Bis(acesulfamato-κ²O⁴,N)bis­(3-methyl­pyridine)copper(II)

In the crystal structure of the title compound {systematic name: bis­[6-methyl-1,2,3-oxa­thia­zin-4(3H)-one 2,2-dioxide(1−)-κ²N³,O⁴]bis­(3-meth­yl­pyridine)copper(II)}, [Cu(C₄H₄NO₄S)₂(C₆H₇N)₂], the Cu^II centre resides on a centre of symmetry and has an octa­hedral geometry that is distorted both by the presence of four-membered chelate rings and because of the Jahn–Teller effect. The equatorial plane is formed by the N atoms of two methyl­pyridine ligands and by the more basic O atoms of the acesulfamate ligands, while the weakly basic N atoms of these ligands are in elongated axial positions with a misdirected valence. The crystal is stabilized by two inter­molecular C—H...O inter­actions involving the methyl and CH groups, and the sulfonyl O atoms of the acesulfamate group.

S1. Comment

The chemistry of the common artificial sweetener acesulfame (acs) is of interest not only because of its biological importance but also because of its coordination properties, since the acesulfamate anion (acs^-) offers different donor atoms to metal centres, namely ring N, carbonyl O, ring O and two sulfonyl O atoms. Despite its potential for diversity in coordination, little has been reported on the coordination behaviour of acesulfamate as a ligand. Recently, we have started to study the synthesis and the spectroscopic and structural properties of acesulfamate metal complexes (İçbudak, Heren et al., 2005; İçbudak, Bulut et al., 2005; Bulut et al., 2005; İçbudak, Adıyaman et al., 2006). The donor sites of the acesulfamate ligand are similar to those of the saccharinate anion, and therefore the coordination behaviour of the title compound, (I), can be compared with the coordination chemistry of saccharine, since all possible bonding patterns of saccharine are well documented by X-ray diffraction studies (İçbudak et al., 2002, and references therein). In order to examine the coordination behaviour of acesulfame in transition metal complexes, complex (I) has been synthesized and its crystal structure is presented here.

The molecular structure and atom-labelling scheme are shown in Fig. 1. The structure is composed of discrete [Cu(acs)₂(mepyr)₂] molecules (mepyr is methylpyridine). The copper centre is bonded to two pyridine N atoms and two bidentate acesulfamate ligands chelated through the O and the N atoms. The geometry around the copper(II) ion (Table 1) is that of a distorted octahedron, of which the equatorial plane (N2/O4/N2ⁱ/O4ⁱ) is formed by two N atoms of two trans pyridine ligands (N2 and N2ⁱ) and two O atoms of two trans-oriented acesulfamate ligands (O4 and O4ⁱ) [symmetry code: (i) -x + 1, -y, -z + 1]. The axial positions in the octahedron are occupied by two N atoms of acesulfamate ligands (N1 and N1ⁱ). The significant difference between the Cu—L_eq bond distances (Cu—O4,O4ⁱ and Cu—N2,N2ⁱ) in the equatorial plane and the Cu—L_ax distances (Cu—N1,N1ⁱ) in the axial positions (Table 1) has also been observed in other chelated copper complexes (Sieroń & Bukowska-Strżyzewska, 1997, and references therein; van Albada et al., 2002; Vinogradova et al., 2002). Sieroń & Bukowska-Strżyzewska (1997) also established a correlation between equatorial Cu—L_eq bond lengths and the average axial Cu—L_ax distances in the mixed-ligand complexes of copper pyridine-2-carboxamide. The correlation clearly indicated that the Cu—L_eq distance is inversely proportional to the axial Cu—L_ax distance. This result can easily be explained if one considers the Jahn–Teller distortion observed in most octahedral copper(II) complexes. The displacement parameter for N1 suggests a slight dynamic component to the Jahn–Teller effect, as the value of Δ(MSDA) [MSDA is mean-square displacement amplitude (Hirshfeld, 1976)] for the Cu1—N1 bond is 0.0116 (14) Ų, a value that is significantly larger than those for all of the other bonds in the structure. We note here also that the Cu1—N1 bond is significantly bent; the misdirected valence, defined as the angle between the Cu1—N1 vector and the external bisector of the C1—N1—S1 angle, has a value of 37.6 Å. The acute bite angle [59.36 (8)°] of the acesulfamate ligand is comparable to the related bite angle of 56.96° in the bis(2-aminopyrimidine)bis(nitrato)copper(II) complex (van Albada et al., 2002) and is slightly larger than that in bis(nicotinamide)bis(salicylato)copper(II) [52.72 (7)°; Leban et al., 1997].

With regard to the acesulfame ligand, the metal coordination of the O atom affects the C—O bond length [1.267 (4) Å], which is greater than the related bond length in [Co(acs)₂(H₂O)₄] (İçbudak, Bulut et al., 2005) and in the potassium salt of acs (Paulus, 1975). It is evident from the Cu—O_eq and Cu—N_ax bond distances that the O atom is coordinated much more strongly than the N atom. This suggests that the O atom is a better donor than the N atom, perhaps because it is more electronegative in the N—C—O link, showing a partial multiple-bond character. Some changes were also observed in the ring angles, and the maximum deviation from the values for the potasium salt is 3.4°, observed for the O1—S1—N1 angle. This change probably originates from the bidentate coordination behaviour of the acesulfamate ligand. The acesulfame ring adopts a half-chair conformation, as is evident from the puckering parameters [Q = 0.365 (2) Å, θ = 61.6 (5)° and φ = 6.902 (14)° for the atom sequence S1—O1—C3—C2—C1—N1 (Cremer & Pople, 1975)]. The 3-methylpyridine ligands are planar. Their individual bond lengths do not depart significantly from their respective mean values and correspond well to those reported for this ligand in other complexes (Rotondo, 2006; Aygün et al., 2005; Goto et al., 2000; Nakagawa et al., 2000).

Because the acesulfamate and saccharinate ligands are similar in terms of donor sites, we can compare the metal coordination of acesulfamate with that of related saccharinate complexes. From that point of view, an N···O_CO chelate of acesulfamate is very interesting, since this behaviour is only observed in cases of high metal coordination numbers for saccharinate complexes and was only suggested for large ionic radii in rare-earth complexes, e.g. europium(III) (Zheng, 1996). This mode has also been exclusively reported in the structure of lead(II) saccharinate, which has N and carbonyl O atoms from the same saccharinate ion coordinated to the same lead(II) cation. These studies for metal saccharine led to a conclusion that the chelating behaviour can only be observed for heavy metals, not for lighter ones (Baran et al., 2000). The strong Cu—O interaction observed in this study is interesting because M—N is the most common coordination mode in transition metal complexes of saccharine. It is also known that M—O coordination only predominates in the case of alkaline and alkaline-earth saccharinates (Falvello et al., 2001; Baran et al., 2000; Haider et al., 1983).

In the crystal structure of (I), there are two intermolecular interactions of type C—H···O, which stabilize the crystal packing (Fig. 2). The first of these is between atom H4C of the methyl group of the acesulfamate ligand and the sulfonyl O atom of a neighbouring molecule. The second is between atom H2 of the acesulfamate ligand and the sulfonyl O atom of an adjacent molecule. There are no other significant interactions, such as π—π and C—H···π interactions, in the crystal structure of (I).

S2. Experimental

[Cu(acs)₂(H₂O)₄] (0.92 g, 2 mmol) was dissolved in methanol (60 ml) and 3-methylpyridine (0.37 g, 4 mmol) in methanol (30 ml) was added to the stirred solution. The mixture was stirred at 323 K for 2 h and was then cooled to ambient temperature and filtered. The resulting dark-blue crystals were washed with methanol and dried under vacuum (yield 77.0%).

S3. Refinement

H atoms were positioned geometrically and treated using a riding model, fixing the bond lengths at 0.96 and 0.93 Å for CH₃ and aromatic atoms, respectively. The displacement parameters of the H atoms were constrained as U_iso(H) = 1.2U_eq(C)[1.5U_eq(C) for methyl H atoms] of the parent atom. The H atoms of one of the methyl groups were found to be disordered over two positions and option AFIX 123 of SHELXL97 (Sheldrick, 1997) was used.

Computing details

Data collection: X-AREA (Stoe & Cie, 2002); cell refinement: X-AREA; data reduction: X-RED32 (Stoe & Cie, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 2003).

Figures

	Fig. 1. A view of the title molecule, with atoms shown as 50% probability displacement elipsoids. Only one set of the disordered methyl H atoms has been included. [Symmetry code: (i) 1 - x, -y, 1 - z.]
	Fig. 2. The hydrogen bonding interactions in the lattice of (I) shown as dashed lines, with atoms shown as 30% probability displacement elipsoids. For clarity, H atoms not involved in hydrogen bonding have been omitted.

Bis[6-methyl-1,2,3-oxathiazin-4(3H)-one 2,2-dioxide(1-)-κ²N³,O⁴]bis(3-methylpyridine)copper(II)

Crystal data

[Cu(C4H4O4NS)2(C6H7N)2]	F(000) = 590
Mr = 574.08	Dx = 1.601 Mg m^−3
MonoclinicP21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 47042 reflections
a = 10.7385 (6) Å	θ = 2.2–27.9°
b = 9.1792 (7) Å	µ = 1.15 mm^−1
c = 12.5005 (8) Å	T = 296 K
β = 104.892 (5)°	Prism, blue
V = 1190.80 (14) Å^3	0.49 × 0.43 × 0.37 mm
Z = 2

Data collection

Stoe IPDS-2 diffractometer	2736 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm long-fine focus	2395 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.046
Detector resolution: 6.67 pixels mm^-1	θmax = 27.6°, θmin = 2.8°
ω scans	h = −13→13
Absorption correction: integration (X-RED32; Stoe & Cie, 2002)	k = −11→11
Tmin = 0.581, Tmax = 0.699	l = −16→16
18687 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)] = 0.048	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.119	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0452P)^2 + 2.0095P] where P = (Fo^2 + 2Fc^2)/3
2736 reflections	(Δ/σ)max = 0.001
155 parameters	Δρmax = 0.92 e Å^−3
0 restraints	Δρmin = −1.29 e Å^−3

Special details

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 > 2σ(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	Occ. (<1)
Cu1	0.5000	0.0000	0.5000	0.03805 (16)
S1	0.15288 (8)	0.04844 (9)	0.31144 (6)	0.0432 (2)
O1	0.0570 (2)	0.1674 (3)	0.34204 (19)	0.0511 (6)
O2	0.0935 (3)	−0.0885 (3)	0.3119 (2)	0.0642 (7)
O3	0.1724 (3)	0.0980 (4)	0.2098 (2)	0.0774 (9)
O4	0.37662 (18)	0.0765 (2)	0.58717 (18)	0.03805 (16)
N1	0.2811 (2)	0.0612 (3)	0.4071 (2)	0.0430 (6)
N2	0.5560 (2)	0.2034 (3)	0.4786 (2)	0.0385 (5)
C1	0.2744 (3)	0.0914 (3)	0.5103 (3)	0.0399 (6)
C2	0.1575 (3)	0.1469 (3)	0.5332 (3)	0.0394 (6)
H2	0.1524	0.1551	0.6061	0.047*
C3	0.0579 (3)	0.1862 (3)	0.4515 (3)	0.0395 (6)
C4	−0.0617 (3)	0.2603 (4)	0.4616 (3)	0.0586 (9)
H4A	−0.1177	0.2758	0.3891	0.088*	0.50
H4B	−0.0400	0.3524	0.4980	0.088*	0.50
H4C	−0.1046	0.2006	0.5041	0.088*	0.50
H4D	−0.0572	0.2767	0.5383	0.088*	0.50
H4E	−0.1349	0.2001	0.4295	0.088*	0.50
H4F	−0.0703	0.3520	0.4234	0.088*	0.50
C5	0.5287 (3)	0.2654 (4)	0.3786 (3)	0.0479 (7)
H5	0.4768	0.2156	0.3187	0.057*
C6	0.5752 (4)	0.4008 (4)	0.3619 (3)	0.0566 (9)
H6	0.5556	0.4417	0.2914	0.068*
C7	0.6512 (3)	0.4752 (4)	0.4506 (3)	0.0519 (8)
H7	0.6838	0.5665	0.4402	0.062*
C8	0.6788 (3)	0.4142 (3)	0.5548 (3)	0.0436 (7)
C9	0.6285 (3)	0.2777 (3)	0.5643 (3)	0.0403 (6)
H9	0.6460	0.2351	0.6341	0.048*
C10	0.7622 (4)	0.4886 (5)	0.6547 (4)	0.0719 (12)
H10A	0.7469	0.4466	0.7205	0.108*
H10B	0.7418	0.5906	0.6521	0.108*
H10C	0.8512	0.4762	0.6554	0.108*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0325 (3)	0.0296 (3)	0.0512 (3)	−0.00081 (18)	0.0092 (2)	−0.0023 (2)
S1	0.0548 (5)	0.0389 (4)	0.0388 (4)	0.0064 (3)	0.0170 (3)	0.0020 (3)
O1	0.0550 (13)	0.0553 (14)	0.0430 (12)	0.0197 (11)	0.0126 (10)	0.0059 (10)
O2	0.0763 (18)	0.0438 (14)	0.0656 (17)	−0.0093 (13)	0.0060 (14)	−0.0075 (12)
O3	0.109 (2)	0.083 (2)	0.0511 (16)	0.0258 (18)	0.0414 (16)	0.0188 (14)
O4	0.0325 (3)	0.0296 (3)	0.0512 (3)	−0.00081 (18)	0.0092 (2)	−0.0023 (2)
N1	0.0408 (13)	0.0370 (13)	0.0569 (16)	0.0028 (11)	0.0229 (12)	−0.0027 (11)
N2	0.0337 (12)	0.0312 (12)	0.0502 (15)	0.0000 (9)	0.0102 (10)	−0.0011 (10)
C1	0.0350 (14)	0.0285 (13)	0.0552 (18)	−0.0006 (11)	0.0099 (13)	−0.0008 (12)
C2	0.0405 (15)	0.0390 (15)	0.0406 (16)	0.0069 (12)	0.0137 (12)	−0.0013 (12)
C3	0.0419 (15)	0.0362 (15)	0.0443 (16)	0.0047 (12)	0.0180 (13)	0.0020 (12)
C4	0.0498 (19)	0.063 (2)	0.068 (2)	0.0234 (17)	0.0230 (17)	0.0121 (18)
C5	0.0532 (19)	0.0430 (17)	0.0450 (18)	−0.0016 (14)	0.0082 (14)	−0.0022 (14)
C6	0.073 (2)	0.0475 (19)	0.052 (2)	0.0034 (17)	0.0201 (18)	0.0111 (16)
C7	0.0527 (19)	0.0354 (16)	0.073 (2)	−0.0051 (14)	0.0257 (17)	0.0032 (15)
C8	0.0339 (14)	0.0345 (15)	0.062 (2)	−0.0001 (12)	0.0107 (13)	−0.0064 (14)
C9	0.0373 (14)	0.0336 (15)	0.0474 (17)	0.0032 (11)	0.0064 (12)	0.0014 (12)
C10	0.061 (2)	0.058 (2)	0.085 (3)	−0.0134 (19)	−0.004 (2)	−0.017 (2)

Geometric parameters (Å, º)

Cu1—N2^i	2.001 (2)	C4—H4A	0.9600
Cu1—N2	2.001 (2)	C4—H4B	0.9600
Cu1—O4	2.044 (2)	C4—H4C	0.9600
Cu1—O4^i	2.044 (2)	C4—H4D	0.9600
Cu1—N1^i	2.405 (3)	C4—H4E	0.9600
Cu1—N1	2.405 (3)	C4—H4F	0.9600
S1—O2	1.411 (3)	C5—C6	1.376 (5)
S1—O3	1.415 (3)	C5—H5	0.9300
S1—N1	1.579 (3)	C6—C7	1.377 (5)
S1—O1	1.613 (2)	C6—H6	0.9300
O1—C3	1.377 (4)	C7—C8	1.378 (5)
O4—C1	1.267 (4)	C7—H7	0.9300
N1—C1	1.340 (4)	C8—C9	1.382 (4)
N2—C5	1.335 (4)	C8—C10	1.501 (5)
N2—C9	1.338 (4)	C9—H9	0.9300
C1—C2	1.449 (4)	C10—H10A	0.9600
C2—C3	1.325 (4)	C10—H10B	0.9600
C2—H2	0.9300	C10—H10C	0.9600
C3—C4	1.487 (4)
N2^i—Cu1—N2	180.00 (5)	H4A—C4—H4B	109.5
N2^i—Cu1—O4	89.49 (9)	C3—C4—H4C	109.5
N2—Cu1—O4	90.51 (9)	H4A—C4—H4C	109.5
N2^i—Cu1—O4^i	90.51 (9)	H4B—C4—H4C	109.5
N2—Cu1—O4^i	89.49 (9)	C3—C4—H4D	109.5
O4—Cu1—O4^i	180.00 (9)	H4A—C4—H4D	141.1
N2^i—Cu1—N1^i	90.42 (9)	H4B—C4—H4D	56.3
N2—Cu1—N1^i	89.58 (9)	H4C—C4—H4D	56.3
O4—Cu1—N1^i	120.64 (8)	C3—C4—H4E	109.5
O4^i—Cu1—N1^i	59.36 (8)	H4A—C4—H4E	56.3
N2^i—Cu1—N1	89.58 (9)	H4B—C4—H4E	141.1
N2—Cu1—N1	90.42 (9)	H4C—C4—H4E	56.3
O4—Cu1—N1	59.36 (8)	H4D—C4—H4E	109.5
O4^i—Cu1—N1	120.64 (8)	C3—C4—H4F	109.5
N1^i—Cu1—N1	180.0	H4A—C4—H4F	56.3
O2—S1—O3	117.5 (2)	H4B—C4—H4F	56.3
O2—S1—N1	111.73 (16)	H4C—C4—H4F	141.1
O3—S1—N1	110.76 (19)	H4D—C4—H4F	109.5
O2—S1—O1	106.57 (16)	H4E—C4—H4F	109.5
O3—S1—O1	104.25 (16)	N2—C5—C6	121.7 (3)
N1—S1—O1	104.84 (13)	N2—C5—H5	119.1
C3—O1—S1	118.61 (19)	C6—C5—H5	119.1
C1—O4—Cu1	100.79 (19)	C5—C6—C7	119.3 (3)
C1—N1—S1	119.5 (2)	C5—C6—H6	120.4
C1—N1—Cu1	82.61 (18)	C7—C6—H6	120.4
S1—N1—Cu1	154.46 (15)	C6—C7—C8	119.9 (3)
C5—N2—C9	118.4 (3)	C6—C7—H7	120.1
C5—N2—Cu1	121.4 (2)	C8—C7—H7	120.1
C9—N2—Cu1	120.1 (2)	C7—C8—C9	117.1 (3)
O4—C1—N1	117.2 (3)	C7—C8—C10	122.6 (3)
O4—C1—C2	121.0 (3)	C9—C8—C10	120.3 (3)
N1—C1—C2	121.8 (3)	N2—C9—C8	123.6 (3)
C3—C2—C1	120.9 (3)	N2—C9—H9	118.2
C3—C2—H2	119.6	C8—C9—H9	118.2
C1—C2—H2	119.6	C8—C10—H10A	109.5
C2—C3—O1	122.0 (3)	C8—C10—H10B	109.5
C2—C3—C4	127.1 (3)	H10A—C10—H10B	109.5
O1—C3—C4	110.8 (3)	C8—C10—H10C	109.5
C3—C4—H4A	109.5	H10A—C10—H10C	109.5
C3—C4—H4B	109.5	H10B—C10—H10C	109.5
O2—S1—O1—C3	80.3 (3)	O4^i—Cu1—N2—C9	−109.1 (2)
O3—S1—O1—C3	−154.7 (3)	N1^i—Cu1—N2—C9	−49.7 (2)
N1—S1—O1—C3	−38.3 (3)	N1—Cu1—N2—C9	130.3 (2)
N2^i—Cu1—O4—C1	−88.37 (18)	Cu1—O4—C1—N1	−2.5 (3)
N2—Cu1—O4—C1	91.63 (18)	Cu1—O4—C1—C2	−179.0 (2)
N1^i—Cu1—O4—C1	−178.56 (16)	S1—N1—C1—O4	168.4 (2)
N1—Cu1—O4—C1	1.44 (16)	Cu1—N1—C1—O4	2.1 (2)
O2—S1—N1—C1	−80.2 (3)	S1—N1—C1—C2	−15.1 (4)
O3—S1—N1—C1	146.8 (3)	Cu1—N1—C1—C2	178.6 (3)
O1—S1—N1—C1	34.9 (3)	O4—C1—C2—C3	168.2 (3)
O2—S1—N1—Cu1	66.9 (4)	N1—C1—C2—C3	−8.1 (5)
O3—S1—N1—Cu1	−66.2 (4)	C1—C2—C3—O1	4.4 (5)
O1—S1—N1—Cu1	−178.1 (3)	C1—C2—C3—C4	−172.4 (3)
N2^i—Cu1—N1—C1	88.31 (18)	S1—O1—C3—C2	21.4 (4)
N2—Cu1—N1—C1	−91.69 (18)	S1—O1—C3—C4	−161.4 (2)
O4—Cu1—N1—C1	−1.35 (15)	C9—N2—C5—C6	1.4 (5)
O4^i—Cu1—N1—C1	178.65 (15)	Cu1—N2—C5—C6	−174.9 (3)
N2^i—Cu1—N1—S1	−63.2 (4)	N2—C5—C6—C7	−0.5 (6)
N2—Cu1—N1—S1	116.8 (4)	C5—C6—C7—C8	−0.5 (6)
O4—Cu1—N1—S1	−152.8 (4)	C6—C7—C8—C9	0.6 (5)
O4^i—Cu1—N1—S1	27.2 (4)	C6—C7—C8—C10	179.3 (4)
O4—Cu1—N2—C5	−112.9 (2)	C5—N2—C9—C8	−1.2 (4)
O4^i—Cu1—N2—C5	67.1 (2)	Cu1—N2—C9—C8	175.1 (2)
N1^i—Cu1—N2—C5	126.5 (2)	C7—C8—C9—N2	0.2 (5)
N1—Cu1—N2—C5	−53.5 (2)	C10—C8—C9—N2	−178.4 (3)
O4—Cu1—N2—C9	70.9 (2)

Symmetry code: (i) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C4—H4C···O2^ii	0.96	2.49	3.334 (5)	146
C2—H2···O3^iii	0.93	2.59	3.194 (4)	123

Symmetry codes: (ii) −x, −y, −z+1; (iii) x, −y+1/2, z+1/2.