THE COOPERATIVE SPIN TRANSITION IN [FEXZN1-X(PTZ)(6)](BF4)(2) .1. ELASTIC PROPERTIES - AN ORIENTED SAMPLE ROTATION STUDY BY BRILLOUIN SPECTROSCOPY

The complete set of seven elastic constants of the Fe(II) spincrossove r compound [Fe(ptz)(6)] (BF4)(2) (ptz = 1-propyltetrazole) with crysta l symmetry R3i was measured by Brillouin spectroscopy at 300 K. The me asurement on the plate-like single crystals were performed using an or iented sample rotation technique and the combination of two scattering geometries. For comparison the elastic constants of two isostructural compounds were also measured at 300 K: the analogous perchlorate spin crossover compound [Fe(ptz)(6)] (ClO4)(2) and the zinc complex [Zn(ptz )(6)] (BF4)(2). The knowledge of the elastic constants is necessary fo r the calculation of the elastic interaction between the spincrossover molecules, and this is the first time that the complete set of elasti c constants of a spincrossover compound has been measured directly.