Ligand defined

Figure 6-25. The hole size of a macrocyclic ligand defines the available bonding cavity for a metal ion. As a first step, a best-fit circle is drawn through the donor atoms, and the radius of this circle measured.

Monomeric Cp3Ce(OtBu) could be separated from the reaction mixture by crystallization (Fig. 32, Table 14). The four ligands define a tetrahedron around the cerium atom with an almost linear Ce-O-C angle (176.3(6)°). 

It is not always the case that the dithiolene ligands are arranged in such a symmetrical fashion about the central metal atom. For example, the anionic portion of [AsPh4][Ta(bdt)3] (355) is shown in Fig. 21. The structure demonstrates two dithiolene ligands, defined by atoms S2 and S3, and S4 and S5, are closer to the TP extreme (0 = 16 and 16°, respectively). The third ligand, defined by atoms SI and S6, is twisted toward the OCT extreme (0 = 54°). This asymmetric distortion leads to large distortion parameters as outlined in Table IV (ASMStrans = 11.5° 8 = 11.8°). 

Figure 21. Atom positions and bonds for the anionic portion of [AsPhJ [Tafbdfb] (355). The structure is distorted (ASMS, = 11.5° 8 = 11.8°) with two ligands (defined by S4 andS5, andS2 and S3) nearer TP geometry than the third.

P2i2j2j. Mismatch occurs everywhere despite the rigidity of the 1,5,8-triazooctane ligand defined by... 

S.N. Ho, S.R. Biggar, D.M. Spencer, S.L. Schreiber, G.R. Crabtree, Dimeric ligands define a role for transcriptional activation domains in reinitiation, Nature 1996, 382, 822. 

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