Pentaammine­nitro­syl­chromium(III) dichloride

The cation in the title compound, [Cr(NO)(NH₃)₅]Cl₂, is distorted octahedral with a linear Cr-N-O moiety. The short Cr-N(nitro­syl) distance of 1.692 (7) Å indicates significant multiple bonding between these atoms. The Cr atom, the NO group and the N atom trans to NO have m2m symmetry and the remaining N and Cl atoms have m symmetry.

Key indicators

• Single-crystal X-ray study
• T = 273 K
• Mean [sigma](O-N) = 0.008 Å
• Disorder in main residue
• R factor = 0.044
• wR factor = 0.117
• Data-to-parameter ratio = 17.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



PLAT_301  Alert B Main Residue Disorder ........................      38.00 Perc.


 Alert Level C:



PLAT_302  Alert C Anion/Solvent Disorder .......................      50.00 Perc.

General Notes



FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and the formula from the _atom_site* data.
          Atom count from _chemical_formula_sum:H15 Cl2 Cr1 N6 O1
          Atom count from the _atom_site data:  H12.5 Cl1 Cr0.25 N2.5 O0.25

ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      1.189
          Tmax scaled      0.841 Tmin scaled      0.698

CELLZ_01
         From the CIF: _cell_formula_units_Z    4
         From the CIF: _chemical_formula_sum  Cl2 Cr1 H15 N6 O1
         TEST: Compare cell contents of formula and atom_site data

         atom    Z*formula  cif sites diff
         Cl         8.00      4.00    4.00
         Cr         4.00      1.00    3.00
         H         60.00     50.00   10.00
         N         24.00     10.00   14.00
         O          4.00      1.00    3.00
          Difference between formula and atom_site contents detected.
          ALERT: Large difference may be due to a
          symmetry error - see SYMMG tests

CHEMW_03
         From the CIF: _cell_formula_units_Z                    4
         From the CIF: _chemical_formula_weight           238.06
         TEST: Calculate formula weight from _atom_site_*
         atom     mass    num     sum
         Cr       52.00    0.25   13.00
         N        14.01    2.50   35.02
         O        16.00    0.25    4.00
         Cl       35.45    1.00   35.45
         H         1.01   12.50   12.60
         Calculated formula weight              100.07
          ALERT: The ratio of given/expected molecular weight as calculated
          from the _atom_site* data lies outside
          the range 0.90 <> 1.10


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

This report is the first example of an X-ray structural study of a pentaamminenitrosylchromium complex, [Cr(NO)(NH₃)₅]²⁺, even though complexes with X = Cl, Br, NO₃, ClO₄, B(C₆H₅)₄ and OC₆H₂(NO₂)₃ have been characterized (Mori et al., 1963; Griffith et al., 1963; Kobayashi et al., 1969). The structure of related compound [Cr(NO)(H₂O)₅]SO₄ (Ardon & Cohen, 1993) has been reported. The results of ab initio calculations on [Cr(NO)(H₂O)₅]²⁺ have also been reported (Shim et al., 1995).

The title compound, [Cr(NO)(NH₃)₅]Cl₂ (Fig. 1 and Table 1), (I), was found to crystallize in the orthorhombic space group Cmcm with the Cr atom, the NO group and the N2 atom, trans to NO, having m2m symmetry imposing disorder in the N2H₃ amine group. The remaining N atoms and the Cl atom are at sites with m symmetry.

The Cr^III centre exists in a slightly distorted octahedral geometry with a strictly linear Cr—N—O arrangement (from symmetry). The N(nitrosyl)—Cr—N(ammonia, cis to NO) angles are 94.2 (1) and 92.8 (1)° so that the Cr—N(ammonia, cis to NO) bonds are slightly bent toward to the ammonia molecule in the trans position to NO.

The short Cr—N(nitrosyl) distance of 1.692 (7) Å indicates the presence of multiple bonding between these atoms. A short Cr—N(nitrosyl) distance of 1.682 (2) Å was also reported for [Cr(NO)(H₂O)₅]²⁺ (Ardon & Cohen, 1993). The Cr—N(ammonia) distances in [Cr(NH₃)₆]³⁺ are 2.070 (8) Å (Clegg et al., 1982) and 2.085 (10) Å (average; Dieterich & Stráhle, 1993). These are close to those of Cr—N(ammonia, cis to NO) in [Cr(NO)(NH₃)₅]²⁺.

The O(nitrosyl) atom appears to form hydrogen bonds with both H3 and H4 of adjacent ammonia molecules, with distances and angles as shown in Table 2.

S2. Experimental

The preparation of [Cr(NO)(NH₃)₅]Cl₂ was carried out according to the literature method (Mori et al., 1963). Crystals of [Cr(NO)(NH₃)₅]Cl₂ were obtained by recrystallization from aqueous hydrochloric acid.

S3. Refinement

All the H atoms were fixed in the refinement with isotropic displacement parameters fixed at 1.2 times the value of the equivalent isotropic displacement parameter of their carrier atom. Since the N2 atom is at a site with m2m symmetry, the six disordered H atoms of the ammonia molecule have been developed by mirror symmetry. The occupancy factors for N2 (at a site with m2m symmetry), H1 (at a site with mirror symmetry) and H2 were set to 1/4, 0.25 and 1/2, respectively.

Computing details

Data collection: CrystalClear (Rigaku, 1996); cell refinement: CrystalClear; data reduction: TEXSAN (Molecular Structure Corporation & Rigaku Corporation, 1999); program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: TEXSAN; molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: TEXSAN.

Figures

Fig. 1. The structure of the [Cr(NO)(NH3)5]^2+ cation. Displacement ellipsoids are plotted at the 50% probability level (Johnson, 1976). For clarity, only three out of the six disordered H atoms of the ammonia molecule trans to NO developed by mirror symmetry are shown.

(I)

Crystal data

[Cr(NO)(NH3)5]Cl2	F(000) = 492
Mr = 238.06	Dx = 1.674 Mg m^−3 Dm = 1.62 Mg m^−3 Dm measured by flotation
Orthorhombic, Cmcm	Mo Kα radiation, λ = 0.7107 Å
Hall symbol: -C 2c 2	Cell parameters from 1131 reflections
a = 10.0236 (9) Å	θ = 3.0–27.5°
b = 9.098 (3) Å	µ = 1.73 mm^−1
c = 10.357 (1) Å	T = 273 K
V = 944.5 (5) Å^3	Prism, orange
Z = 4	0.20 × 0.10 × 0.10 mm

Data collection

Rigaku/MSC Mercury CCD diffractometer	389 reflections with F^2 > 2σ(F^2)
Detector resolution: 7.32 pixels mm^-1	Rint = 0.084
ω scans	θmax = 27.2°
Absorption correction: multi-scan (TEXSAN; Molecular Structure Corporation & Rigaku Corporation, 1999)	h = −11→12
Tmin = 0.587, Tmax = 0.707	k = −11→11
5457 measured reflections	l = −13→11
601 independent reflections

Refinement

Refinement on F^2	H-atom parameters not refined
R[F^2 > 2σ(F^2)] = 0.044	w = 1/[σ^2(Fo^2) + (0.034P^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.117	(Δ/σ)max < 0.001
S = 0.83	Δρmax = 0.88 e Å^−3
601 reflections	Δρmin = −0.48 e Å^−3
34 parameters

Special details

Refinement. Refinement using reflections with F² > -10.0 σ(F²). The weighted R-factor (wR) and goodness of fit (S) are based on F². R-factor (gt) are based on F. The threshold expression of F² > 2.0 σ(F²) is used only for calculating R-factor (gt).

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Cr1	0.5000	0.3005 (1)	0.7500	0.0167 (3)	0.25
Cl1	0.2168 (1)	0.5000	1.0000	0.0214 (3)	0.50
O1	0.5000	0.6166 (7)	0.7500	0.028 (2)	0.25
N1	0.5000	0.4870 (7)	0.7500	0.017 (2)	0.25
N2	0.5000	0.0668 (7)	0.7500	0.025 (2)	0.25
N3	0.2926 (5)	0.2834 (5)	0.7500	0.023 (1)	0.50
N4	0.5000	0.2890 (5)	0.9513 (4)	0.020 (1)	0.50
H1	0.5894	0.0320	0.7500	0.0295*	0.25
H2	0.4553	0.0320	0.8249	0.0295*	0.50
H3	0.2678	0.1827	0.7500	0.0272*	0.50
H4	0.2578	0.3299	0.8249	0.0272*
H5	0.5000	0.1890	0.9775	0.0246*	0.50
H6	0.4226	0.3365	0.9840	0.0246*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr1	0.0186 (6)	0.0169 (7)	0.0146 (6)	0.0000	0.0000	0.0000
Cl1	0.0219 (6)	0.0220 (7)	0.0203 (6)	0.0000	0.0000	−0.0007 (5)
O1	0.023 (3)	0.038 (4)	0.025 (3)	0.0000	0.0000	0.0000
N1	0.018 (3)	0.019 (4)	0.014 (3)	0.0000	0.0000	0.0000
N2	0.034 (4)	0.017 (4)	0.022 (4)	0.0000	0.0000	0.0000
N3	0.023 (2)	0.021 (3)	0.024 (2)	−0.004 (2)	0.0000	0.0000
N4	0.023 (2)	0.018 (2)	0.020 (2)	0.0000	0.0000	0.000 (2)

Geometric parameters (Å, º)

Cr1—N1	1.697 (7)	N2—H2^ii	0.950
Cr1—N2	2.126 (7)	N2—H2^i	0.950
Cr1—N3	2.085 (4)	N2—H2^iii	0.950
Cr1—N3^i	2.085 (4)	N3—H3	0.950
Cr1—N4	2.087 (4)	N3—H4	0.950
Cr1—N4^ii	2.087 (4)	N3—H4^ii	0.950
O1—N1	1.179 (8)	N4—H5	0.950
N2—H1	0.950	N4—H6	0.950
N2—H1^i	0.950	N4—H6^i	0.950
N2—H2	0.950
Cl1···N3	3.341 (3)	Cl1···N4	3.464 (3)
Cl1···N3^iv	3.341 (3)	Cl1···N4^iv	3.464 (3)
Cl1···N2^v	3.434 (2)	O1···N4^iv	3.211 (5)
Cl1···N2^vi	3.434 (2)	O1···N4^vii	3.211 (5)
Cl1···N4^v	3.448 (4)	O1···N3^viii	3.302 (5)
Cl1···N4^vi	3.448 (4)	O1···N3^ix	3.302 (5)
N1—Cr1—N2	180.0	H1—N2—H2^i	56.2
N1—Cr1—N3	94.3 (1)	H1—N2—H2^iii	56.2
N1—Cr1—N3^i	94.3 (1)	H1^i—N2—H2	56.2
N1—Cr1—N4	92.9 (1)	H1^i—N2—H2^ii	56.2
N1—Cr1—N4^ii	92.9 (1)	H1^i—N2—H2^i	109.4
N2—Cr1—N3	85.7 (1)	H1^i—N2—H2^iii	109.4
N2—Cr1—N3^i	85.7 (1)	H2—N2—H2^ii	109.5
N2—Cr1—N4	87.1 (1)	H2—N2—H2^i	56.2
N2—Cr1—N4^ii	87.1 (1)	H2—N2—H2^iii	141.0
N3—Cr1—N3^i	171.4 (3)	H2^ii—N2—H2^i	141.0
N3—Cr1—N4	89.79 (1)	H2^ii—N2—H2^iii	56.2
N3—Cr1—N4^ii	89.79 (1)	H2^i—N2—H2^iii	109.5
N3^i—Cr1—N4	89.79 (1)	Cr1—N3—H3	109.5
N3^i—Cr1—N4^ii	89.79 (1)	Cr1—N3—H4	109.5
N4—Cr1—N4^ii	174.3 (3)	Cr1—N3—H4^ii	109.5
Cr1—N1—O1	180.0	H3—N3—H4	109.5
Cr1—N2—H1	109.5	H3—N3—H4^ii	109.5
Cr1—N2—H1^i	109.5	H4—N3—H4^ii	109.5
Cr1—N2—H2	109.5	Cr1—N4—H5	109.5
Cr1—N2—H2^ii	109.5	Cr1—N4—H6	109.5
Cr1—N2—H2^i	109.5	Cr1—N4—H6^i	109.5
Cr1—N2—H2^iii	109.5	H5—N4—H6	109.5
H1—N2—H1^i	141.0	H5—N4—H6^i	109.5
H1—N2—H2	109.4	H6—N4—H6^i	109.4
H1—N2—H2^ii	109.4

Symmetry codes: (i) −x+1, y, z; (ii) x, y, −z+3/2; (iii) −x+1, y, −z+3/2; (iv) x, −y+1, −z+2; (v) x−1/2, y+1/2, z; (vi) x−1/2, −y+1/2, −z+2; (vii) x, −y+1, z−1/2; (viii) x+1/2, y+1/2, z; (ix) −x+1/2, y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···O1^x	0.95	2.75	3.302 (6)	118
N3^i—H3^i···O1^xi	0.95	2.75	3.302 (6)	118
N4—H6···O1^xii	0.950	2.894	3.211 (5)	100.801
N4—H6^i···O1^xii	0.950	2.894	3.211 (5)	100.801
N4^ii—H6^ii···O1^xiii	0.950	2.894	3.211 (5)	100.801
N4^ii—H6^iii···O1^xiii	0.950	2.894	3.211 (5)	100.801

Symmetry codes: (i) −x+1, y, z; (ii) x, y, −z+3/2; (iii) −x+1, y, −z+3/2; (x) −x+1/2, y−1/2, z; (xi) x+1/2, y−1/2, z; (xii) x, −y+1, z+1/2; (xiii) x, −y+1, −z+1.