Crystal structure of anhydrous poly[bis­(μ2-sarcosinato-κ3O,N:O′)copper(II)]

Butcher, R.J.; Brewer, G.; Zemba, M.

doi:10.1107/S1600536814020418

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Volume 70| Part 10| October 2014| Pages 207-209

doi:10.1107/S1600536814020418

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Crystal structure of anhydrous poly[bis(μ₂-sarcosinato-κ³O,N:O′)copper(II)]

Ray J. Butcher,^a ^* Greg Brewer ^b and Matthew Zemba ^b

^aDepartment of Chemistry, Howard University, 525 College Street NW, Washington, DC 20059, USA, and ^bDepartment of Chemistry, The Catholic University of America, 620 Michigan Ave., N.E., Washington, DC 20064, USA
^*Correspondence e-mail: rbutcher99@yahoo.com

Edited by M. Weil, Vienna University of Technology, Austria (Received 30 August 2014; accepted 11 September 2014; online 17 September 2014)

The title compound, [Cu(C₃H₆NO₂)₂]_n, is a bis-complex of the anion of sarcosine (N-methylglycine). The asymmetric unit consists of a copper(II) ion, located on a center of inversion, and one molecule of the uninegative sarcosinate anion. The copper(II) ion exhibits a typical Jahn–Teller distorted [4 + 2] coordination geometry. The four shorter equatorial bonds are to the nitrogen and carboxylate O atoms of two sarcosinate anions, and the longer axial bonds are to carboxylate O atoms of neighboring complexes. The overall structure is made up from two chains formed by these longer axial Cu—O bonds, one extending parallel to [011] and the other parallel to [0-11]. Each one-dimensional array is connected by the equatorial bridging moieties to the chains on either side, creating an extended two-dimensional framework parallel to (100). There is a single intermolecular hydrogen-bonding interaction within the sheets between the amino NH group and an O atom of an adjacent molecule.

Keywords: crystal structure; anhydrous bis(sarcosinato)copper(II); non-proteinogenic amino acid.

CCDC reference: 961026

1. Chemical context

The α-amino acids are essential for life as they are the building blocks of all proteins and enzymes and a great deal is known about their structures and complexes. N-Methyl amino acids, such as sarcosine, are non-proteinogenic and hence differ from the proteinogenic amino acids used in living systems in that the amino N atom is achiral in the free molecule but chiral, R or S, when bound to a metal. Examples of complexes of sarcosine that exhibit chirality due to coordination of the amino N atom have been reported (Blount et al., 1967 ; Larsen et al., 1968 ; Prout et al., 1972 ). This is similar to the chirality that is observed on the binding of reduced tripodal Schiff base complexes of metals (Brewer et al., 2014 ; Al-Obaidi et al., 1996 ). In these cases, the binding of three achiral (due to rapid inversion) amine N atoms of the free ligand to the same metal resulted in the observation of a single enantiomeric pair (RRR and SSS) or a single enantiomer (RRR or SSS) if the molecule crystallized in one of the Sohncke space groups. In these cases, the binding of an organic ligand containing three achiral N atoms to a metal resulted in a preference for chirality correlation of the N atoms, RRR or SSS, resulting in homochiral complexes. Similarly, the reduced Schiff base complexes of the condensate of amino acids with salicylaldehyde have an energetic preference for the stereoisomer in which the chirality of the α-C atom and the amine N atom are correlated (Koh et al., 1996 ).

This preference for homochirality is not always observed: the copper complex of a Schiff base condensate of tyrosine is heterochiral as is the bis-adduct of cobalt(III) with histidine (Pradeep et al., 2006 ; Zie et al., 2007 ). The present complex was investigated to determine if there was a preference for homo- (RR or SS) versus heterochirality (RS) in a M(sarcosinato)₂ complex (M = divalent transition metal). Heterochirality, RS, was observed in this complex. Future work will focus on related complexes such as M′(sarcosinato)₃ (M′ = trivalent transition metal) to determine if the presence of three chiral ligands bound to a single metal favors homochirality, which can serve as a method of enantiomeric separation.

2. Structural commentary

The title compound, [Cu(C₃H₆NO₂)₂]_n, is a bis-complex of the sarcosinate anion with copper(II). The central metal cation is located on a center of inversion. It is six-coordinate and has a distorted octahedral [4 + 2] coordination sphere characteristic for Jahn–Teller systems. The four shorter equatorial bonds are to the amino N atom and carboxylate O atom of two sarcosinate anions (Fig. 1). The N and O atoms are trans to one another. The related [Cu(sarcosinato)₂]·2H₂O structure (Krishnakumar et al., 1994 ) is much simpler in that the two longer axial bonds are to water molecules so that there is no extended bonding to neighboring complexes. In both structures, the equatorial Cu—O and Cu—N bond lengths are very similar [Cu—O = 1.9758 (8) Å and Cu—N = 2.0046 (9) Å in the title compound, and 1.970 and 2.007 Å in the dihydrate], but the axial Cu—O distances are significantly different at 2.5451 (10) and 2.461 Å.

Figure 1
Part of a chain in the title compound, with the atom-numbering scheme and atomic displacement parameters drawn at the 30% probability level. Hydrogen bonding is shown by dashed lines. [Symmetry codes: (A) 1 − x, 1 − y, 1 − z; (B) 1 − x, y − $[{1\over 2}]$ , $[{1\over 2}]$ − z; (C) x, $[{3\over 2}]$ − y, $[{1\over 2}]$ + z.]

3. Supramolecular features

In the title compound, the individual coordination polyhedra are linked by longer axial Cu—O bonds into two chains, one extending parallel to [011] and the other parallel to [0 $[\overline{1}]$ 1]. The one-dimensional array is linked by equatorial bridging bonds to the chains on either side, creating an extended two-dimensional framework (Fig. 2) parallel to (100). There is a single intermolecular hydrogen-bonding interaction within the sheets between the amino NH and an carboxylate O atom of an adjacent molecule (Table 1).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1ⁱ	0.93	2.13	2.9729 (13)	150
Symmetry code: (i) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 2
Packing diagram of the title compound viewed along the a axis. Hydrogen bonding is shown by dashed lines.

4. Database survey

The structure of the zwitterionic form of sarcosine has been reported by Rodrigues et al. (2005 ). The structure of the copper(II) and nickel(II) complexes of this same ligand have been reported as their dihydrates by Krishnakumar et al. (1994) and Guha (1973 ), respectively.

5. Synthesis and crystallization

Sarcosine (N-methylglycine) was purchased from Aldrich Chemical. Sarcosine (1.87 mmol, 0.166 g) was dissolved in 0.10 M aqueous potassium hydroxide (18.7 ml, 1.87 mmol). Copper chloride dihydrate (0.468 mmol, 0.078 g) was added to the above solution and crystals of the title compound were grown by slow evaporation.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms were positioned geometrically and refined using a riding model, with C—H distances of 0.93–0.99 Å, and with U_iso(H) = 1.2U_eq(C) or 1.5U_eq(C) for methyl H atoms. The H attached to N was located in a difference Fourier map and refined using a riding model, with an N—H distance of 0.93 Å and U_iso(H) = 1.2U_eq(N).

Table 2
Experimental details

Crystal data
Chemical formula	[Cu(C₃H₆NO₂)₂]
M_r	239.72
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	123
a, b, c (Å)	7.9031 (3), 5.9461 (2), 8.9907 (3)
β (°)	90.039 (3)
V (Å³)	422.50 (3)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	2.57
Crystal size (mm)	0.51 × 0.45 × 0.12

Data collection
Diffractometer	Agilent Xcalibur Ruby Gemini
Absorption correction	Multi-scan (CrysAlis PRO; Agilent, 2012 )
T_min, T_max	0.478, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	5479, 1768, 1542
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.808

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.023, 0.061, 1.08
No. of reflections	1768
No. of parameters	63
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.64, −0.36
Computer programs: CrysAlis PRO (Agilent, 2012), SIR97 (Altomare et al., 1999 ), SHELXL97 and SHELXTL (Sheldrick, 2008 ).

Supporting information

CCDC reference: 961026

Crystal structure: contains datablock I. DOI: 10.1107/S1600536814020418/wm5056sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536814020418/wm5056Isup2.hkl

checkCIF report

Chemical context top

The α-amino acids are essential for life as they are the building blocks of all proteins and enzymes and a great deal is known about their structures and complexes. N-Methyl amino acids, such as sarcosine, are non-proteinogenic and hence differ from the proteinogenic amino acids used in living systems in that the amino N atom is achiral in the free molecule but chiral, R or S, when bound to a metal. Examples of complexes of sarcosine that exhibit chirality due to coordination of the amino N atom have been reported (Blount et al., 1967; Larsen et al., 1968; Prout et al., 1972). This is similar to the chirality that is observed on the binding of reduced tripodal Schiff base complexes of metals (Brewer et al., 2014; Al-Obaidi et al., 1996). In these cases, the binding of three achiral (due to rapid inversion) amine N atoms of the free ligand to the same metal resulted in the observation of a single enantiomeric pair (RRR and SSS) or a single enantiomer (RRR or SSS) if the molecule crystallized in one of the Sohncke space groups. In these cases, the binding of an organic ligand containing three achiral N atoms to a metal resulted in a preference for chirality correlation of the N atoms, RRR or SSS, resulting in homochiral complexes. Similarly, the reduced Schiff base complexes of the condensate of amino acids with salicylaldehyde have an energetic preference for the stereoisomer in which the chirality of the α-C atom and the amine N atom are correlated (Koh et al., 1996).

This preference for homochirality is not always observed: the copper complex of a Schiff base condensate of tyrosine is heterochiral as is the bis-adduct of cobalt(III) with histidine (Pradeep et al., 2006; Zie et al., 2007). The present complex was investigated to determine if there was a preference for homo- (RR or SS) versus heterochirality (RS) in a M(sarcosinato)₂ complex (M = divalent transition metal). Heterochirality, RS, was observed in this complex. Future work will focus on related complexes such as M'(sarcosinato)₃ (M' = trivalent transition metal) to determine if the presence of three chiral ligands bound to a single metal favors homochirality, which can serve as a method of enantiomeric separation.

Structural commentary top

The title compound, [Cu(C₃H₆NO₂)₂]_n, is a bis-complex of the sarcosinate anion with copper(II). The central metal cation is located on a center of inversion. It is six-coordinate and has a distorted octahedral [4+2] coordination sphere characteristic for Jahn–Teller systems. The four shorter equatorial bonds are to the amino N atom and carboxylate O atom of two sarcosinate anions (Fig. 1). The N and O atoms are trans to one another. The related [Cu(sarcosinato)₂].2H₂O structure (Krishnakumar et al., 1994) is much simpler in that the two longer axial bonds are to water molecules so that there is no extended bonding to neighboring complexes. In both structures, the equatorial Cu—O and Cu—N bond lengths are very similar [Cu—O = 1.9758 (8) Å and Cu—N = 2.0046 (9) Å in the title compound, and 1.970 and 2.007 Å in the dihydrate], but the axial Cu—O distances are significantly different at 2.5451 (10) and 2.461 Å.

Supramolecular features top

In the title compound, the individual coordination polyhedra are linked by longer axial Cu—O bonds into two chains, one extending parallel to [011] and the other parallel to [011]. The one-dimensional array is linked by equatorial bridging bonds to the chains on either side, creating an extended two-dimensional framework (Fig. 2) parallel to (100). There is a single intermolecular hydrogen-bonding interaction within the sheets between the amino NH and an carboxylate O atom of an adjacent molecule (Table 1).

Database survey top

The structure of the zwitterionic form of sarcosine has been reported by Rodrigues et al. (2005). The structure of the copper(II) and nickel(II) complexes of this same ligand have been reported as their dihydrates by Krishnakumar et al. (1994) and Guha (1973), respectively.

Synthesis and crystallization top

Refinement top

Related literature top

For related literature, see: Al-Obaidi, Jensen, McGarvey, Toftlund, Jensen, Bell & Carroll (1996); Blount et al. (1967); Brewer et al. (2014); Guha (1973); Koh et al. (1996); Krishnakumar et al. (1994); Larsen et al. (1968); Pradeep et al. (2006); Prout et al. (1972); Rodrigues et al. (2005); Zie et al. (2007).

Computing details top

Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top

	Fig. 1. Part of a chain in the title compound, with the atom-numbering scheme and atomic displacement parameters drawn at the 30% probability level. Hydrogen bonding is shown by dashed lines. [Symmetry codes: (A) 1-x, 1-y, 1-z; (B) 1-x, y-1/2, 1/2-z; (C) x, 3/2-y, 1/2+z.]
	Fig. 2. Packing diagram of the title compound viewed along the a axis. Hydrogen bonding is shown by dashed lines.

Poly[bis(µ₂-sarcosinato-κ³O,N:O')copper(II)] top

Crystal data top

[Cu(C₃H₆NO₂)₂]	F(000) = 246
M_r = 239.72	D_x = 1.884 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2393 reflections
a = 7.9031 (3) Å	θ = 3.4–35.0°
b = 5.9461 (2) Å	µ = 2.57 mm⁻¹
c = 8.9907 (3) Å	T = 123 K
β = 90.039 (3)°	Plate, dark blue
V = 422.50 (3) Å³	0.51 × 0.45 × 0.12 mm
Z = 2

Data collection top

Agilent Xcalibur Ruby Gemini diffractometer	1768 independent reflections
Radiation source: Enhance (Mo) X-ray Source	1542 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.025
Detector resolution: 10.5081 pixels mm^-1	θ_max = 35.0°, θ_min = 4.1°
ω scans	h = −12→11
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)	k = −9→8
T_min = 0.478, T_max = 1.000	l = −14→14
5479 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.023	H-atom parameters constrained
wR(F²) = 0.061	w = 1/[σ²(F_o²) + (0.0285P)² + 0.0835P] where P = (F_o² + 2F_c²)/3
S = 1.08	(Δ/σ)_max < 0.001
1768 reflections	Δρ_max = 0.64 e Å⁻³
63 parameters	Δρ_min = −0.36 e Å⁻³
0 restraints	Extinction correction: SHELXTL (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.014 (3)

Crystal data top

[Cu(C₃H₆NO₂)₂]	V = 422.50 (3) Å³
M_r = 239.72	Z = 2
Monoclinic, P2₁/c	Mo Kα radiation
a = 7.9031 (3) Å	µ = 2.57 mm⁻¹
b = 5.9461 (2) Å	T = 123 K
c = 8.9907 (3) Å	0.51 × 0.45 × 0.12 mm
β = 90.039 (3)°

Data collection top

Agilent Xcalibur Ruby Gemini diffractometer	1768 independent reflections
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2012)	1542 reflections with I > 2σ(I)
T_min = 0.478, T_max = 1.000	R_int = 0.025
5479 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.023	0 restraints
wR(F²) = 0.061	H-atom parameters constrained
S = 1.08	Δρ_max = 0.64 e Å⁻³
1768 reflections	Δρ_min = −0.36 e Å⁻³
63 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

	x	y	z	U_iso*/U_eq
Cu	0.5000	0.5000	0.5000	0.01076 (7)
O1	0.53710 (10)	0.74236 (14)	0.35326 (9)	0.01390 (16)
O2	0.72233 (12)	0.85036 (16)	0.17943 (10)	0.0221 (2)
N1	0.69539 (12)	0.35314 (16)	0.39628 (10)	0.01218 (17)
H1A	0.6524	0.2775	0.3140	0.015*
C1	0.67866 (14)	0.72698 (19)	0.28370 (12)	0.01373 (19)
C2	0.79685 (14)	0.5444 (2)	0.34046 (13)	0.0135 (2)
H2A	0.8718	0.4933	0.2590	0.016*
H2B	0.8685	0.6048	0.4215	0.016*
C3	0.79798 (15)	0.1919 (2)	0.48149 (14)	0.0171 (2)
H3A	0.8941	0.1425	0.4209	0.026*
H3B	0.7284	0.0615	0.5080	0.026*
H3C	0.8398	0.2642	0.5723	0.026*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cu	0.00955 (10)	0.01254 (10)	0.01019 (10)	0.00153 (6)	0.00211 (6)	0.00253 (6)
O1	0.0127 (3)	0.0158 (4)	0.0132 (3)	0.0014 (3)	0.0018 (3)	0.0034 (3)
O2	0.0215 (4)	0.0249 (5)	0.0199 (4)	0.0014 (4)	0.0060 (3)	0.0105 (4)
N1	0.0111 (4)	0.0142 (4)	0.0112 (4)	−0.0001 (3)	0.0001 (3)	0.0001 (3)
C1	0.0132 (4)	0.0152 (5)	0.0128 (4)	−0.0016 (4)	0.0005 (4)	0.0008 (4)
C2	0.0107 (4)	0.0165 (5)	0.0132 (5)	−0.0008 (4)	0.0011 (4)	0.0012 (4)
C3	0.0161 (5)	0.0168 (5)	0.0183 (5)	0.0040 (4)	0.0003 (4)	0.0020 (4)

Geometric parameters (Å, º) top

Cu—O1ⁱ	1.9758 (8)	N1—C2	1.4796 (15)
Cu—O1	1.9758 (8)	N1—H1A	0.9300
Cu—N1ⁱ	2.0046 (9)	C1—C2	1.5200 (17)
Cu—N1	2.0046 (9)	C2—H2A	0.9900
Cu—O2ⁱⁱ	2.5451 (10)	C2—H2B	0.9900
Cu—O2ⁱⁱⁱ	2.5451 (10)	C3—H3A	0.9800
O1—C1	1.2853 (13)	C3—H3B	0.9800
O2—C1	1.2396 (14)	C3—H3C	0.9800
N1—C3	1.4705 (15)

O1ⁱ—Cu—O1	180.0	C3—N1—H1A	107.4
O1ⁱ—Cu—N1ⁱ	83.82 (3)	C2—N1—H1A	107.4
O1—Cu—N1ⁱ	96.18 (3)	Cu—N1—H1A	107.4
O1ⁱ—Cu—N1	96.18 (3)	O2—C1—O1	124.66 (11)
O1—Cu—N1	83.82 (3)	O2—C1—C2	120.34 (10)
N1ⁱ—Cu—N1	180.0	O1—C1—C2	114.98 (10)
O1ⁱ—Cu—O2ⁱⁱ	86.24 (3)	N1—C2—C1	109.26 (9)
O1—Cu—O2ⁱⁱ	93.76 (3)	N1—C2—H2A	109.8
N1ⁱ—Cu—O2ⁱⁱ	94.85 (3)	C1—C2—H2A	109.8
N1—Cu—O2ⁱⁱ	85.15 (3)	N1—C2—H2B	109.8
O1ⁱ—Cu—O2ⁱⁱⁱ	93.76 (3)	C1—C2—H2B	109.8
O1—Cu—O2ⁱⁱⁱ	86.24 (3)	H2A—C2—H2B	108.3
N1ⁱ—Cu—O2ⁱⁱⁱ	85.15 (3)	N1—C3—H3A	109.5
N1—Cu—O2ⁱⁱⁱ	94.85 (3)	N1—C3—H3B	109.5
O2ⁱⁱ—Cu—O2ⁱⁱⁱ	180.0	H3A—C3—H3B	109.5
C1—O1—Cu	113.74 (7)	N1—C3—H3C	109.5
C3—N1—C2	112.28 (9)	H3A—C3—H3C	109.5
C3—N1—Cu	117.79 (7)	H3B—C3—H3C	109.5
C2—N1—Cu	103.93 (7)

O1ⁱ—Cu—O1—C1	−64 (100)	O1—Cu—N1—C2	29.24 (7)
N1ⁱ—Cu—O1—C1	166.53 (8)	N1ⁱ—Cu—N1—C2	80 (100)
N1—Cu—O1—C1	−13.47 (8)	O2ⁱⁱ—Cu—N1—C2	−65.08 (7)
O2ⁱⁱ—Cu—O1—C1	71.23 (8)	O2ⁱⁱⁱ—Cu—N1—C2	114.92 (7)
O2ⁱⁱⁱ—Cu—O1—C1	−108.77 (8)	Cu—O1—C1—O2	174.29 (10)
O1ⁱ—Cu—N1—C3	−25.85 (8)	Cu—O1—C1—C2	−6.96 (12)
O1—Cu—N1—C3	154.15 (8)	C3—N1—C2—C1	−167.81 (9)
N1ⁱ—Cu—N1—C3	−155 (100)	Cu—N1—C2—C1	−39.44 (10)
O2ⁱⁱ—Cu—N1—C3	59.83 (8)	O2—C1—C2—N1	−148.69 (11)
O2ⁱⁱⁱ—Cu—N1—C3	−120.17 (8)	O1—C1—C2—N1	32.50 (13)
O1ⁱ—Cu—N1—C2	−150.76 (7)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+3/2, z+1/2; (iii) −x+1, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1ⁱⁱⁱ	0.93	2.13	2.9729 (13)	150

Symmetry code: (iii) −x+1, y−1/2, −z+1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1ⁱ	0.93	2.13	2.9729 (13)	149.8

Symmetry code: (i) −x+1, y−1/2, −z+1/2.

Experimental details

Crystal data
Chemical formula	[Cu(C₃H₆NO₂)₂]
M_r	239.72
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	123
a, b, c (Å)	7.9031 (3), 5.9461 (2), 8.9907 (3)
β (°)	90.039 (3)
V (Å³)	422.50 (3)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	2.57
Crystal size (mm)	0.51 × 0.45 × 0.12

Data collection
Diffractometer	Agilent Xcalibur Ruby Gemini diffractometer
Absorption correction	Multi-scan (CrysAlis PRO; Agilent, 2012)
T_min, T_max	0.478, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	5479, 1768, 1542
R_int	0.025
(sin θ/λ)_max (Å⁻¹)	0.808

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.023, 0.061, 1.08
No. of reflections	1768
No. of parameters	63
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.64, −0.36

Computer programs: CrysAlis PRO (Agilent, 2012), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).

Acknowledgements

RJB wishes to acknowledge the NSF–MRI program (grant No. CHE-0619278) for funds to purchase the diffractometer. GB wishes to acknowledge support of this work from NASA (NNX10AK71A)

References

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Volume 70| Part 10| October 2014| Pages 207-209

doi:10.1107/S1600536814020418

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