Strontium manganese diselenite, SrMn(SeO₃)₂, containing unusual MnO₅₊₁ polyhedra

Hydro­thermally prepared SrMn(SeO₃)₂ contains infinite chains of vertex-sharing irregular MnO₅₊₁ polyhedra [mean Mn-O 2.226 (3) Å], which are fused into layers via pyramidal SeO₃ groups [mean Se-O 1.698 (3) Å]. Nine-coordinate Sr²⁺ cations [mean Sr-O 2.715 (4) Å] complete the layered structure.

S1. Comment

SrMn(SeO₃)₂ (Fig. 1) is isostructural with the synthetic compound SrZn(SeO₃)₂ (Johnston & Harrison, 2001), but with subtly different divalent metal coordination. In SrZn(SeO₃)₂, the Zn atom is coordinated by six O atoms in an unusual 4 + 2 coordination, described as bicapped tetrahedral. In the title compound, the Mn atom has six O atom neighbours, with one Mn—O bond distinctly longer than the other five. The average Mn—O separation for the five near-neighbour O atoms (2.180 Å) is in very good agreement with the ionic-radius sum for high-spin Mn^II and O^2- (2.19 Å; Shannon, 1976). However, the bond-valence sum (BVS; Brown, 1996) of 1.76 for Mn is much lower than the expected value of 2.00. If the more distant O atom [Mn—O 2.452 (3) Å] is considered, the Mn BVS rises to 1.93. This MnO_{5 + 1} coordination is so grossly distorted from octahedral as to be better regarded as irregular; the nominal trans O—Mn—O bond angles are 144.6, 149.0 and 166.9°. The variance of the cis O—Mn—O angles (mean 91.2°), as quantified by the method of Robinson et al. (1971), has the exceptionally large value of 239.5.

Both of the [SeO₃]^2- groups in SrMn(SeO₃)₂ adopt their usual pyramidal coordination (Hawthorne et al., 1987; Harrison, 1999), with BVS(Se1) = 4.08 and BVS(Se2) = 4.06 (expected value 4.00). The Sr²⁺ cation has irregular ninefold coordination by oxygen [mean Sr—O 2.715 Å], with BVS(Sr) = 1.98 (expected value 2.00). The next-nearest O atom is some 3.99 Å distant. As well as their Mn and Se neighbours, all of the O atoms are bonded to one or more Sr²⁺ cations. The average Sr—O separation in SrZn(SeO₃)₂ is 2.700 (5) Å.

The overall structure consists of infinite chains of vertex-linked MnO_{5 + 1} groups orientated along the [100] direction. The SeO₃ units are fused on to these chains via edge sharing. The SeO₃ pyramids containing Se1 link adjacent chains in the [001] direction, forming sheets perpendicular to [010], while the SeO₃ pyramids containing Se2 are grafted on to the chains. The interlayer Sr²⁺ cations bind adjacent sheets in the [100] direction and provide charge balancing. In a [100] projection (Fig. 2), there appear to be small channels present at (y = 0, z = 0) and symmetry-equivalent locations. These are probably associated with the Se^IV lone pairs and do not represent voids accessible by other chemical species.

Other manganese selenites exhibit distorted Mn^IIO₆ polyhedra. In Mn₃(SeO₃)₃·H₂O (Johnston et al., 2002), one of the MnO₆ groups is extremely distorted, with four short bonds [Mn—O < 2.24 Å] and two longer bonds (Mn—O > 2.39 Å) in cis configuration. Similarly, in the mixed-valence phase Mn^IIMn^III₂O(SeO₃)₃ (Wildner, 1994), the divalent species is described as an MnO_{4 + 2} grouping, with four short and two long Mn—O bonds. These distorted Mn^II environments can be partly attributed to the inter-polyhedral connectivity of the MnO₆ and SeO₃ groups.

S2. Experimental

SrCO₃ (0.154 g, 1 mmol), MnCl₂·4H₂O (0.3956 g, 2 mmol), 0.5M H₂SeO₃ (6 ml) and 1M LiOH (4.5 ml), at a pre-oven pH of 8.5, were hydrothermally reacted in a 23 ml-capacity sealed Teflon-lined steel bomb in an oven at 453 K. The bomb was removed after 67 h and cooled over 3 h. Upon opening, the bomb contained a clear solution, unidentified white and brown powders, and colourless rod-shaped single crystals of the title compound. The products were recovered by vacuum filtration, and washed with water and then acetone.

S3. Refinement

The highest difference peak is 0.83 Å from Se2; the deepest difference hole is 0.95 Å from Sr1.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SMART; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); 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. A fragment of SrMn(SeO3)2 with 50% probability displacement ellipsoids, showing the edge sharing of the SeO3 and MnO5 + 1 moieties [symmetry codes: (i) 1/2 + x, 3/2 - y, z - 1/2; (ii) 1/2 - x, y - 1/2, 1/2 - z; (iii) 3/2 - x, y - 1/2, 1/2 - z; (iv) x - 1/2, 3/2 - y, z - 1/2; (v) 1 + x, y, z].
	Fig. 2. A packing diagram for SrMn(SeO3)2 viewed down [100], in polyhedral representation. The SeO3 pyramids (light shading) are represented by SeO3E tetrahedra, where the dummy atom E, geometrically placed 1.0 Å from Se and indicated by a small sphere, represents the Se^IV lone pair. Sr^2+ cations are represented by spheres of arbitrary radius.

Strontium manganese diselenite

Crystal data

SrMn(SeO3)2	F(000) = 716
Mr = 396.48	Dx = 4.184 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 4.4432 (2) Å	Cell parameters from 3396 reflections
b = 14.8002 (7) Å	θ = 2.5–32.5°
c = 9.5955 (5) Å	µ = 22.01 mm^−1
β = 94.072 (1)°	T = 298 K
V = 629.41 (5) Å^3	Rod, colourless
Z = 4	0.34 × 0.05 × 0.02 mm

Data collection

Bruker SMART 1000 CCD area-detector diffractometer	2273 independent reflections
Radiation source: fine-focus sealed tube	1869 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.050
ω scans	θmax = 32.5°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −6→6
Tmin = 0.048, Tmax = 0.640	k = −22→21
7110 measured reflections	l = −13→14

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: From the isostructural SrZn(SeO3)2 (Mn replacing Zn)
R[F^2 > 2σ(F^2)] = 0.036	Secondary atom site location: none
wR(F^2) = 0.090	w = 1/[σ^2(Fo^2) + (0.0535P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.001
2273 reflections	Δρmax = 2.37 e Å^−3
91 parameters	Δρmin = −1.83 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
Sr1	0.74150 (8)	0.61630 (3)	0.03467 (5)	0.01109 (10)
Mn1	0.72489 (15)	0.84759 (5)	0.20800 (8)	0.01329 (15)
Se1	0.77964 (9)	0.69993 (3)	0.42195 (5)	0.01248 (11)
Se2	0.26501 (9)	1.00100 (3)	0.21735 (5)	0.01160 (11)
O1	1.1306 (7)	0.6989 (2)	0.5023 (4)	0.0177 (7)
O2	0.7042 (7)	0.8130 (2)	0.4338 (4)	0.0168 (6)
O3	0.8461 (8)	0.7035 (2)	0.2511 (4)	0.0206 (7)
O4	0.1939 (7)	0.8868 (2)	0.2289 (4)	0.0157 (7)
O5	0.2332 (7)	1.0328 (2)	0.3851 (4)	0.0165 (6)
O6	0.6423 (7)	0.9922 (2)	0.2158 (5)	0.0224 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sr1	0.01211 (17)	0.00868 (18)	0.0126 (2)	−0.00057 (12)	0.00192 (13)	−0.00168 (14)
Mn1	0.0161 (3)	0.0094 (3)	0.0142 (3)	−0.0006 (2)	−0.0001 (2)	−0.0014 (3)
Se1	0.01392 (19)	0.0095 (2)	0.0139 (2)	−0.00099 (14)	−0.00003 (14)	0.00044 (16)
Se2	0.01154 (18)	0.00946 (19)	0.0139 (2)	0.00064 (13)	0.00138 (14)	0.00088 (16)
O1	0.0138 (14)	0.0217 (17)	0.0174 (17)	−0.0002 (12)	−0.0010 (11)	0.0069 (14)
O2	0.0201 (14)	0.0096 (14)	0.0212 (18)	0.0025 (11)	0.0042 (12)	−0.0016 (13)
O3	0.0375 (19)	0.0115 (15)	0.0121 (17)	0.0000 (13)	−0.0018 (14)	−0.0008 (13)
O4	0.0149 (14)	0.0083 (14)	0.0241 (19)	0.0001 (11)	0.0027 (12)	−0.0036 (13)
O5	0.0232 (16)	0.0143 (15)	0.0117 (17)	0.0006 (12)	−0.0008 (12)	−0.0039 (13)
O6	0.0107 (14)	0.0149 (16)	0.042 (2)	−0.0006 (11)	0.0047 (13)	−0.0003 (16)

Geometric parameters (Å, º)

Sr1—O3	2.461 (4)	Mn1—O6	2.174 (3)
Sr1—O2^i	2.558 (3)	Mn1—O3	2.231 (3)
Sr1—O5^ii	2.607 (3)	Mn1—O2	2.235 (4)
Sr1—O5^i	2.632 (3)	Mn1—O4	2.452 (3)
Sr1—O5^iii	2.704 (3)	Se1—O3	1.687 (4)
Sr1—O2^iv	2.721 (3)	Se1—O1	1.690 (3)
Sr1—O1^iv	2.792 (4)	Se1—O2	1.711 (3)
Sr1—O4^i	2.927 (4)	Se2—O6	1.683 (3)
Sr1—O6^iii	3.033 (4)	Se2—O5	1.693 (3)
Mn1—O1^iv	2.104 (4)	Se2—O4	1.725 (3)
Mn1—O4^v	2.159 (3)
O3—Sr1—O2^i	89.76 (12)	O1^iv—Mn1—O2	144.61 (13)
O3—Sr1—O5^ii	96.18 (11)	O4^v—Mn1—O2	94.43 (13)
O2^i—Sr1—O5^ii	173.98 (12)	O6—Mn1—O2	100.00 (14)
O3—Sr1—O5^i	153.44 (11)	O3—Mn1—O2	68.11 (13)
O2^i—Sr1—O5^i	96.74 (11)	O1^iv—Mn1—O4	91.48 (12)
O5^ii—Sr1—O5^i	77.50 (12)	O4^v—Mn1—O4	148.98 (15)
O3—Sr1—O5^iii	83.78 (11)	O6—Mn1—O4	66.32 (11)
O2^i—Sr1—O5^iii	66.05 (10)	O3—Mn1—O4	115.60 (12)
O5^ii—Sr1—O5^iii	113.55 (12)	O2—Mn1—O4	82.45 (12)
O5^i—Sr1—O5^iii	75.55 (12)	O3—Se1—O1	102.95 (18)
O3—Sr1—O2^iv	101.94 (11)	O3—Se1—O2	94.75 (17)
O2^i—Sr1—O2^iv	114.60 (13)	O1—Se1—O2	99.03 (17)
O5^ii—Sr1—O2^iv	65.14 (10)	O6—Se2—O5	100.39 (18)
O5^i—Sr1—O2^iv	98.67 (10)	O6—Se2—O4	96.42 (15)
O5^iii—Sr1—O2^iv	174.19 (11)	O5—Se2—O4	100.58 (17)
O3—Sr1—O1^iv	66.51 (11)	Se1—O1—Mn1^vi	123.14 (17)
O2^i—Sr1—O1^iv	72.37 (10)	Se1—O1—Sr1^vi	101.07 (15)
O5^ii—Sr1—O1^iv	110.90 (10)	Mn1^vi—O1—Sr1^vi	101.21 (14)
O5^i—Sr1—O1^iv	139.94 (10)	Se1—O2—Mn1	97.93 (16)
O5^iii—Sr1—O1^iv	128.39 (10)	Se1—O2—Sr1^vii	126.28 (17)
O2^iv—Sr1—O1^iv	55.96 (9)	Mn1—O2—Sr1^vii	111.26 (13)
O3—Sr1—O4^i	148.20 (10)	Se1—O2—Sr1^vi	103.22 (14)
O2^i—Sr1—O4^i	68.27 (10)	Mn1—O2—Sr1^vi	99.27 (12)
O5^ii—Sr1—O4^i	106.63 (10)	Sr1^vii—O2—Sr1^vi	114.60 (13)
O5^i—Sr1—O4^i	56.15 (9)	Se1—O3—Mn1	98.81 (16)
O5^iii—Sr1—O4^i	106.13 (10)	Se1—O3—Sr1	140.17 (19)
O2^iv—Sr1—O4^i	69.53 (10)	Mn1—O3—Sr1	108.44 (15)
O1^iv—Sr1—O4^i	84.51 (10)	Se2—O4—Mn1^viii	115.94 (16)
O3—Sr1—O6^iii	68.91 (11)	Se2—O4—Mn1	92.58 (13)
O2^i—Sr1—O6^iii	116.77 (10)	Mn1^viii—O4—Mn1	148.98 (15)
O5^ii—Sr1—O6^iii	64.90 (10)	Se2—O4—Sr1^vii	94.56 (14)
O5^i—Sr1—O6^iii	85.27 (10)	Mn1^viii—O4—Sr1^vii	95.15 (12)
O5^iii—Sr1—O6^iii	53.37 (9)	Mn1—O4—Sr1^vii	94.42 (11)
O2^iv—Sr1—O6^iii	127.57 (9)	Se2—O5—Sr1^ix	122.45 (17)
O1^iv—Sr1—O6^iii	134.41 (11)	Se2—O5—Sr1^vii	106.63 (15)
O4^i—Sr1—O6^iii	141.08 (10)	Sr1^ix—O5—Sr1^vii	102.50 (12)
O1^iv—Mn1—O4^v	107.57 (13)	Se2—O5—Sr1^x	105.63 (15)
O1^iv—Mn1—O6	109.38 (15)	Sr1^ix—O5—Sr1^x	113.55 (12)
O4^v—Mn1—O6	84.05 (12)	Sr1^vii—O5—Sr1^x	104.45 (11)
O1^iv—Mn1—O3	83.70 (14)	Se2—O6—Mn1	104.32 (16)
O4^v—Mn1—O3	91.19 (13)	Se2—O6—Sr1^x	93.44 (15)
O6—Mn1—O3	166.89 (15)	Mn1—O6—Sr1^x	127.15 (17)

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