Mixed ligand trans 2+ complex

Another example demonstrating that technetium compounds are more reactive than the analogous compounds of rhenium is the racemization of the penicillamine complexes of Tc(V) and Re(V). The complexes are six-coordinate in solution with one tridentate and one bidentatc penicillamine (pen) and one oxo ligand. Both mixed ligand anionic complexes l(/9-pcn)(L-pcn)TcO] and [(D-pcn)(T-pen)ReO]" undergo a unimolecular racemization by exchange of carboxylates at the site trans to the oxo ligand ... 

The bidentate phosphine dppe (l,2-bis(diphenylphosphino)ethane) and the aminophosphine eddp (2-aminoethyl-diphenylphosphine) form mixed ligand (N, P, O) complexes such as Co(acac) (edpp)2 and Co(acac)(en)(dppe). A preference for trans N-Co-P and P-Co-P configurations over N-Co-N was found for the bis(edpp) complexes.925... 

Pseudooctahedral coordination of rhenium(III) centers has also been found for mixed-ligand complexes with tertiary phosphines and A-heterocyclic thiols which coordinate as their neutral thione tautomers. A representative example with thiazoline-2-thiol (HSthiaz) has been characterized structurally. The paramagnetic complex [ReCl3(HSthiaz)2(PPh3)] (235) contains the HSthiaz ligands in trans position. ... 

Partial replacement of isocyanide in [Cr(CNR)6](PF6)2 or [CrCl(CNPh)5]PF6 by phosphines PR3, bis(diphenylphosphino)ethane (dppe) or bis(diphenylphosphino)methane (dppm) provides two series of mixed-ligand complexes (Scheme 4).22,23 The complexes [Cr(CNR)4(dppe)](PF6)2, which must be cis, have more complicated spectra in the v(CN) region than the complexes [Cr(CNR)4(PR3)2](PF6)2j which are therefore trans (Table 3). Nitric oxide reacts with [Cr(CNR)6](PF6)2 to give [Cr(NO)(CNR)5](PF6)2 from which many mixed nitrosyl isocyanide complexes of Cr1 and Cr° can be derived (Section 35.4.2.6). 

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