The dehydrated copper silicate Na2[Cu2Si4O11]: a three-dimensional microporous framework with a linear Si—O—Si linkage

Cunha-Silva, L.; Brandão, P.; Rocha, J.; Almeida Paz, F.A.

doi:10.1107/S1600536808001608

inorganic compounds

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Volume 64| Part 2| February 2008| Pages i13-i14

doi:10.1107/S1600536808001608

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The dehydrated copper silicate Na₂[Cu₂Si₄O₁₁]: a three-dimensional microporous framework with a linear Si—O—Si linkage

Luís Cunha-Silva,^a Paula Brandão,^a João Rocha ^a and Filipe A. Almeida Paz ^a ^*

^aDepartment of Chemistry, University of Aveiro, CICECO, 3810-193 Aveiro, Portugal
^*Correspondence e-mail: filipe.paz@ua.pt

(Received 28 November 2007; accepted 15 January 2008; online 23 January 2008)

The structure of the title dehydrated copper silicate, disodium dicopper undecaoxide tetrasilicate, Na₂(Cu₂O₁₁Si₄), was determined by single-crystal X-ray diffraction from a non-merohedral twin. It exhibits an effective three-dimensional microporous framework with the major channels, in which the Na⁺ cations are placed, running along the a-axis direction and smaller channels observed along the b-axis direction. The structure is unusual in that it contains a symmetry-constrained Si—O—Si angle of 180°. The Cu centre is coordinated to five O atoms, exhibiting a slightly distorted square-pyramidal coordination geometry. The Na cation is interacting with five neighbouring O atoms, exhibiting an uncharacteristic coordination environment.

Related literature

For related literature, see: Brandão et al. (2005 ); Haile & Wuensch (2000 ); Liebau (1985 ); Rocha & Anderson (2000 ); Rocha & Lin (2005 ); dos Santos et al. (2005 ); Ananias et al. (2001 , 2006 ); Anderson et al. (1994 ); Ferreira et al. (2003 ).

Experimental

Crystal data

Na₂(Cu₂O₁₁Si₄)
M_r = 461.44
Triclinic, $[P \overline 1]$
a = 5.190 (2) Å
b = 6.299 (3) Å
c = 8.196 (4) Å
α = 96.390 (7)°
β = 97.281 (7)°
γ = 100.461 (7)°
V = 258.9 (2) Å³
Z = 1
Mo Kα radiation
μ = 4.71 mm⁻¹
T = 298 (2) K
0.28 × 0.08 × 0.04 mm

Data collection

Bruker SMART CCD 1000 diffractometer
Absorption correction: multi-scan (TWINABS; Sheldrick, 2002 ) T_min = 0.627, T_max = 0.834
1587 measured reflections
1043 independent reflections
782 reflections with I > 2σ(I)
R_int = 0.042

Refinement

R[F² > 2σ(F²)] = 0.042
wR(F²) = 0.119
S = 1.01
1043 reflections
88 parameters
Δρ_max = 1.40 e Å⁻³
Δρ_min = −1.58 e Å⁻³

Table 1
Selected bond lengths (Å)

Cu1—O5ⁱ	1.909 (3)
Cu1—O2	1.950 (4)
Cu1—O6ⁱⁱ	1.970 (4)
Cu1—O6	1.974 (3)
Cu1—O2ⁱⁱⁱ	2.316 (4)
Symmetry codes: (i) x, y-1, z; (ii) -x+1, -y, -z+2; (iii) -x+2, -y, -z+2.

Data collection: SMART (Bruker, 1998 ); cell refinement: SMART; data reduction: SAINT-Plus (Bruker, 2003 ); program(s) used to solve structure: SIR92 (Altomare et al., 1993 ); program(s) used to refine structure: SHELXTL (Sheldrick, 2008 ); molecular graphics: DIAMOND (Brandenburg, 2007 ); software used to prepare material for publication: SHELXTL.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808001608/br2065sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808001608/br2065Isup2.hkl

checkCIF report

Comment top

Molecular sieves containing metal cations with a range of coordination geometries have been extensively studied due to their novel topologies, interesting chemical properties and potential aplications in optoelectronics, batteries, magnetic materials and sensors (besides the traditional applications of zeolites) (Rocha & Anderson, 2000; Rocha & Lin, 2005). In the last decade, we have been interested in the synthesis and structural characterization of novel open-frameworks containing Si and metal cations (such as Ti, V, Cr, Nb, Zr and Sn) in tetrahedral and (more commonly) octahedral coordination environments, and lanthanide silicates exhibiting interesting photoluminescence properties (Anderson et al., 1994; Ananias et al., 2001; Ferreira et al., 2003; Ananias et al., 2006). As part of this research line, we prepared and characterized the hydrated copper silicate Na₂(Cu₂Si₄O₁₁).2H₂O (Brandão et al., 2005). This compound was dehydrated and the magnetic properties of both hydrated and dehydrated forms were investigated (Santos et al., 2005), however the crystalline structure of the dehydrated compound was not reported. Here we describe the structure of the dehydrated microporous copper silicate, Na₂(Cu₂Si₄O₁₁) (I).

The asymmetric unit of the copper silicate (I) comprises one Cu(II) cation, two corner-shared SiO₄ groups and one Na⁺ counter-cation (Figure 1). The crystallographic unique Cu(II) metal centre is coordinated to five O-atoms from five distinct SiO₄ tetrahedral moieties (four basal SiO₄ and one apical SiO₄), in a geometry resembling a distorted square pyramid for which the apical Cu—O bond is longer than the basal ones (Figure 2a and Table 1).

Adjacent SiO₄ tetrahedral moieties are linked along the a direction by corner-shared oxygen atoms (O3 and O4 are shared alternately) leading to the formation of zigzag metallic anionic chains, [(Cu₂Si₄O₁₁)_∞]^2-, in which the Cu···Cu distances alternate between 2.9921 (8) Å (via bridging basal SiO₄, green bonds in Fig. 2 b) and 3.1031 (10) Å (via the apical SiO₄ tetrahedron, yellow bonds in Fig. 2 b). [(Cu₂Si₄O₁₁)_∞]^2- chains are interconnected via corner-sharing SiO₄ tetrahedra through linear interactions Si1–O1–Si^iv [angle is 180.0°; symmetry code: (iv) 2 - x, -y, 1 - z] to form infinite layers (Fig. 2c). This linear Si–O–Si interaction is very rare and represents a remarkable structural feature of the copper silicate (I) framework. We note that such occurrence was also recently reported in the lanthanide silicate K₃(NdSi₇O₁₇) (Haile & Wuensch, 2000). From the evaluation of the structures of several hundred silicates it was concluded that the average of an unstrained Si—O—Si bond angle is ca 139° and that truly linear bonds are energetically unfavorable (Liebau, 1985). In fact, the crystallographically determined values of 180° are more likely to represent a time average rather than the actual value of the bond angle. The bond, at any instant in time, should have an O-atom displaced from its average position such that the instantaneous value of Si—O—Si is less than 180° (Haile & Wuensch, 2000). This structural feature is ultimately reflected in the anisotropic displacement parameters associated with this bridging O-atom. Indeed, the thermal parameters associated with this atom are unusually large, with the greatest displacement occurring in the plane perpendicular to the Si1···Si1^iv vector (Figure 2c).

As observed for the chains, adjacent layers are also interconnected via corner-sharing SiO₄ tetrahedra generating a three-dimensional microporous framework with the major channels running along the a direction, formed by eight-membered rings and having a cross-section of ca 7.5 × 4.3 Å (Figure 3a). Interestingly, the Na⁺ cations are located within the channels but are remarkably close to the previously described layers, creating an effective porous copper framework (Figure 3a). In addition, remarkably large channels are also observed along the b direction, which are formed by six-membered rings and display a cros-section of ca 5.2 × 4.6 Å (Figure 3 b).

Related literature top

For related literature, see: Brandão et al. (2005); Haile & Wuensch (2000); Liebau (1985); Rocha & Anderson (2000); Rocha & Lin (2005); dos Santos et al. (2005); Ananias et al. (2001, 2006); Anderson et al. (1994); Ferreira et al. (2003).

Experimental top

Chemicals were purchased from commercial sources and used without further purification. An alkaline solution was prepared by mixing 13.86 g of a sodium silicate solution (Na₂O 8 wt%, SiO₂ 27 wt%), 16.13 g H₂O and 4.11 g NaOH, and a second solution was prepared by mixing 17.87 g H₂O with 7.60 g of Cu(SO₄).15H₂O. These two solutions were combined, stirred thoroughly during 2 h and the resulting gel, with a molar composition of CuO: 3.1SiO₂: 1.4Na₂O: 94.5H₂O, was autoclaved for 10 days at 503 K. A crystalline material was obtained [Na₂(Cu₂Si₄O₁₁).2H₂O], filtered and treated thermally at 573 K for six hours leads to the removal of the crystallization water molecules.

Computing details top

Data collection: SMART (Bruker, 1998); cell refinement: SMART (Bruker, 1998); data reduction: SAINT-Plus (Bruker, 2003); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2007); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. Fragment of the crystal structure of the title compound with the atoms represented as thermal displacement ellipsoids drawn at the 50% probability level [Symmetry codes: (i) 2 - x, -y, 2 - z; (ii) x, -1 + y, z; (iii) 1 - x, -y, 2 - z; (iv) 2 - x, 1 - y, 2 - z; (v) x, y, 1 + z; (vi) 1 + x, y, z].
	Fig. 2. (a) Mixed ball-and-stick and polyhedral representation of the coordination environment of the Cu(II) cations and (b) the metallic chain [(Cu₂Si₄O₁₁)_n]^2- running along the a direction of the unit cell. (c) Schematic representation of the linear Si—O—Si bond connecting adjacent Si1 centres via the O1 atom. [Symmetry codes: (i) 2 - x, -y, 2 - z; (ii) x, -1 + y, z; (iii) 1 - x, -y, 2 - z; (iv) 2 - x, -y, 1 - z].
	Fig. 3. Perspective views of the crystal packing arrangement along the (a) [100] and (b) [010] directions of unit cell.

disodium dicopper undecaoxide tetrasilicate top

Crystal data top

Na₂(Cu₂O₁₁Si₄)	Z = 1
M_r = 461.44	F(000) = 224
Triclinic, P1	D_x = 2.960 Mg m⁻³
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.190 (2) Å	Cell parameters from 758 reflections
b = 6.299 (3) Å	θ = 8.1–58.1°
c = 8.196 (4) Å	µ = 4.71 mm⁻¹
α = 96.390 (7)°	T = 298 K
β = 97.281 (7)°	Plate, black
γ = 100.461 (7)°	0.28 × 0.08 × 0.04 mm
V = 258.9 (2) Å³

Data collection top

Bruker SMART CCD 1000 diffractometer	1043 independent reflections
Radiation source: fine-focus sealed tube	782 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.042
ω scans	θ_max = 26.4°, θ_min = 3.9°
Absorption correction: multi-scan (TWINABS; Sheldrick, 2002)	h = −6→6
T_min = 0.627, T_max = 0.834	k = −7→7
1587 measured reflections	l = 0→10

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F² > 2σ(F²)] = 0.042	Secondary atom site location: difference Fourier map
wR(F²) = 0.119	w = 1/[σ²(F_o²) + (0.0809P)²] where P = (F_o² + 2F_c²)/3
S = 1.01	(Δ/σ)_max < 0.001
1043 reflections	Δρ_max = 1.40 e Å⁻³
88 parameters	Δρ_min = −1.58 e Å⁻³

Crystal data top

Na₂(Cu₂O₁₁Si₄)	γ = 100.461 (7)°
M_r = 461.44	V = 258.9 (2) Å³
Triclinic, P1	Z = 1
a = 5.190 (2) Å	Mo Kα radiation
b = 6.299 (3) Å	µ = 4.71 mm⁻¹
c = 8.196 (4) Å	T = 298 K
α = 96.390 (7)°	0.28 × 0.08 × 0.04 mm
β = 97.281 (7)°

Data collection top

Bruker SMART CCD 1000 diffractometer	1043 independent reflections
Absorption correction: multi-scan (TWINABS; Sheldrick, 2002)	782 reflections with I > 2σ(I)
T_min = 0.627, T_max = 0.834	R_int = 0.042
1587 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.042	88 parameters
wR(F²) = 0.119	0 restraints
S = 1.01	Δρ_max = 1.40 e Å⁻³
1043 reflections	Δρ_min = −1.58 e Å⁻³

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

	x	y	z	U_iso*/U_eq
Cu1	0.70666 (10)	−0.10891 (9)	0.93472 (8)	0.0096 (3)
Na1	0.8700 (4)	0.3540 (3)	1.1990 (3)	0.0235 (6)
Si1	1.0175 (2)	0.1358 (2)	0.67930 (18)	0.0087 (4)
Si2	0.5954 (3)	0.3456 (2)	0.80969 (18)	0.0089 (4)
O1	1.0000	0.0000	0.5000	0.0217 (13)
O2	1.0064 (7)	−0.0190 (6)	0.8196 (5)	0.0127 (8)
O3	0.7804 (6)	0.2736 (6)	0.6719 (5)	0.0126 (8)
O4	0.2923 (6)	0.3209 (5)	0.7137 (5)	0.0144 (8)
O5	0.7200 (7)	0.5899 (6)	0.8873 (5)	0.0170 (9)
O6	0.5974 (6)	0.1760 (5)	0.9452 (5)	0.0107 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu1	0.0054 (4)	0.0083 (4)	0.0159 (4)	0.0011 (2)	0.0051 (2)	0.0018 (2)
Na1	0.0137 (11)	0.0161 (12)	0.0396 (16)	0.0021 (9)	0.0072 (10)	−0.0030 (10)
Si1	0.0048 (7)	0.0096 (7)	0.0124 (8)	0.0018 (5)	0.0034 (5)	0.0009 (5)
Si2	0.0040 (6)	0.0078 (7)	0.0155 (8)	0.0013 (5)	0.0042 (5)	0.0018 (5)
O1	0.020 (3)	0.024 (3)	0.021 (3)	0.006 (2)	0.007 (2)	−0.006 (2)
O2	0.0078 (17)	0.0137 (18)	0.018 (2)	0.0033 (13)	0.0040 (14)	0.0045 (14)
O3	0.0057 (16)	0.0169 (19)	0.018 (2)	0.0068 (14)	0.0049 (14)	0.0018 (14)
O4	0.0063 (16)	0.0140 (18)	0.023 (2)	0.0017 (14)	0.0014 (14)	0.0061 (15)
O5	0.0145 (18)	0.0100 (18)	0.028 (2)	0.0000 (14)	0.0129 (16)	0.0016 (15)
O6	0.0082 (16)	0.0111 (17)	0.016 (2)	0.0039 (13)	0.0061 (14)	0.0050 (14)

Geometric parameters (Å, º) top

Cu1—O5ⁱ	1.909 (3)	Si1—O4^iv	1.642 (4)
Cu1—O2	1.950 (4)	Si2—O5	1.583 (4)
Cu1—O6ⁱⁱ	1.970 (4)	Si2—O6	1.625 (4)
Cu1—O6	1.974 (3)	Si2—O4	1.639 (3)
Cu1—O2ⁱⁱⁱ	2.316 (4)	Si2—O3	1.650 (4)
Cu1—Cu1ⁱⁱ	2.9921 (13)	Si2—Cu1ⁱⁱ	3.1221 (19)
Cu1—Cu1ⁱⁱⁱ	3.1031 (15)	O1—Si1^v	1.5991 (14)
Cu1—Si2ⁱⁱ	3.1221 (19)	O2—Cu1ⁱⁱⁱ	2.316 (4)
Cu1—Si1	3.1673 (19)	O4—Si1^vi	1.642 (4)
Si1—O2	1.588 (4)	O5—Cu1^vii	1.909 (3)
Si1—O1	1.5991 (14)	O6—Cu1ⁱⁱ	1.970 (4)
Si1—O3	1.629 (3)

O5ⁱ—Cu1—O2	92.49 (15)	O2ⁱⁱⁱ—Cu1—Si1	100.98 (10)
O5ⁱ—Cu1—O6ⁱⁱ	91.91 (15)	Cu1ⁱⁱ—Cu1—Si1	115.23 (4)
O2—Cu1—O6ⁱⁱ	175.60 (13)	Cu1ⁱⁱⁱ—Cu1—Si1	64.33 (4)
O5ⁱ—Cu1—O6	164.27 (15)	Si2ⁱⁱ—Cu1—Si1	179.25 (4)
O2—Cu1—O6	94.42 (14)	O2—Si1—O1	111.33 (15)
O6ⁱⁱ—Cu1—O6	81.32 (16)	O2—Si1—O3	112.6 (2)
O5ⁱ—Cu1—O2ⁱⁱⁱ	105.60 (16)	O1—Si1—O3	108.16 (15)
O2—Cu1—O2ⁱⁱⁱ	87.05 (15)	O2—Si1—O4^iv	111.48 (19)
O6ⁱⁱ—Cu1—O2ⁱⁱⁱ	91.76 (14)	O1—Si1—O4^iv	108.08 (16)
O6—Cu1—O2ⁱⁱⁱ	88.87 (14)	O3—Si1—O4^iv	104.92 (18)
O5ⁱ—Cu1—Cu1ⁱⁱ	131.06 (12)	O1—Si1—Cu1	115.96 (7)
O2—Cu1—Cu1ⁱⁱ	135.03 (10)	O3—Si1—Cu1	84.08 (15)
O6ⁱⁱ—Cu1—Cu1ⁱⁱ	40.70 (10)	O4^iv—Si1—Cu1	129.55 (15)
O6—Cu1—Cu1ⁱⁱ	40.62 (10)	O5—Si2—O6	113.2 (2)
O2ⁱⁱⁱ—Cu1—Cu1ⁱⁱ	90.41 (9)	O5—Si2—O4	111.75 (19)
O5ⁱ—Cu1—Cu1ⁱⁱⁱ	103.18 (12)	O6—Si2—O4	109.3 (2)
O2—Cu1—Cu1ⁱⁱⁱ	48.19 (11)	O5—Si2—O3	107.1 (2)
O6ⁱⁱ—Cu1—Cu1ⁱⁱⁱ	130.50 (11)	O6—Si2—O3	107.00 (19)
O6—Cu1—Cu1ⁱⁱⁱ	91.93 (10)	O4—Si2—O3	108.15 (19)
O2ⁱⁱⁱ—Cu1—Cu1ⁱⁱⁱ	38.86 (9)	O5—Si2—Cu1ⁱⁱ	109.62 (16)
Cu1ⁱⁱ—Cu1—Cu1ⁱⁱⁱ	116.74 (4)	O4—Si2—Cu1ⁱⁱ	81.61 (15)
O5ⁱ—Cu1—Si2ⁱⁱ	73.75 (12)	O3—Si2—Cu1ⁱⁱ	134.72 (14)
O2—Cu1—Si2ⁱⁱ	156.11 (11)	Si1^v—O1—Si1	180.0
O6ⁱⁱ—Cu1—Si2ⁱⁱ	26.72 (10)	Si1—O2—Cu1	126.8 (2)
O6—Cu1—Si2ⁱⁱ	103.96 (11)	Si1—O2—Cu1ⁱⁱⁱ	116.29 (18)
O2ⁱⁱⁱ—Cu1—Si2ⁱⁱ	78.31 (10)	Cu1—O2—Cu1ⁱⁱⁱ	92.95 (15)
Cu1ⁱⁱ—Cu1—Si2ⁱⁱ	64.59 (4)	Si1—O3—Si2	132.7 (3)
Cu1ⁱⁱⁱ—Cu1—Si2ⁱⁱ	115.04 (5)	Si2—O4—Si1^vi	137.0 (2)
O5ⁱ—Cu1—Si1	106.73 (13)	Si2—O5—Cu1^vii	152.9 (2)
O2—Cu1—Si1	23.68 (11)	Si2—O6—Cu1ⁱⁱ	120.24 (18)
O6ⁱⁱ—Cu1—Si1	153.39 (10)	Si2—O6—Cu1	130.3 (2)
O6—Cu1—Si1	75.74 (11)	Cu1ⁱⁱ—O6—Cu1	98.68 (16)

Symmetry codes: (i) x, y−1, z; (ii) −x+1, −y, −z+2; (iii) −x+2, −y, −z+2; (iv) x+1, y, z; (v) −x+2, −y, −z+1; (vi) x−1, y, z; (vii) x, y+1, z.

Experimental details

Crystal data
Chemical formula	Na₂(Cu₂O₁₁Si₄)
M_r	461.44
Crystal system, space group	Triclinic, P1
Temperature (K)	298
a, b, c (Å)	5.190 (2), 6.299 (3), 8.196 (4)
α, β, γ (°)	96.390 (7), 97.281 (7), 100.461 (7)
V (Å³)	258.9 (2)
Z	1
Radiation type	Mo Kα
µ (mm⁻¹)	4.71
Crystal size (mm)	0.28 × 0.08 × 0.04

Data collection
Diffractometer	Bruker SMART CCD 1000 diffractometer
Absorption correction	Multi-scan (TWINABS; Sheldrick, 2002)
T_min, T_max	0.627, 0.834
No. of measured, independent and observed [I > 2σ(I)] reflections	1587, 1043, 782
R_int	0.042
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.119, 1.01
No. of reflections	1043
No. of parameters	88
Δρ_max, Δρ_min (e Å⁻³)	1.40, −1.58

Computer programs: SMART (Bruker, 1998), SAINT-Plus (Bruker, 2003), SIR92 (Altomare et al., 1993), SHELXTL (Sheldrick, 2008), DIAMOND (Brandenburg, 2007).

Selected bond lengths (Å) top

Cu1—O5ⁱ	1.909 (3)	Cu1—O6	1.974 (3)
Cu1—O2	1.950 (4)	Cu1—O2ⁱⁱⁱ	2.316 (4)
Cu1—O6ⁱⁱ	1.970 (4)

Symmetry codes: (i) x, y−1, z; (ii) −x+1, −y, −z+2; (iii) −x+2, −y, −z+2.

Acknowledgements

We are grateful to the Fundação para a Ciência e a Tecnologia (FCT, Portugal) for their general financial support under the POCI programme (supported by FEDER) and for a Postdoctoral Fellowship (SFRH/BPD/14410/2003) to LCS.

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