were discussed in CCC (1987).210 The /3-diketonate complexes of scandium and yttrium and the lanthanides were also discussed in CCC (1987).1 Many reported systems contained adducts formed by the metal /3-diketonate complexes. In solution some of the complexes with bidentate ligands can expand their coordination number to seven by coordination to a suitable donor ligand. A solvent extraction method has been used to show that Sc(acac)3 does not form an adduct with trioctylphosphine oxide but tris(tropolonato)scandium(III) and tris-(ethylmatolato)scandium(III) do coordinate with trioctylphosphine oxide.211... 

A Owing to the systematic removal of oxygen from the lattice, yttrium and barium have different coordination numbers. For yttrium the coordination number is eight, but for barium it is ten. 

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