Group 17 elements ligands, halide ions

In the reaction of group 13 element halides with metal carbonyl dianions, the analysis is more complex than observed for the reactions with metal monoanions. Upon addition of metal dianions to EX3 or REX3, either one or two halide ions may be eliminated. When only one halide ion is eliminated per added metal dianion, the complexes may still be viewed as E3+ derivatives (Equations (33)-(36)).19 This may be controlled to some extent by the stoichiometry of the reaction. Comparison of Equations (33)19 and (34)19 shows that the electron demand at the main group element can be satisfied by coordination either to an electron-rich metal center 26 or formation of a halide bridge 27. Ligand-stabilized forms may also be prepared in this fashion (Equation (36)).19... 

It did not prove possible to synthesize a substituent-free Ga complex with formula Cp (CO)2Fe Fe(CO)4 Ga (Scheme 13).43 Addition of bipy to 30 resulted in halide elimation, but the main group element in the product 31 was coordinated by the bipy ligand. Upon addition of dppe, however, substitution of the carbonyl ligands occurred instead along with halide ion elimination to produce the substituent-free Ga complex 32. It has a linear coordination environment (Fe-Ga-Fe angle = 176.01(4)°), and the Ga-Fe bond distances are much shorter than in those related adducts where donor ligands are also bound to the Ga atom.43 The authors attributed the non-observation of the carbonyl derivative to a need for an electron-rich metal center to stabilize the Fe-Ga bond via 7r-backdonation. 

The Group 12 atoms are on the edge of the transition metal part of the periodic table, and because these elements don t form any compounds in which the d-orbital shell is not full, they re not considered a transition metal. They do, however, resemble the d-group elements in their ability to form complexes with amines, halide ions, ammonia, and even cyanide. In the case of bonding with cyanide, CN, the possibility for dre bonding between the metals and the ligand is much lower when compared with the rest of the transition metals. 

Those in which the metal atoms are in somewhat higher oxidation states (+2 to +4) and the ligands are typically halide, sulfide, or oxide ions and some others of the same ilk as those in mononuclear Werner complexes. Clusters of this type are most common among the early transition elements, groups 5-7. 

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