65X-ray Structure Analysis Online 2012, VOL. 28 65

2012 © The Japan Society for Analytical Chemistry

The crystal structure of the hexa-DMF nickel(II) complex [Ni(DMF)6](BPh4)2 (DMF = N,N-dimethylformamide) was previously determined,1 and its coordination geometry around the nickel(II) ion was found to be trigonally compressed. A distortion of this type is related to a sign of zero-field splitting,2 and controlling the distortion leads to controlling the magnetic behavior. Moreover, the structure of the nickel(II) complex could be approximated to a rather rare S6 point group. In the present work we studied a cobalt(II) derivative with the aim of revealing its structural features: distortion and symmetry.

A cobalt(II) derivative was prepared by refluxing a DMF solution (1.0 ml) of cobalt(II) nitrate hexahydrate (1.0 mmol, 0.29 g) for 1.5 h; the addition of sodium tetraphenylborate (2.0 mmol, 0.69 g) and 2-propanol (1.0 ml) resulted in the precipitation of purple micro crystals. Single-crystals suitable for X-ray analysis were grown by slow diffusion of 2-propanol

into a DMF solution of the complex.The crystal data are included in Table 1. The structure was

solved by direct methods, and expanded using Fourier techniques. The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were refined using the

X-ray Structure Analysis Online

Synthesis and Crystal Structure of a Hexa-DMF Cobalt(II) Complex that belongs to an S6 Point Group

Keita ABE,* Yukako CHIBA,** Daisuke YOSHIOKA,*** Ryo YAMAGUCHI,** Masahiro MIKURIYA,*** and Hiroshi SAKIYAMA**†

*Wayo Konodai Girls’ Senior High School, 2-3-1 Konodai, Chiba 272-8533, Japan ** Department of Material and Biological Chemistry, Faculty of Science, Yamagata University,

1-4-12 Kojirakawa, Yamagata 990-8560, Japan*** Department of Chemistry and Research Center for Coordination Molecule-based Devices, School of

Science and Technology, Kwansei Gakuin University, Gakuen 2-1, Sanda 669-1337, Japan

The cobalt(II) complex [Co(DMF)6](BPh4)2 [DMF = N,N-dimethylformamide] [hexakis(N,N-dimethylformamide-kO)cobalt(II) bis(tetraphenylborate)] was prepared, and characterized by a single-crystal X-ray method. The compound crystallizes in the orthorhombic spaces group Pca21 and Z = 4 with cell parameters a = 30.240(4)Å, b = 9.2394(13)Å, c = 22.073(3)Å, V = 6167.1(15)Å3. Six DMF molecules coordinate to a cobalt(II) center, and the complex cation can be approximately classified into an S6 point group, and its coordination geometry is trigonally compressed.

(Received June 15, 2012; Accepted July 28, 2012; Published on web August 10, 2012)

Table 1 Crystal and experimental data

Chemical formula: C66H82B2CoN6O6

Formula weight = 1135.93T = 90 KCrystal system: orthorhombic Space group: Pca21

a = 30.240(4)Åb = 9.2394(13)Åc = 22.073(3)ÅV = 6167.1(15)Å3 Z = 4Dx = 1.223 g/cm3

Radiation: Mo Ka (l = 0.71073 Å)m(Mo Ka) = 0.334 mm–1 F(000) = 2420Crystal size = 0.54 ¥ 0.33 ¥ 0.35 mm3

No. of re�ections collected = 36843No. of independent re�ections = 11288 [R(int) = 0.0393]q range for data collection: 1.63 to 28.57˚Data/Restraints/Parameters = 11288/1/731Goodness-of-�t on F2 = 0.882Flack parameter: 0.194(9)R indices [I > 2s(I)]: R1 = 0.0340, wR2 = 0.0619R indices (all data): R1 = 0.0462, wR2 = 0.0643(D/s)max = 0.000(Dr)max = 0.696 eÅ–3 (Dr)min = –0.455 eÅ–3

Measurement: Bruker Smart APEX CCD diffractometerProgram system: SHELXTLStructure determination: Direct methods (SHELXS-97)Re�nement: full matrix least-squares (SHELXL-97)CCDC deposition number: 886452

Fig. 1 Chemical structure of [Co(DMF)6](BPh4)2.

† To whom correspondence should be addressed.E-mail: saki@sci.kj.yamagata-u.ac.jp

66 X-ray Structure Analysis Online 2012, VOL. 28

riding model. The final cycle of full-matrix least-squares refinement on F2 led to satisfactory convergence with R1 = 0. 0340 [I > 2s(I)]. The crystal is isomorphous to that of a nickel(II) complex, [Ni(DMF)6](BPh4)2.1

The crystal consists of complex cations, [Co(DMF)6]2+, and tetraphenylborate anions in a 1:2 molar ratio. The chemical structure is shown in Fig. 1, and an ORTEP view for the complex cation is shown in Fig. 2. In the complex cation, six DMF molecules coordinate to a cobalt(II) ion to form an octahedral geometry. The symmetry of the complex cation can be approximated to a rather rare S6 point group as well as the case with the nickel(II) complex; its pseudo-S6 axis is perpendicular to the paper in Fig. 1. Earlier, the crystal structure of [Co(DMF)6](ClO4)2 was determined, and it contained two crystallographically different [Co(DMF)6]2+ cations; although both cations can be approximated to S6, their distortion patterns are different from each other, and different

from the present [Co(DMF)6]2+ cation in this study.The present complex cation looks symmetrical, and the Co–O

distances (2.05 – 2.10 Å) are not so differ from each other (Table 2); however, comparing the distances between opposite vertices of the octahedron, the O(1)·O(4) distance (4.142 Å) is slightly shorter than the other distances (4.190 – 4.193 Å) (Table 3), indicating a tendency of slight shrinkage along the O(1)–Co(1)–O(4) axis, whereas no tendency was observed for the nickel(II) derivative.1 Moreover, the equatorial coordination plane O(2)–O(3)–O(5)–O(6), which is perpendicular to the O(1)–Co(1)–O(4) axis, is approximated to a rectangle; the O(2)·O(6) and O(3)·O(5) distances (3.04 – 3.05 Å) are longer than the O(2)·O(3) and O(5)·O(6) distances (2.84 – 2.92 Å); the O(2)–Co(1)–O(6) and O(3)–Co(1)–O(5) angles (~93˚) are larger than the O(2)–Co(1)–O(3) and O(5)–Co(1)–O(6) angles (85 – 89˚). Therefore, the CoO6 geometry can be approximated to D2h, while the whole [Co(DMF)6]2+ cation can be approximated to S6.

Another structural feature is trigonal compression, which was observed along the pseudo-S6 axis. The distances between the opposite faces of the octahedron are also included in Table 3, and only the distance along the pseudo-S6 axis (2.346 Å) is 2.7% shorter than the average distance (2.410 Å). The bond angles around the central cobalt(II) ion (Table 2) also indicate trigonal compression.

In conclusion, the [Co(DMF)6]2+ complex cation was found to be approximated to the S6 point group, and has a trigonally compressed coordination geometry. Moreover, in a precise sense, a tendency for shrinkage was also observed along a coordination axis.

Supporting Information

A CIF format file. This material is available free of charge on the Web at http://www.jsac.or.jp/xraystruct/.

References

1. R. Yamaguchi, M. Yamasaki, and H. Sakiyama, X-ray Struct. Anal. Online, 2011, 27, 71.

2. R. Boba, Coord. Chem. Rev., 2004, 248, 757. 3. F. Eissmann, T. Böhle, F. O. R. L. Mertens, and E. Weber,

Acta Cryst. E., 2010, 66, m279.

Atom

Atom Atom Angle (˚)

Distance (Å)

Table 2 Selected bond distances and angles

Atom Distance (Å)

Atom Atom Angle (˚) Atom Atom

Atom Atom

Deviationc

(%)

Table 3 Selected distances between the opposite vertices and between the opposite faces

Atom Atom Distance (Å) Deviationa (Å) Deviationa (%)

Triangularface

Triangularface

Distanceb

(Å)Deviationc

(Å)

aDeviation from the average distance (4.175 Å).bDistance between the middle points of the triangular faces at the opposite positions.

cDeviation from the average distance (2.410 Å).Fig. 2 Molecular structure of [Co(DMF)6]2+ with atom labeling. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity.