Bis(acesulfamato-κ²N³,O⁴)bis­(2-amino­pyrimidine-κN¹)copper(II)

In the crystal structure of the title compound, bis­(2-amino­pyrimidine-κN¹)bis­[6-meth­yl-1,2,3-oxathia­zin-4(3H)-one 2,2-dioxide(1−)-κ²N³,O⁴]copper(II), [Cu(C₄H₄NO₄S)₂(C₄H₅N₃)₂], the first mixed-ligand complex of acesulfame, 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 by the Jahn–Teller effect. The equatorial plane is formed by the N atoms of two amino­pyrimidine (ampym) ligands and by the weakly basic carbonyl O atoms of the acesulfamate ligands, while the more basic deprotonated N atoms of these ligands are in the elongated axial positions with a strong misdirected valence. The crystal is stabilized by pyrimidine ring stacking and by inter­molecular hydrogen bonding involving the NH₂ moiety of the ampym ligand and the carbon­yl O atom of the acesulfamate moiety.

S1. Comment

The chemistry of the common artificial sweetener acesulfame (acs; C₄H₅SO₄N) is of interest not only because of its biological importance but also because of its coordination properties, since the acesulfame anion (acs⁻) offers different donor atoms to metal centers, namely N, O(carbonyl), O(ring) and two O(sulfonyl) 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). The donor sites of the acesulfamate ligand are similar to those of the saccharinate anion, and therefore the coordination behaviour of the title compound 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). As a part of our ongoing research on the coordination behaviour of acesulfame in transition metal complexes, the title complex has been synthesized and its crystal structure determined.

The molecular structure and atom labeling scheme are shown in Fig. 1. The structure is composed of discrete [Cu(ampym)₂(acs)₂] molecules. The copper centre is bonded to two pyrimidine N atoms and two bidentate acesulfamate ligands chelated through the carbonyl 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—O1—N2ⁱ—O1ⁱ) is formed by two N atoms of two trans ampym ligands (N2 and N2ⁱ) and two carbonyl O atoms of two trans-oriented acesulfamate ligands (O1 and O1ⁱ) [symmetry code: (i) 1 − x, −y, −z]. The axial positions in the octahedron are occupied by two N atoms of acesulfamate ligands (N1 and N1ⁱ), with a Cu—N1 distance of 2.4597 (16) Å. The significant difference between Cu—L bond distances [Cu—O1/O1ⁱ = 2.0107 (13) Å and Cu—N2/N2ⁱ = 2.0046 (16) Å] in the equatorial plane and the Cu—L distances [Cu—N1/N1ⁱ = 2.4597 (16) Å] in the axial positions was also observed in other chelated copper complexes (Sieron & Bukowska-Strzyzewska, 1997, and references therein; Albada et al., 2002). Sieron & Bukowska-Strzyzewska (1997) also established a correlation between equatorial Cu—L bond lengths and the average axial Cu—L distances in the mixed-ligand complexes of copper pyridine-2-carboxamide. The correlation clearly indicated that the Cu—L distance in the equatorial plane is inversely proportional to the axial Cu—L distance. This result can easily be explained if one considers the Jahn–Teller distortion observed in most octahedral copper(II) complexes. The displacement parameters for N1 and O1 suggest a slight dynamic component to the Jahn–Teller effect, as the values of Δ(MSDA) (Hirshfeld, 1976) for the Cu1—N1 and Cu1—O1 bonds are 0.0047 (9) and 0.0046 (7) Ų, respectively, values which are 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 mis-directed valence, defined as the angle between the Cu1—N1 vector and the external bisector of the C1—N1—S1 angle, has a value of 41.8°. The acute angle [58.79 (5)°] of the acesulfamate ligand is comparable to the related bite angle of 56.96° in the 2-aminopyrimidinenitrato–copper(II) complex (Albada et al., 2002) and is slightly larger than that of nicotinamide salicylato copper(II) [52.72 (7)°; Leban et al., 1997].

With regard to the acesulfame ligand, the metal coordination of the carbonyl O atom affects the C—O bond length [1.274 (2) Å], which is greater than the related bond length in [Co(acs)₂(H₂O)₄] (İçbudak & Bulut et al., 2005) and in the potasium salt of acs (Paulus, 1975). Some changes were also observed in the ring angles, and the maximum deviation from its potasium salt is 3.6°, observed for O2—S1—N1. This change probably originates from the bidentate coordination behaviour of the acesulfamate ligand. The 2-aminopyrimidine ligands are almost 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 (Albada et al., 2004; Altin et al., 2004; Prince et al., 2003; Masaki et al., 2002).

Because of the similarities of acesulfamate ligand with the saccharinate ligand in terms of donor sites, we can compare the metal coordination of acesulfamate with 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). It is worth mentioning here that 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).

The lattice is stabilized by stacking of the pyrimidine rings, with an interplanar distance of 3.9502 (15) Å, and by the hydrogen-bonding interaction between H4 of the amine group and the carbonyl O atom of a neighbouring molecule [H4D···O1 = 2.245 Å, N4—H4D···O1 = 161.89° and N4···O1 = 3.074 (2) Å].

S2. Experimental

[Cu(acs)₂(H₂O)₄] (0.460 g, 1 mmol) was dissolved in ethanol (30 ml), and 2-aminopryminide (0.190 g, 2 mmol, ampym) in ethanol (30 ml) was added to the stirred solution. The mixture was further stirred at 323 K for 1 h and was then cooled to ambient temperature. The resulting blue crystals were washed with acetone and dried under vacuum. Yield: 93.00%.

S3. Refinement

The methyl H atoms were placed at idealized positions (C—H = 0.96 Å) with the torsion angles established from a difference map, and were allowed to ride on the parent atom [U_iso(H) = 1.5U_eq(C)]. The other H atoms were placed at calculated positions (C—H = 0.93 Å and N—H = 0.85 Å) and were allowed to ride on the parent atom [U_iso(H) = 1.2U_eq(C,N)]. The highest peak is 0.90 Å atom Cu1.

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 (Burnett & Johnson, 1996); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. : An ORTEPIII view of the title molecule, with atoms illustrated by 50% probability displacement elipsoids. [Symmetry code: (ii) 1 − x, −y, −z.]
	Fig. 2. : The three-dimensional structure of the neutral complex. Dashed lines illustrate the π–π and hydrogen-bond interactions. H atoms, except for NH2 H atoms, have been omitted for clarity. [Symmetry codes: (ii) 1 − x, 1 − y, 1 − z; (iii) −1/2 + x, 1/2 − y, 1/2 + z.]

bis[6-methyl-1,2,3-oxathiazin-4(3H)-one 2,2-dioxide(1-)-κ²N³,O⁴]bis(2-aminopyrimidine-κN¹)copper(II)

Crystal data

[Cu(C4H4NO4S)2(C4H5N3)2]	F(000) = 590
Mr = 578.04	Dx = 1.730 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 12380 reflections
a = 10.6129 (9) Å	θ = 2.1–27.6°
b = 8.9750 (5) Å	µ = 1.24 mm^−1
c = 12.6808 (10) Å	T = 296 K
β = 113.227 (6)°	Prism, blue
V = 1109.96 (14) Å^3	0.54 × 0.47 × 0.20 mm
Z = 2

Data collection

STOE IPDS-II diffractometer	2458 independent reflections
Radiation source: sealed X-ray tube, 12 x 0.4 mm fine focus	2345 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.121
Detector resolution: 6.67 pixels mm^-1	θmax = 27.3°, θmin = 2.1°
ω scans	h = −13→13
Absorption correction: integration X-RED32 (Stoe & Cie, 2002)	k = −11→11
Tmin = 0.467, Tmax = 0.582	l = −16→16
16919 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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.116	H-atom parameters constrained
S = 1.22	w = 1/[σ^2(Fo^2) + (0.0713P)^2 + 0.1622P] where P = (Fo^2 + 2Fc^2)/3
2458 reflections	(Δ/σ)max = 0.001
161 parameters	Δρmax = 1.27 e Å^−3
0 restraints	Δρmin = −0.69 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 > 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
C1	0.72164 (19)	0.1135 (2)	−0.00912 (16)	0.0298 (4)
C2	0.85671 (19)	0.1692 (2)	0.01033 (17)	0.0347 (4)
H2	0.9131	0.2034	0.0829	0.042*
C3	0.9020 (2)	0.1723 (2)	−0.07398 (19)	0.0364 (4)
C4	1.0415 (2)	0.2159 (3)	−0.0634 (3)	0.0523 (6)
H4A	1.1034	0.2129	0.0159	0.078*
H4B	1.0389	0.3150	−0.0926	0.078*
H4C	1.0724	0.1478	−0.1066	0.078*
C5	0.66279 (19)	−0.2708 (2)	0.11587 (17)	0.0315 (4)
C6	0.6838 (4)	−0.4791 (3)	0.0236 (3)	0.0545 (7)
H6	0.7156	−0.5761	0.0258	0.065*
C7	0.6122 (3)	−0.4163 (3)	−0.0825 (2)	0.0507 (6)
H7	0.5969	−0.4671	−0.1504	0.061*
C8	0.5650 (2)	−0.2745 (2)	−0.08194 (19)	0.0400 (4)
H8	0.5159	−0.2275	−0.1515	0.048*
Cu1	0.5000	0.0000	0.0000	0.02679 (15)
N1	0.63142 (16)	0.0758 (2)	−0.11324 (14)	0.0338 (4)
N2	0.58751 (17)	−0.20133 (18)	0.01641 (14)	0.0305 (3)
N3	0.7103 (2)	−0.4109 (2)	0.12225 (18)	0.0446 (4)
N4	0.6951 (2)	−0.1999 (2)	0.21567 (15)	0.0413 (4)
H4D	0.7436	−0.2440	0.2789	0.050*
H4E	0.6675	−0.1101	0.2167	0.050*
O1	0.68686 (14)	0.09273 (16)	0.07514 (12)	0.0335 (3)
O2	0.82033 (17)	0.12882 (19)	−0.18348 (14)	0.0437 (4)
O3	0.6014 (2)	0.0349 (3)	−0.31489 (16)	0.0607 (5)
O4	0.61899 (19)	0.28807 (19)	−0.24314 (15)	0.0508 (4)
S1	0.65560 (5)	0.13551 (6)	−0.22164 (4)	0.03653 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0310 (8)	0.0239 (8)	0.0307 (9)	0.0004 (6)	0.0082 (7)	−0.0002 (6)
C2	0.0297 (9)	0.0352 (10)	0.0331 (9)	−0.0039 (7)	0.0058 (7)	−0.0019 (7)
C3	0.0316 (9)	0.0342 (10)	0.0407 (10)	0.0015 (7)	0.0113 (8)	0.0040 (8)
C4	0.0363 (11)	0.0551 (15)	0.0680 (16)	−0.0005 (10)	0.0234 (11)	0.0116 (12)
C5	0.0320 (9)	0.0271 (9)	0.0377 (10)	0.0014 (7)	0.0161 (8)	0.0044 (7)
C6	0.0770 (19)	0.0263 (10)	0.0728 (18)	0.0078 (10)	0.0431 (16)	−0.0002 (10)
C7	0.0723 (16)	0.0366 (11)	0.0540 (13)	−0.0050 (11)	0.0367 (13)	−0.0136 (10)
C8	0.0490 (11)	0.0369 (11)	0.0360 (10)	−0.0052 (9)	0.0188 (9)	−0.0064 (8)
Cu1	0.0280 (2)	0.0239 (2)	0.0261 (2)	−0.00003 (9)	0.00814 (15)	0.00042 (9)
N1	0.0308 (8)	0.0371 (9)	0.0296 (8)	−0.0056 (6)	0.0075 (6)	−0.0007 (6)
N2	0.0336 (8)	0.0276 (8)	0.0306 (8)	0.0006 (6)	0.0130 (6)	−0.0008 (6)
N3	0.0559 (11)	0.0294 (9)	0.0535 (11)	0.0089 (8)	0.0267 (10)	0.0079 (8)
N4	0.0483 (10)	0.0368 (10)	0.0314 (9)	0.0090 (7)	0.0078 (7)	0.0034 (7)
O1	0.0345 (7)	0.0346 (7)	0.0294 (7)	−0.0035 (5)	0.0104 (5)	−0.0008 (5)
O2	0.0430 (8)	0.0532 (10)	0.0380 (8)	0.0002 (7)	0.0191 (7)	−0.0030 (7)
O3	0.0761 (14)	0.0649 (11)	0.0339 (9)	−0.0209 (10)	0.0141 (9)	−0.0175 (8)
O4	0.0520 (9)	0.0443 (10)	0.0445 (9)	0.0029 (7)	0.0065 (7)	0.0112 (7)
S1	0.0389 (3)	0.0386 (3)	0.0262 (3)	−0.00461 (18)	0.0065 (2)	−0.00175 (18)

Geometric parameters (Å, º)

C1—O1	1.274 (2)	C6—H6	0.9300
C1—N1	1.333 (3)	C7—C8	1.368 (3)
C1—C2	1.444 (3)	C7—H7	0.9300
C2—C3	1.334 (3)	C8—N2	1.345 (3)
C2—H2	0.9300	C8—H8	0.9300
C3—O2	1.372 (3)	Cu1—N2	2.0046 (16)
C3—C4	1.485 (3)	Cu1—O1	2.0107 (13)
C4—H4A	0.9600	Cu1—N1	2.4597 (16)
C4—H4B	0.9600	N1—S1	1.5876 (17)
C4—H4C	0.9600	N4—H4D	0.8600
C5—N4	1.335 (3)	N4—H4E	0.8600
C5—N3	1.345 (3)	O2—S1	1.6207 (17)
C5—N2	1.350 (3)	O3—S1	1.4172 (18)
C6—N3	1.320 (4)	O4—S1	1.4200 (17)
C6—C7	1.379 (4)
O1—C1—N1	117.45 (16)	N2—Cu1—O1^i	90.35 (6)
O1—C1—C2	120.23 (17)	N2^i—Cu1—O1	90.35 (6)
N1—C1—C2	122.25 (17)	N2—Cu1—O1	89.65 (6)
C3—C2—C1	121.16 (18)	N2—Cu1—N1^i	92.08 (6)
C3—C2—H2	119.4	O1—Cu1—N1^i	121.21 (5)
C1—C2—H2	119.4	N2^i—Cu1—N1	92.08 (6)
C2—C3—O2	121.43 (18)	N2—Cu1—N1	87.92 (6)
C2—C3—C4	126.5 (2)	O1^i—Cu1—N1	121.21 (5)
O2—C3—C4	112.1 (2)	O1—Cu1—N1	58.79 (5)
C3—C4—H4A	109.5	C1—N1—S1	118.27 (13)
C3—C4—H4B	109.5	C1—N1—Cu1	80.98 (11)
H4A—C4—H4B	109.5	S1—N1—Cu1	157.12 (10)
C3—C4—H4C	109.5	C8—N2—C5	117.63 (17)
H4A—C4—H4C	109.5	C8—N2—Cu1	116.00 (14)
H4B—C4—H4C	109.5	C5—N2—Cu1	126.34 (13)
N4—C5—N3	116.01 (19)	C6—N3—C5	116.2 (2)
N4—C5—N2	120.09 (17)	C5—N4—H4D	120.0
N3—C5—N2	123.89 (18)	C5—N4—H4E	120.0
N3—C6—C7	124.4 (2)	H4D—N4—H4E	120.0
N3—C6—H6	117.8	C1—O1—Cu1	102.76 (11)
C7—C6—H6	117.8	C3—O2—S1	117.91 (13)
C8—C7—C6	115.9 (2)	O3—S1—O4	117.64 (13)
C8—C7—H7	122.0	O3—S1—N1	110.87 (11)
C6—C7—H7	122.0	O4—S1—N1	111.49 (11)
N2—C8—C7	121.9 (2)	O3—S1—O2	105.11 (12)
N2—C8—H8	119.1	O4—S1—O2	105.92 (10)
C7—C8—H8	119.1	N1—S1—O2	104.63 (9)
O1—C1—C2—C3	170.64 (19)	N1^i—Cu1—N2—C8	120.50 (15)
N1—C1—C2—C3	−6.3 (3)	N1—Cu1—N2—C8	−59.50 (15)
C1—C2—C3—O2	2.8 (3)	O1^i—Cu1—N2—C5	−116.35 (15)
C1—C2—C3—C4	−175.1 (2)	O1—Cu1—N2—C5	63.65 (15)
N3—C6—C7—C8	−1.2 (4)	N1^i—Cu1—N2—C5	−57.57 (16)
C6—C7—C8—N2	0.1 (4)	N1—Cu1—N2—C5	122.43 (16)
O1—C1—N1—S1	165.36 (14)	C7—C6—N3—C5	0.0 (4)
C2—C1—N1—S1	−17.6 (3)	N4—C5—N3—C6	−177.1 (2)
O1—C1—N1—Cu1	−1.48 (16)	N2—C5—N3—C6	2.4 (3)
C2—C1—N1—Cu1	175.57 (17)	N1—C1—O1—Cu1	1.84 (19)
N2^i—Cu1—N1—C1	90.13 (12)	C2—C1—O1—Cu1	−175.28 (15)
N2—Cu1—N1—C1	−89.87 (12)	N2^i—Cu1—O1—C1	−93.25 (12)
O1^i—Cu1—N1—C1	−179.02 (10)	N2—Cu1—O1—C1	86.75 (12)
O1—Cu1—N1—C1	0.98 (10)	N1^i—Cu1—O1—C1	178.97 (11)
N2^i—Cu1—N1—S1	−58.8 (3)	N1—Cu1—O1—C1	−1.03 (11)
N2—Cu1—N1—S1	121.2 (3)	C2—C3—O2—S1	23.6 (3)
O1^i—Cu1—N1—S1	32.0 (3)	C4—C3—O2—S1	−158.28 (16)
O1—Cu1—N1—S1	−148.0 (3)	C1—N1—S1—O3	150.47 (18)
C7—C8—N2—C5	2.1 (3)	Cu1—N1—S1—O3	−64.8 (3)
C7—C8—N2—Cu1	−176.18 (18)	C1—N1—S1—O4	−76.40 (18)
N4—C5—N2—C8	176.02 (19)	Cu1—N1—S1—O4	68.3 (3)
N3—C5—N2—C8	−3.4 (3)	C1—N1—S1—O2	37.64 (18)
N4—C5—N2—Cu1	−5.9 (3)	Cu1—N1—S1—O2	−177.7 (2)
N3—C5—N2—Cu1	174.60 (15)	C3—O2—S1—O3	−157.88 (17)
O1^i—Cu1—N2—C8	61.72 (15)	C3—O2—S1—O4	76.90 (17)
O1—Cu1—N2—C8	−118.28 (15)	C3—O2—S1—N1	−41.02 (17)

Symmetry code: (i) −x+1, −y, −z.