Crystal structure of [Co(NH₃)₆][Co(CO)₄]₂

Hexaamminecobalt(II) bis­[tetra­carbonyl­cobaltate(-I)], [Co(NH₃)₆][Co(CO)₄]₂, was synthesized by reaction of liquid ammonia with Co₂(CO)₈. The Co^II atom is coordinated by six ammine ligands. The resulting polyhedron, the hexa­amminecobalt(II) cation, exhibits point group symmetry -3. The Co^-I atom is coordinated by four carbonyl ligands, leading to a tetra­carbonyl­cobaltate(−I) anion in the shape of a slightly distorted tetra­hedron, with point group symmetry 3. The crystal structure is related to that of high-pressure BaC₂ (space group R-3m), with the [Co(NH₃)₆]²⁺ cations replacing the Ba sites and the [Co(CO)₄]⁻ anions replacing the C sites. N—H⋯O hydrogen bonds between cations and anions stabilize the structural set-up in the title compound.

1. Chemical context

The reaction of Co₂(CO)₈ with bases has already been described in the literature (Hieber et al., 1960). In addition, the reaction of dicobalt octa­carbonyl with liquid ammonia has been known for several decades (Behrens & Wakamatsu, 1966). Thereby Co₂(CO)₈ forms with NH₃ hexa­ammine­cobalt(II) bis­[tetra­carbonyl­cobaltate(–I)], [Co(NH₃)₆][Co(CO)₄]₂, which is obtained as orange air-sensitive crystals. During this reaction, CO is released and reacts with ammonia to urea. However, structural data of of the title compound were missing and are presented in this communication.

2. Structural commentary

The cobalt atom Co1 of the hexa­amminecobalt(II) cation occupies Wyckoff position 3a with site symmetry .. It is coordinated by six symmetry-related ammine ligands in form of a slightly distorted octa­hedron. The Co—N distance in the [Co(NH₃)₆] octa­hedron is 2.1876 (16) Å which compares well with those of other reported hexa­amminecobalt(II) structures (Barnet et al., 1966).

The cobalt atom Co2 of the tetra­carbonyl­cobaltate(–I) anion occupies Wyckoff position 6c and exhibits site symmetry 3.. It is coordinated by four carbonyl ligands in a shape close to an ideal tetra­hedron. The distances between the Co2 atom and the carbon atoms C1 and C2 of the ligands are 1.7664 (18) and 1.779 (3) Å, respectively. In the literature, distances in the range from 1.77 (2) to 1.82 (2) Å are reported for Co—C in the compound Co₂(CO)₈ (Sumner et al., 1964). In the carbonyl ligands, the observed distances are in the expected range with 1.153 (2) and 1.140 (4) Å for C1—O1 and C2—O2, respectively. For the compound Co₂(CO)₈ distances from 1.14 (2) to 1.33 (2) Å were reported (Sumner et al., 1964).

The crystal structure of [Co(NH₃)₆][Co(CO)₄]₂ can be derived from the high-pressure rhombohedral phase of BaC₂ (BaC₂ -HP1, Rm) (Efthimiopoulos et al., 2012). Formally, the Ba sites on Wyckoff position 3a are replaced by the hexa­ammine cobalt(II) octa­hedra and the C site on position 6c is replaced by the tetra­carbonyl­cobaltate(–I) tetra­hedron.

The mol­ecular components of the title compound are shown in Fig. 1. The unit cell of [Co(NH₃)₆][Co(CO)₄]₂ projected along [001] is shown in Fig. 2.

Figure 1 The mol­ecular structures of the tetra­carbonyl­cobaltate(−I) anion and of the hexa­amminecobalt(II) cation of the title compound. Displacement ellipsoids are shown at the 70% probability level. Labelling of symmetry-equivalent atoms has been omitted for clarity.

Figure 2 The unit cell of [Co(NH3)6][Co(CO)4]2, viewed along [001]. Displacement ellipsoids are shown at the 70% probability level.

3. Supra­molecular features

The arrangement of [Co(NH₃)₆]²⁺ octa­hedra and [Co(CO)₄]⁻ tetra­hedra in the crystal structure is stabilized by N—H⋯O hydrogen bonds with the N1 atom as donor and the oxygen atoms O1 and O2 as acceptors atoms. One of the hydrogen bonds (N—H1C) is forked while, remarkably, in the neighbourhood of the hydrogen atom H1B no acceptor atom in the range of the sum of the van der Waals radii is present. Detailed information about hydrogen-bonding distances and angles are given in Table 1.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1^i	0.87 (4)	2.49 (4)	3.159 (2)	135 (3)
N1—H1C⋯O1^ii	0.87 (3)	2.59 (3)	3.290 (2)	138 (3)
N1—H1C⋯O2^iii	0.87 (3)	2.49 (3)	3.249 (3)	146 (3)
Symmetry codes: (i) -x+y-1, -x-1, z; (ii) ; (iii) .

4. Synthesis and crystallization

86 mg (29.4 mmol) of Co₂(CO)₈ were placed in a flame-dried bomb tube under argon. 0.2 ml of liquid ammonia were condensed to the bomb tube. The bomb tube, now containing an orange solution, was flame-sealed and stored at room temperature. The reaction equation is given in Fig. 3. After six months of crystallization time, moisture- and temperature-sensitive, orange single crystals of the title compound were obtained in almost qu­anti­tative yield from the still orange solution. After manual separation of the crystals under a light-optical microscope and evaporation of the solvent only a minute orange residue remained.

Figure 3 Reaction equation for the preparation of the title compound.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms of the ammine ligands were located from a difference Fourier map and were refined isotropically without any further restraints.

Table 2
Experimental details

Crystal data
Chemical formula	[Co(NH3)6][Co(CO)4]2
Mr	503.07
Crystal system, space group	Trigonal, R
Temperature (K)	100
a, c (Å)	9.3679 (4), 18.3089 (18)
V (Å^3)	1391.48 (18)
Z	3
Radiation type	Mo Kα
μ (mm^−1)	2.70
Crystal size (mm)	0.16 × 0.12 × 0.08
Data collection
Diffractometer	Stoe IPDS2T
Absorption correction	Integration (X-RED32 and X-SHAPE; Stoe & Cie, 2009)
Tmin, Tmax	0.649, 0.907
No. of measured, independent and observed [I > 2σ(I)] reflections	7025, 994, 910
Rint	0.087
(sin θ/λ)max (Å^−1)	0.724
Refinement
R[F^2 > 2σ(F^2)], wR(F^2), S	0.034, 0.090, 1.08
No. of reflections	994
No. of parameters	52
H-atom treatment	All H-atom parameters refined
Δρmax, Δρmin (e Å^−3)	0.87, −0.65
Computer programs: X-AREA (Stoe & Cie, 2011), X-RED32 (Stoe & Cie, 2009), SHELXT (Sheldrick, 2015a), SHELXLE (Hübschle et al., 2011) and SHELXL2014 (Sheldrick, 2015b), DIAMOND (Brandenburg, 2015) and publCIF (Westrip, 2010).

Supporting information

Computing details

Data collection: X-AREA (Stoe & Cie, 2011); cell refinement: X-AREA (Stoe & Cie, 2011); data reduction: X-RED32 (Stoe & Cie, 2009); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXLE (Hübschle et al., 2011) and SHELXL2014 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg, 2015); software used to prepare material for publication: publCIF (Westrip, 2010).

Hexaamminecobalt(II) bis[tetracarbonylcobaltate(-I)]

Crystal data

[Co(NH3)6][Co(CO)4]2	Dx = 1.801 Mg m^−3
Mr = 503.07	Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3	Cell parameters from 15618 reflections
a = 9.3679 (4) Å	θ = 3.3–33.4°
c = 18.3089 (18) Å	µ = 2.70 mm^−1
V = 1391.48 (18) Å^3	T = 100 K
Z = 3	Block, orange
F(000) = 759	0.16 × 0.12 × 0.08 mm

Data collection

Stoe IPDS-2T diffractometer	994 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	910 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.087
Detector resolution: 6.67 pixels mm^-1	θmax = 31.0°, θmin = 3.3°
rotation method scans	h = −13→13
Absorption correction: integration (X-RED32 and X-SHAPE; Stoe & Cie, 2009)	k = −13→13
Tmin = 0.649, Tmax = 0.907	l = −26→26
7025 measured reflections

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.034	w = 1/[σ^2(Fo^2) + (0.0529P)^2 + 1.0515P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.090	(Δ/σ)max < 0.001
S = 1.08	Δρmax = 0.87 e Å^−3
994 reflections	Δρmin = −0.65 e Å^−3
52 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.0040 (8)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Co1	0.0000	0.0000	0.0000	0.01863 (18)
Co2	−0.6667	−0.3333	0.04221 (2)	0.01972 (17)
O1	−0.61903 (19)	−0.02591 (18)	0.10467 (9)	0.0315 (3)
O2	−0.6667	−0.3333	−0.11725 (14)	0.0298 (5)
N1	−0.0266 (2)	−0.2037 (2)	0.06820 (9)	0.0245 (3)
C1	−0.6354 (2)	−0.1451 (2)	0.07846 (10)	0.0231 (3)
C2	−0.6667	−0.3333	−0.05497 (19)	0.0237 (5)
H1A	−0.121 (5)	−0.295 (5)	0.0656 (19)	0.054 (10)*
H1B	0.034 (4)	−0.247 (4)	0.0558 (17)	0.038 (7)*
H1C	−0.001 (4)	−0.176 (4)	0.1135 (19)	0.043 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0160 (2)	0.0160 (2)	0.0240 (3)	0.00799 (10)	0.000	0.000
Co2	0.01726 (19)	0.01726 (19)	0.0247 (3)	0.00863 (9)	0.000	0.000
O1	0.0323 (7)	0.0236 (7)	0.0410 (8)	0.0158 (6)	−0.0025 (6)	−0.0036 (5)
O2	0.0316 (8)	0.0316 (8)	0.0262 (12)	0.0158 (4)	0.000	0.000
N1	0.0209 (7)	0.0212 (7)	0.0307 (7)	0.0101 (6)	−0.0002 (5)	0.0015 (5)
C1	0.0192 (7)	0.0203 (7)	0.0292 (8)	0.0095 (6)	−0.0007 (6)	0.0009 (6)
C2	0.0198 (8)	0.0198 (8)	0.0317 (15)	0.0099 (4)	0.000	0.000

Geometric parameters (Å, º)

Co1—N1^i	2.1876 (16)	Co2—C1	1.7664 (18)
Co1—N1^ii	2.1876 (16)	Co2—C1^vi	1.7664 (18)
Co1—N1^iii	2.1876 (16)	Co2—C1^vii	1.7664 (18)
Co1—N1^iv	2.1876 (16)	Co2—C2	1.779 (3)
Co1—N1	2.1877 (16)	O1—C1	1.153 (2)
Co1—N1^v	2.1877 (16)	O2—C2	1.140 (4)
N1^i—Co1—N1^ii	180.00 (9)	N1^iii—Co1—N1^v	90.65 (6)
N1^i—Co1—N1^iii	90.65 (6)	N1^iv—Co1—N1^v	89.35 (6)
N1^ii—Co1—N1^iii	89.35 (6)	N1—Co1—N1^v	180.0
N1^i—Co1—N1^iv	89.35 (6)	C1—Co2—C1^vi	106.76 (7)
N1^ii—Co1—N1^iv	90.65 (6)	C1—Co2—C1^vii	106.75 (7)
N1^iii—Co1—N1^iv	180.00 (11)	C1^vi—Co2—C1^vii	106.75 (7)
N1^i—Co1—N1	89.35 (6)	C1—Co2—C2	112.07 (6)
N1^ii—Co1—N1	90.65 (6)	C1^vi—Co2—C2	112.07 (6)
N1^iii—Co1—N1	89.35 (6)	C1^vii—Co2—C2	112.07 (6)
N1^iv—Co1—N1	90.65 (6)	O1—C1—Co2	177.07 (17)
N1^i—Co1—N1^v	90.65 (6)	O2—C2—Co2	180.0
N1^ii—Co1—N1^v	89.35 (6)

Symmetry codes: (i) x−y, x, −z; (ii) −x+y, −x, z; (iii) y, −x+y, −z; (iv) −y, x−y, z; (v) −x, −y, −z; (vi) −y−1, x−y, z; (vii) −x+y−1, −x−1, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^vii	0.87 (4)	2.49 (4)	3.159 (2)	135 (3)
N1—H1C···O1^viii	0.87 (3)	2.59 (3)	3.290 (2)	138 (3)
N1—H1C···O2^ix	0.87 (3)	2.49 (3)	3.249 (3)	146 (3)

Symmetry codes: (vii) −x+y−1, −x−1, z; (viii) x−y+2/3, x+1/3, −z+1/3; (ix) x+2/3, y+1/3, z+1/3.