New Prussian blue analogues constructed from the [Cr(CN)5NO(3-)] and [Cr(CN)(6)(4-)] anions. A building block approach to high T-N ferrimagnets

The synthesis and characterization of Prussian blue analogues derived from the pentacyanonitrosylchromate(I) and hexacyanochromate (II) ions are discussed. By addition of triflate salts of either Mn-II or Cr-II, occasionally in the presence of a cesium source, four new molecular magnets have been obtained: K0.5Mn[Cr(CN)(5)NO](0.83). 4H(2)O . 1.5MeOH (1), Cs0.5Cr[Cr(CN)(5)NO](0.83). 2H(2)O . 0.6MeOH (2), Cr[Cr(CN)(5)NO](0.5). 2H(2)O . 1.8MeOH (3), and Cr[Cr(CN)(6)](0.5). 3H(2)O (4). The powder XRD patterns for (1) and (4) can be indexed to face-centered cubic unit cells with a = 10.63(4) and 10.37(4) Angstrom, respectively. IR spectra are consistent with the view that the nitfosyl ligands in the pentacyanonitrosylchromate salts are bridging: the v(NO) stretching frequency is ca. 60-110 cm(-1) higher than that of the potassium salt K-3[Cr(CN)(5)NO] The compounds undergo spontaneous fenimagnetic ordering at temperatures of 31, 89, 127, and 238 K, respectively, and they exhibit hysteretic behavior at 4.5 K with coercive fields of 8, 10, 11, and 330 G. For the solids containing chromium(II) centers, saturation magnetization and room temperature susceptibility measurements suggest that these centers are low-spin (S=1). Overall, the [Cr(CN)(5)NO3-] anion affords Prussian blue analogues with lower magnetic ordering temperatures than does the related [Cr(CN)(6)(3-)] anion; this probably reflects the lower symmetry of the pen tacyanonitrosylchrom ate ion and the fact that it contain s fewer unpaired electrons.