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The title compound, di­bromo­bis­[tris­(di­methyl­amino)­phos­phine oxide]­cobalt(II), [CoBr2(C6H18N3OP)2], displays tetrahedral coordination about cobalt. The mol­ecule has twofold crystallographic site symmetry. The short P-N bonds and the planarity of the di­methyl­amino groups indicate the importance of d[pi]-p[pi] interactions. One of the NMe2 groups has an irregular conformation about the P-N bond and deviates from planarity. It is ascribed to the steric hindrance induced by coordination at the O atom of hexa­methyl­phospho­ric tri­amide.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270101005960/sk1472sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270101005960/sk1472Isup2.hkl
Contains datablock I

CCDC reference: 166979

Comment top

Hexamethylphosphoric triamide (HMPA) is an important solvent with very high nucleophilicity (the donor number DN = 38.8) (Normant, 1967; Gutmann, 1978). Its bulky mushroom-like molecular shape leads to the tendency to form tetrahedral complexes with first-row bivalent metal ions except for MnII (Wayland & Drago, 1965; Ozutsumi et al., 1994). Steric interactions between coordinated HMPA molecules control the thermodynamics of formation of halogeno complexes in this solvent (Abe et al., 1989; Abe & Ishiguro, 1991; Abe et al., 1992). To obtain detailed structural information on HMPA in the tetrahedral coordination environment, we have performed an X-ray diffraction study on the single-crystal of the title complex, (I). \sch

The structure (Fig. 1) shows the tetrahedral geometry of the complex with the twofold crystallographic site symmetry, in which two Br atoms and two crystallographically equivalent HMPA molecules coordinate. The coordination bond length of HMPA [Co—O = 1.957 (4) Å] is similar to those in [Co(HMPA)4]2+ [1.94 (1) Å] and [CoCl(HMPA)3]+ [1.95 (1) Å] in solution determined by the fluorescent EXAFS method (Ozutsumi et al., 1994). The coordination bond angle [Co—O—P = 145.3 (3)°] is near the smallest side within the wide range of metal-O—P angles (144–173°) found in octahedral HMPA complexes (Carpentier et al., 1972; Viossat et al., 1977).

The intramolecular bond lengths and angles of HMPA are consistent with the reported values for this molecule. The P—N bonds [1.618 (5)–1.641 (5) Å] are much shorter than the typical single bond length (1.77 Å), indicating partial double-bond character (Radonovich & Glick, 1973). This is further supported by the flattened dimethylamino groups; the NMe2 groups are approximately planar, with the P—N—C and C—N—C angles close to 120°, which points to sp2 hybridization and strong dπ-pπ interactions.

The geometry around phosphorus is nearly tetrahedral; however, the molecule shows marked deviations from threefold rotational symmetry around the PO bond. One of the dimethylamino group (N1, C1 and C2) is clearly distinguished from the other two in the conformation around the P—N bond. This is manifested in its torsion angles O—P—N—C = 54.1 (6) and -91.8 (6)° as compared with the corresponding values for the N2 [39.4 (6) and -153.8 (7)°] and N3 [35.9 (7) and -160.4 (6)°] moieties. Hence the molecule adopts a propeller conformation, in which one of the wings is nearly perpendicular to the others.

A closer look reveals that the geometry of the N1 group is also markedly distorted from planarity towards pyramidal geometry. The planarity of these groups has been checked by defining a least-squares plane with PCC atoms of a particular group. The N1 atom is 0.257 (7) Å apart from the plane defined by P, C1 and C2, whereas the N2 atom is 0.093 (8) Å apart from the P—C3—C4 plane and N3 is 0.120 (8) Å apart from the P—C5—C6 plane. It is also noted that the P—N1 bond is slightly longer than the other two. This is consistent with the observation that the dimethylamino group tends to depart from planarity towards pyramidal geometry as the P—N bond becomes longer (Hussain et al., 1970).

The conformational and geometrical deviation of one dimethylamino group from the other two has commonly been observed in HMPA complexes and adducts, so that one might consider it as a fundamental structural feature of the molecule. There is an important exception, however, in which all three NMe2 groups of HMPA adopt similar conformation and planarity (Brown et al., 1981). In the crystal structure of the adduct of AsMePh2S and HMPA, the torsion angles O—P—N—C are all similar [42.8 (9)–46.7 (9)° and -139.5 (10)–151.3 (9)°] and the NMe2 groups are all planar. An unusual feature of this structure is that there is no interaction between HMPA and the sulfide other than van der Waals forces.

This suggests that coordination at oxygen atom may induce the conformational and geometrical change of one NMe2 group in the HMPA complex. The torsion angle Co—O—P—N1 = 9.3 (6)° indeed indicates that the N1 moiety is particularly close to Co. Therefore, we have examined possible steric hindrance by assuming a hypothetical structure of the complex, in which the N1 group is rotated about the P—N1 bond to make the `unusual' conformation, i.e., all the NMe2 groups similar. In the resulted structure, the Co···C1 distance is estimated to be 3.2–3.5 Å. This is appreciably smaller than the closest distance [Co···C1 = 3.840 (8) Å] in the real structure. The steric repulsion may go beyond tolerance in the hypothetical conformation, leading to the rotation of one NMe2 group and the actual conformation.

Related literature top

For related literature, see: Abe & Ishiguro (1991); Abe et al. (1989, 1992); Brown et al. (1981); Gutmann (1978); Hussain et al. (1970); Normant (1967); Ozutsumi et al. (1994); Radonovich & Glick (1973); Viossat et al. (1977); Wayland & Drago (1965).

Experimental top

The complex was prepared according to the literature (Bolster & Groeneveld, 1971). The single-crystal was grown from a solution of the complex in nitromethane, and sealed in a capillary tube in the glove box over P2O5.

Refinement top

Methyl H atoms were placed at idealized tetrahedral positions with a fixed C—H distance and H—C—H angle, and refined using a riding-rotating model via SHELXL97 HFIX/AFIX 137 facility. The initial torsion angle was taken from the position of the maximum electron density in the loci of possible hydrogen positions; the H atoms were re-idealized at the start of each cycle, and the torsion angles were allowed to refine while keeping the C—H distances and H—C—H angles fixed. The displacement parameter was set as 1.5 times the equivalent isotropic displacement parameter of the methyl carbon.

Computing details top

Data collection: AFC-5S Diffractometer Control Software; cell refinement: AFC-5S Diffractometer Control Software; data reduction: AFC-5S Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Molecular diagram of (I) showing the labelling of the non-H atoms [symmetry (i): -x + 1, y, -z + 3/2]. Displacement ellipsoids are shown at 50% probability levels; H atoms are drawn as small circles of arbitrary radius.
dibromobis(hexamethylphosphoric triamide)cobalt(II) top
Crystal data top
[CoBr2(C6H18N3OP)2]F(000) = 1172
Mr = 577.16Dx = 1.585 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 23.525 (7) ÅCell parameters from 25 reflections
b = 8.2344 (8) Åθ = 13–15°
c = 15.841 (5) ŵ = 4.16 mm1
β = 127.996 (14)°T = 296 K
V = 2418.2 (11) Å3Prism, blue
Z = 40.20 × 0.20 × 0.20 mm
Data collection top
Rigaku AFC-5S
diffractometer
2027 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.115
Graphite monochromatorθmax = 28.3°, θmin = 2.2°
ω–2θ scansh = 3130
Absorption correction: ψ scan
(North et al., 1968)
k = 1010
Tmin = 0.434, Tmax = 0.435l = 2016
5914 measured reflections3 standard reflections every 60 min
2921 independent reflections intensity decay: 2%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.055Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.212H atoms treated by a mixture of independent and constrained refinement
S = 1.26 w = 1/[σ2(Fo2) + (0.0907P)2 + 4.3903P]
where P = (Fo2 + 2Fc2)/3
2921 reflections(Δ/σ)max = 0.001
120 parametersΔρmax = 1.08 e Å3
0 restraintsΔρmin = 1.04 e Å3
Crystal data top
[CoBr2(C6H18N3OP)2]V = 2418.2 (11) Å3
Mr = 577.16Z = 4
Monoclinic, C2/cMo Kα radiation
a = 23.525 (7) ŵ = 4.16 mm1
b = 8.2344 (8) ÅT = 296 K
c = 15.841 (5) Å0.20 × 0.20 × 0.20 mm
β = 127.996 (14)°
Data collection top
Rigaku AFC-5S
diffractometer
2027 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.115
Tmin = 0.434, Tmax = 0.4353 standard reflections every 60 min
5914 measured reflections intensity decay: 2%
2921 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0550 restraints
wR(F2) = 0.212H atoms treated by a mixture of independent and constrained refinement
S = 1.26Δρmax = 1.08 e Å3
2921 reflectionsΔρmin = 1.04 e Å3
120 parameters
Special details top

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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Co0.50000.19115 (12)0.75000.0328 (3)
Br0.59563 (4)0.34159 (10)0.77117 (7)0.0623 (3)
O0.4595 (2)0.0560 (5)0.6231 (3)0.0409 (9)
P0.39998 (7)0.05738 (17)0.54490 (11)0.0326 (3)
N10.3482 (3)0.1162 (7)0.5758 (4)0.0433 (12)
N20.4331 (3)0.2236 (6)0.5370 (5)0.0434 (12)
N30.3494 (3)0.0322 (7)0.4283 (4)0.0476 (12)
C10.3846 (4)0.1891 (10)0.6824 (6)0.061 (2)
H1A0.35260.26480.68010.091*
H1B0.42730.24480.70300.091*
H1C0.39760.10530.73350.091*
C20.2838 (4)0.0292 (11)0.5379 (7)0.066 (2)
H2A0.29630.06940.57800.098*
H2B0.25790.00370.46340.098*
H2C0.25410.09500.54670.098*
C30.4958 (4)0.2190 (10)0.5388 (7)0.0536 (17)
H3A0.48070.23660.46770.080*
H3B0.51880.11490.56420.080*
H3C0.52920.30250.58550.080*
C40.3988 (5)0.3856 (9)0.5063 (8)0.071 (3)
H4A0.43430.46660.55200.107*
H4B0.36130.38790.51380.107*
H4C0.37850.40770.43320.107*
C50.3018 (5)0.0596 (14)0.3303 (6)0.080 (3)
H5A0.30290.01430.27550.120*
H5B0.31750.17070.34260.120*
H5C0.25350.05480.30790.120*
C60.3353 (5)0.2058 (9)0.4187 (7)0.065 (2)
H6A0.28840.22430.39970.098*
H6B0.37110.25760.48590.098*
H6C0.33690.25000.36420.098*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Co0.0345 (5)0.0272 (5)0.0296 (5)0.0000.0161 (5)0.000
Br0.0635 (5)0.0594 (5)0.0634 (5)0.0289 (4)0.0388 (4)0.0141 (4)
O0.040 (2)0.043 (2)0.035 (2)0.0120 (18)0.0203 (19)0.0118 (19)
P0.0313 (7)0.0316 (7)0.0319 (7)0.0055 (5)0.0180 (6)0.0042 (6)
N10.041 (3)0.053 (3)0.044 (3)0.008 (2)0.030 (2)0.004 (3)
N20.045 (3)0.032 (2)0.058 (3)0.008 (2)0.034 (3)0.009 (2)
N30.051 (3)0.045 (3)0.033 (3)0.004 (2)0.019 (2)0.001 (2)
C10.059 (4)0.073 (5)0.053 (4)0.008 (4)0.036 (4)0.010 (4)
C20.039 (3)0.077 (5)0.077 (5)0.005 (4)0.034 (4)0.004 (5)
C30.054 (4)0.057 (4)0.064 (5)0.000 (3)0.043 (4)0.008 (4)
C40.076 (5)0.041 (4)0.111 (8)0.020 (4)0.065 (6)0.028 (5)
C50.066 (5)0.108 (8)0.032 (3)0.009 (5)0.014 (4)0.010 (5)
C60.062 (5)0.050 (4)0.063 (5)0.008 (4)0.028 (4)0.021 (4)
Geometric parameters (Å, º) top
Co—Bri2.4041 (10)C1—H1C0.9600
Co—Br2.4041 (10)C2—H2A0.9600
Co—Oi1.957 (4)C2—H2B0.9600
Co—O1.957 (4)C2—H2C0.9600
O—P1.493 (4)C3—H3A0.9600
P—N11.641 (5)C3—H3B0.9600
P—N21.618 (5)C3—H3C0.9600
P—N31.633 (6)C4—H4A0.9600
N1—C11.472 (9)C4—H4B0.9600
N1—C21.431 (9)C4—H4C0.9600
N2—C31.458 (8)C5—H5A0.9600
N2—C41.478 (8)C5—H5B0.9600
N3—C51.447 (9)C5—H5C0.9600
N3—C61.454 (9)C6—H6A0.9600
C1—H1A0.9600C6—H6B0.9600
C1—H1B0.9600C6—H6C0.9600
Co···P3.297 (2)N1···C53.361 (10)
Co···Pi3.297 (2)N2···C13.150 (9)
Br···O3.471 (4)N2···C53.104 (11)
O···Oi3.220 (8)N3···C22.990 (10)
O···C13.178 (9)N3···C33.433 (9)
O···C33.008 (8)C1···C3i3.491 (11)
O···C62.982 (10)C1···C43.415 (12)
N1···C43.028 (10)C2···C63.403 (12)
Br—Co—Bri117.97 (6)N1—C2—H2B109.5
Br—Co—O104.99 (12)N1—C2—H2C109.5
Br—Co—Oi109.11 (12)H2A—C2—H2B109.5
Bri—Co—O109.11 (13)H2A—C2—H2C109.5
Bri—Co—Oi104.99 (12)H2B—C2—H2C109.5
Oi—Co—O110.7 (3)N2—C3—H3A109.5
Co—O—P145.3 (3)N2—C3—H3B109.5
O—P—N1115.2 (3)N2—C3—H3C109.5
O—P—N2110.1 (3)H3A—C3—H3B109.5
O—P—N3108.3 (3)H3A—C3—H3C109.5
N1—P—N2104.8 (3)H3B—C3—H3C109.5
N1—P—N3108.2 (3)N2—C4—H4A109.5
N2—P—N3110.2 (3)N2—C4—H4B109.5
P—N1—C1116.6 (4)N2—C4—H4C109.5
P—N1—C2121.0 (5)H4A—C4—H4B109.5
C1—N1—C2113.8 (6)H4A—C4—H4C109.5
P—N2—C3120.4 (5)H4B—C4—H4C109.5
P—N2—C4126.7 (5)N3—C5—H5A109.5
C3—N2—C4111.8 (6)N3—C5—H5B109.5
P—N3—C5121.4 (6)N3—C5—H5C109.5
P—N3—C6121.5 (5)H5A—C5—H5B109.5
C5—N3—C6115.2 (7)H5A—C5—H5C109.5
N1—C1—H1A109.5H5B—C5—H5C109.5
N1—C1—H1B109.5N3—C6—H6A109.5
N1—C1—H1C109.5N3—C6—H6B109.5
H1A—C1—H1B109.5N3—C6—H6C109.5
H1A—C1—H1C109.5H6A—C6—H6B109.5
H1B—C1—H1C109.5H6A—C6—H6C109.5
N1—C2—H2A109.5H6B—C6—H6C109.5
Co—O—P—N19.3 (6)N1—P—N2—C3163.8 (5)
Co—O—P—N2127.5 (5)N1—P—N2—C429.3 (8)
Co—O—P—N3112.0 (5)N1—P—N3—C574.0 (7)
Br—Co—O—P172.1 (5)N1—P—N3—C689.6 (6)
Bri—Co—O—P44.7 (5)N2—P—N1—C166.9 (6)
Oi—Co—O—P70.3 (5)N2—P—N1—C2147.1 (6)
O—P—N1—C154.1 (6)N2—P—N3—C540.0 (7)
O—P—N1—C291.8 (6)N2—P—N3—C6156.4 (6)
O—P—N2—C339.4 (6)N3—P—N1—C1175.5 (5)
O—P—N2—C4153.8 (7)N3—P—N1—C229.5 (6)
O—P—N3—C5160.4 (6)N3—P—N2—C380.0 (6)
O—P—N3—C635.9 (7)N3—P—N2—C486.8 (7)
Symmetry code: (i) x+1, y, z+3/2.

Experimental details

Crystal data
Chemical formula[CoBr2(C6H18N3OP)2]
Mr577.16
Crystal system, space groupMonoclinic, C2/c
Temperature (K)296
a, b, c (Å)23.525 (7), 8.2344 (8), 15.841 (5)
β (°) 127.996 (14)
V3)2418.2 (11)
Z4
Radiation typeMo Kα
µ (mm1)4.16
Crystal size (mm)0.20 × 0.20 × 0.20
Data collection
DiffractometerRigaku AFC-5S
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.434, 0.435
No. of measured, independent and
observed [I > 2σ(I)] reflections
5914, 2921, 2027
Rint0.115
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.055, 0.212, 1.26
No. of reflections2921
No. of parameters120
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.08, 1.04

Computer programs: AFC-5S Diffractometer Control Software, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), SHELXL97.

Selected geometric parameters (Å, º) top
Co—Br2.4041 (10)N1—C11.472 (9)
Co—O1.957 (4)N1—C21.431 (9)
O—P1.493 (4)N2—C31.458 (8)
P—N11.641 (5)N2—C41.478 (8)
P—N21.618 (5)N3—C51.447 (9)
P—N31.633 (6)N3—C61.454 (9)
Br—Co—Bri117.97 (6)N2—P—N3110.2 (3)
Br—Co—O104.99 (12)P—N1—C1116.6 (4)
Br—Co—Oi109.11 (12)P—N1—C2121.0 (5)
Oi—Co—O110.7 (3)C1—N1—C2113.8 (6)
Co—O—P145.3 (3)P—N2—C3120.4 (5)
O—P—N1115.2 (3)P—N2—C4126.7 (5)
O—P—N2110.1 (3)C3—N2—C4111.8 (6)
O—P—N3108.3 (3)P—N3—C5121.4 (6)
N1—P—N2104.8 (3)P—N3—C6121.5 (5)
N1—P—N3108.2 (3)C5—N3—C6115.2 (7)
Co—O—P—N19.3 (6)O—P—N2—C339.4 (6)
Co—O—P—N2127.5 (5)O—P—N2—C4153.8 (7)
Co—O—P—N3112.0 (5)O—P—N3—C5160.4 (6)
O—P—N1—C154.1 (6)O—P—N3—C635.9 (7)
O—P—N1—C291.8 (6)
Symmetry code: (i) x+1, y, z+3/2.
 

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