Capped trigonal prismatic complex

MFg] , capped trigonal prismatic [MFv], and even square-antiprismatic [MFg] salts can all be isolated. By contrast with the fluorides, aqueous solutions of MCI5 and MBrs (M = Mb, Ta) yield only oxochloro- and oxobromo-complexes, though the application of non-aqueous procedures allows their use as starting materials. 

Examples of monomeric Mo11 complexes are much less common. It has been demonstrated that the [Mo(CN)7]5 ion has a pentagonal bipyramidal structure. Other examples are nitrile (i.e. isocyanide) complexes [Mo(CNR)7]2+, which has a capped trigonal prismatic structure, and the diarsine complex [Mo(diars)2X2]. 

We may also mention that there are numerous isocyanide complexes. Isoleptic species are obtained smoothly by the reaction of RNC with Mo2(02CCH3)4 and isolated as [Mo(RNC)7](PF6)2, and in other ways, some of which allow preparation of analogous W" complexes. Substitution of RCN ligands by phosphines, phen, bipy, and so on, lead to many other complexes, particularly the types [M(RCN) L7 ]2+. The [MoX2(CO)4]2 compounds react with RNC to give Mo(RNC)sX2. The [Mo(CNR)6I]+ and [Mo(CNR)7]2+ ions can be made by reaction of Mo(CO)6 with RNC and I2 or by alkylation and reduction of [Mo(CN)8]4. Both types have capped trigonal prismatic geometry. 

Using bulkier R groups (R = R = CMes, for example) affords more congested diketo-nate complexes that are more tractable Ln(Me3.CO.CH.CO.CMe3)3 [often abbreviated to Ln(dpm)3 or Ln(tmhd)3] are monomers in solution and sublime in vacuo at 100-200 °C in the solid state they are dimers for Ln = La-Dy (CN 7) and monomers for Dy-Lu (CN 6) and have trigonal prismatic coordination. They tend to hydrate readily, forming adducts [e.g. capped trigonal prismatic Ln(dpm)3(H20)]. 

Among seven-coordinate structures, many involve dike-tonate complexes Ln(diket)3 L these generally have either capped-octahedral or capped trigonal prismatic geometry. A considerable number of complexes with neutral donors (e g. thf) of the type LnX3L4 (X = halide, NCS), however, have structures closest to pentagonal bipyramidal, similarly found in the erbium perchlorate complex with 2,6-dimethyl-4-pyrone (Section 3.7.4). 

---