Kh. Sugiyarto et Ha. Goodwin, COOPERATIVE SPIN TRANSITIONS IN IRON(II) DERIVATIVES OF 1,2,4-TRIAZOLE, Australian Journal of Chemistry, 47(2), 1994, pp. 263-277
Complexes of stoichiometry Fe(trzH)2(trz)X, where trzH is 1,2,4-triazo
le and X = BF4, ClO4, PF6, have been prepared. All three salts display
, temperature-induced singlet (1A1) reversible quintet (5T2) transitio
ns which are generally discontinuous and associated with a broad hyste
resis loop. The salts are strongly thermochromic, being white above an
d pink-lilac below the transition region. Several samples of each salt
were obtained and the detailed behaviour varied somewhat from one sam
ple to another. For the fluoroborate and perchlorate salts the transit
ion is centred above room temperature while for the hexafluorophosphat
e salt it occurs below room temperature. The perchlorate salt was also
isolated in a form which showed a continuous transition but the natur
e of its electronic properties changed as the sample aged. In one form
of the hexafluorophosphate salt the hysteresis loop spans room temper
ature and it has been possible to characterize both the singlet and th
e quintet state species at that temperature. For all three salts the t
ransition has been characterized by measurement of the temperature dep
endence of the magnetism and Mossbauer and electronic spectra. These m
easurements establish that the complexes all contain an FeN6 coordinat
ion core and this must be achieved through bridging of the triazole un
its.