Tetrahedrally coordinated sphere

The first spirogallanate [Li(thf)12-crown-4][(PhC=CPhPhC=CPh)2Ga] 281 was isolated from the reaction of 1,4-dilithiotetraphenylbutadiene and GaCl3.198 The gallium center adopts a severely distorted tetrahedral coordination sphere with bond angles ranging from 87.4(2)° to 131.8(2)° (Figure 14). 

The subunit pmoC, colored red in Figure 7.51, is comprised of five TM a-helices that are oriented approximately parallel to the membrane normal and to each other. A single zinc metal ion, in a distorted tetrahedral coordination sphere, has been modeled within the membrane. Conserved amino acid resi-... 

The spectrum of the tetrahedrally coordinated tetraphenyl titanate does not resemble the type IV spectrum, primarily due to enlargement of the 20 ev. absorption peak. The second tetrahedral coordination sphere in this compound, consisting of carbon atoms, may account for this change. An analogous change, also attributed to the second coordination sphere, is observed for the octahedral hexacyanides as compared to the other octahedral compounds. 

Salts of the type [H2L][ZnX(] (X = Cl or Br H2L = HN+(CH2CH2)3N+H) have been prepared and show interesting behaviour on thermal decomposition.191 Heating to 423 K results in elimination of HX to form the ZnX3LH complex, in which the HL molecule now also occupies a position in a deformed tetrahedral coordination sphere. 

The very reactive Rieke cadmium metal was allowed to react under vacuum with benzoquinone in THF. This resulted in the formation of several different paramagnetic species, [Cd(C6H402 )(THF)3]+,C6H402 or [Cd(C6H402 )(THF)3]+ + C6H402 [215]. The tetrahedral coordination sphere for each species consists of three THF molecules and an anion radical that is asymmetrically or symmetrically coordinated to the metal dication. The original apparatus for the generation of the benzoquinone anion radical via electron transfer from cadmium metal was reported... 

In virtually all mononuclear hydride complexes, the H ligand occupies a stereo-chemically active position in other words, it is usually possible to infer H positions by searching for holes in the coordination sphere around the metal atom. Exceptions, however, are found in the structures of HCo(PF3)4 6I), HRh(PPh3)4 62), and HRh(PPh3)3(AsPh3)63). In these complexes, the P and As atoms define almost tetrahedral coordination spheres around the central atom (Fig. 12). Under these circumstances, it is not obvious from X-ray results alone where the H atoms might be located. 

The calix[6]arene 128 with a syn-arrangement of the a-picolyl groups is < 3v symmetric by its constitution. It forms a copper(I) complex [Cul28X] where the tetrahedral coordination sphere of the copper ion is built up by the three picolyl... 

The controlled motion of the ring between the two coordinating sites of the string (schematically represented in Figure 2.33) in Cu(I)-complexed [2]-rotaxane 96 takes place as follows in the initial metallorotaxane the complexed ring stays at the phenanthroline site, because of the stereoelectronic requirements (tetrahedral coordination sphere) of Cu(I). Electrochemical oxidation of Cu(I) to Cu(II) resulted in the movement of the macrocycle to the terpyridine site, since Cu(II) requires higher coordination numbers than Cu(I). This translational motion occurs at a rate of 1.5 x 10-4 s-1 at room temperature... 

Fig. 13 Structure of the first trefoil knot as it exists in its crystals, with the copper(I) ions shown as clear spheres in the tetrahedral coordination sphere of two phenanthroline ligands...

Stirring 1 with excess Li in THF gave rise to the formation of 1,2-dilithiodisilane 3-Li. Alternatively, 3-Li was obtained by reaction of 2-Li with Li (Scheme 1). The X-ray structure determination (Fig. 2) shows the lithium centers in 3-Li to have a different environment whereas Lil is coordinated intramoleculary by two Me2N-groups, Li2 interacts with only one amino function. The tetrahedral coordination sphere of the lithium centers is completed by one and two of THF molecules, respectively. 

The sulfur atoms create bicapped trigonal prismatic arrangement around the Tbl, Tb2, and Tb3 atoms. Monocapped trigonal prism occurs only around the Tb4 atoms. The shortest Tb-S distance is 0.2692 ran. The silicon atom is located in a tetrahedron formed by the S atoms. The shortest Si-S distance is 0.2059 nm. The SI, S3, S6, SIO, and Sll atoms have triangular surroimdings formed by 2Tb and ISi atoms. All other independent sulfur atoms have tetrahedral coordination spheres. Several of them, that is the S2, S4, S5, S7, and S8 atoms are located outside their respective tetrahedra. Each CP of the sulfur atom is formed by 3Tb and ISi atoms. 

The other examples of electrochemically driven ring motions in [2]catenanes are from the class of metal complexed catenanes (i.e., catenates) that have been synthesized and studied in our groups. These compounds, the synthesis of which relies on the ability of copper( I) to gather the bidentate phenanthroline ligand around its tetrahedral coordination sphere, are produced in remarkable yield [9, 28, 57f]. The principle of operation is essentially based on the different stereoelectronic requirements of copper(I) and copper(II). Whereas a coordination number of 4, with a tetrahedral or distorted tetrahedral arrangement is preferred by copper(I),... 

---