Crystal structure of anhydrous poly[bis-(μ2-sarcosinato-κ(3) O,N:O')copper(II)].

The title compound, [Cu(C3H6NO2)2] n , is a bis-complex of the anion of sarcosine (N-methyl-glycine). The asymmetric unit consists of a copper(II) ion, located on a center of inversion, and one mol-ecule 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 nitro-gen and carboxyl-ate O atoms of two sarcosinate anions, and the longer axial bonds are to carboxyl-ate 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 inter-molecular hydrogen-bonding inter-action within the sheets between the amino NH group and an O atom of an adjacent mol-ecule.

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 pan class="Chemical">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 pan class="Chemical">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

The title compound, [Cu(C3H6NO2)2], is a bis-complex of the sarcosinate anion with pan class="Chemical">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 − ,  − z; (C) x,  − y,  + z.]

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 [01]. 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 pan class="Chemical">hydrogen-bonding inter­action within the sheets between the amino NH and an carboxyl­ate O atom of an adjacent mol­ecule (Table 1 ▶).

Figure 2

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

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) .

Database survey

The structure of the zwitterionic form of sarcosine has been reported by Rodrigues et al. (2005 ▶). The structure of the pan class="Chemical">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

Sarcosine (N-methyl­glycine) was purchased from Aldrich Chemical. pan class="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.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▶. pan class="Disease">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 pan class="Disease">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(H) = 1.2U(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[F 2 > 2σ(F 2)], wR(F 2), S	0.023, 0.061, 1.08
No. of reflections	1768
No. of parameters	63
H-atom treatment	H-atom parameters constrained
Δρmax, Δρmin (e Å−3)	0.64, −0.36

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

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

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

CCDC reference: 961026

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Cu(C3H6NO2)2]	F(000) = 246
Mr = 239.72	Dx = 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

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

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(Fo2) + (0.0285P)2 + 0.0835P] where P = (Fo2 + 2Fc2)/3
S = 1.08	(Δ/σ)max < 0.001
1768 reflections	Δρmax = 0.64 e Å−3
63 parameters	Δρmin = −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)

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.

	x	y	z	Uiso*/Ueq
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*

	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)

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)

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