trans-K3[TcO2(CN)4]

The structure of the title compound, tripotassium trans-tetracyanidodioxidotechnetate(V), is isotypic with its Re analogue. The [TcO2(CN)4]3− trans-tetracyanidodioxidotechnetate anion has a slightly distorted octahedral configuration. The Tc atom is located on a center of inversion and is bound to two O atoms in axial and to four cyanide ligands in equatorial positions. The Tc—O distance is consistent with a double-bond character. The two potassium cations, one located on a center of inversion and one in a general position, reside in octahedral or tetrahedral environments, respectively. K⋯O and K⋯N interactions occur in the 2.7877 (19)–2.8598 (15) Å range.


Related literature
The isotypic rhenate(V) analogue was reported by Fenn et al. (1971) (neutron study) and Murmann & Schlemper (1971) (X-ray study). For further information on dioxidotetracyanido anions of Tc and Re, see : Fackler et al. (1985); Kastner et al. (1982Kastner et al. ( , 1984; Kremer et al. (1997). Luminescence properties of Tc complexes were reported by Del Negro et al. (2005Negro et al. ( , 2006. For further information on hydroxidooxidotetracyanido or aquaoxidotetracyanido anions of Tc and Re, see: Baldas et al. (1990); Purcell et al. (1989Purcell et al. ( , 1990. For general reviews on technetium structures, see: Bandoli et al. (2001Bandoli et al. ( , 2006; Bartholoma et al. (2010); Tisato et al. (1994). Synthetic details were given by Trop et al. (1980). For a description of the Cambridge Structural Database, see: Allen (2002 Table 1 Selected geometric parameters (Å , ).  (Bruker, 2006); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL and DIAMOND (Brandenburg, 2010); software used to prepare material for publication: SHELXTL. Tc is the most significant long-lived product of uranium fission. In addition to a long half-life (2.13x10 5 yrs), it is readily water soluble, making it extremely mobile in the environment. This, coupled with its ability to form anionic species, causes major concern when considering long-term disposal of high-level radioactive waste. Thus, it is imperative to provide methods for chemical detection of 99 Tc. Under normal environmental conditions, 99 Tc composition is dominated by the pertechnetate anion (TcO 4 -) which lacks a characteristic spectral signature. This prevents its rapid, sensitive and economic in situ detection. In order to address this problem, our research is focused on designing a suitable sensor for the detection of TcO 4 -. The ultimate aim is to chemically convert the pertechnetate anion to an organic-ligated species that will have a readily characterizable spectral signature. As a first step to address this problem, our group has been able to identify several technetium complexes with long-lived excited states. Thus, the luminescence properties of technetium(V)-dioxidotetrapyridyl and technetium(II)-tris(1,2-bis(dimethylphosphino)ethane) were reported by Del Negro et al. (2005,2006). However, the significant dearth of Tc structures in general (Bandoli et al., 2001(Bandoli et al., , 2006Bartholoma et al., 2010;Tisato et al., 1994) has resulted in a substantial knowledge gap in the structures and bonding of technetium complexes, thereby preventing the correlation of the electronic properties with structural parameters. As a representative comparison, the Cambridge Structural Database (CSD, version 5.31; Allen, 2002) currently contains 21 dioxidotechnetium complexes compared to 141 structures reported for dioxidorhenium and dioxidomanganese complexes. In an attempt to bridge this gap, we are focusing on the structural characterization of a series of dioxidotechnetium(V) complexes. Herein, we report the structure of K 3 [TcO 2 (CN) 4 ], (I), a tetracyanidodioxidotechnetium(V) salt.
The unit cell of (I) is comprised of three K + cations and one discrete [TcO 2 (CN) 4 ] 3anion. The configuration of the anion is shown in Fig. 1. The Tc atom (located on an inversion center) resides in an octahedral environment defined by two oxido and four cyanido ligands. The trans basal C-Tc-C angles are linear resulting in a square planar arrangement of the tetracyanido groups about the Tc center.

Experimental
(I) is prepared from [TcO 2 (py) 4 ]Cl (py = pyridyl) by the method of Trop et al. (1980). Complete cyanide substitution of the pyridyl groups of the starting material is achieved by adding an excess of alkaline cyanide.
In a typical preparation, 0.5 g of [TcO 2 (py) 4 ]Cl was dissolved in a minimum amount of methanol. Addition of 50 ml of 1.2M KCN in 5:1 (v/v) methanol/water to the above resulted in an immediate green solution which turned yellow in approx. 5 minutes. This was followed by a gradual appearance of a fine yellow precipitate. The mixture was stirred on a hot plate set to low heat for an additional hour to ensure complete conversion. The supernatant was drawn off and the yellow precipitate was washed with diethyl ether. The yellow precipitate was dissolved in a minimal amount of water, followed by slow diffusion of methanol vapors, to yield crystals of (I) suitable for X-ray diffraction.
CAUTION! All syntheses and characterizations were performed with 99 Tc, which is a β-emitting isotope with a half-life of 2.13x10 5 years. The handling of small quantities (generally <100 milligrams) of this material does not pose a serious health hazard since common laboratory materials provide adequate shielding. However, radiation safety procedures must be used to prevent contamination! Figures   Fig. 1. : The structural moieties of (I) with the atomic labelling scheme and 50% probability ellipsoids. [Symmetry code: (i) -x + 1, -y + 1, -z + 1].

Special details
Experimental. A suitable crystal was mounted on a glass fiber and immediately transferred to the goniostat bathed in a cold stream.
CAUTION!All syntheses and characterizations were performed with 99 Tc, which is a β-emitting isotope with a half-life of 2.13x10 5 years. The handling of small quantities (generally <100 milligrams) of this material does not pose a serious health hazard since common laboratory materials provide adequate shielding. However, radiation safety procedures must be used to prevent contamination.