Dinuclear Cyano-Bridged Co^III−Fe^II Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity

Abstract

The preparation and characterization of a series of trinuclear mixed-valence cyano-bridged Co(III)-Fe(II)-Co(III) compounds derived from known dinuclear [[L(n)Co(III)(mu-NC)]Fe(II)(CN)(5)](-) complexes (L(n)() = N(5) or N(3)S(2) n-membered pendant amine macrocycle) are presented. All of the new trinuclear complexes were fully characterized spectroscopically (UV-vis, IR, and (13)C NMR). Complexes exhibiting a trans and cis arrangement of the Co-Fe-Co units around the [Fe(CN)(6)](4-) center are described (i.e., cis/trans-[{L(n)Co(III)(mu-NC)](2)Fe(II)(CN)(4)](2+)), and some of their structures are determined by X-ray crystallography. Electrochemical experiments revealed an expected anodic shift of the Fe(III/II) redox potential upon addition of a tripositively charged [Co(III)L(n)] moiety. The Co(III/II) redox potentials do not change greatly from the di- to the trinuclear complex, but rather behave in a fully independent and noncooperative way. In this respect, the energies and extinction coefficients of the MMCT bands agree with the formal existence of two mixed-valence Fe(II)-CN-Co(III) units per molecule. Solvatochromic experiments also indicated that the MMCT band of these compounds behaves as expected for a class II mixed-valence complex. Nevertheless, its extinction coefficient is dramatically increased upon increasing the solvent donor number.

Mechanistic aspects of the chemistry of mononuclear CrIII complexes with pendant-arm macrocyclic ligands and formation of discrete CrIII/FeII and CrIII/FeII/CoIII cyano-bridged mixed valence compounds

“…In the spectrum the two independent signals of the Fe IIto-Cr III and Fe II -to-Co III units are visible (340 nm, 4000 M -1 cm -1 and 490 nm, 500 (sh) M -1 cm -1 ). Despite the fact that these results agree with the lack of changes in the MMCT band position observed on going from di-to tri-or tetranuclear aggregates, 11, 17 and on other recently reported mixed valence complexes, 59 the extinction coefficients have always been found to vary significantly with changes in nuclearity. For the Co III n /Fe II aggregates the addition of each cobalt unit doubles the value of e from the parent species.…”

“…The iron signal shows an additive positive shift that corresponds practically to the expected (150 + 300) mV or (150 + 200) mV (water or hydroxo ligand attached to the Cr III centre) Co III +Cr III contributions, while the signal for the cobalt and chromium units corresponds to the expected di-to trinuclear shift observed for other systems. 17 4 ] 3+ complex. Examination of the UVvis spectra of the complex, particularly at alkaline pH is more revealing.…”

Supramolecular assembly of new heteropolymetalic molecules based on tetraiminodiphenolate macrocycle and hexacyanometallate anions: Magnetostructural and spectroscopic properties

“…These building blocks combined with coordinatively unsaturated systems, like cationic Schiff-bases, produce 1D, 2D or 3D network structures. These assemblies also called Prussian blue analogues gained importance due to the innumerous possibilities to prepare novel extended lattices [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”

Outer‐Sphere Redox Reactions Leading to the Formation of Discrete CoIII/FeII Pyrazine‐Bridged Mixed‐Valence Compounds

“…[13][14][15] We have been involved in the kinetic and mechanistic study of the outer-sphere redox processes between [Fe II -(CN) 6 ] 4-(Scheme 1, Red 2 ) and Co III or Cr III complexes of pentadentate macrocyclic (N) 5 ligands (Scheme 1, Oxd 1 ). [10,[16][17][18] In these studies the careful tuning of both the reactants and reaction conditions has been possible, and the characterization of a large family of molecular di-, triand tetranuclear discrete mixed-valence (electron donor-acceptor) cyano-bridged Co III /Fe II and Cr III /Fe II has been accomplished. The compounds include species with acceptor metal ions in different environments and protonation states.…”