Kh. Sugiyarto et al., STRUCTURAL, MAGNETIC AND MOSSBAUER SPECTRAL STUDIES OF SALTS OF BIS[2,6-BIS(PYRAZOL-3-YL)PYRIDINE]IRON(II) - A SPIN-CROSSOVER SYSTEM, Australian Journal of Chemistry, 47(5), 1994, pp. 869-890
The magnetic and Mossbauer spectral properties of hydrated and anhydro
us complex salts [Fe(bpp)2]X2, where bpp = [2,6-bis(pyrazol-3-yl)pyrid
ine] and X = PF6, BF4, Br, I, NO3, are indicative of a temperature-ind
uced singlet (1A1) reversible quintet (5T2) transition in the complex
cation. The nature of the transition depends on the anion and the degr
ee of hydration. The transition is displaced to lower temperatures in
the anhydrous species and for the hydrated is only partial above room
temperature. The transition in the hydrated hexafluorophosphate salt o
ccurs in two steps, and that in the anhydrous hexafluorophosphate is i
ncomplete, a high residual fraction of quintet state species being ret
ained below the transition temperature. For the anhydrous complexes th
e transition is discontinuous and that in the complex iodide is associ
ated with a narrow thermal hysteresis with transition temperatures T(c
)down = 203 K and T(c)up = 205 K. The structures of [Fe(bpp)2]I2.4H2O
and [Fe(bPP)2][BF4]2.3H2O have been determined at 298 K. Both complex
salts are essentially low spin at this temperature and have an average
Fe-N distance of 1.95 angstrom. The structures reveal in both instanc
es an extended hydrogen-bonded network involving the uncoordinated >NH
groups of the ligands, the anions and lattice water. It is suggested
that it is this bonding which is responsible for the favouring of the
singlet state in the hydrated salts. Bis[2,6-bis(pyrazol-3-yl)pyridine
]iron(II) diiodide tetrahydrate: triclinic, space group P1BAR, a 8.276
(8), b 8.305(7), c 21.941(27) angstrom, alpha 98.11(5), beta 90.08(6),
gamma 90.82(6)-degrees, Z 2. Bis[2,6-bis(pyrazol-3-yl)pyridine]iron(I
I) bis(tetrafluoroborate) trihydrate: monoclinic, space group C2/c, a
31.222(15), b 14.456(3), c 12.907(5) angstrom, beta 99.40(2)-degrees,
Z 8.