Iodo­(picolinato-κ²N,O)(picolinic acid-κ²N,O)mercury(II)

The title compound, [Hg(C₆H₄NO₂)I(C₆H₅NO₂)], has twofold symmetry along the Hg—I bond. The Hg^II ion coordinates one I atom [at 2.6045 (4) Å], two N and two O atoms [at 2.298 (3) and 2.481 (2) Å] from one picolinate ion, and one picolinic acid mol­ecule in a very irregular trigonal–bipyramidal coordination. The single hydr­oxy H atom required for chemical neutrality is both statistically (by crystal symmetry) and structurally disordered, and is involved in an inter­molecular O—H...O hydrogen bond [O...O = 2.455 (4) Å], connecting the mol­ecules into one-dimensional infinite chains along the [101] direction.

S1. Comment

We started recently to investigate mercury(II) coordination chemistry with ligands containing N– and O-atom donors, such as monopyridine carboxylic acids acting as N,O- or O,O-chelating ligands (Popović et al., 1999; Matković-Čalogović et al., 2001; Matković-Čalogović et al., 2002). The focus of our research is the competition between halide ions and ligands containing N,O donors for the coordination sites of the mercury(II) ion. Interestingly we have found that the replacement of only one halide atom occurs with the above ligands when the complexes are derived from HgCl₂ or HgBr₂. The tendency of mercury to achieve effective coordination (Grdenić, 1965, 1981) including both covalent bonds and van der Waals interactions, along with the spatial arrangement of donor atoms (such as that provided by pyridine carboxylic acids), leads to various, mostly irregular, coordination polyhedra of mercury. We distinguish between covalent bonds and van der Waals interactions in mercury(II) compounds by geometrical criteria using published covalent and van der Waals radii of mercury and corresponding atoms (Pauling, 1960; Bondi, 1964; Nyburg & Faerman, 1985; Matković-Čalogović, 1994).

In a survey of the Cambridge Structural Database (CSD; Version 5.26 of August 2005; Allen, 2002), 34 structural fragments are found containing only one mercury-to-iodine covalent bond. There are five structures containing, in addition to one or more Hg—I covalent bonds, Hg—O and Hg—N contacts [CSD refcodes NEJXEF and NEJXIJ (Pickardt & Wiese, 1997), HGTXZO (Malmsten, 1979), VAQHOK (González-Duarte et al., 1998), and XANBIX (Pickardt & Wiese, 2000)]. These latter compounds contain different coordination environments of mercury and have `bond' distance ranges for Hg—I of 2.601–2.758 Å, Hg—N of 2.21–2.72 Å and Hg—O of 2.62–2.91 Å.

By contrast, there are only three structures of mercury complexes with picolinic acid or its derivatives, but none similar to the title complex. In the structure of mercury(II) picolinate (Álvarez-Larena et al., 1994) with the characteristic bridging coordination mode for carboxylates, a linear polymer is formed, and the mercury achieves (2 + 4) octahedral coordination with shorter mercury-to-nitrogen [2.125 (2) Å] and longer mercury-to-oxygen distances [2.470 (2) and 2.756 (2) Å]. P. González-Duarte et al. (1998 or ??? 1988) reported the complexes with the iso-propyl ester of picolinic acid and HgBr₂ and HgI₂ (VAXHOK). These complexes are centrosymmetric dimers with irregular square-pyramidal mercury coordination (4 + 1 effective coordination) formed by one mercury-to-nitrogen [2.455 (6) Å], one mercury-to-oxygen [2.658 (6) Å] and three mercury-to-iodine [2.601 (6), 2.638 (2) and 3.411 (2) Å] (or bromine) bonds.

In the title compound, (I), mercury and iodine are situated on a crystallographic twofold axis. Mercury(II) is coordinated via one I atom, two N atoms and two O atoms (N,O-chelate bidentate mode of ligand) in the form of a very irregular trigonal–bypiramidal (3 + 2)-coordination, rather than the (4 + 1)-coordination mode. The Hg—I distance is at the shorter end of the range noted above (2.601–2.758 Å) and smaller than that predicted for covalent Hg—I distances in mercury(II) compounds with digonal [trigonal?] coordination (2.66 Å; Pauling, 1960; Bondi, 1964; Nyburg & Faerman, 1985; Matković-Čalogović, 1994). It is also comparable to the Hg—I bond in the yellow form of mercury(II) iodide (Jeffrey & Vlasse, 1967), where mercury is diagonally coordinated [2.615 (6) and 2.620 (6) Å]. The shortest value of the Hg—I covalent bond in the mercury(II) complexes with one Hg—I bond is found in bis(ethylenediamine)triiododimercury(II) triiodomercurate(II) (Grdenić et al., 1977) which contains a trigonal–bipyramidal cation and an Hg—I bond distance of 2.571 (3) Å.

The Hg—N distances are within the range noted above and should be considered stronger then van der Waals contacts but longer than a normal covalent bond. An example of the latter is the Hg—N bond in mercury(II) picolinate at 2.125 (2) Å. A similar scenario exists for the Hg—O distances: the value here is shorter than the range 2.62–2.91 Å noted above but also longer than that in the structure of mercury(II) picolinate [Hg—O = 2.470 (2) Å].

The chelate ring defined by the atoms Hg, O1, C6, C1 and N2 is approximately planar, with a maximum deviation out of the plane of 0.039 (3) Å for atom C6. This plane makes a small angle of 1.7 (2)° with the planar pyridine ring (atoms C1–C5 and N2). The carboxylate plane (atoms C1, C6 and O2) is not coplanar with the chelate ring mean plane, the interplanar angle being 6.0 (4)°.

The molecules are connected into one-dimensional infinite chains along the (101) direction via an O—H···O intermolecular hydrogen bond (Table 2). The H atom involved (H220) is structurally disordered.

S2. Experimental

A solution of picH (0.084 g, 0.682 mmol) in ethanol (10 ml) was added dropwise to a solution of HgI₂ (0.30 g, 0.660 mmol) in tetrahydrofuran (THF, 10 ml). After two weeks, pale-yellow crystals were filtered off, washed with THF and dried in air. Yield 0.14 g (70%). Analysis calculated for HgI(pic)(picH): C 25.17, H 1.58, N 4.89%; found: C 25.19, H 1.73, N 4.81%.

S3. Refinement

H atoms bonded to C atoms were introduced at calculated positions and refined by applying the riding model [U_iso(H) = 1.2U_eq(C) and C—H = 0.93 Å]. To maintain complex neutrality, the H2 atom is statistically disordered (by crystal symmetry) between the two ligands in each complex. The refinement models that were tried are noted in the CIF. The maximum and minimum electron densities in the final difference Fourier map are located 1.97 and 0.71 Å from from the I and Hg atoms, respectively.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2004); cell refinement: CrysAlis CCD or RED (Oxford Diffraction, 2004); data reduction: CrysAlis RED (Oxford Diffraction, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON98 (Spek, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The structure of HgI(pic)(picH), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. The hydroxy H atom is disordered (only the major component is shown).
	Fig. 2. PLATON (Spek, 1998) view of crystal structure of (I). The disordered atom H2O2 is not shown, but the hydrogen bonds [involving atoms O2 and O2^i; (i) symmetry code: −1/2 − x, 5/2 − y, −z] linking molecules along the (101) direction are shown as dashed lines.

Iodo(picolinato-κ²N,O)(picolinic acid-κ²N,O)mercury(II)

Crystal data

[Hg(C6H4NO2)I(C6H5NO2)]	F(000) = 1040
Mr = 572.70	Dx = 2.579 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 8558 reflections
a = 14.2329 (8) Å	θ = 14.0–21.0°
b = 7.3321 (4) Å	µ = 12.56 mm^−1
c = 14.9255 (10) Å	T = 296 K
β = 109.030 (6)°	Prism, pale-yellow
V = 1472.46 (15) Å^3	0.27 × 0.26 × 0.13 mm
Z = 4

Data collection

Oxford Diffraction Xcalibur2 diffractometer with Sapphire 3 CCD detector	2149 independent reflections
Radiation source: fine-focus sealed tube	2117 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
ω scans	θmax = 30.0°, θmin = 4.6°
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2004)	h = −20→20
Tmin = 0.096, Tmax = 0.201	k = −10→10
18474 measured reflections	l = −20→20

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.021	H-atom parameters constrained
wR(F^2) = 0.047	w = 1/[σ^2(Fo^2) + (0.0187P)^2 + 3.3936P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max = 0.001
2149 reflections	Δρmax = 1.70 e Å^−3
94 parameters	Δρmin = −1.36 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00199 (9)

Special details

Refinement. Three refinement models of the carboxylic hydrogen atom position were attempted. Firstly, the peak-density of the carboxylic hydrogen atom position was found in the electron-density Fourier map at the chemically reasonable position (0.87 Å from O2 atom and 1.59 Å from O2ⁱ, (i = −1/2 − x,5/2 − y,-z)), as a small electron-density peak (0.37 electrons per ų). This (H2) hydrogen atom position was then refined freely with a half occupancy factor, giving a rather short O2—H2 distance of 0.67 (8) Å. Then, the HFIX87 SHELXL97 instruction was applied in order to improve this distance, but this was finally rejected due to the impact of this type of refinement on the H2···O2ⁱ contact. Finally, the difference map coordinates were used to fix the H220 position and the isotropic temperature factor was allowed to refine freely. A reasonable result, given the disorder, was obtained (see Table 2).

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Hg1	0.0000	0.90092 (2)	0.2500	0.03986 (7)
I1	0.0000	0.54570 (5)	0.2500	0.05808 (10)
O1	−0.13602 (15)	1.0406 (4)	0.11888 (16)	0.0449 (5)
O2	−0.16235 (19)	1.2481 (4)	0.0045 (2)	0.0572 (7)
H2	−0.2252	1.2402	−0.0021	0.05 (2)*	0.50
N2	0.06502 (18)	1.0812 (3)	0.15876 (18)	0.0360 (5)
C1	0.0027 (2)	1.1667 (4)	0.08402 (19)	0.0332 (5)
C2	0.0363 (3)	1.2740 (5)	0.0246 (2)	0.0431 (7)
H2A	−0.0084	1.3301	−0.0280	0.052*
C3	0.1377 (3)	1.2965 (5)	0.0447 (3)	0.0524 (8)
H3	0.1621	1.3692	0.0063	0.063*
C4	0.2016 (3)	1.2099 (6)	0.1223 (3)	0.0545 (9)
H4	0.2699	1.2238	0.1374	0.065*
C5	0.1633 (2)	1.1025 (5)	0.1775 (3)	0.0481 (8)
H5	0.2068	1.0427	0.2294	0.058*
C6	−0.1069 (2)	1.1469 (5)	0.0695 (2)	0.0371 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.03946 (9)	0.03163 (10)	0.04506 (10)	0.000	0.00910 (6)	0.000
I1	0.0873 (3)	0.02960 (15)	0.05205 (18)	0.000	0.01543 (16)	0.000
O1	0.0328 (9)	0.0519 (14)	0.0470 (11)	−0.0031 (9)	0.0089 (8)	0.0126 (10)
O2	0.0390 (11)	0.0654 (17)	0.0596 (15)	0.0052 (11)	0.0057 (10)	0.0271 (13)
N2	0.0314 (10)	0.0367 (14)	0.0387 (12)	−0.0007 (9)	0.0098 (9)	0.0011 (9)
C1	0.0351 (12)	0.0300 (13)	0.0344 (12)	−0.0013 (11)	0.0114 (10)	−0.0042 (11)
C2	0.0512 (17)	0.0398 (17)	0.0425 (15)	0.0002 (13)	0.0210 (13)	0.0009 (12)
C3	0.058 (2)	0.050 (2)	0.060 (2)	−0.0090 (16)	0.0341 (17)	0.0011 (16)
C4	0.0381 (15)	0.065 (3)	0.064 (2)	−0.0095 (15)	0.0222 (15)	−0.0035 (17)
C5	0.0325 (13)	0.056 (2)	0.0538 (18)	−0.0008 (13)	0.0117 (12)	0.0036 (15)
C6	0.0326 (12)	0.0380 (15)	0.0370 (13)	−0.0015 (11)	0.0061 (10)	0.0001 (11)

Geometric parameters (Å, º)

Hg1—N2^i	2.298 (3)	C1—C2	1.383 (4)
Hg1—N2	2.298 (3)	C1—C6	1.510 (4)
Hg1—O1^i	2.481 (2)	C2—C3	1.384 (5)
Hg1—O1	2.481 (2)	C2—H2A	0.9300
Hg1—I1	2.6045 (4)	C3—C4	1.373 (6)
O1—C6	1.233 (4)	C3—H3	0.9300
O2—C6	1.271 (4)	C4—C5	1.373 (5)
O2—H2	0.869 (3)	C4—H4	0.9300
N2—C1	1.334 (4)	C5—H5	0.9300
N2—C5	1.343 (4)
N2^i—Hg1—N2	109.78 (13)	C2—C1—C6	121.4 (3)
N2^i—Hg1—O1^i	69.91 (8)	C1—C2—C3	118.9 (3)
N2—Hg1—O1^i	82.45 (9)	C1—C2—H2A	120.5
N2^i—Hg1—O1	82.45 (9)	C3—C2—H2A	120.5
N2—Hg1—O1	69.91 (8)	C4—C3—C2	119.0 (3)
O1^i—Hg1—O1	131.23 (12)	C4—C3—H3	120.5
N2^i—Hg1—I1	125.11 (6)	C2—C3—H3	120.5
N2—Hg1—I1	125.11 (6)	C3—C4—C5	119.2 (3)
O1^i—Hg1—I1	114.38 (6)	C3—C4—H4	120.4
O1—Hg1—I1	114.38 (6)	C5—C4—H4	120.4
C6—O1—Hg1	113.84 (18)	N2—C5—C4	122.1 (3)
C6—O2—H2	114.1 (3)	N2—C5—H5	118.9
C1—N2—C5	118.9 (3)	C4—C5—H5	118.9
C1—N2—Hg1	118.63 (19)	O1—C6—O2	125.4 (3)
C5—N2—Hg1	122.5 (2)	O1—C6—C1	120.5 (3)
N2—C1—C2	121.9 (3)	O2—C6—C1	114.1 (3)
N2—C1—C6	116.7 (3)
N2^i—Hg1—O1—C6	110.8 (2)	Hg1—N2—C1—C6	4.0 (3)
N2—Hg1—O1—C6	−3.5 (2)	N2—C1—C2—C3	−1.5 (5)
O1^i—Hg1—O1—C6	56.1 (2)	C6—C1—C2—C3	175.9 (3)
I1—Hg1—O1—C6	−123.9 (2)	C1—C2—C3—C4	0.8 (5)
N2^i—Hg1—N2—C1	−74.3 (2)	C2—C3—C4—C5	0.4 (6)
O1^i—Hg1—N2—C1	−139.7 (2)	C1—N2—C5—C4	0.2 (5)
O1—Hg1—N2—C1	−0.6 (2)	Hg1—N2—C5—C4	179.7 (3)
I1—Hg1—N2—C1	105.7 (2)	C3—C4—C5—N2	−0.9 (6)
N2^i—Hg1—N2—C5	106.2 (3)	Hg1—O1—C6—O2	−172.7 (3)
O1^i—Hg1—N2—C5	40.8 (3)	Hg1—O1—C6—C1	6.9 (4)
O1—Hg1—N2—C5	179.9 (3)	N2—C1—C6—O1	−7.6 (4)
I1—Hg1—N2—C5	−73.8 (3)	C2—C1—C6—O1	174.8 (3)
C5—N2—C1—C2	1.0 (5)	N2—C1—C6—O2	171.9 (3)
Hg1—N2—C1—C2	−178.5 (2)	C2—C1—C6—O2	−5.6 (4)
C5—N2—C1—C6	−176.5 (3)

Symmetry code: (i) −x, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O2^ii	0.869 (3)	1.591 (3)	2.455 (4)	172 (1)

Symmetry code: (ii) −x−1/2, −y+5/2, −z.