Cobalt and Silver Complexes of Terdentate Pyrazine‐Based Amide Ligands and Assembly of Monocobalt Building Blocks through a Silver Connector

• Published in: European Journal of Inorganic Chemistry 2009-03, Vol.2009 (9), p.1162-1171
• Main Authors: Hellyer, Ryan M., Larsen, David S., Brooker, Sally
• Format: Article
• Language: English
• Subjects: Amides; Cobalt; Electrochemistry; Mixed‐metal complexes; Pyrazine; Silver
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.200801187

Two terdentate pyrazine‐based amide ligands have been prepared from methyl pyrazine‐2‐carboxylate and 2‐(aminomethyl)pyridine (HL1M) or 2‐(2‐aminoethyl)pyridine (HL1E) in order to probe the potential of the “spare” nitrogen atom “out the back” of the pyrazine ring to coordinate to a different metal ion and thereby act as a linker between complexes. Two inert cobalt(III) complexes, [CoIII(L1M)2](BF4)·${1 \over 4}$H2O and [CoIII(L1E)2](BF4)·${1 \over 2}$H2O, have been prepared as building blocks and the silver(I) coordination of the ligands also probed, forming {[AgI(HL1M)]BF4}∞ and [AgI2(HL1LE)2](BF4)2. The [CoIII(L1E)2](BF4) building block has been successfully connected to a second such complex by coordination of silver(I) to a “spare” pyrazine nitrogen atom on each complex, resulting in [{CoIII(L1E)2}2AgI](BF4)(NO3)2. All five complexes have been structurally characterised. Mass spectra and cyclic voltammetry studies on “aged” (kept in solution in air for 2 d) samples clearly showed that the cobalt complex of the methylene‐linked ligand was prone to slow ligand oxidation, forming [CoIII(L1Mox)(L1M)](BF4) and [CoIII(L1Mox)2](BF4). Fresh samples of [CoIII(L1M)2](BF4)·${1 \over 4}$H2O and [CoIII(L1E)2](BF4)·${1 \over 2}$H2O undergo a chemically reversible one‐electron reduction in dry acetonitrile, at –0.71 and –0.48 V vs. 0.01 M AgNO3/Ag, respectively, consistent with the methylene‐linked ligand being better able to stabilise the higher oxidation state of cobalt than the ethylene‐linked ligand.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) A two‐step complexation procedure using cobalt(III) to prepare building blocks, then silver(I) to connect them through the “spare” nitrogen atoms “outthe back” of the building block complexes, was successful generating {[CoIII(L1E)2]2[AgI(H2O)]}(BF4)(NO3)2 (structure shown).