THE [FE(ETZ)(6)](BF4)(2) SPIN-CROSSOVER SYSTEM .1. HIGH-SPIN REVERSIBLE-ARROW LOW-SPIN TRANSITION IN 2 LATTICE SITES

The [Fe(etz)(6)](BF4)(2) spin-crossover system (etz = 1-ethyl-1H-tetra zole) crystallizes in space group P (1) over bar, with the following l attice constants at 298 K: a = 10.419(3), b = 15.709(1), c = 18.890(2) Angstrom; alpha = 71.223(9), beta = 77.986(10), and gamma = 84.62(1)de grees; V = 2862.0(9)Angstrom(3) and Z = 3. Two nonequivalent lattice s ites, one without (site A) and one with (site B) inversion symmetry, a re observed. The population of the two sites n(A):n(B) is 2:1. Iron(II ) on site A undergoes a thermal low-spin (LS) reversible arrow high-sp in (HS) transition with T-1/2 = 105 K, whereas that on site B remains in the high-spin state down to cryogenic temperatures. Application of external pressure of up to 1200 bar between 200 and 60 K does not caus e formation of the low-spin state on site B. On site A the high-spin s tate can be populated as a metastable state at 20 K by irradiating the sample with lambda = 514.5 nm; on site B a light-induced population o f the low-spin state can be achieved with lambda = 820 nm.