Oxygen atoms, coordination polyhedra

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. 

In this compound, each Nd(III) ion is coordinated by six carboxylate and two water oxygen atoms. The Nd—0 distances are in the range of 2.3—2.6 A. The coordination polyhedron around Nd(III) has been described as a square antiprism. 

The Yb(III) ion in [Yb(acac)3 H2O 0.5CeH6] is seven coordinated and the coordination polyhedron for this complex is identical with the polyhedron found for Yb(l) in the unsolvated complex, i.e. a capped trigonal prism. Like the unsolvated complex, the hemibenzene solvated ones are also linked in pairs by hydrogen bonds. The benzene molecule occupies a centre of S3unmetry in the complex. All intermolecular contacts involving benzene carbon atoms and acac carbons or oxygens are above 3.5 A (84). 

The distortion in [Lu(DPM)3(NCeH7)] stems from the fact that the Lu—N bond (2.492 A) is 0.25 A longer than the average Lu—O distance of 2.238 A, while the average chelate bite remains at 2.74 A Hke other /S-diketonate complexes. Such distortion is not uncommon. Even when all seven atoms are oxygens, a long M—O distance contributes to the distortion of the coordination polyhedron as in the case of [Dy(DPM)3(OH2)] (57), where the Dy—O (water) is longer by 0.11 A compared to the Dy—O (chelate) bond. 

Shinn and Eick 212) found that the orthorhombic crystals of La2(C03)3-8H2O contains two distinctive decacoordinated La(III) ions (space group Peon, Z—A, a =8.934, 6 = 9.580, c = 17.00 A). The coordination polyhedron of La is made up of ten oxygen atoms from water molecules, bidentate carbonates and xmidentate carbonates. One fourth of the water molecules in this compound are not bonded to the metal ion but these are situated between layers. The coordination polyhedron is assumed to be distorted Civ The oxygens of the bidentate carbonate ion form longest La—O bond [La(l)—0(bident. CO3) =2.73 A, La(2)— O (bident. C03)=2.74A], whereas the water molecules are nearer to the lan-thanium ion (La—OH2 =2.63 A). 

In the orthorhombic Eu2(mal)3 8H2O (Pnma, Z=4) malonate complex, there are two independent europium ions 195). The coordination polyhedron aroimd one of the Eu(III) ions is a distorted square antiprism with average Eu—O =2.42 A. The other Eu(III) ion is nonacoordinated, with nine oxygen atoms... 

The p3-bridged carbonato complex posseses a pseudo-3-fold molecular symmetry. Each of the Cu atoms is five coordinate with the four nitrogen atoms of tren and one oxygen atom of the carbonate ligand (C). The coordination polyhedron of the Cu atom can be described as almost (TBP), the copper ions being slightly out of the plane (0.15 A) of the three primary amine groups (Fig. 5). 

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