Details
| Original language | English |
|---|---|
| Pages (from-to) | 1523-1531 |
| Number of pages | 9 |
| Journal | Journal of the Chemical Society, Dalton Transactions |
| Issue number | 10 |
| Publication status | Published - 1994 |
Abstract
Cationic complexes with a series of tridentate ligands, L = 4X-substituted 2,6-bis(benzimidazol-2-yl)pyridines, [ML2][ClO4]2 (M = Fe or Ni; X = H, OH or Cl), were isolated and characterized, together with the free pyridines, by elemental analysis, Fourier-transform IR, 1H NMR and UV/VIS spectroscopy. The syntheses were performed via condensation of o-phenylenediamine with 4-substituted pyridine-2,6-dicarboxylic acids. Ligand-field parameters were estimated for the nickel complexes. The [FeL2]2+ species show thermally induced spin-crossover behaviour (1A1→5T2g) which has been investigated in methanol, nitromethane and 20% (v/v) dimethylformamide in MeOH. The behaviour is complicated by two complex dissociation equilibria, for which equilibrium constants have been evaluated. Ligand substitution is reflected in a change of the spin state in solution (μexptl = 2.50, X = H; 4.19, OH; and 4.49 μB, Cl at 295 K, in MeOH) and in the metal-to-ligand charge-transfer band (500-557 nm); when M = Fe and X = H there is a pronounced spin-crossover equilibrium in methanolic solution (μexptl = 1.31-3.45 μB for 213-328 K). A small variation of the magnetic moments when M = Fe and X = OH (μexptl = 3.77-4.73 μB at 220-332 K) might indicate a temperature-variable population of the 5Eg sublevel or variation in hydrogen bonding. The results are compared with quasi-relativistic quantum-mechanical calculations, and the spin-crossover behaviour of the new ligands, L, with substituents X = CHO, NH2, CN, Me, NO2, OH, CONH2, COCl, SH, F, Cl, Br or I has been estimated. The differences in the calculated heats of formation between the high-and low-spin forms of [FeL2]2+ when plotted against Δδ (=1H NMR para increment for substituents X in benzene) show a turning point in the region around X = H and in this region spin-crossover behaviour is observed. Outside this region there is very little or no such behaviour and it is therefore possible to predict the spin-crossover behaviour for other substituents X from the Δδ value.
ASJC Scopus subject areas
- Chemistry(all)
- General Chemistry
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In: Journal of the Chemical Society, Dalton Transactions, No. 10, 1994, p. 1523-1531.
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}
TY - JOUR
T1 - Spin-state equilibria in non-aqueous solution and quantum-mechanical investigations of iron(II) and nickel(II) complexes with 4-substituted 2,6-bis(benzimidazol-2-yl)pyridines
AU - Linert, Wolfgang
AU - Konecny, Michael
AU - Renz, Franz
PY - 1994
Y1 - 1994
N2 - Cationic complexes with a series of tridentate ligands, L = 4X-substituted 2,6-bis(benzimidazol-2-yl)pyridines, [ML2][ClO4]2 (M = Fe or Ni; X = H, OH or Cl), were isolated and characterized, together with the free pyridines, by elemental analysis, Fourier-transform IR, 1H NMR and UV/VIS spectroscopy. The syntheses were performed via condensation of o-phenylenediamine with 4-substituted pyridine-2,6-dicarboxylic acids. Ligand-field parameters were estimated for the nickel complexes. The [FeL2]2+ species show thermally induced spin-crossover behaviour (1A1→5T2g) which has been investigated in methanol, nitromethane and 20% (v/v) dimethylformamide in MeOH. The behaviour is complicated by two complex dissociation equilibria, for which equilibrium constants have been evaluated. Ligand substitution is reflected in a change of the spin state in solution (μexptl = 2.50, X = H; 4.19, OH; and 4.49 μB, Cl at 295 K, in MeOH) and in the metal-to-ligand charge-transfer band (500-557 nm); when M = Fe and X = H there is a pronounced spin-crossover equilibrium in methanolic solution (μexptl = 1.31-3.45 μB for 213-328 K). A small variation of the magnetic moments when M = Fe and X = OH (μexptl = 3.77-4.73 μB at 220-332 K) might indicate a temperature-variable population of the 5Eg sublevel or variation in hydrogen bonding. The results are compared with quasi-relativistic quantum-mechanical calculations, and the spin-crossover behaviour of the new ligands, L, with substituents X = CHO, NH2, CN, Me, NO2, OH, CONH2, COCl, SH, F, Cl, Br or I has been estimated. The differences in the calculated heats of formation between the high-and low-spin forms of [FeL2]2+ when plotted against Δδ (=1H NMR para increment for substituents X in benzene) show a turning point in the region around X = H and in this region spin-crossover behaviour is observed. Outside this region there is very little or no such behaviour and it is therefore possible to predict the spin-crossover behaviour for other substituents X from the Δδ value.
AB - Cationic complexes with a series of tridentate ligands, L = 4X-substituted 2,6-bis(benzimidazol-2-yl)pyridines, [ML2][ClO4]2 (M = Fe or Ni; X = H, OH or Cl), were isolated and characterized, together with the free pyridines, by elemental analysis, Fourier-transform IR, 1H NMR and UV/VIS spectroscopy. The syntheses were performed via condensation of o-phenylenediamine with 4-substituted pyridine-2,6-dicarboxylic acids. Ligand-field parameters were estimated for the nickel complexes. The [FeL2]2+ species show thermally induced spin-crossover behaviour (1A1→5T2g) which has been investigated in methanol, nitromethane and 20% (v/v) dimethylformamide in MeOH. The behaviour is complicated by two complex dissociation equilibria, for which equilibrium constants have been evaluated. Ligand substitution is reflected in a change of the spin state in solution (μexptl = 2.50, X = H; 4.19, OH; and 4.49 μB, Cl at 295 K, in MeOH) and in the metal-to-ligand charge-transfer band (500-557 nm); when M = Fe and X = H there is a pronounced spin-crossover equilibrium in methanolic solution (μexptl = 1.31-3.45 μB for 213-328 K). A small variation of the magnetic moments when M = Fe and X = OH (μexptl = 3.77-4.73 μB at 220-332 K) might indicate a temperature-variable population of the 5Eg sublevel or variation in hydrogen bonding. The results are compared with quasi-relativistic quantum-mechanical calculations, and the spin-crossover behaviour of the new ligands, L, with substituents X = CHO, NH2, CN, Me, NO2, OH, CONH2, COCl, SH, F, Cl, Br or I has been estimated. The differences in the calculated heats of formation between the high-and low-spin forms of [FeL2]2+ when plotted against Δδ (=1H NMR para increment for substituents X in benzene) show a turning point in the region around X = H and in this region spin-crossover behaviour is observed. Outside this region there is very little or no such behaviour and it is therefore possible to predict the spin-crossover behaviour for other substituents X from the Δδ value.
UR - http://www.scopus.com/inward/record.url?scp=37049087370&partnerID=8YFLogxK
U2 - 10.1039/DT9940001523
DO - 10.1039/DT9940001523
M3 - Article
AN - SCOPUS:37049087370
SP - 1523
EP - 1531
JO - Journal of the Chemical Society, Dalton Transactions
JF - Journal of the Chemical Society, Dalton Transactions
SN - 1472-7773
IS - 10
ER -