Pyrazolyl Methyls Prescribe the Electronic Properties of Iron(II) Tetra(pyrazolyl)lutidine Chloride Complexes

A series of iron(II) chloride complexes of pentadentate ligands related to α,α,α′,α′-tetra(pyrazolyl)-2,6-lutidine, pz4lut, has been prepared to evaluate whether pyrazolyl substitution has any systematic impact on the electronic properties of the complexes. For this purpose, the new tetrakis(3,4,5-trimethylpyrazolyl)lutidine ligand, pz**4lut, was prepared via a CoCl2-catalyzed rearrangement reaction. The equimolar combination of ligand and FeCl2 in methanol gives the appropriate 1:1 complexes [FeCl(pzR4lut)]Cl that are each isolated in the solid state as a hygroscopic solvate. In solution, the iron(II) complexes have been fully characterized by several spectroscopic methods and cyclic voltammetry. In the solid state, the complexes have been characterized by X-ray diffraction, and, in some cases, by Mössbauer spectroscopy. The Mössbauer studies show that the complexes remain high spin to 4 K and exclude spin-state changes as the cause of the surprising solid-state thermochromic properties of the complexes. Non-intuitive results of spectroscopic and structural studies showed that methyl substitution at the 3- and 5- positions of the pyrazolyl rings reduces the ligand field strength through steric effects whereas methyl substitution at the 4-position of the pyrazolyl rings increases the ligand field strength through inductive effects

Cyclic versus Polymeric Supramolecular Architectures in Metal Complexes of Dinucleating Ligands: Silver(I) Trifluoromethanesulfonate Complexes of the Isomers of Bis(di(1H-pyrazolyl)methyl)-1,1′-biphenyl

In the search for new examples of systems that self-assemble into cyclic metal–organic architectures, the six isomers of X,Y′-bis(di(1H-pyrazolyl)methane)-1,1′-biphenyl, LXY, and their silver(I) trifluoromethanesulfonate complexes were prepared. Five of the six silver complexes gave crystals suitable for single crystal X-ray diffraction, with only the microcrystalline derivative of 2,3′-bis(di(1H-pyrazolyl)methane)-1,1′-biphenyl, L23, proving to be unsuitable for this analysis. Of the structurally characterized silver(I) complexes, that with L22 showed an unusual trans-spanning chelating coordination mode to silver. At the same time the ligand was also bound to a second silver center giving rise to a cyclic supramolecular isomer with a 22-membered metallacycle. The complex of L34 also gave a cyclic dication but with a remarkable 28-membered metallacycle ring. The remaining three derivatives were polymeric. The results of this study underscore that a 120° angle between dipyrazolylmethyl moieties across aromatic spacers will give rise to a cyclic dication but this is not an exclusive requirement for the formation of cyclic architectures. Also, the supramolecular structures of complexes are assembled via a variety of noncovalent interactions involving the di(pyrazolyl)methyl cation most notably by weak hydrogen bonding interactions involving the methine hydrogen and an oxygen atom of the triflate anion

Proton-Coupled Electron Transfer at a [Co-OHx]z Unit in Aqueous Media: Evidence for a Concerted Mechanism

The proton-coupled electron transfer (PCET) chemistry associated with the [Co-OH]2+/[Co-OH2]2+ redox couple for [Co(PY5)(OH2)]2+ (1; PY5 = 2,6-(bis(bis-2-pyridyl)-methoxymethane)-pyridine) and [CoII(pz4depy)(OH2)]2+ (2; pz4depy = 2,6-bis(1,1-di(1H-pyrazol-1-yl)ethyl)pyridine) is reported. It is found that the couple is acutely sensitive to the geometry of the axially ligated group in addition to the electronic-donating/-withdrawing character of the ligand. Interrogation of the electron-transfer kinetics by electrochemical methods also shows for the first time that the interconversion of [CoIII-OH]2+ and [CoII-OH2]2+ proceeds through a concerted pathway in favour of energetically unfavourable stepwise electron-transfer or proton-transfer reaction steps

Cyclic versus Polymeric Supramolecular Architectures in Metal Complexes of Dinucleating Ligands: Silver(I) Trifluoromethanesulfonate Complexes of the Isomers of Bis(di(1H-pyrazolyl)methyl)-1,1′-biphenyl.

In the search for new examples of systems that self-assemble into cyclic metal–organic architectures, the six isomers of <i>X</i>,<i>Y</i>′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>XY</b>, and their silver­(I) trifluoromethanesulfonate complexes were prepared. Five of the six silver complexes gave crystals suitable for single crystal X-ray diffraction, with only the microcrystalline derivative of 2,3′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>23</b>, proving to be unsuitable for this analysis. Of the structurally characterized silver­(I) complexes, that with <b>L</b>_<b>22</b> showed an unusual trans-spanning chelating coordination mode to silver. At the same time the ligand was also bound to a second silver center giving rise to a cyclic supramolecular isomer with a 22-membered metallacycle. The complex of <b>L</b>_<b>34</b> also gave a cyclic dication but with a remarkable 28-membered metallacycle ring. The remaining three derivatives were polymeric. The results of this study underscore that a 120° angle between dipyrazolylmethyl moieties across aromatic spacers will give rise to a cyclic dication but this is not an exclusive requirement for the formation of cyclic architectures. Also, the supramolecular structures of complexes are assembled via a variety of noncovalent interactions involving the di­(pyrazolyl)­methyl cation most notably by weak hydrogen bonding interactions involving the methine hydrogen and an oxygen atom of the triflate anion

Cyclic versus Polymeric Supramolecular Architectures in Metal Complexes of Dinucleating Ligands: Silver(I) Trifluoromethanesulfonate Complexes of the Isomers of Bis(di(1H-pyrazolyl)methyl)-1,1′-biphenyl.

In the search for new examples of systems that self-assemble into cyclic metal–organic architectures, the six isomers of <i>X</i>,<i>Y</i>′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>XY</b>, and their silver­(I) trifluoromethanesulfonate complexes were prepared. Five of the six silver complexes gave crystals suitable for single crystal X-ray diffraction, with only the microcrystalline derivative of 2,3′-bis­(di­(1<i>H</i>-pyrazolyl)­methane)-1,1′-biphenyl, <b>L</b>_<b>23</b>, proving to be unsuitable for this analysis. Of the structurally characterized silver­(I) complexes, that with <b>L</b>_<b>22</b> showed an unusual trans-spanning chelating coordination mode to silver. At the same time the ligand was also bound to a second silver center giving rise to a cyclic supramolecular isomer with a 22-membered metallacycle. The complex of <b>L</b>_<b>34</b> also gave a cyclic dication but with a remarkable 28-membered metallacycle ring. The remaining three derivatives were polymeric. The results of this study underscore that a 120° angle between dipyrazolylmethyl moieties across aromatic spacers will give rise to a cyclic dication but this is not an exclusive requirement for the formation of cyclic architectures. Also, the supramolecular structures of complexes are assembled via a variety of noncovalent interactions involving the di­(pyrazolyl)­methyl cation most notably by weak hydrogen bonding interactions involving the methine hydrogen and an oxygen atom of the triflate anion