Effect of N4-substituent choice on spin crossover in dinuclear iron(II) complexes of bis-terdentate 1,2,4-triazole-based ligands.
Seven new dinuclear iron(II) complexes of the general formula [Fe(II)2(PMRT)2](BF4)4·solvent, where PMRT is a 4-substituted-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole, have been prepared in order to investigate the substituent effect on the spin crossover event. Variable temperature magnetic susceptibility and (57)Fe Mössbauer spectroscopy studies show that two of the complexes, [Fe(II)2(PMPT)2](BF4)4·H2O (N(4) substituent is pyrrolyl) and [Fe(II)2(PM(Ph)AT)2](BF4)4 (N(4) is N,N-diphenylamine), are stabilized in the [HS-HS] state between 300 and 2 K with weak antiferromagnetic interactions between the iron(II) centers. Five of the complexes showed gradual half spin crossover, from [HS-HS] to [HS-LS], with the following T(1/2) (K) values: 234 for [Fe(II)2(PMibT)2](BF4)4·3H2O (N(4) is isobutyl), 147 for [Fe(II)2(PMBzT)2](BF4)4 (N(4) is benzyl), 133 for [Fe(II)2(PM(CF3)PhT)2](BF4)4·DMF·H2O (N(4) is 3,5-bis(trifluoromethyl)phenyl), 187 for [Fe(II)2(PMPhT)2](BF4)4 (N(4) is phenyl), and 224 for [Fe(II)2(PMC16T)2](BF4)4 (N(4) is hexadecyl). Structure determinations carried out for three complexes, [Fe(II)2(PMPT)2](BF4)4·4DMF, [Fe(II)2(PMBzT)2](BF4)4·CH3CN, and [Fe(II)2(PM(Ph)AT)2](BF4)4·solvent, revealed that in all three complexes both iron(II) centers are stabilized in the high spin state at 90 K. A general and reliable 4-step route to PMRT ligands is also detailed.
Department of Chemistry and the MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Otago , P.O. Box 56, Dunedin 9054, New Zealand.
Jonathan A
JA
Kitchen
Juan
J
Olguín
Rafal
R
Kulmaczewski
Nicholas G
NG
White
Victoria A
VA
Milway
Guy N L
GN
Jameson
Jeffery L
JL
Tallon
Sally
S
Brooker