Square pyramidal complex

Cu(OMc)4]2 anion is bridged to outer square-pyramidal Cu(L) + cations) and a mononuclear square-pyramidal complex (331c). 

The coordinated macrocycle readily reacts with alkoxide ions to yield products of type (71) (Taylor, Urbach Busch, 1969). In so doing additional flexibility is imparted to the ring which may reduce ring strain and, in part, provide a driving force for the reaction. Thus the coordinated imine carbons appear predisposed to attack by such nucleophiles. Based on this knowledge, elegant template syntheses of three-dimensional derivatives have been performed. The syntheses involved the reaction of [M(taab)]2+ (M = Ni, Cu) with the dialkoxide ions derived from bis(2-hydroxyethyl)sulphide or bis(2-hydroxyethyl)methylamine (Katovic, Taylor Busch, 1969). The products were demonstrated to be monomeric square-pyramidal complexes of type (72). The condensation... 

The Co system is more reactive as well as much more selective than the Ni and Rh catalyst systems (Table XVII). The best systems allow almost 100% conversion with almost 100% yield of c -l,4-hexadiene. The best of the Ni and Rh systems known so far are still far from such amazing selectivity. The tremendous difference between the Ni system and the Co or Fe system must be linked to the difference in the nature of the coordination structures of the complexes, i.e., hexacoordinated (octahedral complexes) in the case of Co and Fe and tetra- or penta-coordinated (square planar or square pyramidal) complexes in the case of Ni. The larger number of coordination sites allows the Co and Fe complex to utilize chelating phosphines which are more effective than monodentate phosphines for controlling the selectivity discussed here. These same ligands are poison for the Ni (and Rh) catalyst system, as shown earlier. 

Dithiolate ligands form stable anionic square pyramidal complexes with the Re03+ core [10]. This has been exploited in the dimer-captosuccinic acid complexes of 186Re and 188Re (vide infra), and in the use of the cyclic anhydride of dimercaptosuccinic acid as a bifunctional chelator for bioconjugate formation. The anhydride, in protected form such as 38, is reacted with antibody or other protein to form an amide or... 

Besides the d° or d10 species, the square pyramidal complexes containing d1 and d2 ions, e.g., VO(OEP) and MoO(OEP) (-+[12] 55), and most of the complexes with lanthanoid ions (56) behave spectrally normal. 

Compared with the huge number of oxo complexes only a few rhenium(V) compound with terminal sulfldo complexes are known. The square-pyramidal complex anion [ReS(S4)2] was first isolated in pure form in 1986 by a reaction of Rc207 with (Ph4P)Br and ammonium polysulfide in acetonitrile and the structure of the Ph4P+ salt has been elucidated. Later, the same complex anion was prepared from starting materials such as [Re2Cl8] , perrhenate, ... 

Very Httle spectral data are available for square pyramidal complexes such as [Fe(C104) (0AsMe3)4]C104 and [Fe(C104) (0PMe3)4]C104 34). These have a single broad band around 10 kK. 

Examples of distorted square-pyramidal complexes are NiBr2(TAS) (81) and NiBr2(PNP) (82) and NiBr2(Ci5H22N4).H20 (83) ). Their spectra (83—85) exhibit a broad band in the 10—20 kK region which contains at least three electronic transitions beneath its envelope. 

The vibrational spectra of oxomolybdenum(V) complexes display an intense band in the range 940 to 1020 cm-1 due to v(Mo—Ot) 5,8° the higher frequencies, corresponding to the shorter molybdenum-oxygen bonds, are found in square pyramidal complexes, in which there is no ligand trans to the oxo group. 

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