BING-2: a layered tin-oxalate potassium fluoride, KSn(C₂O₄)F

The title compound, KSn(C₂O₄)F, is a two-dimensional material related to our previously reported three-dimensional framework, Na₄Sn₄(C₂O₄)₃F₆. Both are alkali-metal tin-oxalate materials, but here the compound is layered and has potassium in place of sodium. The material was synthesized solvothermally at 423 K and crystallized in the monoclinic space group P2₁/c. The structure consists of potassium fluoride layers in the bc plane, which are sandwiched on both sides by tin-oxalate chains that extend along the c axis.

Key indicators

• Single-crystal X-ray study
• T = 273 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.025
• wR factor = 0.059
• Data-to-parameter ratio = 20.5

checkCIF results

No syntax errors found



ADDSYM reports no extra symmetry


 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.658     0.808
          Tmin and Tmax expected:      0.566     0.808
          RR =      1.163
          Please check that your absorption correction is appropriate.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

We are interested in group 14 metal-based extended materials for a variety of potential applications, particularly ion exchange and sensors. Our methods involve both commonly used, as well as non-traditional, templating agents. We have discovered a series of new materials, which we denote BING-n, where BING denotes State University of New York (SUNY) at Binghamton, and n denotes the structure type. These materials can be clusters (Oliver et al., 2001) or extended in one [BING-4, Sn(C₂O₄)(C₅H₅N); Oliver et al., 2001], two (BING-3, SnO₃PC₆H₅; Oliver et al., 2001) or three [BING-1, Na₄Sn₄(C₂O₄)₃F₆; Salami et al., 2001] dimensions. Here, we report the crystal structure of BING-2, a layered tin–oxalate potassium fluoride material.

Two layered tin–oxalates have been reported recently by Cheetham and co-workers (Ayyappan et al., 1998; Natarajan et al., 1999). The tin centres are octahedral and possess three oxalate groups that bridge to neighbouring Sn atoms in the layer. Traditional cationic organic ammonium templating agents were used to produce these materials, and reside in the interlayer region.

One of the thrusts of our studies is the exclusion of traditional templating agents from the synthesis mixture, and the use instead of other possible building blocks or templating agents. BING-2 was isolated from a predominantly non-aqueous pyridine solvent, to which tin oxalate, hydrogen fluoride (50% aqueous) and potassium tetrafluoroborate were added. Potassium and fluoride in this case became a building-block for the resultant product, and combined with tin oxalate to create the BING-2 structure (Fig. 1).

The layer of BING-2 is a sandwich structure, with two tin–oxalate sheets that connect to a central potassium fluoride layer. The latter is buckled and shown in Fig. 1. This buckling allows the KF layer to bond to the two surrounding Sn–oxalate layers, which are made up of discrete tin–oxalate chains that propogate along the c axis (one such layer is shown in Fig. 2). The Sn centers are chelated to one oxalate group, and connect to two neighbouring oxalate groups in the chain through longer contact distances (shown by the broken line, Fig. 2). The O atoms on the other side of the oxalate groups connect to potassium centres of the potassium fluoride layer. The BING-2 layer is therefore a triple layer (Fig. 3).

The asymmetric unit is relatively simple, containing only one type of each atom in the formula unit (Fig. 4). The oxalate group in BING-2 is not planar (Table 1). This is the first time that we have seen this feature in our published BING-n structures (Salami et al., 2001), those of others (Ayyappan et al., 1998; Natarajan et al., 1999) as well an unpublished one-dimensional tin–oxalate structure (BING-4; Oliver et al., 2001). This non-planarity may allow the formation of a three-dimensional tin–oxalate open-framework. We are currently studying other combinations of tin–oxalate and various structure directing agents, in order to isolate inorganic materials capable of our target application of both anion and cation exchange.

S2. Experimental

The reaction mixture consisted of pyridine, H₂O, HF, KBF₄ and Sn(C₂O₄) in a molar ratio of 20:4:1:1:1. Solvothermal synthesis was conducted in a 23 ml capacity Teflon-lined Parr autoclave, at 423 K for 5 d. The BING-3 crystals were colourless plates, and were manually separated for single-crystal X-ray analysis.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Dowty, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The crystallographic a-projection of the central potassium fluoride in one BING-2 layer (colour scheme: K – light blue and F – yellow).
	Fig. 2. The same projection as Fig. 1, but showing one tin–oxalate layer, highlighting the tin–oxalate chains that propagate along the c axis (colour scheme: Sn – dark green, O – red and C – light green).
	Fig. 3. The crystallographic b-projection of BING-2, indicating the manner in which the tin–oxalate and potassium fluoride layers connect along the a axis.
	Fig. 4. Displacement ellipsoids and labelling scheme for BING-2, with ellipsoids shown at 50% probability levels.

Tin(II) oxalate potassium fluoride

Crystal data

[Sn(C2O4)]KF	F(000) = 488
Mr = 264.81	Dx = 3.181 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.0692 (5) Å	Cell parameters from 4624 reflections
b = 9.5398 (6) Å	θ = 5–63°
c = 7.7245 (4) Å	µ = 5.33 mm^−1
β = 111.600 (1)°	T = 273 K
V = 552.86 (6) Å^3	Plate, colorless
Z = 4	0.11 × 0.10 × 0.04 mm

Data collection

CCD area-detector diffractometer	1685 independent reflections
Radiation source: fine-focus sealed tube	1443 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ω scans	θmax = 30.5°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −11→11
Tmin = 0.658, Tmax = 0.808	k = −13→13
10746 measured reflections	l = −11→11

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.025	Secondary atom site location: difference Fourier map
wR(F^2) = 0.059	w = 1/[σ^2(Fo^2) + (0.0288P)^2 + 0.1128P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max = 0.001
1685 reflections	Δρmax = 0.75 e Å^−3
82 parameters	Δρmin = −0.45 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
Sn1	0.86411 (3)	0.81285 (2)	0.49210 (3)	0.02678 (8)
K1	0.39785 (10)	0.82173 (7)	0.59318 (9)	0.03195 (15)
F1	0.6033 (3)	0.8618 (2)	0.3982 (3)	0.0390 (4)
O1	0.8055 (3)	0.6245 (2)	0.3074 (3)	0.0327 (5)
O2	0.7907 (3)	0.3916 (2)	0.3044 (3)	0.0337 (5)
O3	0.7898 (3)	0.6360 (2)	0.6399 (3)	0.0330 (5)
O4	0.7184 (4)	0.4100 (2)	0.6296 (3)	0.0405 (6)
C1	0.7884 (4)	0.5046 (3)	0.3763 (4)	0.0234 (5)
C2	0.7617 (4)	0.5140 (3)	0.5653 (4)	0.0256 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn1	0.03053 (13)	0.01964 (11)	0.03241 (12)	−0.00227 (8)	0.01424 (9)	−0.00087 (8)
K1	0.0423 (4)	0.0284 (3)	0.0310 (3)	−0.0060 (3)	0.0204 (3)	−0.0041 (3)
F1	0.0317 (10)	0.0521 (12)	0.0368 (10)	0.0048 (9)	0.0167 (8)	0.0045 (9)
O1	0.0564 (15)	0.0221 (11)	0.0244 (10)	−0.0029 (10)	0.0204 (10)	0.0007 (8)
O2	0.0496 (14)	0.0218 (11)	0.0350 (11)	−0.0027 (10)	0.0218 (10)	−0.0073 (8)
O3	0.0579 (16)	0.0205 (10)	0.0283 (10)	−0.0078 (10)	0.0251 (10)	−0.0058 (8)
O4	0.0742 (18)	0.0224 (12)	0.0334 (11)	−0.0091 (11)	0.0297 (12)	0.0000 (9)
C1	0.0256 (14)	0.0236 (14)	0.0221 (12)	0.0024 (11)	0.0101 (11)	0.0014 (10)
C2	0.0327 (16)	0.0223 (14)	0.0234 (12)	−0.0044 (12)	0.0122 (12)	−0.0017 (10)

Geometric parameters (Å, º)

Sn1—F1	2.0122 (19)	K1—O1^ii	3.133 (3)
Sn1—O1	2.234 (2)	F1—K1^i	2.913 (2)
Sn1—O3	2.239 (2)	F1—K1^vii	3.020 (2)
Sn1—O3^i	2.608 (2)	O1—C1	1.290 (3)
Sn1—O1^ii	2.714 (2)	O1—K1^i	3.133 (3)
Sn1—O2^iii	3.288 (2)	O2—C1	1.216 (3)
K1—F1	2.6461 (19)	O2—K1^iv	2.823 (2)
K1—O4^iv	2.746 (2)	O2—K1^viii	2.958 (2)
K1—O4^v	2.767 (2)	O3—C2	1.281 (3)
K1—O2^iv	2.823 (2)	O4—C2	1.217 (3)
K1—F1^ii	2.913 (2)	O4—K1^iv	2.746 (2)
K1—O2^vi	2.958 (2)	O4—K1^ix	2.767 (2)
K1—F1^vii	3.020 (2)	C1—C2	1.555 (4)
F1—Sn1—O1	90.50 (9)	O2^iv—K1—F1^vii	135.08 (6)
F1—Sn1—O3	85.28 (9)	F1^ii—K1—F1^vii	126.04 (4)
O1—Sn1—O3	71.68 (7)	O2^vi—K1—F1^vii	78.07 (6)
F1—Sn1—O3^i	76.83 (7)	F1—K1—O1^ii	61.39 (6)
O1—Sn1—O3^i	64.60 (7)	O4^iv—K1—O1^ii	120.87 (7)
O3—Sn1—O3^i	132.15 (8)	O4^v—K1—O1^ii	97.50 (7)
F1—Sn1—O1^ii	76.57 (7)	O2^iv—K1—O1^ii	122.65 (7)
O1—Sn1—O1^ii	133.19 (7)	F1^ii—K1—O1^ii	59.80 (6)
O3—Sn1—O1^ii	62.65 (7)	O2^vi—K1—O1^ii	123.39 (6)
O3^i—Sn1—O1^ii	147.81 (7)	F1^vii—K1—O1^ii	80.54 (6)
F1—Sn1—O2^iii	154.09 (7)	Sn1—F1—K1	123.54 (9)
O1—Sn1—O2^iii	76.77 (7)	Sn1—F1—K1^i	111.13 (8)
O3—Sn1—O2^iii	69.39 (7)	K1—F1—K1^i	94.84 (6)
O3^i—Sn1—O2^iii	116.03 (6)	Sn1—F1—K1^vii	103.61 (8)
O1^ii—Sn1—O2^iii	95.65 (6)	K1—F1—K1^vii	97.12 (6)
F1—K1—O4^iv	84.30 (7)	K1^i—F1—K1^vii	127.81 (7)
F1—K1—O4^v	149.18 (7)	C1—O1—Sn1	118.67 (16)
O4^iv—K1—O4^v	126.51 (9)	C1—O1—K1^i	96.45 (18)
F1—K1—O2^iv	141.16 (7)	Sn1—O1—K1^i	98.04 (8)
O4^iv—K1—O2^iv	60.01 (6)	C1—O2—K1^iv	114.24 (18)
O4^v—K1—O2^iv	68.34 (7)	C1—O2—K1^viii	125.83 (19)
F1—K1—F1^ii	104.94 (7)	K1^iv—O2—K1^viii	90.25 (6)
O4^iv—K1—F1^ii	89.11 (7)	C2—O3—Sn1	119.45 (17)
O4^v—K1—F1^ii	79.11 (6)	C2—O4—K1^iv	118.96 (18)
O2^iv—K1—F1^ii	62.95 (6)	C2—O4—K1^ix	142.55 (19)
F1—K1—O2^vi	64.35 (6)	K1^iv—O4—K1^ix	96.03 (7)
O4^iv—K1—O2^vi	66.69 (7)	O2—C1—O1	125.2 (2)
O4^v—K1—O2^vi	122.93 (7)	O2—C1—C2	120.7 (2)
O2^iv—K1—O2^vi	109.21 (8)	O1—C1—C2	114.1 (2)
F1^ii—K1—O2^vi	153.76 (6)	O4—C2—O3	126.0 (3)
F1—K1—F1^vii	82.88 (6)	O4—C2—C1	119.7 (2)
O4^iv—K1—F1^vii	144.65 (7)	O3—C2—C1	114.3 (2)
O4^v—K1—F1^vii	70.97 (6)
O1—C1—C2—O3	−11.0 (4)	O2—C1—C2—O3	169.5 (3)
O1—C1—C2—O4	169.3 (3)	O2—C1—C2—O4	−10.1 (4)

Symmetry codes: (i) x, −y+3/2, z−1/2; (ii) x, −y+3/2, z+1/2; (iii) −x+2, −y+1, −z+1; (iv) −x+1, −y+1, −z+1; (v) −x+1, y+1/2, −z+3/2; (vi) −x+1, y+1/2, −z+1/2; (vii) −x+1, −y+2, −z+1; (viii) −x+1, y−1/2, −z+1/2; (ix) −x+1, y−1/2, −z+3/2.