Serendipity: Werner's argument that the `two-only forms' (green and violet) of [CoCl₂(en)₂]⁺ salts demanded his octa­hedral model was correct. True?

Chemists of the late 19th century, including Alfred Werner, prepared salts containing either green or violet cations of com­position [CoCl₂(en)₂]⁺ (en is ethyl­enedi­amine, C₂H₈N₂); we now refer to these as trans-di­chloro and cis-di­chloro species. We have discovered a third salt, purple in color, containing cat­ions of the same elemental com­position and whose asymmetric unit com­position is [CoCl₂(en)₂]₂Cl₂·3H₂O, in which the cobalt cations are a cis:trans di­chloro pair. Such a discovery would undermine Werner's argument that if only two forms can be prepared, his octa­hedral theory was proven. Probably because his students never examined their crystals under a microscope, they failed to observe the `third' species, thereby ruining Werner's argument since he relied strictly on color to identify them. That was fortunate since our purple salt would have led him to abandon, or certainly delay, his momentous discovery. Our crystals consist of a 1:1 mixture of the cis and trans cations, thereby sharing the same elemental analysis and conductivity as the single salts, but not their crystal structure, inasmuch as X-ray diffraction had not even been discovered then. Serendipitously, our discovery would have been a great boon to his theoretical acumen, while his `two-color' argument may have doomed him.

Computing details

Data collection: APEX2 (Bruker, 2008); cell refinement: APEX2 (Bruker, 2008); data reduction: SAINT (Bruker, 2008); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

(I)

Crystal data

[CoCl2(C2H8N2)2]2Cl2·3H2O	Z = 2
Mr = 625.02	F(000) = 644
Triclinic, P1	Dx = 1.696 Mg m^−3
a = 8.7163 (3) Å	Cu Kα radiation, λ = 1.54178 Å
b = 11.1146 (4) Å	Cell parameters from 9124 reflections
c = 14.0703 (5) Å	θ = 3.3–70.0°
α = 105.540 (2)°	µ = 16.88 mm^−1
β = 94.630 (2)°	T = 100 K
γ = 108.581 (2)°	Plate, purple
V = 1224.06 (8) Å^3	0.61 × 0.19 × 0.07 mm

Data collection

Bruker SMART CCD APEXII area-detector diffractometer	4191 independent reflections
Radiation source: fine-focus sealed tube	3864 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
φ and ω scans	θmax = 70.1°, θmin = 3.3°
Absorption correction: numerical (SADABS; Bruker, 2008)	h = −10→10
Tmin = 0.041, Tmax = 0.512	k = −13→13
11708 measured reflections	l = −16→17

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.038	Hydrogen site location: mixed
wR(F^2) = 0.097	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.046P)^2 + 2.482P] where P = (Fo^2 + 2Fc^2)/3
4191 reflections	(Δ/σ)max = 0.001
262 parameters	Δρmax = 0.63 e Å^−3
6 restraints	Δρmin = −0.61 e Å^−3

Special details

Experimental. Crystal mounted on a Cryoloop using Paratone-N.

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

Refinement. A suitable crystal was mounted on a Bruker-AXS SMART APEX II CCD diffractometer at 100 (1)K. The cell dimensions and the intensities were all collected with CuKα radiation (λ = 1.54178 Å). Data processing, Lorentz-polarization, and face-indexed numerical absorption corrections were performed using SAINT, APEX, and SADABS computer programs (see Table 1). The structures were solved by direct methods and refined by full-matrix least-squares methods on F², using the SHELXTL V6.14 program package. All non-hydrogen atoms were refined anisotropically.

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

	x	y	z	Uiso*/Ueq
Co1	0.42187 (7)	0.73638 (5)	0.14491 (4)	0.01168 (15)
Co2	0.79303 (6)	0.68956 (5)	0.51970 (4)	0.00924 (14)
Cl1	0.32764 (11)	0.57545 (8)	−0.00666 (6)	0.01721 (19)
Cl2	0.51347 (10)	0.89359 (8)	0.29573 (6)	0.01563 (19)
Cl3	0.63440 (10)	0.58474 (8)	0.36448 (6)	0.01373 (18)
Cl4	0.78767 (10)	0.49270 (8)	0.54045 (6)	0.01316 (18)
Cl5	0.76001 (12)	0.71852 (9)	0.82366 (6)	0.0227 (2)
Cl6	0.01374 (10)	0.10534 (8)	0.68451 (6)	0.01470 (18)
O1	0.1100 (4)	0.7779 (4)	0.9406 (3)	0.0414 (8)
H17	0.148 (4)	0.733 (4)	0.897 (2)	0.062*
H18	0.016 (2)	0.770 (5)	0.914 (4)	0.062*
O2	0.7664 (5)	0.3860 (4)	0.2156 (2)	0.0432 (8)
H19	0.747 (5)	0.435 (4)	0.266 (2)	0.065*
H20	0.745 (7)	0.410 (4)	0.1658 (18)	0.065*
O3	0.5023 (4)	0.1432 (3)	0.1398 (2)	0.0305 (7)
H21	0.593 (3)	0.206 (3)	0.155 (4)	0.046*
H22	0.426 (3)	0.174 (3)	0.144 (4)	0.046*
N1	0.2064 (4)	0.7574 (3)	0.1388 (2)	0.0159 (6)
H1	0.212914	0.833261	0.186719	0.019*
H2	0.173412	0.763287	0.077745	0.019*
N2	0.3316 (4)	0.6019 (3)	0.2111 (2)	0.0144 (6)
H3	0.313452	0.518920	0.168638	0.017*
H4	0.404666	0.616195	0.266533	0.017*
N3	0.6337 (4)	0.7098 (3)	0.1477 (2)	0.0142 (6)
H5	0.692505	0.745603	0.211330	0.017*
H6	0.616971	0.620975	0.126728	0.017*
N4	0.5159 (4)	0.8733 (3)	0.0821 (2)	0.0160 (6)
H7	0.470585	0.843071	0.015773	0.019*
H8	0.493480	0.947905	0.111382	0.019*
N5	0.6062 (3)	0.6816 (3)	0.5887 (2)	0.0120 (6)
H9	0.512396	0.619685	0.547593	0.014*
H10	0.622078	0.657047	0.644405	0.014*
N6	0.7769 (3)	0.8544 (3)	0.5035 (2)	0.0109 (6)
H11	0.863005	0.925717	0.544269	0.013*
H12	0.781225	0.853698	0.438964	0.013*
N7	0.9474 (3)	0.7845 (3)	0.6464 (2)	0.0125 (6)
H13	0.953437	0.871052	0.667513	0.015*
H14	0.912190	0.746168	0.694002	0.015*
N8	0.9891 (3)	0.7074 (3)	0.4581 (2)	0.0126 (6)
H15	1.000030	0.626268	0.435687	0.015*
H16	0.978514	0.737298	0.404589	0.015*
C1	0.0869 (4)	0.6391 (4)	0.1558 (3)	0.0170 (8)
H1A	0.052416	0.561342	0.094154	0.020*
H1B	−0.011974	0.658018	0.174596	0.020*
C2	0.1742 (5)	0.6107 (4)	0.2403 (3)	0.0173 (8)
H2B	0.196065	0.683405	0.304030	0.021*
H2A	0.105949	0.525646	0.249139	0.021*
C3	0.7253 (5)	0.7758 (4)	0.0804 (3)	0.0188 (8)
H3B	0.685320	0.718241	0.009783	0.023*
H3A	0.844292	0.792811	0.097853	0.023*
C4	0.6966 (5)	0.9058 (4)	0.0943 (3)	0.0203 (8)
H4A	0.751559	0.968917	0.161818	0.024*
H4B	0.740980	0.947287	0.043471	0.024*
C5	0.5898 (4)	0.8145 (3)	0.6176 (3)	0.0132 (7)
H5A	0.672188	0.875470	0.678075	0.016*
H5B	0.478506	0.806985	0.632244	0.016*
C6	0.6185 (4)	0.8662 (3)	0.5296 (3)	0.0131 (7)
H6A	0.527159	0.812728	0.471989	0.016*
H6B	0.625832	0.960587	0.547557	0.016*
C7	1.1125 (4)	0.7791 (4)	0.6318 (3)	0.0149 (7)
H7B	1.116821	0.690845	0.630727	0.018*
H7A	1.198949	0.848989	0.686762	0.018*
C8	1.1372 (4)	0.8025 (3)	0.5325 (3)	0.0149 (7)
H8A	1.149399	0.895619	0.536881	0.018*
H8B	1.237270	0.786491	0.513006	0.018*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0127 (3)	0.0127 (3)	0.0100 (3)	0.0057 (2)	0.0001 (2)	0.0032 (2)
Co2	0.0078 (3)	0.0098 (3)	0.0107 (3)	0.0033 (2)	0.0007 (2)	0.0042 (2)
Cl1	0.0178 (4)	0.0176 (4)	0.0134 (4)	0.0068 (3)	−0.0008 (3)	0.0010 (3)
Cl2	0.0187 (4)	0.0157 (4)	0.0114 (4)	0.0072 (3)	0.0004 (3)	0.0019 (3)
Cl3	0.0126 (4)	0.0139 (4)	0.0128 (4)	0.0035 (3)	−0.0008 (3)	0.0035 (3)
Cl4	0.0116 (4)	0.0120 (4)	0.0181 (4)	0.0054 (3)	0.0023 (3)	0.0068 (3)
Cl5	0.0304 (5)	0.0235 (5)	0.0175 (4)	0.0105 (4)	0.0080 (4)	0.0095 (4)
Cl6	0.0155 (4)	0.0131 (4)	0.0146 (4)	0.0041 (3)	0.0006 (3)	0.0047 (3)
O1	0.0399 (19)	0.048 (2)	0.0365 (18)	0.0127 (17)	−0.0047 (16)	0.0193 (16)
O2	0.048 (2)	0.052 (2)	0.0345 (18)	0.0232 (18)	0.0060 (17)	0.0148 (17)
O3	0.0455 (19)	0.0290 (16)	0.0280 (15)	0.0239 (15)	0.0119 (16)	0.0120 (14)
N1	0.0162 (15)	0.0182 (16)	0.0144 (14)	0.0088 (13)	0.0005 (13)	0.0043 (13)
N2	0.0137 (15)	0.0154 (15)	0.0147 (14)	0.0056 (12)	0.0015 (13)	0.0055 (12)
N3	0.0122 (14)	0.0183 (16)	0.0131 (14)	0.0070 (12)	0.0010 (12)	0.0049 (12)
N4	0.0233 (17)	0.0119 (15)	0.0114 (14)	0.0061 (13)	0.0007 (13)	0.0022 (12)
N5	0.0105 (14)	0.0166 (15)	0.0129 (13)	0.0066 (12)	0.0043 (12)	0.0080 (12)
N6	0.0103 (14)	0.0110 (14)	0.0126 (13)	0.0039 (12)	0.0016 (12)	0.0055 (12)
N7	0.0128 (15)	0.0109 (14)	0.0129 (13)	0.0031 (12)	0.0002 (13)	0.0043 (12)
N8	0.0117 (14)	0.0127 (14)	0.0151 (14)	0.0054 (12)	0.0018 (13)	0.0060 (12)
C1	0.0124 (17)	0.0208 (19)	0.0172 (17)	0.0067 (15)	0.0026 (15)	0.0039 (15)
C2	0.0179 (19)	0.0171 (18)	0.0186 (17)	0.0065 (15)	0.0057 (16)	0.0070 (15)
C3	0.0180 (19)	0.023 (2)	0.0148 (17)	0.0061 (16)	0.0024 (16)	0.0061 (16)
C4	0.0199 (19)	0.022 (2)	0.0166 (17)	0.0040 (16)	0.0022 (16)	0.0071 (16)
C5	0.0110 (17)	0.0144 (17)	0.0158 (16)	0.0067 (14)	0.0046 (15)	0.0041 (14)
C6	0.0130 (17)	0.0137 (17)	0.0154 (16)	0.0075 (14)	0.0019 (15)	0.0057 (14)
C7	0.0112 (17)	0.0143 (18)	0.0183 (17)	0.0054 (14)	−0.0020 (15)	0.0041 (15)
C8	0.0073 (16)	0.0130 (17)	0.0221 (18)	0.0015 (14)	0.0005 (15)	0.0051 (15)

Geometric parameters (Å, º)

Co1—N4	1.952 (3)	N5—H9	0.9100
Co1—N2	1.958 (3)	N5—H10	0.9100
Co1—N3	1.960 (3)	N6—C6	1.494 (4)
Co1—N1	1.963 (3)	N6—H11	0.9100
Co1—Cl2	2.2460 (9)	N6—H12	0.9100
Co1—Cl1	2.2713 (10)	N7—C7	1.487 (4)
Co2—N7	1.950 (3)	N7—H13	0.9100
Co2—N6	1.952 (3)	N7—H14	0.9100
Co2—N5	1.953 (3)	N8—C8	1.483 (4)
Co2—N8	1.956 (3)	N8—H15	0.9100
Co2—Cl4	2.2703 (9)	N8—H16	0.9100
Co2—Cl3	2.2719 (9)	C1—C2	1.517 (5)
O1—H17	0.8400 (10)	C1—H1A	0.9900
O1—H18	0.8401 (11)	C1—H1B	0.9900
O2—H19	0.8401 (10)	C2—H2B	0.9900
O2—H20	0.8402 (10)	C2—H2A	0.9900
O3—H21	0.8400 (11)	C3—C4	1.509 (5)
O3—H22	0.8400 (10)	C3—H3B	0.9900
N1—C1	1.485 (5)	C3—H3A	0.9900
N1—H1	0.9100	C4—H4A	0.9900
N1—H2	0.9100	C4—H4B	0.9900
N2—C2	1.489 (5)	C5—C6	1.506 (5)
N2—H3	0.9100	C5—H5A	0.9900
N2—H4	0.9100	C5—H5B	0.9900
N3—C3	1.481 (5)	C6—H6A	0.9900
N3—H5	0.9100	C6—H6B	0.9900
N3—H6	0.9100	C7—C8	1.508 (5)
N4—C4	1.484 (5)	C7—H7B	0.9900
N4—H7	0.9100	C7—H7A	0.9900
N4—H8	0.9100	C8—H8A	0.9900
N5—C5	1.480 (4)	C8—H8B	0.9900
N4—Co1—N2	178.53 (13)	Co2—N6—H11	109.8
N4—Co1—N3	86.20 (13)	C6—N6—H12	109.8
N2—Co1—N3	93.22 (12)	Co2—N6—H12	109.8
N4—Co1—N1	94.44 (13)	H11—N6—H12	108.2
N2—Co1—N1	86.19 (12)	C7—N7—Co2	109.2 (2)
N3—Co1—N1	178.15 (13)	C7—N7—H13	109.8
N4—Co1—Cl2	89.21 (9)	Co2—N7—H13	109.8
N2—Co1—Cl2	89.45 (9)	C7—N7—H14	109.8
N3—Co1—Cl2	91.06 (9)	Co2—N7—H14	109.8
N1—Co1—Cl2	90.69 (9)	H13—N7—H14	108.3
N4—Co1—Cl1	91.52 (9)	C8—N8—Co2	109.9 (2)
N2—Co1—Cl1	89.82 (9)	C8—N8—H15	109.7
N3—Co1—Cl1	89.05 (9)	Co2—N8—H15	109.7
N1—Co1—Cl1	89.20 (9)	C8—N8—H16	109.7
Cl2—Co1—Cl1	179.27 (4)	Co2—N8—H16	109.7
N7—Co2—N6	92.48 (12)	H15—N8—H16	108.2
N7—Co2—N5	91.09 (12)	N1—C1—C2	106.6 (3)
N6—Co2—N5	85.64 (12)	N1—C1—H1A	110.4
N7—Co2—N8	85.45 (12)	C2—C1—H1A	110.4
N6—Co2—N8	93.14 (12)	N1—C1—H1B	110.4
N5—Co2—N8	176.28 (12)	C2—C1—H1B	110.4
N7—Co2—Cl4	89.50 (9)	H1A—C1—H1B	108.6
N6—Co2—Cl4	174.82 (9)	N2—C2—C1	106.4 (3)
N5—Co2—Cl4	89.54 (9)	N2—C2—H2B	110.4
N8—Co2—Cl4	91.79 (9)	C1—C2—H2B	110.4
N7—Co2—Cl3	174.39 (9)	N2—C2—H2A	110.4
N6—Co2—Cl3	86.60 (9)	C1—C2—H2A	110.4
N5—Co2—Cl3	94.36 (9)	H2B—C2—H2A	108.6
N8—Co2—Cl3	89.08 (9)	N3—C3—C4	107.3 (3)
Cl4—Co2—Cl3	91.89 (3)	N3—C3—H3B	110.3
H17—O1—H18	108 (5)	C4—C3—H3B	110.3
H19—O2—H20	108 (4)	N3—C3—H3A	110.3
H21—O3—H22	110 (4)	C4—C3—H3A	110.3
C1—N1—Co1	108.1 (2)	H3B—C3—H3A	108.5
C1—N1—H1	110.1	N4—C4—C3	106.7 (3)
Co1—N1—H1	110.1	N4—C4—H4A	110.4
C1—N1—H2	110.1	C3—C4—H4A	110.4
Co1—N1—H2	110.1	N4—C4—H4B	110.4
H1—N1—H2	108.4	C3—C4—H4B	110.4
C2—N2—Co1	109.1 (2)	H4A—C4—H4B	108.6
C2—N2—H3	109.9	N5—C5—C6	106.2 (3)
Co1—N2—H3	109.9	N5—C5—H5A	110.5
C2—N2—H4	109.9	C6—C5—H5A	110.5
Co1—N2—H4	109.9	N5—C5—H5B	110.5
H3—N2—H4	108.3	C6—C5—H5B	110.5
C3—N3—Co1	108.5 (2)	H5A—C5—H5B	108.7
C3—N3—H5	110.0	N6—C6—C5	106.5 (3)
Co1—N3—H5	110.0	N6—C6—H6A	110.4
C3—N3—H6	110.0	C5—C6—H6A	110.4
Co1—N3—H6	110.0	N6—C6—H6B	110.4
H5—N3—H6	108.4	C5—C6—H6B	110.4
C4—N4—Co1	109.1 (2)	H6A—C6—H6B	108.6
C4—N4—H7	109.9	N7—C7—C8	106.1 (3)
Co1—N4—H7	109.9	N7—C7—H7B	110.5
C4—N4—H8	109.9	C8—C7—H7B	110.5
Co1—N4—H8	109.9	N7—C7—H7A	110.5
H7—N4—H8	108.3	C8—C7—H7A	110.5
C5—N5—Co2	109.2 (2)	H7B—C7—H7A	108.7
C5—N5—H9	109.8	N8—C8—C7	106.6 (3)
Co2—N5—H9	109.8	N8—C8—H8A	110.4
C5—N5—H10	109.8	C7—C8—H8A	110.4
Co2—N5—H10	109.8	N8—C8—H8B	110.4
H9—N5—H10	108.3	C7—C8—H8B	110.4
C6—N6—Co2	109.4 (2)	H8A—C8—H8B	108.6
C6—N6—H11	109.8

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H18···Cl5^i	0.84 (3)	2.29 (4)	3.126 (4)	171 (6)
O3—H21···O2	0.84 (4)	1.99 (4)	2.797 (5)	162 (3)
O2—H19···Cl3	0.84 (3)	2.38 (4)	3.181 (4)	160 (3)
N2—H3···Cl5^ii	0.91	2.54	3.279 (3)	138
N4—H7···O3^iii	0.91	2.26	3.066 (4)	147
O1—H17···O2^ii	0.84 (3)	2.12 (3)	2.966 (5)	178 (4)

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