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The title compound, bis­(pyridine-N)­mercury(II) dichrom­ate(VI), [Hg(C5H5N)2][Cr2O7], is the first structurally determined representative of metal dichromates with additional pyridine ligands of general formula [M(py)n]mCr2O7 (py = pyridine) and can be used for a quick assay method to quantify HgII ions in solution. Two distinct Hg atoms, both located on special positions with symmetry 2 and \overline 1, respectively, are coordinated octahedrally by two axial N atoms of pyridine rings at short distances \overline {\it d}(Hg-N) = 2.101 Å and four equatorial O atoms of dichromate groups at longer distances \overline {\it d}(Hg-O) = 2.620 Å. The dichromate group has a skew conformation with a bridging angle of 138.62 (17)°.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801010455/cf6087sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801010455/cf6087Isup2.hkl
Contains datablock I

CCDC reference: 170750

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.006 Å
  • R factor = 0.018
  • wR factor = 0.046
  • Data-to-parameter ratio = 18.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry








Comment top

The preparation of metal dichromates(VI) with additional pyridine ligands (py) of general formula [M(py)n]mCr2O7 (n = 4, m = 1: MII = Cu, Ni, Co, Zn, Cd, Mn; n = 3, m = 2: MI = Ag; n = 2, m = 2: MI = Ag; n = 2, m = 1: MII = Hg) was described nearly 100 years ago (Briggs, 1908), but no crystallographic or structural data of these compounds have been reported in the meantime. Since the mercury compound is of considerable interest for application as a quick assay method to quantify mercury(II) ions in solution (Spacu & Dick, 1929), a structure analysis seemed desirable.

The two crystallographically independent mercury atoms are located at special positions with site symmetry 2 for Hg1 (Fig. 1) and 1 for Hg2 (Fig. 2), respectively. Both have a distorted octahedral coordination with two short axial bonds to N atoms of pyridine rings, ¯d(Hg—N) = 2.101 Å, and four longer equatorial bonds to terminal O atoms of the dichromate groups, ¯d(Hg—O) = 2.620 Å.

The Cr2O7 group (Fig. 3) displays a skew conformation with a dihedral angle of -31.58 (16)° for O2—Cr1···Cr2—O6 and a (Cr1—O4—Cr2) bridging angle of 138.62 (17)°. The two distinct [CrO4] tetrahedra show three short bonds ¯d(Cr—O)t = 1.614 Å to the terminal O atoms and a long bond ¯d(Cr—O)b = 1.768 Å to the bridging atom O4. The observed bond lengths and the bridging angle are in a range typical for other structures with dichromate groups and agree with those generally observed for [X2O7]2- anions (X = P, Cr, As, V) in inorganic compounds (Brown & Calvo, 1970; Clark & Morley, 1976; Nord & Kierkegaard, 1980).

Single building units of Hg(py)22+ and Cr2O72- groups form layers parallel to the ac plane and extend along [101] (Fig. 4). The two-dimensional connection within a layer is achieved via bonding of different mercury atoms to shared dichromate groups, whereas no covalent bonding between two adjacent layers is evident. The junction between two parallel layers is mainly accomplished by van der Waals interactions. A further weak interaction between terminal O atoms of one layer and pyridine H atoms of adjacent layers with distances d(O2—H10) and d(O6—H2) of ca 2.30 Å leads to additional stabilization. Except for O2 and O6, which are exclusively bonded to Cr atoms, all other O atoms show coordination number 2.

Experimental top

Microcrystalline Hg(py)2Cr2O7 was prepared according to the method of Spacu & Dick (1929). Single crystals were grown by cooling an aqueous solution of the microcrystalline material, with two drops of pyridine added, from 393 K down to room temperature with a cooling rate of 2 K h-1. The reaction was performed in a 5 ml Teflon-lined stainless steel container which was two-thirds filled. The orange crystals are light sensitive and blacken within a few days under normal daylight.

Refinement top

H atoms were located by difference Fourier maps and refined with a riding model.

Computing details top

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS for WINDOWS (Dowty, 1998); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The coordination around Hg1, drawn with ellipsoids at the 25% probability level.
[Figure 2] Fig. 2. The coordination around Hg2, drawn with ellipsoids at the 25% probability level.
[Figure 3] Fig. 3. The dichromate group with skew conformation; ellipsoids are drawn at the 50% probability level.
[Figure 4] Fig. 4. Projection of the structure along [010], showing atoms as spheres (Hg red, N yellow, C cyan and O white) and the dichromate group as Cr2O7 tetrahedra (green). For clarity, H atoms have been omitted.
bis(pyridine-N)mercury(II) dichromate(VI) top
Crystal data top
[Hg(C5H5N)2][Cr2O7]F(000) = 2144
Mr = 574.79Dx = 2.583 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 15.4741 (5) ÅCell parameters from 10078 reflections
b = 15.0135 (5) Åθ = 2.7–28.3°
c = 14.0407 (5) ŵ = 11.84 mm1
β = 115.018 (1)°T = 293 K
V = 2955.89 (17) Å3Parallelepiped, orange
Z = 80.10 × 0.07 × 0.04 mm
Data collection top
Siemens SMART CCD area-detector
diffractometer
3683 independent reflections
Radiation source: fine-focus sealed tube3186 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.030
ω scansθmax = 28.3°, θmin = 2.0°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 2020
Tmin = 0.366, Tmax = 0.612k = 2020
19668 measured reflectionsl = 1818
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.018H-atom parameters constrained
wR(F2) = 0.046 w = 1/[σ2(Fo2) + (0.0166P)2 + 2.3706P]
where P = (Fo2 + 2Fc2)/3
S = 1.21(Δ/σ)max = 0.001
3683 reflectionsΔρmax = 1.06 e Å3
204 parametersΔρmin = 0.58 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.000071 (11)
Crystal data top
[Hg(C5H5N)2][Cr2O7]V = 2955.89 (17) Å3
Mr = 574.79Z = 8
Monoclinic, C2/cMo Kα radiation
a = 15.4741 (5) ŵ = 11.84 mm1
b = 15.0135 (5) ÅT = 293 K
c = 14.0407 (5) Å0.10 × 0.07 × 0.04 mm
β = 115.018 (1)°
Data collection top
Siemens SMART CCD area-detector
diffractometer
3683 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
3186 reflections with I > 2σ(I)
Tmin = 0.366, Tmax = 0.612Rint = 0.030
19668 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0180 restraints
wR(F2) = 0.046H-atom parameters constrained
S = 1.21Δρmax = 1.06 e Å3
3683 reflectionsΔρmin = 0.58 e Å3
204 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
Hg10.00000.774387 (11)0.25000.02787 (6)
Hg20.25000.75001.00000.03017 (6)
Cr10.01526 (4)0.73603 (3)0.53425 (4)0.02824 (12)
Cr20.23539 (4)0.73338 (3)0.72142 (4)0.02824 (12)
O10.0124 (2)0.79567 (19)0.4289 (2)0.0482 (7)
O20.0232 (2)0.63289 (18)0.5100 (2)0.0539 (7)
O30.06502 (18)0.74723 (17)0.5787 (2)0.0401 (6)
O40.12511 (18)0.77627 (19)0.6295 (2)0.0465 (7)
O50.31376 (18)0.73993 (17)0.6739 (2)0.0414 (6)
O60.22471 (19)0.63117 (18)0.7478 (2)0.0550 (8)
O70.2678 (2)0.79329 (19)0.8269 (2)0.0464 (6)
N10.00000.6354 (2)0.25000.0309 (9)
N20.00000.9137 (2)0.25000.0281 (8)
N30.25972 (19)0.61034 (18)0.9887 (2)0.0309 (6)
C10.0582 (3)0.5909 (2)0.2192 (3)0.0376 (8)
H10.10010.62300.19810.045*
C20.0589 (3)0.4998 (3)0.2175 (3)0.0551 (11)
H20.09990.46900.19400.066*
C30.00000.4534 (4)0.25000.0623 (19)
H30.00000.39010.25000.075*
C40.0726 (3)0.9588 (2)0.2457 (3)0.0386 (8)
H40.12420.92680.24240.046*
C50.0745 (3)1.0503 (3)0.2459 (3)0.0495 (10)
H50.12711.08110.24330.059*
C60.00001.0967 (3)0.25000.0491 (15)
H60.00001.16000.25000.059*
C70.3310 (3)0.5734 (2)0.9725 (3)0.0376 (8)
H70.37540.61100.96170.045*
C80.3418 (3)0.4825 (3)0.9712 (3)0.0465 (10)
H80.39330.45760.96020.056*
C90.2766 (3)0.4282 (3)0.9860 (3)0.0502 (10)
H90.28240.36520.98510.060*
C100.2036 (3)0.4664 (3)1.0021 (3)0.0507 (10)
H100.15830.42991.01280.061*
C110.1959 (3)0.5571 (3)1.0029 (3)0.0414 (9)
H110.14470.58311.01360.050*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Hg10.02884 (10)0.02207 (10)0.03451 (11)0.0000.01514 (8)0.000
Hg20.02762 (11)0.02790 (11)0.03573 (11)0.00094 (6)0.01411 (8)0.00063 (6)
Cr10.0192 (3)0.0356 (3)0.0280 (3)0.00306 (19)0.0081 (2)0.0006 (2)
Cr20.0187 (3)0.0342 (3)0.0293 (3)0.00174 (19)0.0076 (2)0.0001 (2)
O10.0507 (17)0.0625 (18)0.0335 (14)0.0083 (13)0.0197 (13)0.0086 (12)
O20.0475 (17)0.0440 (16)0.0625 (19)0.0086 (12)0.0157 (15)0.0097 (13)
O30.0266 (14)0.0554 (17)0.0408 (15)0.0004 (10)0.0169 (12)0.0007 (11)
O40.0212 (12)0.0487 (17)0.0555 (17)0.0010 (10)0.0026 (12)0.0003 (11)
O50.0270 (14)0.0551 (17)0.0468 (16)0.0006 (10)0.0201 (13)0.0036 (11)
O60.0456 (17)0.0435 (16)0.0665 (19)0.0089 (12)0.0146 (15)0.0128 (13)
O70.0446 (16)0.0588 (17)0.0339 (14)0.0033 (13)0.0148 (13)0.0081 (12)
N10.028 (2)0.025 (2)0.036 (2)0.0000.0095 (18)0.000
N20.028 (2)0.025 (2)0.031 (2)0.0000.0126 (17)0.000
N30.0282 (16)0.0295 (15)0.0356 (16)0.0006 (11)0.0141 (13)0.0008 (11)
C10.031 (2)0.042 (2)0.038 (2)0.0061 (14)0.0129 (16)0.0011 (15)
C20.061 (3)0.042 (2)0.052 (3)0.017 (2)0.014 (2)0.0065 (18)
C30.078 (5)0.026 (3)0.065 (4)0.0000.013 (4)0.000
C40.042 (2)0.035 (2)0.041 (2)0.0045 (15)0.0191 (18)0.0008 (15)
C50.066 (3)0.038 (2)0.043 (2)0.0169 (19)0.022 (2)0.0019 (16)
C60.082 (5)0.024 (3)0.035 (3)0.0000.019 (3)0.000
C70.034 (2)0.040 (2)0.042 (2)0.0027 (15)0.0195 (17)0.0033 (15)
C80.051 (3)0.042 (2)0.049 (2)0.0104 (17)0.024 (2)0.0046 (17)
C90.066 (3)0.033 (2)0.048 (2)0.0005 (18)0.022 (2)0.0017 (16)
C100.054 (3)0.041 (2)0.059 (3)0.0163 (18)0.026 (2)0.0006 (18)
C110.034 (2)0.046 (2)0.048 (2)0.0064 (16)0.0210 (18)0.0022 (16)
Geometric parameters (Å, º) top
Hg1—N12.087 (4)N2—C4i1.334 (4)
Hg1—N22.092 (4)N2—C41.334 (4)
Hg1—O12.618 (3)N3—C71.337 (4)
Hg1—O1i2.618 (3)N3—C111.350 (4)
Hg1—O5ii2.625 (3)C1—C21.367 (5)
Hg1—O5iii2.625 (3)C1—H10.950
Hg2—N3iv2.113 (3)C2—C31.369 (5)
Hg2—N32.113 (3)C2—H20.950
Hg2—O3v2.596 (3)C3—C2i1.369 (5)
Hg2—O3vi2.596 (3)C3—H30.950
Hg2—O7iv2.640 (3)C4—C51.375 (5)
Hg2—O72.640 (3)C4—H40.950
Cr1—O21.601 (3)C5—C61.370 (5)
Cr1—O31.617 (3)C5—H50.950
Cr1—O11.624 (3)C6—C5i1.370 (5)
Cr1—O41.766 (3)C6—H60.950
Cr1—Cr23.3075 (7)C7—C81.376 (5)
Cr2—O61.604 (3)C7—H70.950
Cr2—O51.615 (3)C8—C91.379 (6)
Cr2—O71.621 (3)C8—H80.950
Cr2—O41.769 (3)C9—C101.369 (6)
O3—Hg2v2.596 (3)C9—H90.950
O5—Hg1iii2.625 (3)C10—C111.368 (5)
N1—C1i1.332 (4)C10—H100.950
N1—C11.332 (4)C11—H110.950
N1—Hg1—N2180.000 (1)Cr2—O5—Hg1iii135.56 (15)
N1—Hg1—O197.01 (6)Cr2—O7—Hg2126.34 (15)
N2—Hg1—O182.99 (6)C1i—N1—C1119.8 (4)
N1—Hg1—O1i97.01 (6)C1i—N1—Hg1120.1 (2)
N2—Hg1—O1i82.99 (6)C1—N1—Hg1120.1 (2)
O1—Hg1—O1i165.98 (13)C4i—N2—C4119.1 (4)
N1—Hg1—O5ii85.30 (6)C4i—N2—Hg1120.5 (2)
N2—Hg1—O5ii94.70 (6)C4—N2—Hg1120.5 (2)
O1—Hg1—O5ii83.52 (9)C7—N3—C11119.2 (3)
O1i—Hg1—O5ii97.64 (9)C7—N3—Hg2121.0 (2)
N1—Hg1—O5iii85.30 (6)C11—N3—Hg2119.8 (2)
N2—Hg1—O5iii94.70 (6)N1—C1—C2121.2 (4)
O1—Hg1—O5iii97.64 (9)N1—C1—H1119.4
O1i—Hg1—O5iii83.52 (9)C2—C1—H1119.4
O5ii—Hg1—O5iii170.61 (11)C1—C2—C3119.5 (4)
N3iv—Hg2—N3180.000 (1)C1—C2—H2120.3
N3iv—Hg2—O3v86.97 (9)C3—C2—H2120.3
N3—Hg2—O3v93.03 (9)C2i—C3—C2118.8 (5)
N3iv—Hg2—O3vi93.03 (9)C2i—C3—H3120.6
N3—Hg2—O3vi86.97 (9)C2—C3—H3120.6
O3v—Hg2—O3vi180.0N2—C4—C5121.7 (4)
N3iv—Hg2—O7iv97.87 (10)N2—C4—H4119.2
N3—Hg2—O7iv82.13 (10)C5—C4—H4119.2
O3v—Hg2—O7iv82.10 (8)C6—C5—C4119.4 (4)
O3vi—Hg2—O7iv97.90 (8)C6—C5—H5120.3
N3iv—Hg2—O782.13 (10)C4—C5—H5120.3
N3—Hg2—O797.87 (10)C5i—C6—C5118.8 (5)
O3v—Hg2—O797.90 (8)C5i—C6—H6120.6
O3vi—Hg2—O782.10 (8)C5—C6—H6120.6
O7iv—Hg2—O7180.000 (1)N3—C7—C8121.8 (3)
O2—Cr1—O3108.87 (15)N3—C7—H7119.1
O2—Cr1—O1110.71 (15)C8—C7—H7119.1
O3—Cr1—O1110.16 (14)C7—C8—C9118.9 (4)
O2—Cr1—O4110.83 (13)C7—C8—H8120.6
O3—Cr1—O4108.83 (14)C9—C8—H8120.6
O1—Cr1—O4107.41 (14)C10—C9—C8119.0 (4)
O6—Cr2—O5108.81 (15)C10—C9—H9120.5
O6—Cr2—O7110.00 (15)C8—C9—H9120.5
O5—Cr2—O7110.35 (14)C11—C10—C9120.0 (4)
O6—Cr2—O4110.80 (13)C11—C10—H10120.0
O5—Cr2—O4109.72 (14)C9—C10—H10120.0
O7—Cr2—O4107.15 (14)N3—C11—C10121.1 (4)
Cr1—O1—Hg1135.12 (15)N3—C11—H11119.4
Cr1—O3—Hg2v136.54 (15)C10—C11—H11119.4
Cr1—O4—Cr2138.62 (17)
Symmetry codes: (i) x, y, z+1/2; (ii) x1/2, y+3/2, z1/2; (iii) x+1/2, y+3/2, z+1; (iv) x+1/2, y+3/2, z+2; (v) x, y, z+3/2; (vi) x+1/2, y+3/2, z+1/2.

Experimental details

Crystal data
Chemical formula[Hg(C5H5N)2][Cr2O7]
Mr574.79
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)15.4741 (5), 15.0135 (5), 14.0407 (5)
β (°) 115.018 (1)
V3)2955.89 (17)
Z8
Radiation typeMo Kα
µ (mm1)11.84
Crystal size (mm)0.10 × 0.07 × 0.04
Data collection
DiffractometerSiemens SMART CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.366, 0.612
No. of measured, independent and
observed [I > 2σ(I)] reflections
19668, 3683, 3186
Rint0.030
(sin θ/λ)max1)0.667
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.018, 0.046, 1.21
No. of reflections3683
No. of parameters204
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)1.06, 0.58

Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SAINT, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS for WINDOWS (Dowty, 1998), SHELXL97.

Selected geometric parameters (Å, º) top
Hg1—N12.087 (4)Hg2—O72.640 (3)
Hg1—N22.092 (4)Cr1—O21.601 (3)
Hg1—O12.618 (3)Cr1—O31.617 (3)
Hg1—O1i2.618 (3)Cr1—O11.624 (3)
Hg1—O5ii2.625 (3)Cr1—O41.766 (3)
Hg1—O5iii2.625 (3)Cr1—Cr23.3075 (7)
Hg2—N3iv2.113 (3)Cr2—O61.604 (3)
Hg2—N32.113 (3)Cr2—O51.615 (3)
Hg2—O3v2.596 (3)Cr2—O71.621 (3)
Hg2—O3vi2.596 (3)Cr2—O41.769 (3)
Hg2—O7iv2.640 (3)
Cr1—O4—Cr2138.62 (17)
Symmetry codes: (i) x, y, z+1/2; (ii) x1/2, y+3/2, z1/2; (iii) x+1/2, y+3/2, z+1; (iv) x+1/2, y+3/2, z+2; (v) x, y, z+3/2; (vi) x+1/2, y+3/2, z+1/2.
 

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