Synthesis of isotope enriched (CN3H6)(2)[Fe-57(CN)(5)NO] starting from Fe-57

A high-yield, mmolar-scale synthesis of pure guanidinium nitroprusside, (CN 3H6)(2)[Fe-(57)(CN)(5)NO] (GNP) from iron metal is described. The iron meta l contained pieces of 95.3% Fe-57 together with normal iron so that an isot ope enrichment in Fe-57 of 25% was achieved. Single-crystals of GNP could b e grown in cubic shape and dimensions of about 3x4x4 mm(3) The purity of th e GNP product and the intermediates K-4[Fe-(57)(CN)(6)]. 3H(2)O and Na-2[Fe -(57)-(CN)(5)NO]. 2H(2)O was ascertained by Fe-57 Mossbauer spectroscopy as well as C-13, N-14 and Fe-57 NMR spectroscopy. The Fe-57 NMR chemical shif t for [Fe-(57)(CN)(5)NO](2-) in GNP was detected at +2004.0 ppm [vs Fe(CO)( 5)].