Donor atoms in complexes

Stereochemical control in the choice of donor atoms in complexes of bifunctional bidentate ligands has been studied for complexes of the ligands ppn (204)... 

Owing to the extensive sharing of valence electrons over the metal and donor atoms in complexes of metals in low oxidation states, the zero oxidation state has little, if any, physical significance, and may be used for classifying purposes only. Outstanding examples are the complexes with nitric oxide which may be considered as NO+, NO- or NO, and consequently different oxidation states may be assigned to the same complex. 

Donor atoms in complexes Hard preferred Hard and soft Hard preferred... 

The CK" ion can act either as a monodentate or bidentate ligand. Because of the similarity of electron density at C and N it is not usually possible to decide from X-ray data whether C or N is the donor atom in monodentate complexes, but in those cases where the matter has been established by neutron diffraction C is always found to be the donor atom (as with CO). Very frequently CK acts as a bridging ligand - CN- as in AgCN, and AuCN (both of which are infinite linear chain polymers), and in Prussian-blue type compounds (p. 1094). The same tendency for a coordinated M CN group to form a further donor-aceeptor bond using the lone-pair of electrons on the N atom is illustrated by the mononuclear BF3 complexes... 

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

Various thioether complexes have been synthesized for example, 6-coordination is found in [Ag(18S6)]+ and [Ag(9S3)2]+ but in [Ag(16S6)]+, tetrahedral coordination occurs, with two unused donor atoms in the ligand [59],... 

Diverse series of diphenyl sulphoxide (DPSO) complexes of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(II) and Mg(II) with various large anions have been reported187-191. The complexes have the general formula M(DPSO)6(Anion) where M is the metal cation. The reflection spectra in the visible and near-IR region indicate an octahedral configuration around the metal ion surrounded by the DPSO molecules. Comparison with the spectra of DMSO complexes shows that they have almost identical structures. IR spectra indicate that the oxygen atom in the sulphinyl group is the donor atom in all these complexes. 

In aqueous solutions at pH 7, there is little evidence of complex formation between [MesSnflV)] and Gly. Potentiometric determination of the formation constants for L-Cys, DL-Ala, and L-His with the same cation indicates that L-Cys binds more strongly than other two amino acids (pKi ca. 10,6, or 5, respectively). Equilibrium and spectroscopic studies on L-Cys and its derivatives (S-methyl-cystein (S-Me-Cys), N-Ac-Cys) and the [Et2Sn(IV)] system showed that these ligands coordinate the metal ion via carboxylic O and the thiolic 5 donor atoms in acidic media. In the case of S-Me-Cys, the formation of a protonated complex MLH was also detected, due to the stabilizing effect of additional thioether coordination. ... 

Coordination of pentafluorophenyl gold(III) to the two free N-donor atoms in 1,1 -bis(2-pyridylthio)ferrocene leads to the dinuclear complex [ Au(C6F5)3 2 Fc(Spy)2 ] structurally characterized [149]. 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

Because the interligand C—C coupling of the acyl carbon donor atoms in metalla-/3-diketonate complexes [Eq. (8)] is such a general (though unusual) reaction that occurs very facilely, we have proposed (without proof) a formal description of how this type of coupling might take place (44,50). This formalism has been adopted by others to explain the C—C coupling shown in Eq. (10) (47). 

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