Tuning the metal-to-metal charge transfer energy of cyano-bridged dinuclear complexes

Abstract

T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4 2 5 8 2 D a l t o n T r a n s . , 2 0 0 4 , 2 5 8 2 -2 5 8 7 The ensuing changes to the MMCT energy have been examined within the framework of Hush theory, and it was found that the free energy change between the redox isomers was the dominant effect in altering the energy of the MMCT transition.

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

“…27 The addition of 2-3 cm 3 of concentrated HClO 4 , followed by slow evaporation, produced the desired compound as crystals suitable for X-ray work. Its elemental analysis agrees with the [Cr(HL 14 , both adjusted to pH 9-10 by the addition of 2 M NaOH. The resulting mixture was heated at 65 • C for 5-6 h and diluted to 500 cm 3 before being loaded onto a Sephadex C-25 cation exchange chromatography column protected from light to avoid decomposition.…”

The Influence of Ligand Substitution at the Electron Donor Center in Molecular Cyano‐Bridged Mixed‐Valent CoIII/FeII and CoIII/RuII Complexes

“…L 14 or L 15 ),2 its geometric isomeric form ( cis or trans ),3 and the donor set of the macrocycle (N 5 or N 3 S 2 )4 all have an effect on the Co III/II redox potential, which in turn is reflected in variations in the MMCT transition energy in accordance with Hush theory. Alternatively, protonation of the terminal cyanide ligands in the hexacyanoferrate(II) moiety9 or the substitution of the metal (Ru for Fe)4 raises the M III/II (M = Fe or Ru) redox potential of the donor and the energy of the MMCT transition accordingly.…”

“…The IR spectra of all [ trans ‐L n Co III (μ‐NC)M II (CN) 3 (bpy) eq,ax ] + ( n = 14 or 15, M = Fe; n = 14, M = Ru) complexes are very similar in the $\tilde {\nu}$ C≡N region, exhibiting three bands around 2060, 2080 and 2100 cm –1 . On the basis of our previous studies,1,2,4 and those on other related cyano‐bridged complexes,13,14 the highest frequency vibration is invariably due to the bridging cyano ligand. The lowest frequency vibration is twice the intensity of the intermediate frequency band and thus is most likely due to the two equivalent (mutually trans ) cyano ligands.…”

“…In recent years we have reported on synthetic strategies leading to molecular , cyano‐bridged, dinuclear1–4 and trinuclear5 d 6 –d 6 heterometallic complexes; this work has been reviewed 6. These Co III /Fe II and Co III /Ru II complexes each display characteristics of a Class II Robin and Day asymmetric, low‐spin d 6 –d 6 mixed‐valent complex,7 exhibiting metal‐to‐metal charge‐transfer (MMCT, Fe II to Co III or Ru II to Co III ) transitions in the visible region, in addition to the transitions characteristic of the two isolated metal‐complex moieties.…”

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

“…The compounds include species with acceptor metal ions in different environments and protonation states. [11,17,19,20] All complexes show Robin and Day Class II character and tuning of the metal-to-metal charge transfer (MMCT) band has been achieved. [21] Scheme 2 summarizes some examples of these compounds.…”