99583-52-5Relevant academic research and scientific papers
Macrobicyclic chromium(III) hexaamine complexes
Comba, Peter,Creaser, Inge I.,Gahan, Lawrence R.,Harrowfield, Jack MacB,Lawrance, Geoffrey A.,Martin, Lisandra L.,Mau, Albert W. H.,Sargeson, Alan M.,Sasse, Wolfgang H. F.,Snow, Michael R.
, p. 384 - 389 (2008/10/08)
The syntheses and characterization of the macrobicyclic hexaamine chromium(III) complexes of diamsar (1,8-diamino-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) and sar (3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane) ligands (1-3) are reported. The complexes were isolated as stable, paramagnetic, and monomeric salts. [Cr(diamsar)]Cl3·H2O crystallized in the space group P21/c, (Z = 4, a = 9.474 (2) A?, b = 13.331 (3) A?, c = 18.221 (5) A?, β = 92.756 (0)°) with the octahedral cation in the C3-let conformation and an average Cr-N distance of 2.070 (3) A?. The complexes are high-spin d3 with room-temperature magnetic moments near the spin-only value of 3.87 μB. The aqueous electrochemistry exhibits a quasi-reversible Cr(III/II) couple below -1 V for each complex and a further irreversible Cr(II/0) reduction near -1.6 V; the chromium(II) complexes are not stable in the coulometric time scales (minutes). The Cr(III) electronic spectra show the expected spin-allowed absorption bands of 4T2g ← 4A2g and 4T1g ← 4A2g origin as well as weak spin-forbidden bands of 2Eg, 2T1g ← 4Ag origin in the visible region. The first of these (4T2g transition) is split by -400 cm-1 and is relatively high in intensity, and the splitting is probably due to the lowered symmetry (D3). Cr(sar)3+ and Cr(diamsar)3+ emit rather strongly at 77 K (φpH2O ≈ 0.02), but give no detectable emission above 273 K. Photodecomposition of Cr(diamsar)3+ is ～104-fold smaller than that of the Cr(en)33+ ion, and possible reasons for this are discussed.
