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The structure of the title compound, NaAuBr4·2H2O is isomorphous with that of NaAuCl4·2H2O. The Na, Au and Br atoms lie on the mirror plane. The AuBr4- anions are nearly square planar with Au-Br bond lengths in the range 2.415 (2)-2.433 (2) Å.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536800021140/ob6012sup1.cif
Contains datablocks I, naaubr4

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536800021140/ob6012Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](Au-Br) = 0.002 Å
  • R factor = 0.049
  • wR factor = 0.097
  • Data-to-parameter ratio = 25.3

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

PLATON alerts of the form PLAT_7?? have been detected for an inorganic
structure. These tests are under development  for inorganics and
comments are welcomed. It is not necessary to supply a data
validation response form for these alerts at this time.


Amber Alert Alert Level B:
CHEMS_01 Alert B The sum formula contains elements in the wrong order. H precedes Au Sequence must be C, H, then alphabetical. PLAT_722 Alert B Angle Calc 129.58, Rep 127.00, Dev. 2.58 Degree NA -O -H1 5.656 1.555 1.555
Yellow Alert Alert Level C:
PLAT_722 Alert C Angle Calc 110.82, Rep 112.00, Dev. 1.18 Degree NA -O -H1 1.555 1.555 1.555 PLAT_722 Alert C Angle Calc 82.87, Rep 81.00, Dev. 1.87 Degree NA -O -H2 5.656 1.555 1.555 General Notes
FORMU_01 There is a discrepancy between the atom counts in the _chemical_formula_sum and _chemical_formula_moiety. This is usually due to the moiety formula being in the wrong format. Atom count from _chemical_formula_sum: H4 Au1 Br4 Na1 O2 Atom count from _chemical_formula_moiety:H2 Au1 Br4 Na1 O2
0 Alert Level A = Potentially serious problem
2 Alert Level B = Potential problem
2 Alert Level C = Please check

Comment top

Previous studies concerning the crystal structure determination of the anhydrous MAuX4 compounds and the corresponding dihydrate MAuX4.2H2O (M is Na or K, X is Cl or Br) have shown that: (i) KAuBr4 (Omrani et al., 1999), KAuBr4.2H2O (Omrani et al., 1986), KAuCl4 (Jones & Bembenek, 1992) and NaAuCl4 (Jones et al., 1988) crystallize in the monoclinic system with the space group P21/c (or P21/n); (ii) NaAuCl4.2H2O (Bonamico & Dessy, 1965) and KAuCl4.2H2O (Theobald & Omrani, 1980) crystallize in the orthorhombic system with the space group Pnma and Pbcn, respectively. All these compounds are characterized by the occurrence of square-planar AuX4- anions with typical Au—X distances (approximately 2.29 Å for Au—Cl bond and 2.43 Å for Au—Br bond). In this class of based gold coordination compounds, only both NaAuBr4 and NaAuBr4.2H2O compounds were not yet characterized. In the present work, we report on the crystal structure of the dihydrate.

The structure of the title compound, NaAuBr4.2H2O, (I), is isomorphous with that of NaAuCl4.2H2O (Bonamico & Dessy, 1965). The orthorhombic cell contains four Au atoms and the AuBr4- anions are nearly square planar (Fig. 1). The Au, Br and Na atoms lie on the mirror plane. The structure can also be described as a pseudo-lamellar compound in which the NaAuBr4 planes (at y = 1/4 and 3/4) are piled up along the b axis and connected via Na—O—Na bonds. There is only one independent Na atom, which is coordinated by four O atoms at distances in the range 2.437 (12)–2.509 (13) Å and three Br atoms at distances in the range 3.150 (10)–3.300 (10) Å (Table 1).

Experimental top

Crystals were prepared by dissolving powder of NaAuCl4.2H2O in aqueous HBr (1 M). The solution was slowly evaporated (two months) at 300 K. After complete crystallization, dark brick red crystals were obtained. A single-crystal was then sealed in Lindemann glass capillary.

Refinement top

In the final electron-density difference map, both minimum (-1.57 e Å-3 at 0.3594, 1/4,0.5494) and maximum (2.09 e Å-3 at 0.4964,0.1831,0.2760) occur respectively at 0.96 Å away from Br4 and 1.72 Å from Na. They may be due to the irregular crystal shape and the approximate absorption correction. The H atoms were fixed with O—H distances of 0.95 Å.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CADAK and SORTAV (Blessing, 1987); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1985); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. Part of the crystal structure. Displacement ellipsoids are shown at 50% probability levels. Symmetry codes: (i) x, y, z - 1; (ii) x, 1/2 - y, z; (iii) 1 - x, 1/2 + y, 1 - z; (iv) 1 - x, -y, 1 - z.
Sodium tetrabromoaurate(III) dihydrate top
Crystal data top
NaAuBr4·2H2ODx = 4.201 Mg m3
Mr = 575.63Ag Kα radiation, λ = 0.5608 Å
Orthorhombic, PnmaCell parameters from 25 reflections
a = 13.320 (6) Åθ = 8.3–10.4°
b = 7.253 (2) ŵ = 18.20 mm1
c = 9.420 (3) ÅT = 293 K
V = 910.1 (6) Å3Parallelepiped, dark red
Z = 40.16 × 0.09 × 0.06 mm
F(000) = 1000
Data collection top
Enraf Nonius CAD-4
diffractometer
905 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.000
Graphite monochromatorθmax = 22.9°, θmin = 2.1°
ω–2θ scansh = 018
Absorption correction: ψ scan
(SORTAV; Blessing, 1987)
k = 010
Tmin = 0.051, Tmax = 0.363l = 013
1368 measured reflections2 standard reflections every 180 min
1368 independent reflections intensity decay: 0.1%
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)] = 0.049H-atom parameters constrained
wR(F2) = 0.097 w = 1/[σ2(Fo2) + (0.0178P)2 + 12.749P]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max < 0.001
1368 reflectionsΔρmax = 2.09 e Å3
54 parametersΔρmin = 1.57 e Å3
3 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0047 (3)
Crystal data top
NaAuBr4·2H2OV = 910.1 (6) Å3
Mr = 575.63Z = 4
Orthorhombic, PnmaAg Kα radiation, λ = 0.5608 Å
a = 13.320 (6) ŵ = 18.20 mm1
b = 7.253 (2) ÅT = 293 K
c = 9.420 (3) Å0.16 × 0.09 × 0.06 mm
Data collection top
Enraf Nonius CAD-4
diffractometer
905 reflections with I > 2σ(I)
Absorption correction: ψ scan
(SORTAV; Blessing, 1987)
Rint = 0.000
Tmin = 0.051, Tmax = 0.3632 standard reflections every 180 min
1368 measured reflections intensity decay: 0.1%
1368 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0493 restraints
wR(F2) = 0.097H-atom parameters constrained
S = 1.09 w = 1/[σ2(Fo2) + (0.0178P)2 + 12.749P]
where P = (Fo2 + 2Fc2)/3
1368 reflectionsΔρmax = 2.09 e Å3
54 parametersΔρmin = 1.57 e Å3
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
Au0.43636 (5)0.25000.01537 (7)0.0258 (2)
Br10.32724 (15)0.25000.1914 (2)0.0422 (5)
Br20.28961 (13)0.25000.16910 (19)0.0364 (5)
Br30.58537 (14)0.25000.1329 (2)0.0411 (5)
Br40.54477 (15)0.25000.2209 (2)0.0462 (6)
Na0.4885 (6)0.25000.5620 (10)0.051 (2)
O0.3845 (7)0.0025 (16)0.4674 (10)0.050 (3)
H10.3210.000.5130.08*
H20.3730.020.3700.08*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Au0.0209 (3)0.0288 (3)0.0276 (3)0.0000.0002 (3)0.000
Br10.0319 (10)0.0647 (15)0.0298 (9)0.0000.0044 (8)0.000
Br20.0236 (8)0.0534 (13)0.0321 (9)0.0000.0017 (7)0.000
Br30.0299 (10)0.0523 (12)0.0410 (11)0.0000.0107 (8)0.000
Br40.0309 (11)0.0710 (15)0.0367 (11)0.0000.0099 (8)0.000
Na0.046 (5)0.053 (5)0.054 (5)0.0000.001 (4)0.000
O0.043 (5)0.072 (8)0.033 (5)0.013 (6)0.003 (4)0.001 (6)
Geometric parameters (Å, º) top
Au—Br42.415 (2)Na—Oiii2.509 (13)
Au—Br32.427 (2)Na—Oiv2.509 (13)
Au—Br12.431 (2)Na—Br3v3.150 (10)
Au—Br22.433 (2)Na—Br1v3.163 (9)
Br1—Nai3.163 (9)Na—Naiv3.823 (6)
Br3—Nai3.150 (10)Na—Navi3.823 (6)
Br4—Na3.300 (10)O—Naiv2.509 (13)
Na—O2.437 (12)O—H10.95
Na—Oii2.437 (12)O—H20.95
Br4—Au—Br388.41 (8)Oiii—Na—Br474.9 (3)
Br4—Au—Br1180.00 (8)Oiv—Na—Br474.9 (3)
Br3—Au—Br191.59 (8)Br3v—Na—Br4142.7 (3)
Br4—Au—Br290.19 (8)Br1v—Na—Br4150.4 (3)
Br3—Au—Br2178.60 (7)O—Na—Naiv40.1 (3)
Br1—Au—Br289.81 (8)Oii—Na—Naiv129.3 (5)
Au—Br1—Nai100.51 (18)Oiii—Na—Naiv127.2 (5)
Au—Br3—Nai100.95 (17)Oiv—Na—Naiv38.7 (3)
Au—Br4—Na130.15 (17)Br3v—Na—Naiv104.2 (3)
O—Na—Oii94.9 (6)Br1v—Na—Naiv106.2 (3)
O—Na—Oiii151.7 (4)Br4—Na—Naiv71.6 (3)
Oii—Na—Oiii78.8 (4)O—Na—Navi129.3 (5)
O—Na—Oiv78.8 (4)Oii—Na—Navi40.1 (3)
Oii—Na—Oiv151.7 (4)Oiii—Na—Navi38.7 (3)
Oiii—Na—Oiv93.8 (5)Oiv—Na—Navi127.2 (5)
O—Na—Br3v124.5 (3)Br3v—Na—Navi104.2 (3)
Oii—Na—Br3v124.5 (3)Br1v—Na—Navi106.2 (3)
Oiii—Na—Br3v79.9 (3)Br4—Na—Navi71.6 (3)
Oiv—Na—Br3v79.9 (3)Naiv—Na—Navi143.1 (5)
O—Na—Br1v83.3 (3)Na—O—Naiv101.2 (4)
Oii—Na—Br1v83.3 (3)Na—O—H1112
Oiii—Na—Br1v122.6 (3)Naiv—O—H1127
Oiv—Na—Br1v122.6 (3)Na—O—H2126
Br3v—Na—Br1v67.0 (2)Naiv—O—H281
O—Na—Br476.9 (3)H1—O—H2107
Oii—Na—Br476.9 (3)
Symmetry codes: (i) x, y, z1; (ii) x, y+1/2, z; (iii) x+1, y+1/2, z+1; (iv) x+1, y, z+1; (v) x, y, z+1; (vi) x+1, y+1, z+1.

Experimental details

Crystal data
Chemical formulaNaAuBr4·2H2O
Mr575.63
Crystal system, space groupOrthorhombic, Pnma
Temperature (K)293
a, b, c (Å)13.320 (6), 7.253 (2), 9.420 (3)
V3)910.1 (6)
Z4
Radiation typeAg Kα, λ = 0.5608 Å
µ (mm1)18.20
Crystal size (mm)0.16 × 0.09 × 0.06
Data collection
DiffractometerEnraf Nonius CAD-4
diffractometer
Absorption correctionψ scan
(SORTAV; Blessing, 1987)
Tmin, Tmax0.051, 0.363
No. of measured, independent and
observed [I > 2σ(I)] reflections
1368, 1368, 905
Rint0.000
(sin θ/λ)max1)0.694
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.049, 0.097, 1.09
No. of reflections1368
No. of parameters54
No. of restraints3
H-atom treatmentH-atom parameters constrained
w = 1/[σ2(Fo2) + (0.0178P)2 + 12.749P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)2.09, 1.57

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, CADAK and SORTAV (Blessing, 1987), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 1985), SHELXL97.

Selected geometric parameters (Å, º) top
Au—Br42.415 (2)Br4—Na3.300 (10)
Au—Br32.427 (2)Na—O2.437 (12)
Au—Br12.431 (2)Na—Oii2.437 (12)
Au—Br22.433 (2)Na—Oiii2.509 (13)
Br1—Nai3.163 (9)Na—Oiv2.509 (13)
Br3—Nai3.150 (10)
Br4—Au—Br388.41 (8)Br4—Au—Br290.19 (8)
Br4—Au—Br1180.00 (8)Br3—Au—Br2178.60 (7)
Br3—Au—Br191.59 (8)Br1—Au—Br289.81 (8)
Symmetry codes: (i) x, y, z1; (ii) x, y+1/2, z; (iii) x+1, y+1/2, z+1; (iv) x+1, y, z+1.
 

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