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The first hexa­aqua/hydroxo complex of the [Re6Se8]2+ cluster species, tetra­aqua­di­hydroxo­hexa­rhen­ium­octa­selenium do­deca­hy­drate, is found to have unusual bonding that involves both inner and outer sphere aqua/hydro­xo species. The Re, one of the Se atoms and one of the O atoms are located on a crystallographic mirror plane, and the second Se atom is located on a special position of site symmetry 3m. Only the O atom in the outer coordination sphere occupies a general position. Crystallographically imposed symmetry prohibits unambiguous identification of the ligands as water or hydroxy O atoms. A lack of counter-ions in the interstices requires the molecular formula [Re6Se8O18] to be recast as [Re6Se8(OH)2(H2O)4]·12H2O

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801013241/bt6069sup1.cif
Contains datablocks I, zz52s

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536801013241/bt6069Isup2.hkl
Contains datablock I

Key indicators

  • Single-crystal X-ray study
  • T = 100 K
  • Mean [sigma](Re-O) = 0.007 Å
  • R factor = 0.027
  • wR factor = 0.068
  • Data-to-parameter ratio = 29.2

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.


Red Alert Alert Level A:
PLAT_732 Alert A Angle Calc 91.44(17), Rep 91.44(2) .... 8.95 s.u-Ratio O1 -RE1 -SE2 1.555 1.555 1.555 PLAT_733 Alert A Torsion Calc -144.35(17), Rep -144.36(1) .... 9.90 s.u-Ratio O1 -RE1 -SE3 -RE1 1.555 1.555 1.555 3.675 PLAT_733 Alert A Torsion Calc 144.36(17), Rep 144.36(1) .... 9.90 s.u-Ratio O1 -RE1 -SE3 -RE1 1.555 1.555 1.555 2.765
Yellow Alert Alert Level C:
ABSTM_02 Alert C The ratio of expected to reported Tmax/Tmin(RR') is < 0.90 Tmin and Tmax reported: 0.629 1.000 Tmin' and Tmax expected: 0.586 0.708 RR' = 0.760 Please check that your absorption correction is appropriate. CHEMW_01 Alert C The ratio of given/expected molecular weight as calculated from the _chemical_formula_sum lies outside the range 0.99 <> 1.01 Calculated formula weight = 2036.8691 Formula weight given = 2071.1499 PLAT_710 Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle # 3 SE2 -RE1 -SE2 -RE1 -21.70 0.80 3.675 1.555 1.555 21.655 PLAT_710 Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle # 10 SE2 -RE1 -SE2 -RE1 49.90 0.80 3.675 1.555 1.555 2.765 PLAT_710 Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle # 16 SE2 -RE1 -SE3 -RE1 35.64 0.02 20.565 1.555 1.555 3.675 PLAT_710 Alert C Delete 1-2-3 or 2-3-4 (CIF) Linear Torsion Angle # 23 SE2 -RE1 -SE3 -RE1 -35.64 0.02 20.565 1.555 1.555 2.765 PLAT_733 Alert C Torsion Calc 70.47(2), Rep 70.47(1) .... 2.86 s.u-Ratio RE1 -RE1 -SE3 -RE1 21.655 1.555 1.555 3.675 PLAT_733 Alert C Torsion Calc -70.46(2), Rep -70.47(1) .... 2.86 s.u-Ratio RE1 -RE1 -SE3 -RE1 20.565 1.555 1.555 2.765 General Notes
ABSTM_02 When printed, the submitted absorption T values will be replaced by the scaled T values. Since the ratio of scaled T's is identical to the ratio of reported T values, the scaling does not imply a change to the absorption corrections used in the study. Ratio of Tmax expected/reported 0.708 Tmax scaled 0.708 Tmin scaled 0.445 CHEMW_03 From the CIF: _cell_formula_units_Z 3 From the CIF: _chemical_formula_weight 2071.15 TEST: Calculate formula weight from _atom_site_* atom mass num sum O 16.00 18.00 287.98 Se 78.96 8.00 631.68 Re 186.21 6.00 1117.24 Calculated formula weight 2036.90 The ratio of given/expected molecular weight as calculated from the _atom_site* data lies outside the range 0.99 <> 1.01
3 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
8 Alert Level C = Please check

Comment top

Since the advent of a facile preparation of the molecular cluster core [Re6Q8]2+ (Q = S, Se, Te) (Long et al., 1996), extensive chemical and physical studies of these interesting species have become feasible. Recent work has demonstrated that the clusters are luminescent (Gray et al., 1999; Yoshimura et al., 1999). The lumniscence is strongly dependent upon the nature of the ligands coordinated at the Re apices and suggests the potential for creating a novel class of optical materials. The redox behavior of the cluster species is also ligand dependent, exhibiting reversible oxidations in the approximate ranges 200–300 and 800–1500 mV for the halide and phosphine ligated systems, respectively. In addition, the cluster core is remarkably robust and readily undergoes extensive substition chemistry at the Re apices (Zheng et al., 1997). The combined physical properties and favorable chemistry make the [Re6Q8]2+ cluster species an ideal precursor to molecular and supramolecular compounds with intriguing behaviors.

Our laboratory has pursued the preparation of discrete supramolecular species which feature geometries dictated by a [Re6Se8]2+ cluster. Use of partial substitution of halides with inert phosphine ligands allows selection of isomers with fixed stereochemistry. The fixed stereochemistry directs self-assembly of multiple clusters into pre-determined arrangements in the presence of stoichiometric amounts of an appropriate ligand (typically a 4,4-dipyridyl derivative). With an eye to the possibility of utilizing hydrogen bonding as the principal linking mode in these cluster assemblies, we have initiated the study of the hydroxide derivatives of the [nBu4]4[Re6Se8I6] cluster. Earlier work on the analogous [Re6S8]2+ system has indicated that the cluster exists in solution as the aqua complex (Fedin et al., 1998). Reported herein is the first persubstituted hexaaqua/hydroxide structure. The structure confirms the feasibility of the hydroxide substitution chemistry and provides the first structural data for the compound central to quantification of the cluster species' reactivities, [Re6Q8(H2O)6]2+.

Several features of the structure of the title compound are of interest. Chief among these is the formulation as [Re6Se8(OH)2(H2O)4].12H2O. This formula is a strictly formal representation of the coordination environment based on the charge requirements of the 24 e- ReIII cluster core. In the actual structure, the classification of apical ligands as OH- or H2O is prohibited by crystallographically imposed m symmetry. The structure may be generally described as the [Re6Se8]2+ core with apical Re sites bound to an inner-sphere O atom (O1). In close hydrogen bonding contact is an outer coordination sphere of 12 water molecules generated from a single oxygen site (O2). Both O1 and O2 are the only unique oxygen atoms in the structure. Hence, all Re—O bonds are equivalent, precluding distinction of the hydroxo and aqua ligands. An isomorphous structure of [Mo6Cl8(OH)4(H2O)14] shares this doubled hydration sphere feature and is also formulated according to charge balance considerations (Brosset, 1945). However, the title complex was prepared under highly basic conditions. This fact, combined with the observation of [Re6S8(H2O)6]2+ under acidic conditions by Fedin and coworkers, suggests that the title compound should exist at least as the neutral title formula, if not as the hexahydroxo tetraanion.

In the neutral scenario, one might expect a lowering of symmetry allowing the proper identification of the ligands. Alternatively, one should observe a lengthening of the apparent Re—O bond due to a larger aqua occupancy in a disordered structure. In the case of the tetraanion, a completely different structure might be expected, and accompanying cations would be easily located. A search of the Cambridge Structural Database (Allen & Kennard, 1993) reveals that the observed bond length [2.146 (7) Å] lies near the mean Re—OH bond length [2.16 (6) Å] but is also within 3σ of the mean Re—OH2 bond length [2.2 (1) Å]. Therefore, although the observed bond length is quite short, we cannot confidently state that the inner sphere consists entirely of hydroxo ligands. Furthermore, the expected four Na cations were not observed in the structure. A possible explanation is that the cluster core was oxidized during synthesis, but this is not supported by the structural parameters of the cluster core. The mean Re—Re and Re—Se bond lengths [2.6037 (6) Å and 2.56 (1) Å] do not differ significantly from those of the starting material. The Re—Re bond is only slightly shorter, and the Re—Se bond slightly longer.

In summary, we have prepared and reported the first structurally characterized `hexaaqua/hydroxo' complex of the [Re6Se8]2+ cluster core. While these data are of general interest and significance, the structure itself has proven to be quite fascinating. While formally [Re6Se8(OH)2(H2O)4].12H2O, the true formula remains uncertain.

Experimental top

The title compound was prepared by dissolving ca 50 mg (0.014 mmol) [nBu4]4[Re6Se8I6] in 100 ml acetone in a 250 ml round-bottomed flask. The resulting green–black solution was vigorously stirred and treated with a large excess of aqueous NaOH, added dropwise from concentrated solution. A straw yellow precipitate was rapidly formed. The mixture was allowed to stir at room temperature for 24 h. The precipitate was collected and washed several times with acetone, dissolved in distilled water, filtered, and left to concentrate. Small golden rhombohedral crystals were obtained after two weeks.

Refinement top

Outer-sphere O atoms were initially modeled as water molecules, which refined satisfactorily. However, it was not possible to model a proper hydrogen-bonding scheme to the inner sphere O1 atoms. A single H-atom site was initially located between the two O atoms, but it invariably moved to form one of the two H atoms of the O2 water. When the O2 water molecules were included in the model, fixing an H atom to O1, regardless of occupancy, made refinement unstable. The final model neglected protons entirely for consistency and reflects the ambiguous relationship between inner- and outer-sphere molecules. The lack of H atoms accounts for the discrepancy between the title formula and the moiety formula.

Computing details top

Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. Displacement ellipsoid plot rendered with 50% probability ellipsoids.
Tetraaquadihydroxohexarheniumoctaselenium dodecahydrate top
Crystal data top
[Re6Se8(OH)2(H2O)4]·12H2ODx = 4.680 Mg m3
Mr = 2071.15Mo Kα radiation, λ = 0.71073 Å
Trigonal, R3mCell parameters from 5277 reflections
a = 15.1655 (6) Åθ = 2.4–31.6°
c = 11.0678 (7) ŵ = 34.58 mm1
V = 2204.48 (19) Å3T = 100 K
Z = 3Rhombohedron, yellow
F(000) = 27000.02 × 0.02 × 0.01 mm
Data collection top
Bruker CCD area-detector
diffractometer
905 independent reflections
Radiation source: fine-focus sealed tube665 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.065
ω scansθmax = 31.5°, θmin = 2.4°
Absorption correction: multi-scan
(Bruker, 2000)
h = 2222
Tmin = 0.629, Tmax = 1.000k = 2222
13294 measured reflectionsl = 1616
Refinement top
Refinement on F20 constraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.027Secondary atom site location: difference Fourier map
wR(F2) = 0.068Hydrogen site location: inferred from neighbouring sites
S = 1.14 w = 1/[σ2(Fo2) + (0.0145P)2 + 149.2289P]
where P = (Fo2 + 2Fc2)/3
905 reflections(Δ/σ)max = 0.002
31 parametersΔρmax = 1.86 e Å3
0 restraintsΔρmin = 2.54 e Å3
Crystal data top
[Re6Se8(OH)2(H2O)4]·12H2OZ = 3
Mr = 2071.15Mo Kα radiation
Trigonal, R3mµ = 34.58 mm1
a = 15.1655 (6) ÅT = 100 K
c = 11.0678 (7) Å0.02 × 0.02 × 0.01 mm
V = 2204.48 (19) Å3
Data collection top
Bruker CCD area-detector
diffractometer
905 independent reflections
Absorption correction: multi-scan
(Bruker, 2000)
665 reflections with I > 2σ(I)
Tmin = 0.629, Tmax = 1.000Rint = 0.065
13294 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0270 restraints
wR(F2) = 0.068 w = 1/[σ2(Fo2) + (0.0145P)2 + 149.2289P]
where P = (Fo2 + 2Fc2)/3
S = 1.14Δρmax = 1.86 e Å3
905 reflectionsΔρmin = 2.54 e Å3
31 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
Re10.942853 (14)0.88571 (3)0.09632 (3)0.00790 (10)
Se21.11106 (4)0.88894 (4)0.09187 (9)0.0124 (2)
Se31.00001.00000.28043 (16)0.0127 (3)
O10.8778 (3)0.7556 (6)0.2135 (7)0.0165 (15)
O20.7625 (5)0.7887 (5)0.3804 (5)0.0262 (13)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Re10.00933 (14)0.00844 (18)0.00562 (16)0.00422 (9)0.00012 (7)0.00024 (13)
Se20.0151 (4)0.0151 (4)0.0098 (5)0.0098 (4)0.00003 (16)0.00003 (16)
Se30.0146 (5)0.0146 (5)0.0089 (7)0.0073 (2)0.0000.000
O10.022 (3)0.011 (3)0.012 (3)0.0056 (17)0.0022 (14)0.004 (3)
O20.028 (3)0.031 (3)0.021 (3)0.016 (3)0.002 (2)0.003 (2)
Geometric parameters (Å, º) top
Re1—O12.146 (7)Re1—Re1i2.6074 (6)
Re1—Se2i2.5187 (10)Re1—Re1iv2.6074 (6)
Re1—Se2ii2.5273 (9)Se2—Re1iv2.5187 (10)
Re1—Se22.5273 (9)Se2—Re1iii2.5273 (9)
Re1—Se32.5310 (15)Se3—Re1ii2.5310 (15)
Re1—Re1iii2.6000 (6)Se3—Re1iii2.5310 (15)
Re1—Re1ii2.6000 (6)
O1—Re1—Se2i93.0 (2)O1—Re1—Re1i136.35 (14)
O1—Re1—Se2ii91.440 (19)Se2i—Re1—Re1i59.05 (2)
Se2i—Re1—Se2ii89.62 (2)Se2ii—Re1—Re1i58.72 (2)
O1—Re1—Se291.440 (19)Se2—Re1—Re1i118.53 (3)
Se2i—Re1—Se289.62 (2)Se3—Re1—Re1i119.18 (2)
Se2ii—Re1—Se2177.05 (4)Re1iii—Re1—Re1i90.0
O1—Re1—Se389.2 (2)Re1ii—Re1—Re1i60.095 (9)
Se2i—Re1—Se3177.84 (4)O1—Re1—Re1iv136.35 (14)
Se2ii—Re1—Se390.33 (2)Se2i—Re1—Re1iv59.05 (2)
Se2—Re1—Se390.33 (2)Se2ii—Re1—Re1iv118.53 (3)
O1—Re1—Re1iii133.62 (15)Se2—Re1—Re1iv58.72 (2)
Se2i—Re1—Re1iii119.14 (2)Se3—Re1—Re1iv119.18 (2)
Se2ii—Re1—Re1iii119.032 (15)Re1iii—Re1—Re1iv60.095 (9)
Se2—Re1—Re1iii59.045 (15)Re1ii—Re1—Re1iv90.0
Se3—Re1—Re1iii59.09 (2)Re1i—Re1—Re1iv59.811 (18)
O1—Re1—Re1ii133.62 (15)Re1iv—Se2—Re1iii62.23 (3)
Se2i—Re1—Re1ii119.14 (2)Re1iv—Se2—Re162.23 (3)
Se2ii—Re1—Re1ii59.045 (15)Re1iii—Se2—Re161.91 (3)
Se2—Re1—Re1ii119.032 (15)Re1—Se3—Re1ii61.81 (4)
Se3—Re1—Re1ii59.09 (2)Re1—Se3—Re1iii61.81 (4)
Re1iii—Re1—Re1ii60.0Re1ii—Se3—Re1iii61.81 (4)
O1—Re1—Se2—Re1iv146.3 (2)O1—Re1—Se3—Re1ii144.356 (9)
Se2i—Re1—Se2—Re1iv53.29 (3)Se2i—Re1—Se3—Re1ii35.64 (2)
Se2ii—Re1—Se2—Re1iv21.7 (8)Se2ii—Re1—Se3—Re1ii52.92 (2)
Se3—Re1—Se2—Re1iv124.54 (3)Se2—Re1—Se3—Re1ii124.208 (19)
Re1iii—Re1—Se2—Re1iv71.585 (15)Re1iii—Re1—Se3—Re1ii71.288 (18)
Re1ii—Re1—Se2—Re1iv70.297 (18)Re1i—Re1—Se3—Re1ii0.820 (19)
Re1i—Re1—Se2—Re1iv0.618 (19)Re1iv—Re1—Se3—Re1ii70.468 (7)
O1—Re1—Se2—Re1iii142.2 (2)O1—Re1—Se3—Re1iii144.356 (9)
Se2i—Re1—Se2—Re1iii124.88 (3)Se2i—Re1—Se3—Re1iii35.64 (2)
Se2ii—Re1—Se2—Re1iii49.9 (8)Se2ii—Re1—Se3—Re1iii124.208 (19)
Se3—Re1—Se2—Re1iii52.96 (3)Se2—Re1—Se3—Re1iii52.92 (2)
Re1ii—Re1—Se2—Re1iii1.29 (3)Re1ii—Re1—Se3—Re1iii71.288 (18)
Re1i—Re1—Se2—Re1iii70.97 (2)Re1i—Re1—Se3—Re1iii70.468 (7)
Re1iv—Re1—Se2—Re1iii71.585 (15)Re1iv—Re1—Se3—Re1iii0.820 (19)
Symmetry codes: (i) y, x+y+1, z; (ii) x+y+1, x+2, z; (iii) y+2, xy+1, z; (iv) xy+1, x, z.

Experimental details

Crystal data
Chemical formula[Re6Se8(OH)2(H2O)4]·12H2O
Mr2071.15
Crystal system, space groupTrigonal, R3m
Temperature (K)100
a, c (Å)15.1655 (6), 11.0678 (7)
V3)2204.48 (19)
Z3
Radiation typeMo Kα
µ (mm1)34.58
Crystal size (mm)0.02 × 0.02 × 0.01
Data collection
DiffractometerBruker CCD area-detector
diffractometer
Absorption correctionMulti-scan
(Bruker, 2000)
Tmin, Tmax0.629, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
13294, 905, 665
Rint0.065
(sin θ/λ)max1)0.735
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.027, 0.068, 1.14
No. of reflections905
No. of parameters31
w = 1/[σ2(Fo2) + (0.0145P)2 + 149.2289P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)1.86, 2.54

Computer programs: SMART (Bruker, 1997), SMART, SHELXTL (Bruker, 1997), SHELXTL.

 

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