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Two square-pyramidal chromium(V)–nitride complexes:
bis(2-methylquinolin-8-olato)nitridochromium(V) and
nitridobis(2-sulfidopyridine N-oxide)chromium(V)

Torben Birk, Henning Osholm Sørensen and Jesper Bendix
Copyright International Union of Crystallography Author(s) of this paper may load this reprint on their own web site provided that this cover page is retained. Republication of this article or itsstorage in electronic databases or the like is not permitted without prior permission in writing from the IUCr.
Acta Cryst. (2005). C61, m231–m233
Birk et al. ¯ [Cr(C10H8NO)2(N)] and [Cr(C5H4NOS)2(N)] ylacetonate) (Niemann et al., 1996), but the method fails for systems where the auxiliary ligand sphere is labile. The lack of general methods of synthesis has been the primary obstacle in the development of the nitride chemistry for the ®rst-row transition metals. Recently, we have found (Birk & Bendix, 2003; Bendix, 2003) that N-atom transfer from the easily accessible [Mn(salen)(N)] to [CrCl3(THF)3] followed by ligand metathesis is a very general synthetic route to chro- mium(V)± nitride complexes. By this method, the uncharged complexes [Cr(quinald)2(N)] (quinald is 2-methylquinolin-8- olate), (I), and [Cr(tpno)2(N)] (tpno is 2-sul®dopyridine Torben Birk,a Henning Osholm Sùrensenb³ and JesperBendixa* aInorganic Chemistry, Department of Chemistry, University of Copenhagen,Universitetsparken 5, DK-2100 Copenhagen, Denmark, and bCentre for Crystallographic Studies, Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark Two new chromium(V)±nitride complexes with a coordination sphere completed by bidentate ligands have been synthesized Complexes (I) and (II) are both ®ve-coordinate, with and structurally characterized. Bis(2-methylquinolin-8-olato)- approximately square-pyramidal coordination around the CrV nitridochromium(V), [Cr(C10H8NO)2(N)], has the coordina- atom and with the metal displaced ca 0.5 AÊ out of the plane of tion sphere completed by an equatorial N2O2 set of ligators.
the basal ligators towards the nitride ligand (Figs. 1 and 2, and The compound crystallizes with the ®ve-coordinate complexes Table 1). Complex (I) crystallizes with the CrV N bond on a at sites with twofold rotational symmetry and all CrÐN bond crystallographic twofold axis, making the basal ligators directions aligned with the crystallographic b axis. Nitri- equivalent in pairs. Interestingly, even though complex (II) has dobis(2-sul®dopyridine N-oxide)chromium(V), [Cr(C5H4N- the possibility for a molecular mirror plane (Fig. 2), this is not OS)2(N)], crystallizes with the molecules on general positions utilized in the crystal packing. The short Cr N bonds of and has an equatorial S2O2 coordination environment, which 1.5609 (11) and 1.5591 (11) AÊ in (II) and (I), respectively, are is unprecedented among nitride complexes of the ®rst-row both within the range of those found for other ®ve-coordinate transition metals. In both systems, Cr N bonds are short at ca CrV±nitride complexes and ca 0.05 AÊ longer than the average MnV N bond length. In both structures, the nitride ligands The nitride ligand (N3À) is the strongest electron-donating ligand known (Nugent & Mayer, 1988). It also stands out by having a much more developed chemistry of second- and third-row transition metals than of their ®rst-row congeners.
The ®rst example of a nitride complex of the ®rst-row tran- sition metals, [Cr(salen)(N)], was therefore prepared as late as 1981 by photolysis of the corresponding CrIII±azide complex (Arshankow & Poznjak, 1981). A few other CrV± and MnV± nitride complexes have been prepared by this route, e.g.
[M(cyclam)(N)(CH3CN)]2+ [cyclam is 1,4,7,11-tetraazacyclo- tetradecane; M = Cr (Meyer, Bendix, Bill et al., 1998) and Mn (Meyer, Bendix, Metzler-Nolte et al., 1998)] and [Cr(tacn)- (acac)(N)]+ (tacn is 1,4,7-triazacyclononane and acac is acet- The molecular structure of (I), including the labelling of the atoms.
³ Present address: Centre for Fundamental Research: Metal Structures in Displacement ellipsoids are drawn at the 50% probability level. H atoms Four Dimensions, Risù National Laboratory, DK-4000 Roskilde, Denmark.
are shown as spheres of arbitrary radii.
# 2005 International Union of Crystallography electronic reprint
are non-bridging. This fact is evidenced by high (CrÐN) parallel) Cr N units results also for (I). This packing mode in stretching frequencies of 1016 and 1007 cmÀ1 for (I) and (II), combination with the electronically isolated molecules (the respectively. In accordance with the low basicity and nucleo- shortest CrÁ Á ÁCr distance is 7.519 AÊ) makes the compound philicity normally observed for [Cr N]2+ and [Mn N]2+ well suited for single-crystal EPR (electron paramagnetic moieties (Meyer, Bendix, Bill et al., 1998; Meyer, Bendix, resonance) studies of the bonding anisotropy in the metal± The vanadyl analogs of both (I) and (II) have been struc- turally characterized (Shiro & Fernando, 1971; Higes-Rolando et al., 1994, respectively) and are isostructural with their For the synthesis of (I), a solution of 8-hydroxyquinaldine (1.559 g, [Cr N]2+ counterparts. The bond lengths to the auxiliary 9.79 mmol, Aldrich 98%) in acetonitrile (6 ml) was added to the ligands in the [VIV(O)] complexes are slightly longer than solution resulting from an N-atom transfer reaction between those found in the [CrV(N)] systems and the pyramidalization [Mn(N)(salen)] (0.810 g, 2.4 mmol) and [CrCl3(THF)3] (0.906 g, is slightly larger for the vanadyl systems (cf. Table 2).
2.416 mmol) in acetonitrile (20 ml), with precipitation commencing Complexes (I) and (II) differ in the con®guration of the immediately. The orange product (0.626 g, 68%) was washed with bidentate ligands, being trans and cis, respectively. This methanol and recrystallized from boiling toluene (180 ml). Slow difference is common for these ligands and thus unrelated to evaporation afforded crystals of X-ray quality. For the synthesis of the metal centre. A rare exception to these preferred con®g- (II), a solution of the sodium salt of 2-mercaptopyridine N-oxide hydrate (0.735 g, 4.93 mmol, Aldrich) in methanol (11 ml) was added to the solution resulting from an N-atom transfer reaction between ligands are in the unusual trans con®guration (Kang et al., 3(THF)3], prepared as described above.
The resulting red precipitate (0.490 g, 64%) was collected by ®ltration The difference in angle between the nitride ligand and and washed with methanol. Crystals suitable for X-ray diffraction equatorial O-atom donors [112.91 (2)] and N-atom donors were obtained by slow evaporation of an acetonitrile solution.
[98.828 (18)] in (I) re¯ects a signi®cant distortion towards a trigonal-bipyramidal structure (with apical N-atom donors from the bidentate ligands). This contrast to the parent square-pyramidal coordination of chromium, is caused by the steric demands of the 2-methyl substituents in (I). The packing of the [Cr(quinald)2(N)] molecules is also in¯uenced by the methyl groups, which prevent the  stacking dominating the structure of [Cr(quinolin-8-olate)2(N)]. Nevertheless, a similar overall situation (cf. Fig. 3) with aligned (parallel and anti- Data collectionNonius KappaCCD diffractometer The molecular structure of (II), including the labelling of the atoms.
Displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radii.
The crystal packing in (I), showing the parallel and antiparallel Cr N orientations. Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted for clarity.
Birk et al.  [Cr(C10H8NO)2(N)] and [Cr(C5H4NOS)2(N)] electronic reprint
0.98 AÊ, respectively). Their isotropic displacement parameters were constrained to 1.2Ueq of the carrier atom (1.5Ueq for methyl groups).
Disorder of the methyl group in (I) could be resolved in two well separated conformations with populations 0.633 (18) and 0.367 (18), Data collection: EVALCCD (Duisenberg et al., 2003) for (I); COLLECT (Nonius, 1999) for (II). For both compounds, cell re®nement: COLLECT (Nonius, 1999); data reduction: EVALCCD; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003).
The authors thank Flemming Hansen, Centre of Crystal- lographic Studies, University of Copenhagen, for collecting the diffraction data. TB thanks The Carlsberg Foundation for a scholarship. Financial support from the Danish Natural Selected geometric parameters (AÊ, ) for nitride complexes (I) and (II).
Research Council (to JB, SNF 1266 and 21-04-0477) is Supplementary data for this paper are available from the IUCr electronic archives (Reference: BG1000). Services for accessing these data are described at the back of the journal.
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Comparative geometric parameters (AÊ, ) for vanadyl complexes.
Higes-Rolando, F. J., Perez-Florindo, A., Valenzuela-Calahorro, C., Martin- Ramos, J. D. & Romero-Garzon, J. (1994). Acta Cryst. C50, 1049±1052.
Kang, B.-S., Xu, Y.-J., Peng, J.-H., Wu, D.-X., Chen, X.-T., Hu, Y.-H., Hong, M.-C. & Lu, J.-X. (1993). Polyhedron, 12, 871±878.
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Notes: (a) Shiro & Fernando (1971); (b) Higes-Rolando et al. (1994).
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Birk et al.  [Cr(C10H8NO)2(N)] and [Cr(C5H4NOS)2(N)] electronic reprint

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