Bidentate ligands, mononuclear complexe

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... 

Reactions of the metallocene derivatives of molybdenum with pyrazole lead to the mononuclear complexes of the type 22. Structure 22 shows that it cannot be used as a ligand for the preparation of dinuclear complexes owing to geometric constraints [80JOM( 197)291 83JOM(253)53]. In acetone, an unusual complex 23 is formed [83JOM(253)53]. The bidentate ligand is the product of the reaction of pyrazole and acetone. 

The l,2-bis(dicyclohexylphosphino)ethane (dcpe) bidentate ligand forms the mononuclear, square-planar Ir1 complexes [Ir(cod)(dcpe)lBPh4, [Ir(dcpe)2]BPh4, and JTIrCl(CO)(dcpe)], which have been characterized by IR, ll, and 31 P 1II) NMR spectroscopy. 1 Products of reaction with CO are discussed. 

Bidentate ligand transfer also occurs between di- and mononuclear complexes via donor-acceptor intermediates. Reactions of the cationic complex [Au2(/i-dppm)2]2+ with [AuX2] (X = C1, Br) salts lead to tri- or dinuclear derivatives depending on the molar ratio (1 1 or 1 2) (Scheme 36).2645... 

Mononuclear Complexes with M(n2-S) Ring Systems (Bidentate Ligands)... 

A few complexes with the bidentate pentasulfido ligand are known. The first one reported was the homoleptic and optically active complex [Pt(S5)3]2 (45).133147 The MS5 moiety has a chair conformation in all known mononuclear complexes. It is worth noting that the bite varies strongly and that the largest one is found in [(S3)Fe(MoS4)]2-.132... 

Some mononuclear complexes containing bidentate S2 ligands could be isolated, e.g. the homoleptic [M(S6)2]2 [M = Zn, Cd, Hg (46)]134 and one containing the S, ligand, namely [AuSg] (47) with a ring structure.135... 

Mononuclear Complexes of Bidentate Ligands and Isomeric Species. .. 150... 

The analogous reactions using such bidentate ligands as en or phen lead (also via evolution of H2 and CO) to quantitative formation of the tetracarbonyl derivatives M(CO)4en and M(CO)4phen (M = Cr, Mo, W) (48). Whereas Na2[M(CO)s] and Na M CO),] react with o-phenylene-diamine and water to give mononuclear (H2NC6H4NH2)Cr(CO)s, with m-and p-phenylenediamine, the dinuclear complexes [(OC)5M]H2NC6H4NH2[M(CO)5] are formed, in which two M(CO)5... 

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