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Compounds [Fe(tzpy)(3)](BF(4))(2) (1), [Fe(tzpy)(2)(NCS)(2)].S (S = 2CHCl(3) (2), H(2)O (3)), and [Fe(tzpy)(2)(NCSe)(2)] (4) (tzpy is 3-(2-pyridyl)[1,2,3]triazolo[1,5-a]pyridine) have been synthesized and characterized. 1 crystallizes in the monoclinic noncentrosymmetric system, Cc space group, Z = 4, with a = 11.4680(6) A, b = 27.449(2) A, c = 12.4510(8) A, beta = 108.860(5) degrees, V = 3709.0(4) A(3), and T = 293(2) K. The structure consists of mononuclear [Fe(tzpy)(3)](2+) diamagnetic species, which stack via pi-interactions. Disordered BF(4)(-) anions fill the voids generated by complex cations. 2 crystallizes in the triclinic system, P one macro space group, Z = 1, with a = 8.3340(4) A, b = 8.6520(4) A, c = 11.6890(6) A, alpha = 89.113(2) degrees, beta = 81.612(2) degrees, gamma = 77.803(2) degrees, V = 814.90(7) A(3), and T = 293(2) K. The structure consists of mononuclear [Fe(tzpy)(2)(NCS)(2)] neutral species, which interact each other via pi-staking defining layers separated by two-dimensional arrays of CHCl(3). The average Fe-N bond distance, 2.176(3) A, corresponds to what is expected for an iron(II) ion in the high-spin state. Compounds 2-4 undergo thermal-driven spin conversion. The regular solution model was applied to account for the corresponding to thermodynamic parameters. The intermolecular interaction parameter, the characteristic temperature, and the enthalpy and entropy changes associated with the spin conversion were estimated as Gamma = 0.86 (2), 0.89 (3), and 3.79 (4) kJ mol(-1), T(1/2) = 75 (2), 118 (3), and 251 K (4), Delta H = 3.67 (2) and 4.08 (3) kJ mol(-1), and Delta S = 34 (2) and 34.5 (3) J K(-1) mol(-1). Delta H = 8.75 kJ mol(-1) and Delta S = 34.8 J K(-1) mol(-1) were estimated from calorimetric measurements and used as fixed parameters for 4. A quantitative light-induced excited spin state trapping (LIESST) effect was observed for 3, and the high-spin to low-spin relaxation was studied in the temperature region 20-63 K.

The first deprotonations of oxazole and benzoxazole using lithium magnesates are described. The reactions occurred in tetrahydrofuran at room temperature using 1/3 equiv of lithium tributylmagnesate. As 2-lithiooxazole and 2-lithiobenzoxazole, lithium tri(2-oxazolyl)magnesate and lithium tri(2-benzoxazolyl)magnesate very rapidly and completely isomerized to the more stable 2-(isocyano)enolate and 2-(isocyano)phenolate type structures, respectively, a result shown by NMR analysis. The isolation of 2-substituted oxazoles and benzoxazoles in medium to good yields after electrophilic trapping was interpreted in two ways: (1) the equilibration between the open and closed structures is faster than the trapping of the open isomers, and the closed isomers are more reactive than the open ones, or (2) the open isomers react with electrophiles in a intramolecular Passerini type reaction. The nonreactivity of the 2-(isocyano)enolate type structure toward anisaldehyde in the absence of lithium bromide makes the intramolecular Passerini type reaction more plausible.