Po/yhedm Vol. 12, No. 19, pp. 233S2341, 1993 Printed in Great Britain 0277-5317/93 $6.00 t.00 0 1993 Pergamon Pm4 Ltd zyxwvu THE SYNTHESIS AND CRYSTAL STRUCTURE OF [C~F(NHdslznC1, DONALD A. HOUSE* Chemistry Department, University of Canterbury, Christchurch, New Zealand zyxwvutsrqponmlkjihg and VICKIE MCKEE* Chemistry Department, Queen’s University, Belfast BT9 5AG, Northern Ireland (Received 6 April 1993 ; accepted 2 June 1993) Abstract-Salts of [CrF(NH,),]X, (X = N03, 1/2ZnCl,) are readily prepared from the reaction between [Cr(NCO)(NH,)J(NO,), and 40% HF. The structure of [CrF(NH,)J[ZnCl,] has been determined by single-crystal X-ray analysis. We are currently interested in the trends observed for Cr-X (X = halide ion) bond lengths in chro- mium(II1) ammine and polyamine complexes. In particular, the observed trends in Cr-Cl bond lengths in [CrCl(RNH2)s]2+ (R = H, Me, Et) have been correlated with acid hydrolysis rates’v2 and there is much current debate on the mechanism of the substitution. 3 Although salts of [CrF(NH,),]‘+ have been known for many years, the synthetic route via fluoride anation of [Cr(NH3),(OH2)](N03),* NH4N034*5 is often poorly described6 and gives variable yields. 7,8 We describe here a simple, high yield preparation of the [CrF(NH3)5]2’ cation and the single-crystal X-ray structural analysis of [CrF(NH3),]ZnC14. EXPERIMENTAL [Cr(NCO)(NH3),](N03)2 was synthesized by the method of Schmidtke and Schiinherr.9,‘o We obtained a 60% yield, with equal weights of urea and Cr(N03)3 * 9H20 (15 g each) in an aluminium foil covered beaker (250 cm’) and an oven tem- perature of 135140°C for 42 h. A green residue was separated from the orange crystals by washing the solid with warm (40°C) 50: 50 ethanol: water (50 cm3). Decant&ion of this wash solution gave *Authors to whom correspondence should be addressed. the crude product, quite suitable for the next step, without further purification. FIuoropentaamminechromium(II1) nitrate, [CrF (NHMNW, The orange [Cr(NCO)(NH,)J(NO,), (5 g, crude) was suspended in 40% HF (20 cm3) in a plastic beaker and the mixture was heated at 80°C (water bath) for ca 10 min, until all effervescence ceased and a clear, wine-red solution was obtained. CAU- TION: Use gloves and an efficient fume hood. HF(g) can cause serious bums on contact with wet skin. Solid NaNO, (3 g) was added and ethanol (20 cm3) added dropwise to the hot solution giving a pink precipitate. The product was collected from the ice cooled solution and recrystallized from water (25 cm3, 80°C) by addition of NaNO, (3 g) and ethanol (25 cm3), as above. Slow cooling to room temperature and then in ice gave 4.2 g (92%) of [CrF(NH,),](NO,), as orange needles, which were washed with ethanol and air dried. Fluoropentaammine chromium(II1) tetrachlorozinc- ate(II), [CrF(NH3),]ZnC1, The nitrate salt (0.2 g) was dissolved in 0.01 M HCl (10 cm3) at room temperature and a solution of ZnC12 (0.5 g) in HCl (5 cm3, 1 M) was added. 2335