Single crystals: These were obtained by slow diffusion of diisopropyl ether (or diethyl ether) in a sealed tube containing a solution of [(TTA)FeCl 2 ] in CH 3 CN or [(TTA)Fe(OTf) 2 ] in CH 2 Cl 2 . X-ray analysis. Single crystals of [(TTA)FeCl 2 ] and [(TTA)Fe(OTf) 2 ] were mounted on a Bruker APEX II DUO Kappa-CCD area detector diffractometer equipped with an Oxford Cryosystem liquid N 2 device, using monochromated Mo-Kα radiation (λ = 0.71073 Å). The crystal-detector distance was 38mm. The

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... ll parameters were determined (APEX2 software) (M86-E01078 APEX2 User Manual, Bruker AXS Inc., Madison, USA, 2006) from reflections taken from tree sets of 12 frames, each at 10 s exposure. The structures were solved by Direct methods using the programme SHELXS-97 (G. M. Sheldrick, 1990, "SHELXS-97 Program for Crystal Structure Determination", Acta Crystallogr., A46, 467-473). The refinement and all further calculations were carried out using SHELXL-97 (Sheldrick, G. M. SHELXL97, Program for the refinement of crystal structures; University of Göttingen: Germany, 1997). The H-atoms were included in calculated positions and treated as riding atoms using SHELXL default parameters. The non-H atoms were refined anisotropically, using weighted fullmatrix least-squares on F 2 . A semi-empirical absorption correction was applied using SADABS in APEX2; transmission factors: T min /T max = 0.511/0.697 for [(TTA)FeCl 2 ] and T min /T max = 0.658/0.764 for [(TTA)Fe(OTf) 2 ]. Crystal data for [(TTA)FeCl 2 ]: green crystals, monoclinic, space group P 21/c, a = 8.3621(3) Å, b = 16.1372(7) Å, c = 15.1144(5) Å,  = 122.684(2)°, V = 1716.61(11) Å 3 , D calcd = 1.684 g.cm -3 , Z = 4.