DYNAMICS AND PHASE-TRANSITIONS IN SPIN-CROSSOVER COMPLEXES - X-RAY STRUCTURES AND BASIC CROSSOVER PHENOMENA IN THE SOLVATE SERIES [FE(3-OET-SALAPA)2](CLO4).S

X-ray structural, Fe-57 Mossbauer, X-band EPR, and magnetic susceptibility data are presented for the series of spin-crossover complexes [Fe(3-OEt-SaIAPA)2] (CL04).S, where the solvate molecule S is either absent or is C6H6, C6H5Cl, C6H5Br, or o-C6H4Cl2 and the ligand 3-OEt-SaIAPA- is the Schiff base condensed from 1 mol of 3-ethoxysalicylaldehyde with N-aminopropylaziridine. [Fe(3-OEt-SalAPA)2](Cl04)-C6H5CI crystallizes in the monoclinic space P2(1)/c which at 296 K has a = 13.834(4) angstrom, b = 17.706(5) angstrom, c = 15.767(3) angstrom, beta = 110.11(2)-degrees, and Z = 4; R = 0.072 and R(w) = 0.075. At 158 K this same C6H5Cl solvate crystallizes in the monoclinic space group P2(1)/a with a = 13.604(12) angstrom, b = 17.475(13) angstrom, c = 15.379(12) angstrom, beta = 109.24(7)-degrees, and Z = 4; R = 0.049 and R(w) = 0.052. In converting from P2(1)/c at 296 K to P2(1)/a at 158 K the cations and anions of [Fe(3-OEt-SaIAPA)2](ClO4).C6H5Cl remain in the same relative positions, however half of the C6H5CI solvate molecules experience a reorientation. [Fe(3-OEt-SalAPA)2](ClO4).C6H5Br makes the same phase transition. At 296 K this C6H5Br solvate crystallizes in the monoclinic space group P2(1)/c with a = 13.860(4) angstrom, b = 17.810(5) angstrom, c = 15.843(3) angstrom, beta = 110.10(2)-degrees, and Z = 4; R = 0.088 and R(w) = 0.090. At 163 K the C6H5Br solvate is found to be in the monoclinic space group P2(1)/a with a = 13.666(4) angstrom, b = 17.554(5) angstrom, c = 15.537(4) angstrom, beta = 109.20(2)-degrees, and Z = 4; R = 0.069 and R(w) = 0.097. [Fe(3-OEt-SalAPA)2] (CI04)-o-C6H4Cl2 crystallizes in the monoclinic space group C2/c, which at 298 K has a = 17.187(8) angstrom, b = 17.807(7) angstrom, c = 13.899(8) angstrom, beta = 119.94(4)-degrees, and Z = 4; R = 0.055 and R = 0.076. From powder XRD data it is found that the nonsolvated [Fe(3-OEt-SaIAPA)2](ClO4) is isostructural to [Fe(3-OMe-SaIAPA)2] (ClO4), which has been reported to crystallize in the triclinic space group P1BAR (Z = 2) at 295 K. In the series there are at least rive different crystallographic phases. Variable-temperature Fe-57 Mossbauer and EPR data show that all complexes in the series are converting from low spin at low temperatures to high spin at high temperatures. Mossbauer spectra run for different preparations of a given complex show that there is a sample history dependence where in some samples the complexes are interconverting between low- and high-spin forms at a rate faster than the Fe-57 Mossbauer time scale and an average signal is seen. For other samples separate signals can be seen for low- and high-spin complexes. From the magnetic susceptibility data it is found that the nonsolvated complex changes most gradually (i.e., large temperature range for complete transformation). The C6H5Cl solvate makes the most abrupt transformation.