SINGLE-CRYSTAL PULSED-NEUTRON DIFFRACTION STRUCTURE OF THE ANTIFERROMAGNET K-2[FECL5(H2O)] WITH AND WITHOUT APPLIED PRESSURE

The crystal structure of K-2[FeCl5(H2O)] was examined at 15 K and ambient pressure (1 bar = 0.1 MPa) and at 15 K and 0.14 GPa (1.4 kbar) by single-crystal time-of-flight neutron diffraction in order to search for structural changes coincident with the discontinuity in the slope of the spin-flop transition field (H-SF) Versus pressure at 60 MPa. It is found that intramolecular and hydrogen-bond distances and angles are statistically equivalent at the two pressures. However, there are significant changes of as much as 0.049(3)Angstrom in the intramolecular Cl...Cl distances which may affect the Fe-Cl...Cl-Fe superexchange pathways and the discontinuity in H-SF. Dipotassium aquapentachloroferrate(III), M(r) = 329.3, F(000) = 636, orthorhombic, Pnma, Z = 4. At 15K and ambient pressure (0.1 MPa), a = 13.452(5), b = 9.631(2), c = 7.003(2)Angstrom, V = 907.3 (5)Angstrom(3), D-x = 2.41 g cm(-3). At 15 K and 0.14 GPa, a = 13.391(4), b = 9.648(2), c = 6.942(2)Angstrom, V = 896.9(4)Angstrom(3), D-x=2.44 g cm(-3). The a and c axes decrease slightly, whereas the b axis increases slightly, under applied pressure.