Bis(2,3,5-triphenyl­tetra­zolium) tetra­thio­cyanato­cobaltate(II)

Kouichi Nakashima; Naoyuki Kawame; Yoshiko Kawamura; Osamu Tamada; Jun Yamauchi

doi:10.1107/S1600536809041464

. 2009 Oct 23;65(Pt 11):m1406–m1407. doi: 10.1107/S1600536809041464

Bis(2,3,5-triphenyltetrazolium) tetrathiocyanatocobaltate(II)

Kouichi Nakashima ^a,^‡, Naoyuki Kawame ^a, Yoshiko Kawamura ^a, Osamu Tamada ^b, Jun Yamauchi ^c,^*

PMCID: PMC2970988 PMID: 21578146

Abstract

The title compound, (C₁₉H₁₅N₄)₂[Co(NCS)₄], has two crystallographycally different molecules of bis(2,3,5-triphenyltetrazolium) tetrathiocyanatecobaltate in the asymmetric unit. There are only minor geometric differences between them. Each cobalt(II) ion is coordinated by the N atoms of four NCS anions, showing the magnitude of the magnetic moment expected from the NCS⁻ crystal field strength.

Related literature

For the use of tetrazolium complexes in studying enzymatic redox reactions, see: Saide & Gilliland (2005 ▶). For studies of tetrazolium complexes and cobaltate compounds, see: Matulis et al. (2003 ▶); Kawamura et al. (1997 ▶); Rizzi et al. (2003 ▶); Marzotto et al. (1999 ▶); Fukui et al. (1992 ▶); Kubo et al. (1979 ▶). For the structures of tetrazolium complexes, see: Matulis et al. (2003 ▶); Kawamura et al. (1997 ▶). For the structure of tetraethylammonium tetrachloridonickelate(II), see: Stucky et al. (1967 ▶). For the magnetic moment as a measure of the crystal field strength, see: Van Vleck (1932 ▶); Ballhausen (1962 ▶). For a bis(formazanato) cobalt(II) complex in which the cobalt(II) ion is in a low spin state, see: Kawamura et al. (1990 ▶). 1,3,5-Triphenylformazan, used in the preparation of the title compound, is well known to be oxidized to the corresponding tetrazolium cation by utilizing some oxidation reagent or air oxidation, see: Nineham (1955 ▶).

Experimental

Crystal data

(C₁₉H₁₅N₄)₂[Co(NCS)₄]
M _r = 889.99
Monoclinic,
a = 9.5667 (2) Å
b = 49.7156 (11) Å
c = 18.9036 (7) Å
β = 102.810 (3)°
V = 8767.0 (4) Å³
Z = 8
Mo Kα radiation
μ = 0.63 mm⁻¹
T = 298 K
0.26 × 0.22 × 0.10 mm

Data collection

Nonus KappaCCD diffractometer
Absorption correction: Gaussian (WinGX routine Gaussian; Farrugia, 1999 ▶; Coppens et al., 1965 ▶) T _min = 0.854, T _max = 0.938
63412 measured reflections
15338 independent reflections
8769 reflections with I > 2σ(I)
R _int = 0.043

Refinement

R[F ² > 2σ(F ²)] = 0.049
wR(F ²) = 0.121
S = 1.03
15338 reflections
1063 parameters
H-atom parameters constrained
Δρ_max = 0.34 e Å⁻³
Δρ_min = −0.33 e Å⁻³

Data collection: COLLECT (Nonius, 1998 ▶); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997 ▶); data reduction: DENZO-SMN and SORTAV (Blessing, 1987 ▶; Blessing & Langs, 1987 ▶); program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536809041464/bt5038sup1.cif

e-65-m1406-sup1.cif^{(51.1KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536809041464/bt5038Isup2.hkl

e-65-m1406-Isup2.hkl^{(734.7KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

The authors gratefully thank Dr John F. Rakovan (Department of Geology, Miami University) for his helpful discussions to improve this study.

supplementary crystallographic information

Comment

Tetrazolium complexes, such as triphenyltetrazolium chloride (TTC), are highly sensitive color indicators of enzymatic redox reactions, and they are used in studies of such reactions (Saide & Gilliland, 2005). Several studies have been conducted on tetrazolium complexes and cobaltate compounds (Matulis et al., 2003; Kawamura et al., 1997; Rizzi et al., 2003; Marzotto et al., 1999; Fukui et al., 1992; Kubo et al., 1979), and a few structures of tetrazolium complexes have been determined (Matulis et al., 2003; Kawamura et al., 1997). Kawamura et al. (1997) studied the crystal structure of a complex composed of a 2,3,5-triphenyltetrazolium cation and a dichloro(1,3,5-triphenylformazanato) cobaltate (II) anion (hereafter designated as complex Type I), with the magnetic properties of Co(II) by means of a superconducting quantum-interference device (SQUID) and electron spin resonance (ESR) spectroscopy. In this communication, we report the crystal structure of bis(2,3,5-triphenyltetrazolium) tetrathiocyanocobaltate ((C₁₉N₄H₁₅)₂Co(NCS)₄), determined from single-crystal X-ray diffraction data, and compare its structure and physical properties to those of the Type I complex.

Since the coordination of Co(II) is an important factor for many physical properties, one objective of the current study was to clarify the ligands around the Co(II) ion, Co(NCS)₄^2- or Co(SCN)₄^2-; the coordination with four N atoms from NCS anions was confirmed to be Co(NCS)₄^2-. Furthermore, the crystallographic result revealed an asymmetric unit composed of a pair of units of (C₁₉N₄H₁₅)₂Co(NCS)₄ and a successive array of four asymmetric units in the b direction with alternating orientation. Both units in an asymmetric moiety are structurally different although the difference is subtle, and, therefore crystallographically distinct. Hereafter, they are referred to as A and B. Within them, an anion, Co(NCS)₄^-, and two cations, both C₁₉N₄H₁₅⁺, would interact as a result of interionic force. The geometry and atomic numbering schemes for A and B complexes are shown in Fig. 1.

The current one exhibited a typical cobalt-blue color because the tetrazolium cation does not have any absorption in the visible range. On the other hand, the ligand formazan molecule has strong absorption of about 580 nm and the color of the Type I complex was almost black. As a result, the absorptions around the Co(II) ion could not be assigned and it was impossible to compare the crystal field strength of the two based upon the absorption. Referring to the bond distances, it could be described that the crystal field of the current one might be stronger than that of the Type I complex, since the shorter distances provide a smaller Co(II) tetrahedral volume than that of the Type I complex.

The magnitude of the magnetic moment also measures the crystal field strength because the crystal field strength is incorporated in magnetic moment; it is generally correct to mention that the larger is the crystal field, the smaller is the magnetic moment (Van Vleck, 1932; Ballhausen, 1962). The magnetic moments of the Type I complex and the current one at room temperature were 4.0 µ_B and 4.5 µ_B, which correspond to the larger and smaller crystal fields, respectively. Therefore, the order is opposite to what is predicted from the structural analysis. In fact, the magnetic moments of the complexes of CoCl₄^2-, CoBr₄^2-, and CoI₄^2-, with the triphenyltetrazolium cation were 4.7, 5.0, and 5.2 µ_B, respectively, and this order corresponds with the inverse of the crystal field strength. And the current complex appropriately followed the order.

One of the authors observed a low spin state of the cobalt(II) ion in the bis(formazanato) cobalt(II) complex on ESR and magnetic susceptibility measurements, and the coordination was supposed to be from four N atoms of two formazan molecules (Kawamura et al., 1990). The fact suggests the larger crystal field and supports the magnitude of the magnetic moment of the Type I complex. Therefore, formazan molecule might provide somewhat stronger coordination than that expected from the structural analysis and lead to the smaller magnetic moment in the Type I complex. It would be correct to state that the crystal field strengths of the present two complexes would follow the order.

The coordination of Co(II) is an important factor in the magnetic, optical absorption (colour) and ESR properties. The Co(II) ion is four-coordinated in the both structures. In the Type I complex, two of the coordinating ligands are N (with an average Co—N distance of 1.959 Å) and two are Cl (with an average Co—Cl distance of 2.248 Å). The average bond distance to Co(II) in the Type I complex is thus 2.104 Å. The two N atoms are members of formazan, that comprise a large complex merged by the triphenyltetrazolium and Co(NCl)^2-. The absorption bands of Co(II) ion are not separated due to the strong absorption of formazan. Therefore,the colour of Type I is (almost) black due to the absorption overlapping of Co(II) ion and formazan molecule. In (C₁₉N₄H₁₅)₂Co(NCS)₄, the two distinct Co(NCS)₄^2- anionic complexes have average Co—N distances of 1.948 Å and 1.947 Å, thus yielding a much smaller Co(II) tetrahedral volume and stronger crystal field compared to the Type I complex. Individual Co(II) ions are separated by more than 11 Å from each other in the structure, thus each Co(NCS)₄^2- complex behaves as a magnetically isolated entity. The crystal exhibits a typical cobalt-blue colour because of the absence of formasan molecule. However, it is impossible to have some comparison about the crystal field difference of the two based upon the absorptions because of the lack of the clear absorption due the cobalt ion in the Type I complex.

Furthermore, the 1,3,5-triphenyltetrazolium ion is also bulkier as the counter ion and very flexible due to the three phenyl groups.

Experimental

The reaction mixture of 430 mg of Co(NO₃)₂.2H₂O, 280 mg of KNCS, and 500 mg of 1,3,5-triphenylformazan in 40 ml ethanol were kept standing in room temperature. 1,3,5-triphenylformazan is well known to be oxidized to the corresponding tetrazolium cation by utilizing some oxidation reagent or air oxidation (Nineham, 1955). 1,3,5-triphenyfomazen was likely to be oxidized probably by air to 2,3,5-tetrazolium in the solution, as the result, to form the complex together with tetrathiocyano cobaltate(II) anion. The complex with deep blue color was crystallized in one week. The crystals were filtrated and washed with ethanol. The result of C, H, and N elemental analyses of the complex was in good accordance with the calculated values in bis(2,3,5-triphenyl tetrazolium) tetrathiocyano cobaltate(II), respectively. The crystals were quite stable in air. The results of elemental analyses are followed; Exp. C; 56.12, H; 3.29, N; 18.89%, Calcd; C;56.67, H; 3.37, N;18.89%