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

Abstract

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)

Crystal structures ofN-(pyridin-2-ylmethyl)pyrazine-2-carboxamide (monoclinic polymorph) andN-(pyridin-4-ylmethyl)pyrazine-2-carboxamide

“…These include a cobalt(III) (Hellyer et al, 2009), a chromium(III) and four copper(II) complexes (Mohamadou et al, 2012;Khavasi et al, 2011), all of which are mononuclear with the ligand coordinating in a tridentate manner. There are also two polymeric mercury chloride complexes (Khavasi & Sadegh, 2010), a binuclear manganese chloride complex (Khavasi et al, 2009), and a polymeric silver tetrafluoroborate complex (Hellyer et al, 2009), where the ligand coordinates in a bis-monodentate manner. Plus the report of the ligand itself as mentioned above (Sasan et al, 2008).…”

The silver(I) nitrate complex of the ligandN-(pyridin-2-ylmethyl)pyrazine-2-carboxamide: a metal–organic framework (MOF) structure

“…A search of the Cambridge Structural Database (Version 5.38, update February 2017; Groom et al, 2016) for the title ligand (L) gave 15 hits. These include a report of the crystal structure of (L) (Cati & Stoeckli-Evans, 2014), and that of a silver(I) BF 4 À coordination polymer (PORZOM; Hellyer et al, 2009). Here the ligand bridges the silver(I) atoms, coordinating in a bidentate (via the pyridine N atom and the carbonyl O atom) and monodentate (to a pyrazine N atom) fashion, forming zigzag chains along [010].…”

Crystal structure of bis((pyrazin-2-ylmethyl)(pyrazine-2-carbonyl)amido-κ3 N,N′,N′′)copper(II), C20H16CuN10O2

“…The crystal structure of pyrazine-pyridine ligands N-(pyridin-2-ylmethyl)-pyrazine-2-carboxamide and N-(pyridin-4-ylmethyl)pyrazine-2-carboxamide and their transition metal chemistry is well developed [5][6][7]. A reported mononuclear Co complex with pyrazine-pyrazine imide ligand reveals unusual spin-crossover properties [8].…”