- Exceptionally high temperature spin crossover in amide-functionalised 2,6-bis(pyrazol-1-yl)pyridine iron(ii) complex revealed by variable temperature Raman spectroscopy and single crystal X-ray diffraction
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The synthesis of a novel amide-functionalised 2,6-bis(pyrazol-1-yl)pyridine-4-carboxamide ligand (bppCONH2) is described. The complex salts [Fe(bppCONH2)2](BF4)2and [Fe(bppCONH2)2](ClO4)2were synthesised and characterised by SQUID magnetometry, differential scanning calorimetry, variable temperature Raman spectroscopy and single crystal X-ray diffraction. DSC measurements of [Fe(bppCONH2)2](BF4)2indicate a spin-crossover (SCO) transition withT↑ at 481 K andT↓ at 461 K, showing a 20 K hysteresis. DSC for the perchlorate salt shows an SCO transition withT↑ at 459 K andT↓ at 445 K with a 14 K hysteresis. For the BF4?salt analysis of low and high-spin state crystal structures at 101, 290 and 500 K, suggest stabilisation of the low spin state due to the formation of 1D hydrogen-bonded cationic chains. Variable temperature Raman studies of the BF4salt support the presence of a high temperature SCO. It is speculated that the presence of hysteresis may be attributed to differences in the inter-molecular hydrogen bonding in the low spin and high spin states.
- Akutsu, Hiroki,Attwood, Max,Blundell, Toby J.,Le Maguere, Pierre,Martin, Lee,Turner, Scott S.
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supporting information
p. 11843 - 11851
(2021/09/06)
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- Rotation in an Enantiospecific Self-Assembled Array of Molecular Raffle Wheels
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Tailored nano-spaces can control enantioselective adsorption and molecular motion. We report on the spontaneous assembly of a dynamic system—a rigid kagome network with each pore occupied by a guest molecule—employing solely 2,6-bis(1H-pyrazol-1-yl)pyridine-4-carboxylic acid on Ag(111). The network cavity snugly hosts the chemically modified guest, bestows enantiomorphic adsorption and allows selective rotational motions. Temperature-dependent scanning tunnelling microscopy studies revealed distinct anchoring orientations of the guest unit switching with a 0.95 eV thermal barrier. H-bonding between the guest and the host transiently stabilises the rotating guest, as the flapper on a raffle wheel. Density functional theory investigations unravel the detailed molecular pirouette of the guest and how the energy landscape is determined by H-bond formation and breakage. The origin of the guest's enantiodirected, dynamic anchoring lies in the specific interplay of the kagome network and the silver surface.
- Meier, Dennis,Adak, Abhishek K.,Knecht, Peter,Reichert, Joachim,Mondal, Sourav,Suryadevara, Nithin,Kuppusamy, Senthil Kumar,Eguchi, Keitaro,Muntwiler, Matthias K.,Allegretti, Francesco,Ruben, Mario,Barth, Johannes V.,Narasimhan, Shobhana,Papageorgiou, Anthoula C.
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supporting information
p. 26932 - 26938
(2021/11/27)
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- Convenient synthesis of tridentate 2,6-di(pyrazol-1-yl)-4-carboxypyridine and tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2,2′- bipyridine ligands
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Citrazinic acid is used as a convenient starting material for both tridentate 2,6-di(pyrazol-1-yl)-pyridine and tetradentate 6,6′-di(pyrazol- 1-yl)-2,2′-bipyridine ligands containing carboxylic groups useful for further anchoring of sensitizer on TiO2 for dye-sensitized solar cells (DSCs). Using 2,6-dichloro-4-carboxypyridine, the synthesis of the terdentate ligands was improved compared to previously used 2,6-dibromo-4- carboxypyridine or 2,6-dichloro-4-ethylcarboxylate pyridine. Controlling the reaction conditions, it is possible to efficiently obtain the monosubstituted 2-chloro-6-pyrazol-1-yl-4-carboxypyridine, a key intermediate for the preparation of tetradentate 6,6′-di(pyrazol-1-yl)-4,4′-dicarboxy-2, 2′-bipyridine ligand.
- Klein, Cédric,Baranoff, Etienne,Gr?tzel, Michael,Nazeeruddin, Md. Khaja
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experimental part
p. 584 - 587
(2011/03/18)
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