A new complex of HgBr₂ and pyrimidine-2-thione: (pyrimidine-2-thionato-κS)(pyrimidinium-2-thionato-κS)mercury(II) tetrabromomercury(II)

The title compound, [Hg(C₄H₄N₂S)(C₄H₃N₂S)]₂[HgBr₄], con­sists of [Hg(pymt)(pymtH)]⁺ complex cations (pymtH is pyrimidine-2-thione) lying across twofold rotation axes in space group Fddd, with linearly coordinated mercury at an Hg—S distance of 2.357 (3) Å, and [HgBr₄]²⁻ anions lying at sites of 222 symmetry. The Hg atom is additionally coordinated by two N and two Br atoms, forming a 2+4 effective coordination sphere. The protonated ligand is connected via N—H...N hydrogen bonds to the neighbouring unprotonated ligand, thus forming infinite chains of cations.

S1. Comment

It is well known that thio-derivatives of pyrimidine play an important role in biological systems. For instance, mercaptopyrimidines exhibit antiviral and antibacterial properties (Rosenfield Mascharak & Arora, 1987; Rosenfield Berends et al., 1987) and have been found to inhibit the synthesis of tRNA, thus acting as antitumour and antithyroid agents (Abbot et al., 1978). In many cases, it seems probable that complex formation is implicated in the biological action of these pyrimidine derivatives. Mercury is found to be a strong inhibitor of human pyrimidine nucleoside monophosphate kinase, a polymeric enzyme which catalyzes the phosphorylation of UMP, CMP and dCMP, using ATP as the preferred phosphate donor (Teng et al., 1976).

We have recently reported the synthesis and structural characterization (IR, NMR, X-ray) of various mercury(II) compounds with heterocyclic thiones (Popović Matković-Čalogović Hasić & Vikić-Topić, 1999; Popović Matković-Čalogović Soldin et al., 1999; Pavlović et al., 2000a,b; Popović et al., 2001; Matković-Čalogović et al., 2001; Popović Pavlović et al., 2002; Popović Soldin Matković-Čalogović et al., 2002; Popović Soldin Pavlović et al., 2002). Continuing this work, we report here the crystal and molecular structure of the title neovel mercury(II) complex with pyrimidine-2-thione (pymtH), (I). \sch

Although many mercury(II) complexes with pyrimidine-2-thione or its derivatives are known (Battistuzzi & Peyronel, 1980; Khullar & Agarwala, 1974; Contreras et al., 1994), only a few of them to date have been characterized by X-ray analysis (Das & Seth, 1997; Romero et al., 1990; Stuart et al., 1980; Tallon et al., 1995). The ability of mercury(II) halides and pseudohalides to form 1:1 and 1:2 complexes with neutral ligands has been known for many years (Dean, 1978; Graddon, 1982). The crystal structures of the 1:2 complexes, HgX₂L₂ (where X is a halide or pseudohalide anion and L is a neutral ligand) usually consist of discrete monomeric molecules with a tetrahedrally coordinated Hg atom (more or less distorted). The structures of the 1:1 complexes, HgX₂L, often consist of discrete halogen-bridged dimeric molecules with the Hg atom also in a deformed tetrahedral environment. The dimeric structure of the complexes HgX₂(pymtH) (where X is Cl⁻, Br⁻ or I⁻) was proposed on the basis of their IR and Raman spectra and also supported by an SCF-MO-MNDO calculation on the HgI₂(pymtH) dimer (Contreras et al., 1994).

The structure of (I) consists of [Hg(pymt)(pymtH)]⁺ complex cations and [HgBr₄]²⁻ anions. In the cation, the Hg atom lies on a twofold axis and is linearly coordinated by two S atoms from the two ligands, of which one is protonated (pymtH) and the other deprotonated (pymt). The H atom on N2 is statistically disordered, since there is only one pymt/pymtH ligand in the asymmetric unit. The Hg1—S distance (Table 1) is slightly longer than the sum of the covalent radii for linear Hg and S (1.30 + 1.04 Å; Pauling, 1960; Grdenić, 1965). There is also a tetrabromomercurate(2-) anion, where the Hg atom lies at the intersection of three twofold axes. The Hg2—Br distance in this approximately tetrahedral anion corresponds well with the mean value [2.604 (4) Å] of 35 independent Hg—Br distances in tetrabromomercurate(2-) anions found in the Cambridge Structural Database (Version?; Allen, 2002).

The Hg atom in the cation of (I) is additionally coordinated by atoms N1 from the two ligands, at a distance of 2.856 (10) Å, and by two Br atoms from the anion at a distance of 3.4255 (14) Å, which is less than the sum of the van der Waals radii of the corresponding atoms, so the effective coordination can be described as 2 + 4 (Pauling, 1960; Grdenić, 1981). These contacts are responsible for the elongation of the Hg—S bond and for the slight deviation from linearity. The effect of additional contacts on the lengthening of the Hg—S distance is also found in other Hg complexes coordinated linearly by different thione ligands. Weak additional Hg···N contacts in the range 2.987 (7)–3.097 (7) Å have little influence on the Hg—S distances [2.338 (3)–2.347 (3) Å] and linearity (178.0 and 180°) in Hg(btzt)₂ (where btzt is 1,3-benzothiazole-2-thione; Popović Soldin Pavlović et al., 2002). However, two strong Hg···N contacts of 2.451 (4) Å in Hg(meimt)₂ (where meimtH is 1-N-methyl-1,3-imidazole-2-thione) cause the linear coordination to be very deformed toward the tetrahedral [S—Hg—S 143.15 (5)°], and also cause a much greater elongation of the Hg—S bond [2.4305 (12) Å; Popović Matković-Čalogović Soldin et al., 1999).

We have recently characterized the 1:1 complexes HgX₂(H₄pymtH) (X is Cl⁻, Br⁻, I⁻, SCN⁻ or CN⁻, and H₄pymtH is 3,4,5,6-tetrahydropyrimidine-2-thione; Popović et al., 2001). The chloro and bromo complexes were found to be isostructural and made up of tetrahalogenomercurate(II) anions and bis(3,4,5,6-tetrahydropyrimidinium-2-thiolato-S)mercury(II) cations, [Hg(H₄pymtH)₂][HgX₄]. In this cation, both N atoms are protonated and cannot form contacts with the Hg atom. The coordination is also 2 + 4, as in (I), and with comparable Hg—S distances [2.359 (4)–2.370 (4) Å], but all four additional contacts are with halogen atoms [Hg···Br 3.201 (2)–3.504 (2) Å].

The cations of (I) are connected by N2—H···N2 hydrogen bonds into infinite chains along the [110] direction.

S2. Experimental

The reaction of HgBr₂ and pymtH in a 1:1 molar ratio gave a mixture of products. Characterization of these compounds is in progress and will be published elsewhere. Crystals of (I) appeared after several weeks from the mother liquor obtained after filtration of the first reaction products.

S3. Refinement

The H atom on N2 was found in a difference Fourier map but was not refined. This H atom is disordered and its occupancy was set to 0.5. A l l other H atoms were treated as riding atoms, with C—H distances of 0.93 Å and N—H distances of 0.86 Å. The residual density in the final difference Fourier map is 0.80 Å from Hg2.

Computing details

Data collection: STADI4 (Stoe & Cie, 1995); cell refinement: X-RED (Stoe & Cie, 1995); data reduction: X-RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON98 (Spek, 1990); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. The Hg···N and Hg···Br contacts are shown by dashed lines.
	Fig. 2. A stereodiagram of the ions in the unit cell of (I), with the hydrogen bonds shown by dashed lines. H atoms attached to C have been omitted for clarity.

(pyrimidine-2-thionato-κS)(pyrimidinium-2-thionato-κS)mercury(II) tetrabromomercury(II)

Crystal data

[Hg(C4H4N2S)(C4H3N2S)]2[HgBr4]	F(000) = 4880
Mr = 1368.00	Dx = 3.090 Mg m^−3
Orthorhombic, Fddd	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -F 2uv 2vw	Cell parameters from 65 reflections
a = 9.0573 (7) Å	θ = 10.2–17.6°
b = 17.1999 (13) Å	µ = 21.37 mm^−1
c = 37.754 (9) Å	T = 293 K
V = 5881.5 (15) Å^3	Plate, yellow
Z = 8	0.49 × 0.40 × 0.05 mm

Data collection

Philips PW1100 updated by Stoe diffractometer	1288 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.078
Graphite monochromator	θmax = 29.9°, θmin = 3.7°
θ/2θ scans	h = −3→12
Absorption correction: integration (X-RED; Stoe & Cie, 1995)	k = −2→24
Tmin = 0.022, Tmax = 0.328	l = −1→52
3401 measured reflections	5 standard reflections every 90 min
2115 independent reflections	intensity decay: 6.1%

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)] = 0.054	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.145	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0814P)^2 + 0.022P] where P = (Fo^2 + 2Fc^2)/3
2115 reflections	(Δ/σ)max < 0.001
81 parameters	Δρmax = 2.39 e Å^−3
0 restraints	Δρmin = −3.63 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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg2	0.1250	0.1250	0.1250	0.0451 (2)
Hg1	0.1250	0.1250	0.011593 (15)	0.0579 (2)
Br	−0.03274 (11)	0.03698 (6)	0.08365 (3)	0.0518 (3)
S	0.2248 (3)	−0.00143 (18)	0.00846 (7)	0.0574 (7)
C1	0.3261 (10)	0.0145 (5)	−0.0290 (3)	0.044 (2)
N1	0.3286 (10)	0.0854 (4)	−0.0433 (3)	0.053 (2)
C2	0.4080 (13)	0.0962 (7)	−0.0729 (3)	0.058 (3)
H2	0.4080	0.1448	−0.0837	0.070*
C3	0.4887 (13)	0.0373 (7)	−0.0876 (3)	0.060 (3)
H3	0.5481	0.0460	−0.1073	0.072*
C4	0.4800 (11)	−0.0346 (7)	−0.0725 (3)	0.060 (3)
H4	0.5313	−0.0760	−0.0826	0.072*
N2	0.3973 (10)	−0.0465 (5)	−0.0431 (3)	0.057 (2)
H	0.3907	−0.0918	−0.0337	0.069*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg2	0.0524 (4)	0.0478 (4)	0.0352 (4)	0.000	0.000	0.000
Hg1	0.0678 (4)	0.0663 (4)	0.0395 (3)	0.0121 (3)	0.000	0.000
Br	0.0573 (5)	0.0529 (5)	0.0453 (5)	−0.0035 (4)	−0.0063 (5)	−0.0130 (5)
S	0.0671 (16)	0.0573 (15)	0.0479 (14)	0.0008 (13)	−0.0031 (13)	0.0152 (12)
C1	0.045 (5)	0.040 (4)	0.047 (5)	−0.006 (4)	−0.005 (4)	−0.004 (4)
N1	0.069 (5)	0.032 (4)	0.058 (5)	−0.003 (3)	0.006 (4)	−0.004 (4)
C2	0.077 (7)	0.044 (5)	0.053 (6)	−0.013 (5)	0.012 (6)	−0.007 (5)
C3	0.062 (6)	0.068 (7)	0.050 (6)	0.003 (5)	0.011 (5)	−0.014 (6)
C4	0.046 (5)	0.059 (6)	0.075 (8)	0.010 (5)	−0.002 (5)	−0.027 (6)
N2	0.065 (5)	0.038 (4)	0.068 (6)	0.008 (4)	−0.012 (5)	−0.008 (4)

Geometric parameters (Å, º)

Hg1—S	2.358 (3)	N1—C2	1.343 (14)
Hg1—S^i	2.358 (3)	C2—C3	1.366 (16)
Hg2—Br	2.6020 (10)	C2—H2	0.9300
Hg2—Br^ii	2.6020 (10)	C3—C4	1.363 (17)
Hg2—Br^iii	2.6020 (10)	C3—H3	0.9300
Hg2—Br^i	2.6020 (10)	C4—N2	1.356 (16)
S—C1	1.710 (10)	C4—H4	0.9300
C1—N1	1.333 (12)	N2—H	0.8600
C1—N2	1.340 (13)
S—Hg1—S^i	174.25 (13)	N1—C2—C3	121.4 (11)
Br—Hg2—Br^ii	113.39 (5)	N1—C2—H2	119.3
Br—Hg2—Br^iii	108.84 (5)	C3—C2—H2	119.3
Br^ii—Hg2—Br^iii	106.26 (5)	C4—C3—C2	118.3 (10)
Br—Hg2—Br^i	106.26 (5)	C4—C3—H3	120.9
Br^ii—Hg2—Br^i	108.84 (5)	C2—C3—H3	120.9
Br^iii—Hg2—Br^i	113.39 (5)	N2—C4—C3	120.6 (10)
C1—S—Hg1	95.7 (3)	N2—C4—H4	119.7
N1—C1—N2	123.3 (10)	C3—C4—H4	119.7
N1—C1—S	119.3 (8)	C1—N2—C4	118.2 (9)
N2—C1—S	117.4 (8)	C1—N2—H	120.9
C1—N1—C2	118.1 (9)	C4—N2—H	120.9
Hg1—S—C1—N1	3.6 (8)	N1—C2—C3—C4	3.9 (18)
Hg1—S—C1—N2	−175.1 (7)	C2—C3—C4—N2	−2.3 (17)
N2—C1—N1—C2	−0.8 (16)	N1—C1—N2—C4	2.3 (15)
S—C1—N1—C2	−179.4 (8)	S—C1—N2—C4	−179.0 (8)
C1—N1—C2—C3	−2.4 (17)	C3—C4—N2—C1	−0.7 (15)

Symmetry codes: (i) −x+1/4, −y+1/4, z; (ii) x, −y+1/4, −z+1/4; (iii) −x+1/4, y, −z+1/4.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H···N2^iv	0.86	1.98	2.730 (12)	145

Symmetry code: (iv) −x+3/4, −y−1/4, z.