cis-Dinitrito(1,4,8,11-tetra­aza­cyclo­tetra­decane-κ⁴N)­chromium(III) nitrite

In the title compound, [Cr(ONO)₂(cyclam)]NO₂ (cyclam is 1,4,8,11-tetra­aza­cyclo­tetra­decane, C₁₀H₂₄N₂), the complex cation is located on a twofold symmetry axis. The central Cr atom has a distorted octahedral coordination, involving two Cr—O bonds, with the monodentate nitrite O atoms adopting a cis configuration, and four Cr—N bonds. The mean Cr—N and Cr—O distances are 2.0895 (14) and 1.9698 (14) Å.

S1. Comment

The nitrite ion is a versatile ligand that can bind transition metal ions in a number of coordination modes, giving rise to mononuclear, dinuclear and polynuclear complexes. This ion can thus act as a monodendate, chelating or bridging-bidentate ligand type (Hitchman & Rowbottom, 1982). In principle, three types of ligand binding modes are possible for mononuclear Cr^III complexes, namely the nitro (Cr—NO₂) and either the monodentate (nitrito-O) or chelating (nitrite-O,O'; Cr—ONO) binding modes. Furthermore, the cyclam (1,4,8,11-tetraazacyclotetradecane) ligand is a moderately flexible structure, which can adopt both planar (trans) and folded (cis) configurations (Poon & Pun, 1980). There are five configurational trans isomers for the cyclam, which differ in the chirality of the sec-NH centers. The trans-V configuration can fold to form the cis-V isomer. The 14-membered cyclam ligand and its derivatives are involved in diverse fields such as catalysis, enzyme mimicry, pharmacology and extraction of metal cations (Meyer et al., 1998b, and references therein). We have previously described spectroscopic and ligand-field properties on the basis of emission, far-IR and electronic spectroscopy of the cis-[Cr^III(cyclam)X₂]ⁿ⁺ system (X=en/2, pn/2, NH₃, F⁻, Cl⁻, Br⁻, NCS⁻, N₃⁻, ONO⁻, ONO₂⁻ and ox²⁻/2; Choi, 2000a; Choi, 2000b; Choi, Hong, & Park, 2002; Choi et al., 2004). The electronic absorption and vibrational spectra can be used diagnostically to identify the geometrical isomers of chromium(III) complexes (Choi, Hong & Park, 2002; Poon & Pun, 1980). However, it should be noted that the assignments based on spectral properties are not always conclusive (Stearns & Armstrong, 1992).

An X-ray crystal analysis of the chromium(III) complex, (I), with the 14-membered macrocyclic cyclam and nitrite groups was undertaken in order to confirm the type of linkage involved and to verify structural assignment made on the basis of spectroscopic measurements.

Selected bond lengths and angles for (I) are listed in Table 1. A perspective drawing of the structure, together with the atomic labeling scheme, is depicted in Fig. 1.

The complex cation is located on a twofold symmetry axis. The coordinated nitrite anions are each bound to chromium via only one O atom. The cyclam ligand is folded along the N2 and N2A direction, with four N atoms coordinating to the Cr atom, and the two nitrite ligands coordinate to the Cr atom in a cis configuration. However, the non-bonded nitrite O atoms are located trans to the Cr atom, in a monodentate nitrite coordination. The fold angle [95.09°] in the cyclam unit is slightly different from the corresponding angles [98.55, 94.51 and 92.8°] in [Cr(cyclam)(ox)]ClO₄, cis-[Cr(cyclam)(N₃)₂]ClO₄ and cis-[Cr(cyclam)Cl₂]Cl, respectively (Choi et al., 2004; Meyer et al., 1998a; Forsellini et al., 1986). The crystal structure contains a dinitrito(cyclam)chromium(III) monocation and a nitrite anion in the molecular ratio 1:1, so that the compound can be formulated as cis-[Cr(cyclam)(ONO)₂]NO₂. This structure is in agreement with the elemental analysis. The Cr1—O1 bond length is 1.9698 (14) Å, which is comparable to the distances (1.972 Å and 1.952 Å) found in the [Cr(dpt)(glygly)]⁺ and [Cr(edma)₂]⁺ moieties, respectively (Choi, Suh & Kwak, 1995; Choi et al., 2002). In (I), the Cr—N bond lengths of the CrN₄ moiety lie in the range 2.0874–2.0916 Å, and the O1—Cr1—O1A angle is 94.03 (9) Å. The Cr—N bond lengths of the secondary amine are also comparable to the Cr—N distances of the amine groups in the trans-[Cr(Me₂tn)₂Br₂]⁺ and [Cr₂(µ-OH)₂(nta)₂]²⁻ complexes (2.054–2.089 Å; Choi, Suzuki & Kaizaki, 2002; Choi, Suzuki & Kaizaki, 2003). The O1—N3 bond length is 1.317 (2) Å, while the O2—N3 bond length is 1.212 (2) Å. The (CrO)N—O bond length is shorter than the (Cr)O—N(O) bond length and is consistent with a localized double bond at this site (DeLeo et al., 2000). However, this situation contrasts with that for the [Cr(NH₃)₅ONO]Cl₂ complex, in which the two N—O distances [1.190 (4) and 1.191 (4) Å] are essentially equal (Nordin, 1978). The Cr—O—N and O—N—O bond angles are 118.99 (11) and 114.19 (16)°, respectively. The N1—Cr1—N1A angle is 169.77 (9)°, while the O1—Cr1—N2A angle is 179.19 (6)°.

As is usually observed, the five-membered chelate rings adopt a gauche configuration, and the six-membered rings adopt chair conformations. The mean bond angles in the five- and six-membered chelate rings around the Cr^III atom are 82.94 (6) and 90.14 (6)°, respectively. The central Cr atom in the complex cation has a distorted octahedral coordination, with four N atoms and with two nitrite O atoms in cis positions.

The crystals are held together by hydrogen bonds between secondary NH groups and nitrite anions. H atoms bonded to atoms N1 and N2 form hydrogen bonds with O atoms of the nitrite anion [N1—O3 = 2.890 (3) and N2—O3 = 2.949 (3) Å], as shown in Fig.2. These hydrogen-bonded networks help to stabilize the crystal structure.

S2. Experimental

The free ligand cyclam was purchased from Stream Chemicals and used as provided. All chemicals were reagent grade and used without further purification. Compound (I) was synthesized according to the method of Ferguson & Tobe (1970). Recrystallization from an ethanol/water solution gave bright orange crystals suitable for crystallographic analysis. Analysis found: C 30.12, H 5.98, N 24.53%; calculated for C₁₀H₂₄CrN₇O₆: C 30.77, H 6.19, N 25.12%.

S3. Refinement

H atoms were placed geometrically, with N—H distances of 0.91 Å and C—H distances of 0.97 Å, and treated as riding.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXTL (Bruker, 1998); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of (I), with displacement ellipsoids shown at the 30% probablility level.
	Fig. 2. The crystal packing of (I). H atoms have been omitted for clarity.

cis-Dinitrito(1,4,8,11-tetraazacyclotetradecane-κ⁴N)chromium(III) nitrite

Crystal data

[Cr(C10H24N2)(NO2)2]NO2	F(000) = 820
Mr = 390.36	Dx = 1.548 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: -C 2yc	Cell parameters from 930 reflections
a = 9.878 (2) Å	θ = 2.7–28.3°
b = 11.813 (2) Å	µ = 0.73 mm^−1
c = 14.837 (3) Å	T = 293 K
β = 104.69 (3)°	Block, orange
V = 1674.7 (6) Å^3	0.5 × 0.3 × 0.3 mm
Z = 4

Data collection

Bruker SMART CCD diffractometer	1977 independent reflections
Radiation source: fine-focus sealed tube	1771 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.073
Detector resolution: 10.00 pixels mm^-1	θmax = 28.3°, θmin = 2.7°
ω scans	h = −11→12
Absorption correction: empirical (SADABS; Sheldrick, 1999)	k = −12→15
Tmin = 0.770, Tmax = 0.804	l = −19→19
5231 measured reflections

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: inferred from neighbouring sites
wR(F^2) = 0.103	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0525P)^2 + 1.3864P] where P = (Fo^2 + 2Fc^2)/3
1977 reflections	(Δ/σ)max < 0.001
110 parameters	Δρmax = 0.45 e Å^−3
0 restraints	Δρmin = −0.79 e Å^−3

Special details

Experimental. none

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
Cr1	0.5000	0.26397 (3)	0.2500	0.01730 (14)
O1	0.39988 (13)	0.37765 (12)	0.16046 (9)	0.0280 (3)
O2	0.40060 (16)	0.52732 (14)	0.08126 (11)	0.0406 (4)
N1	0.67670 (15)	0.24817 (13)	0.19758 (11)	0.0228 (3)
H1	0.7268	0.3128	0.2147	0.027*
N2	0.39478 (14)	0.14469 (14)	0.15360 (10)	0.0226 (3)
H2	0.4250	0.0746	0.1750	0.027*
N3	0.47079 (18)	0.46261 (16)	0.13757 (12)	0.0344 (4)
C1	0.6582 (2)	0.23830 (18)	0.09495 (14)	0.0303 (4)
H1A	0.7491	0.2272	0.0825	0.036*
H1B	0.6198	0.3087	0.0655	0.036*
C2	0.5620 (2)	0.1410 (2)	0.05152 (13)	0.0335 (5)
H2A	0.5635	0.1337	−0.0133	0.040*
H2B	0.5984	0.0712	0.0829	0.040*
C3	0.4113 (2)	0.1561 (2)	0.05677 (12)	0.0306 (4)
H3A	0.3786	0.2303	0.0329	0.037*
H3B	0.3532	0.1000	0.0173	0.037*
C4	0.24362 (18)	0.15440 (18)	0.15242 (13)	0.0279 (4)
H4A	0.1917	0.0910	0.1190	0.033*
H4B	0.2048	0.2238	0.1215	0.033*
C5	0.23305 (17)	0.15471 (17)	0.25202 (13)	0.0258 (4)
H5A	0.1367	0.1666	0.2540	0.031*
H5B	0.2643	0.0826	0.2813	0.031*
N4	0.5000	−0.1376 (2)	0.2500	0.0482 (8)
O3	0.39362 (18)	−0.08144 (16)	0.2376 (2)	0.0767 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cr1	0.0149 (2)	0.0194 (2)	0.0188 (2)	0.000	0.00665 (14)	0.000
O1	0.0245 (6)	0.0267 (7)	0.0335 (7)	−0.0006 (5)	0.0084 (5)	0.0070 (6)
O2	0.0462 (9)	0.0336 (9)	0.0459 (9)	0.0079 (7)	0.0185 (7)	0.0147 (7)
N1	0.0206 (7)	0.0249 (8)	0.0261 (8)	−0.0008 (5)	0.0120 (6)	−0.0001 (6)
N2	0.0205 (7)	0.0278 (8)	0.0198 (7)	−0.0009 (6)	0.0056 (5)	0.0003 (6)
N3	0.0358 (9)	0.0328 (10)	0.0374 (9)	−0.0007 (7)	0.0144 (7)	0.0070 (8)
C1	0.0317 (9)	0.0382 (12)	0.0269 (9)	0.0010 (8)	0.0182 (8)	0.0038 (8)
C2	0.0371 (10)	0.0453 (13)	0.0221 (9)	0.0007 (9)	0.0148 (8)	−0.0049 (8)
C3	0.0314 (9)	0.0433 (12)	0.0169 (8)	−0.0022 (8)	0.0059 (7)	−0.0042 (8)
C4	0.0184 (8)	0.0356 (11)	0.0287 (9)	−0.0049 (7)	0.0045 (7)	−0.0010 (8)
C5	0.0198 (8)	0.0281 (10)	0.0317 (9)	−0.0018 (6)	0.0106 (7)	0.0026 (8)
N4	0.0312 (13)	0.0264 (14)	0.088 (2)	0.000	0.0168 (14)	0.000
O3	0.0287 (8)	0.0321 (10)	0.170 (2)	0.0005 (7)	0.0254 (11)	0.0067 (13)

Geometric parameters (Å, º)

Cr1—O1^i	1.9698 (14)	C1—H1A	0.9700
Cr1—O1	1.9698 (14)	C1—H1B	0.9700
Cr1—N2	2.0874 (16)	C2—C3	1.521 (3)
Cr1—N2^i	2.0874 (16)	C2—H2A	0.9700
Cr1—N1^i	2.0916 (15)	C2—H2B	0.9700
Cr1—N1	2.0916 (15)	C3—H3A	0.9700
O1—N3	1.317 (2)	C3—H3B	0.9700
O2—N3	1.212 (2)	C4—C5	1.508 (3)
N1—C1	1.491 (3)	C4—H4A	0.9700
N1—C5^i	1.495 (2)	C4—H4B	0.9700
N1—H1	0.9100	C5—N1^i	1.495 (2)
N2—C3	1.492 (2)	C5—H5A	0.9700
N2—C4	1.493 (2)	C5—H5B	0.9700
N2—H2	0.9100	N4—O3	1.216 (2)
C1—C2	1.525 (3)	N4—O3^i	1.216 (2)
O1^i—Cr1—O1	94.03 (9)	N1—C1—H1A	109.0
O1^i—Cr1—N2	179.19 (6)	C2—C1—H1A	109.0
O1—Cr1—N2	85.44 (7)	N1—C1—H1B	109.0
O1^i—Cr1—N2^i	85.44 (7)	C2—C1—H1B	109.0
O1—Cr1—N2^i	179.19 (6)	H1A—C1—H1B	107.8
N2—Cr1—N2^i	95.09 (9)	C3—C2—C1	113.76 (17)
O1^i—Cr1—N1^i	97.68 (6)	C3—C2—H2A	108.8
O1—Cr1—N1^i	89.31 (6)	C1—C2—H2A	108.8
N2—Cr1—N1^i	82.94 (6)	C3—C2—H2B	108.8
N2^i—Cr1—N1^i	90.14 (6)	C1—C2—H2B	108.8
O1^i—Cr1—N1	89.31 (6)	H2A—C2—H2B	107.7
O1—Cr1—N1	97.68 (6)	N2—C3—C2	112.71 (15)
N2—Cr1—N1	90.14 (6)	N2—C3—H3A	109.0
N2^i—Cr1—N1	82.94 (6)	C2—C3—H3A	109.0
N1^i—Cr1—N1	169.77 (9)	N2—C3—H3B	109.0
N3—O1—Cr1	118.99 (11)	C2—C3—H3B	109.0
C1—N1—C5^i	110.86 (14)	H3A—C3—H3B	107.8
C1—N1—Cr1	119.26 (12)	N2—C4—C5	107.84 (14)
C5^i—N1—Cr1	109.14 (10)	N2—C4—H4A	110.1
C1—N1—H1	105.5	C5—C4—H4A	110.1
C5^i—N1—H1	105.5	N2—C4—H4B	110.1
Cr1—N1—H1	105.5	C5—C4—H4B	110.1
C3—N2—C4	109.56 (14)	H4A—C4—H4B	108.5
C3—N2—Cr1	116.20 (12)	N1^i—C5—C4	108.14 (14)
C4—N2—Cr1	106.19 (11)	N1^i—C5—H5A	110.1
C3—N2—H2	108.2	C4—C5—H5A	110.1
C4—N2—H2	108.2	N1^i—C5—H5B	110.1
Cr1—N2—H2	108.2	C4—C5—H5B	110.1
O2—N3—O1	114.19 (16)	H5A—C5—H5B	108.4
N1—C1—C2	113.09 (15)	O3—N4—O3^i	113.9 (3)

Symmetry code: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O3^ii	0.91	2.03	2.890 (3)	158
N2—H2···O3	0.91	2.12	2.949 (3)	151

Symmetry code: (ii) x+1/2, y+1/2, z.