Tetrachlorobis(N¹-phenylacet­amidino-κN²)rhenium(IV) at 11 K by X-­ray diffraction and at 20 K by neutron diffraction

The crystal structure of the title compound, [ReCl₄(C₈H₁₀N₂)₂], has been determined by X-ray diffraction at 11 K and by neutron diffraction at 20 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters at these very low temperatures is good. The results will facilitate re-examination of the magnetic structure of the complex. The Re atom lies on a special position and the molecule has twofold crystallographic symmetry.

S1. Comment

The magnetic structure of tetrachlorobis(N-phenylacetamidino)rhenium(IV), [ReCl₄(C₈H₁₀N₂)₂], (I), is of interest in chemistry and physics, as the complex is a metamagnet. It has been investigated by polarized neutron diffraction (Reynolds et al., 1997), and by examining its powder neutron diffraction structure factors at very low temperatures with and without the presence of a large magnetic field (Reynolds et al., 1999). However, the powder data do not determine the molecular structure with worthwhile accuracy, so that the interpretation of the magnetization data (Reynolds et al., 1997) depends to a large extent on the 92 K X-ray structure of Engelhardt et al. (1996). Here, we report the structure of (I) as determined by single-crystal X-ray diffraction at 11 K and neutron diffraction at 20 K. These results will allow a more accurate definition of the magnetic structure of (I) to be made. \sch

Selected bond lengths and angles for (I) are given in Table 1. The molecular structure and the thermal motion we obtained at 11 K by X-ray diffraction are illustrated in Fig. 1. Lists of calculated and observed structure factors are given in the supplementary material.

At 11 and 20 K, only zero-point thermal motion is expected to remain, so ideally the X-ray and neutron position and atomic displacement parameters should be the same. The agreement between the X-ray and neutron positional parameters is good for the C and N atoms, with average difference/sum(s.u.) = 1.2. However, for the heavier Cl and Re atoms, the results are less satisfactory, with the ratio averaging 2.5 for Cl and being 5.6 for the sole parameter, z, of Re. It may be that the s.u. for that parameter is unrealistically low. The agreement for the non-H atomic displacement parameters is quite satisfactory, with an average difference/sum(s.u.) of 1.1, although U₁₁ for Re is an exception. Probably because the X-ray experiment involved only a quadrant rather than a full sphere of data, the position is a little poorer than we have obtained previously with other very low-temperature X-ray-plus-neutron diffraction structure studies, such as for (ND₄)₂Cu(SO₄)₂·six-dimensional₂O (Iversen et al., 1994), Ni(ND₃)₄(NO₂)₂ (Iverson et al. 1996), (ND₄)₂Fe(SO₄)₂·six-dimensional₂O (Figgis et al. 1998) and Na₂Fe(CN)₅(NO)·two-dimensional₂O (Schultz et al., 2000). As pointed out by Abrahams (1997) after a detailed statistical analysis of our Ni(ND₃)₄(NO₂)₂ results, it appears probable that here, as in the earlier studies, our s.u.s are probably underestimated by a factor approaching two.

The bond lengths between Re and Cl, and within the N-phenylacetamidine ligand, agree well between the X-ray and neutron methods [average difference/sum(s.u.) = 0.6]. However, the Re—N11 bond length does not agree well, that ratio having the value of 4.3, and the length difference is 0.013 Å. This bond is directed roughly along the c crystal axis, so the discrepancy is associated with the disagreement in the Re z positional parameter.

On lowering the temperature from 92 to 11 K, the light-atom bond lengths within the N-phenylacetamidine ligand increase very slightly, but not at the significance level. The Re—N11 bond is also unchanged, but the Re—Cl bonds lengthen by ~0.05 Å, which is several times the significance level.

The refined neutron scattering length of 0.94 × 10 ^-5Å is greater by about 2% than the accepted source value of 0.92 × 10 ^-5Å (Sears, 1992). A similar difference was observed for another rhenium complex (Bullock et al., 1992).

S2. Experimental

For the X-ray structural determination, a crystal of (I) was selected from material used in previous X-ray and magnetic structural measurements (Engelhardt et al., 1996; Reynolds et al., 1999). For the neutron diffraction experiment, a crystal from the batch prepared for magnetic susceptibility measurements was chosen (Reynolds et al., 1997).

S3. Refinement

The hydrogen atoms were refined as riding on the carbon or nitrogen atom to which they are bonded. In the case of the methyl group, rotation of the hydrogen atoms about the c11–C12 bond was allowed with individual lengths to C12 but the H–C12–H angles remaining constant.

Computing details

Data collection: local diffractometer control software for (I); IPNS data acquisition software for (II). Cell refinement: local diffractometer control software for (I); LATCON (local Argonne program) for (II). Data reduction: PROFIT (Streltsov & Zavodnik, 1989) for (I); ANVRED (local Argonne program) for (II). Program(s) used to solve structure: SHELXS97 (Sheldrick, 1990) for (I). Program(s) used to refine structure: SHELXL97 (Sheldrick, 1997) for (I); ANVLS (local version of ORFLS; Busing et al., 1962) for (II). Molecular graphics: SHELXTL (Bruker, 1997) for (I); ORTEPIII (Burnett & Johnson, 1996) for (II). Software used to prepare material for publication: SHELXTL for (I).

Figures

Fig. 1. The molecular structure of (I) at 11 K. Displacement ellipsoids are shown at the 75% probability level.

(I) Tetrachlorobis(N¹-phenylacetamidino-N²)rhenium(IV)

Crystal data

[ReCl4(C8H10N2)2]	Dx = 2.029 Mg m^−3
Mr = 596.36	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pccn	Cell parameters from 14 reflections
a = 21.604 (4) Å	θ = 15.3–17.9°
b = 7.268 (1) Å	µ = 6.78 mm^−1
c = 12.436 (2) Å	T = 11 K
V = 1952.7 (5) Å^3	Bipyramid, purple
Z = 4	0.26 × 0.26 × 0.25 mm
F(000) = 1148

Data collection

Huber 512 goniometer diffractometer	2406 reflections with I > 2σ(I)
Radiation source: normal-focus sealed tube	Rint = 0.026
None monochromator	θmax = 30.1°, θmin = 1.9°
ω/2θ scans	h = −30→30
Absorption correction: gaussian (Xtal3.7; Hall et al., 2000)	k = 0→10
Tmin = 0.238, Tmax = 0.297	l = 0→17
5671 measured reflections	3 standard reflections every 100 reflections
2873 independent reflections	intensity decay: 1%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.022	H-atom parameters constrained
wR(F^2) = 0.051	w = 1/[σ^2(Fo^2) + (0.0228P)^2 + 1.5368P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.001
2873 reflections	Δρmax = 1.58 e Å^−3
131 parameters	Δρmin = −2.01 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00123 (10)

Special details

Experimental. The 11 K X-ray data set was collected on a locally assembled Huber 512 goniometer equipped with a Displex 202D cryogenic refrigerator (Henriksen et al., 1986; Larsen, 1995). For the 20 K time-of-flight neutron diffraction experiment, the sample was mounted on the Single-Crystal Diffractometer (SCD) at the Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory and cooled with a Displex closed-cycle helium refrigerator. One histogram of data was collected to check for crystal quality and to determine the initial orientation matrix using an auto-indexing routine. Seventeen time-of-flight histograms were collected with different χ and ϕ settings and covered nearly two octants of data (+/-h, +k, +l). Bragg reflections in each histogram were integrated and corrected for the Lorentz factor, the incident spectrum and the detector efficiency. A wavelength-dependent spherical absorption correction was applied, but symmetry-related reflections were not averaged because of the wavelength dependence of extinction. The unit-cell parameters for this experiment were taken from those of the 11 K X-ray experiment. For the 11 K X-ray data collection, correction for the absorption by the Be shield was performed by PROFIT (Streltsov & Zavodnik, 1989).

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 (Ų)

	x	y	z	Uiso*/Ueq
Re	0.2500	0.2500	0.083209 (10)	0.00397 (5)
Cl1	0.33668 (3)	0.05424 (8)	0.09090 (4)	0.00716 (11)
Cl2	0.29326 (3)	0.43940 (8)	−0.05339 (4)	0.00710 (10)
N1	0.28804 (10)	0.4120 (3)	0.20389 (17)	0.0075 (4)
H11	0.2648 (12)	0.4233 (7)	0.258 (3)	0.022*
N2	0.38612 (10)	0.4763 (3)	0.14182 (18)	0.0085 (4)
H12	0.3796 (3)	0.386 (4)	0.092 (2)	0.026*
C11	0.34124 (12)	0.5012 (3)	0.2137 (2)	0.0067 (4)
C12	0.35108 (12)	0.6356 (4)	0.3038 (2)	0.0092 (5)
H12A	0.3227 (12)	0.613 (3)	0.3578 (18)	0.041*
H12B	0.3459 (14)	0.754 (3)	0.2784 (9)	0.041*
H12C	0.3906 (12)	0.622 (3)	0.3307 (18)	0.041*
C13	0.44366 (11)	0.5745 (4)	0.1325 (2)	0.0070 (4)
C14	0.45149 (12)	0.6880 (4)	0.0434 (2)	0.0082 (4)
H14	0.4183 (16)	0.7117 (12)	−0.003 (2)	0.025*
C15	0.50933 (12)	0.7661 (4)	0.0237 (2)	0.0097 (5)
H15	0.5154 (3)	0.846 (4)	−0.040 (3)	0.029*
C16	0.55837 (12)	0.7321 (4)	0.0929 (2)	0.0088 (5)
H16	0.597 (2)	0.786 (3)	0.0793 (7)	0.026*
C17	0.55031 (12)	0.6195 (4)	0.1824 (2)	0.0084 (5)
H17	0.5849 (15)	0.5967 (10)	0.231 (2)	0.025*
C18	0.49289 (12)	0.5390 (4)	0.2026 (2)	0.0077 (4)
H18	0.4875 (3)	0.465 (4)	0.260 (3)	0.023*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re	0.00452 (7)	0.00618 (7)	0.00120 (7)	−0.00034 (5)	0.000	0.000
Cl1	0.0068 (2)	0.0093 (2)	0.0054 (2)	0.0012 (2)	0.00021 (19)	0.0001 (2)
Cl2	0.0077 (2)	0.0097 (2)	0.0038 (2)	−0.0010 (2)	0.0004 (2)	0.0014 (2)
N1	0.0085 (9)	0.0102 (10)	0.0037 (8)	−0.0007 (8)	−0.0009 (8)	−0.0007 (8)
N2	0.0076 (9)	0.0125 (10)	0.0054 (8)	−0.0034 (8)	0.0011 (8)	−0.0034 (8)
C11	0.0077 (10)	0.0078 (10)	0.0046 (9)	0.0020 (8)	−0.0010 (9)	0.0019 (8)
C12	0.0092 (10)	0.0115 (11)	0.0068 (11)	−0.0007 (9)	0.0023 (9)	−0.0028 (9)
C13	0.0064 (10)	0.0095 (11)	0.0051 (10)	−0.0008 (9)	−0.0003 (8)	−0.0024 (9)
C14	0.0104 (11)	0.0102 (10)	0.0040 (10)	0.0006 (9)	−0.0008 (9)	0.0001 (9)
C15	0.0131 (11)	0.0104 (12)	0.0057 (10)	−0.0003 (9)	0.0027 (9)	−0.0005 (9)
C16	0.0080 (10)	0.0096 (11)	0.0087 (11)	−0.0020 (9)	0.0015 (9)	−0.0019 (10)
C17	0.0074 (10)	0.0107 (11)	0.0072 (10)	0.0011 (9)	−0.0015 (9)	−0.0035 (9)
C18	0.0101 (11)	0.0080 (11)	0.0049 (10)	−0.0004 (9)	−0.0013 (9)	0.0001 (9)

Geometric parameters (Å, º)

Re—N1	2.077 (2)	C12—H12B	0.939
Re—N1^i	2.077 (2)	C12—H12C	0.939
Re—Cl1	2.3539 (7)	C13—C14	1.392 (4)
Re—Cl1^i	2.3539 (7)	C13—C18	1.399 (3)
Re—Cl2^i	2.3778 (6)	C14—C15	1.394 (4)
Re—Cl2	2.3778 (6)	C14—H14	0.934
N1—C11	1.325 (3)	C15—C16	1.387 (4)
N1—H11	0.842	C15—H15	0.986
N2—C11	1.331 (3)	C16—C17	1.393 (4)
N2—C13	1.438 (3)	C16—H16	0.946
N2—H12	0.910	C17—C18	1.394 (4)
C11—C12	1.502 (4)	C17—H17	0.976
C12—H12A	0.923	C18—H18	0.902
N1—Re—N1^i	87.46 (12)	C11—C12—H12A	110
N1—Re—Cl1	89.91 (6)	C11—C12—H12B	110
N1^i—Re—Cl1	86.73 (6)	H12A—C12—H12B	110
N1—Re—Cl1^i	86.73 (6)	C11—C12—H12C	110
N1^i—Re—Cl1^i	89.91 (6)	H12A—C12—H12C	110
Cl1—Re—Cl1^i	175.34 (3)	H12B—C12—H12C	110
N1—Re—Cl2^i	179.15 (6)	C14—C13—C18	120.9 (2)
N1^i—Re—Cl2^i	91.87 (6)	C14—C13—N2	117.6 (2)
Cl1—Re—Cl2^i	89.53 (2)	C18—C13—N2	121.0 (2)
Cl1^i—Re—Cl2^i	93.80 (2)	C13—C14—C15	119.3 (2)
N1—Re—Cl2	91.87 (6)	C13—C14—H14	120
N1^i—Re—Cl2	179.15 (6)	C15—C14—H14	120
Cl1—Re—Cl2	93.80 (2)	C16—C15—C14	120.3 (2)
Cl1^i—Re—Cl2	89.53 (2)	C16—C15—H15	120
Cl2^i—Re—Cl2	88.81 (3)	C14—C15—H15	120
C11—N1—Re	133.41 (19)	C15—C16—C17	120.3 (2)
C11—N1—H11	113	C15—C16—H16	120
Re—N1—H11	113	C17—C16—H16	120
C11—N2—C13	128.0 (2)	C16—C17—C18	120.1 (2)
C11—N2—H12	116	C16—C17—H17	120
C13—N2—H12	116	C18—C17—H17	120
N1—C11—N2	120.2 (2)	C17—C18—C13	119.2 (2)
N1—C11—C12	120.7 (2)	C17—C18—H18	120
N2—C11—C12	119.1 (2)	C13—C18—H18	120

Symmetry code: (i) −x+1/2, −y+1/2, z.

(II) Tetrachlorobis(N¹-phenylacetamidino-N²)rhenium(IV)

Crystal data

[ReCl4(C8H10N2)2]	Dx = 2.029 Mg m^−3
Mr = 596.36	Pulsed neutron radiation, λ = 0.7-4.2 Å
Orthorhombic, Pccn	Cell parameters from 14 reflections
a = 21.604 (4) Å	θ = 15.3–17.9°
b = 7.268 (1) Å	µ = 1.28 + 1.05 (λ) cm^-1 mm^−1
c = 12.436 (2) Å	T = 11 K
V = 1952.7 (5) Å^3	Prism, purple
Z = 4	3.0 × 2.0 × 2.0 mm
F(000) = 1148

Data collection

IPNS Single-Crystal Diffractometer	4488 reflections with I > 3σ(I)
time of flight scans	Rint = 0
Absorption correction: gaussian IPNS ANVRED program	h = −47→46
Tmin = 0.350, Tmax = 0.704	k = −15→3
5705 measured reflections	l = −3→27
5705 independent reflections

Refinement

Refinement on F	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: refall
R[F^2 > 2σ(F^2)] = 0.072	Weighting scheme based on measured s.u.'s w = [2Fo/σ(Fo^2)]^2
wR(F^2) = 0.059	(Δ/σ)max = 0.01
S = 1.58	Δρmax = 0.38 e Å^−3
4488 reflections	Δρmin = −0.28 e Å^−3
131 parameters	Extinction correction: secondary, Type I
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0-1.4 (2) × 10^-5

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

	x	y	z	Uiso*/Ueq
Re	0.25	0.25	0.08265 (9)	0.0024 (2)
Cl1	0.33682 (4)	0.0550 (1)	0.09064 (7)	0.0070 (2)
Cl2	0.29311 (4)	0.4401 (1)	−0.05358 (7)	0.0066 (2)
N1	0.28806 (4)	0.4126 (1)	0.20433 (7)	0.0065 (2)
N2	0.38596 (4)	0.4772 (1)	0.14110 (8)	0.0096 (2)
C11	0.34108 (5)	0.5017 (2)	0.2135 (1)	0.0061 (2)
C12	0.35103 (6)	0.6351 (2)	0.3038 (1)	0.0093 (3)
C13	0.44345 (6)	0.5744 (2)	0.1319 (1)	0.0067 (2)
C14	0.45163 (6)	0.6890 (2)	0.0431 (1)	0.0079 (3)
C15	0.50932 (6)	0.7666 (2)	0.0233 (1)	0.0096 (3)
C16	0.55872 (6)	0.7322 (2)	0.0934 (1)	0.0093 (3)
C17	0.55006 (6)	0.6194 (2)	0.1832 (1)	0.0078 (3)
C18	0.49233 (6)	0.5400 (2)	0.2025 (1)	0.0081 (3)
H11	0.2590 (1)	0.4380 (4)	0.2669 (2)	0.0202 (7)
H12A	0.3164 (2)	0.6201 (6)	0.3660 (3)	0.037 (1)
H12B	0.3488 (3)	0.7727 (4)	0.2721 (4)	0.044 (1)
H12C	0.3964 (2)	0.6215 (7)	0.3380 (4)	0.044 (1)
H12	0.3749 (2)	0.3995 (5)	0.0764 (3)	0.0330 (10)
H14	0.4128 (2)	0.7131 (5)	−0.0101 (3)	0.0259 (8)
H15	0.5169 (2)	0.8522 (5)	−0.0468 (3)	0.0271 (9)
H16	0.6036 (1)	0.7915 (4)	0.0772 (3)	0.0253 (8)
H17	0.5883 (1)	0.5909 (5)	0.2371 (3)	0.0281 (9)
H18	0.4864 (2)	0.4462 (5)	0.2695 (3)	0.0245 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Re	0.0004 (4)	0.0053 (4)	0.0016 (4)	−0.0012 (3)	0.0	0.0
Cl1	0.0048 (3)	0.0095 (3)	0.0067 (3)	0.0009 (3)	−0.0008 (3)	−0.0004 (3)
Cl2	0.0053 (3)	0.0093 (3)	0.0052 (3)	−0.0022 (3)	0.0000 (2)	0.0016 (3)
N1	0.0050 (3)	0.0095 (3)	0.0050 (3)	−0.0015 (3)	0.0003 (3)	−0.0011 (3)
N2	0.0064 (3)	0.0155 (4)	0.0070 (3)	−0.0047 (3)	0.0010 (3)	−0.0031 (4)
C11	0.0044 (4)	0.0088 (4)	0.0050 (4)	−0.0020 (4)	0.0006 (4)	−0.0007 (4)
C12	0.0087 (5)	0.0096 (4)	0.0097 (5)	−0.0020 (4)	0.0004 (4)	−0.0034 (5)
C13	0.0053 (4)	0.0096 (4)	0.0053 (4)	−0.0019 (4)	0.0004 (4)	−0.0001 (4)
C14	0.0074 (5)	0.0091 (4)	0.0070 (5)	0.0009 (4)	−0.0008 (4)	0.0022 (5)
C15	0.0089 (5)	0.0105 (5)	0.0092 (5)	−0.0009 (4)	0.0025 (4)	0.0009 (5)
C16	0.0081 (5)	0.0088 (4)	0.0111 (5)	−0.0015 (4)	0.0035 (4)	−0.0011 (5)
C17	0.0061 (4)	0.0105 (4)	0.0070 (5)	−0.0007 (4)	−0.0030 (4)	−0.0013 (5)
C18	0.0087 (5)	0.0087 (4)	0.0069 (4)	−0.0016 (4)	−0.0024 (4)	0.0033 (5)
H11	0.0169 (11)	0.028 (1)	0.016 (1)	−0.003 (1)	0.0049 (10)	−0.008 (1)
H12A	0.033 (2)	0.052 (2)	0.025 (2)	−0.025 (2)	0.020 (1)	−0.021 (2)
H12B	0.084 (3)	0.013 (1)	0.036 (2)	−0.002 (2)	0.002 (2)	0.001 (1)
H12C	0.024 (2)	0.068 (2)	0.040 (2)	0.013 (2)	−0.015 (2)	−0.032 (2)
H12	0.0273 (15)	0.051 (2)	0.020 (1)	−0.020 (2)	0.011 (1)	−0.019 (2)
H14	0.0226 (15)	0.035 (2)	0.021 (1)	0.004 (1)	−0.009 (1)	0.004 (2)
H15	0.0378 (19)	0.025 (1)	0.019 (1)	−0.004 (1)	0.007 (1)	0.008 (1)
H16	0.0160 (12)	0.028 (1)	0.031 (2)	−0.008 (1)	0.005 (1)	0.002 (2)
H17	0.0187 (13)	0.036 (2)	0.030 (2)	−0.002 (1)	−0.010 (1)	0.004 (2)
H18	0.0267 (14)	0.026 (1)	0.021 (1)	−0.007 (1)	−0.004 (1)	0.014 (1)

Geometric parameters (Å, º)

Re—N1	2.0888 (12)	C13—C14	1.3940 (18)
Re—Cl1	2.3532 (9)	C13—C18	1.3957 (18)
Re—Cl2	2.3764 (12)	C14—H14	1.084 (4)
N1—H11	1.017 (3)	C14—C15	1.3901 (19)
N1—C11	1.3207 (15)	C15—H15	1.083 (4)
N2—H12	1.012 (4)	C15—C16	1.401 (2)
N2—C11	1.3350 (15)	C16—H16	1.080 (3)
N2—C13	1.4334 (15)	C16—C17	1.3985 (19)
C11—C12	1.499 (2)	C17—H17	1.083 (4)
C12—H12C	1.073 (4)	C17—C18	1.3949 (18)
C12—H12B	1.075 (4)	C18—H18	1.084 (3)
C12—H12A	1.081 (4)
N1—Re—N1^i	87.16 (7)	Cl1—Re—Cl1^i	175.16 (7)
N1—Re—Cl1	89.80 (4)	Cl1—Re—Cl2	93.90 (4)
N1—Re—Cl1^i	86.69 (4)	Cl1—Re—Cl2^i	89.55 (4)
N1—Re—Cl2	91.90 (3)	Cl2^i—Re—Cl2	89.05 (6)
N1—Re—Cl2^i	178.88 (5)

Symmetry code: (i) −x+1/2, −y+1/2, z.