Di­chloro­bis­(glycocy­amine-O)copper(II)

The title compound, [CuCl₂(C₃H₇N₃O₂)₂], is a new copper(II) complex with glycocy­amine [(di­amino­methyl­ene­amino)­acetic acid], the first complex ever reported with this organic mol­ecule. It is composed of discrete centrosymmetric coordinated Cu^II monomers, the Cu atoms being located at inversion centers. Each metal ion is square-planar coordinated by two Cl atoms and two glycocy­amine O atoms. The coordinating glycocy­amine mol­ecule exists as a zwitterion, the H atom from the carboxyl group being transferred to the guanidinium group. A three-dimensional network of hydrogen bonds links the monomers and stabilizes the structure.

S1. Comment

Our recent work has been dedicated to the study of molecular-based magnets in order to understand the magnetic interactions observed between inorganic spin carriers bridged by organic molecules and develop structure-function relationships enabling the design of new magnetic materials. We have been specially focused on the magnetic interaction in copper(II) complexes of aminoacids (and substituted aminoacids). Copper ions are often grouped in dinuclear complexes or even bridged in such a way as to form infinite chains, which results in interesting magnetic behaviour. In these complexes the copper ions are linked by different types of chemical paths, allowing evaluation of superexchange interactions transmitted over long distances via molecular bridges. We report here the synthesis and structure of a new copper(II) complex with glycocyamine (guanidineacetic acid), (I), the first complex ever reported with this organic molecule. Glycocyamine exists in living organisms and is one of the intermediate compounds in the synthesis of creatine in vivo. It contains a guanidinium group that has been widely studied by theoretical (Williams & Gready, 1989) and experimental techniques (Kozak et al., 1987) due to the aromatic character of the delocalized π-bonding and its ability to establish intermolecular hydrogen bonds. Glycocyamine has been used as a food supplement for men and animals. An inspection of the Cambridge Structural Database (release April 2000; Allen & Kennard, 1993) shows that only three structures containing this molecule have been reported, namely that of crystalline glycocyamine (Guha, 1973; Berthou et al., 1976) and those of the Cl and Br halides (Majumdar et al., 1977; Roy et al., 1967). \sch

The title compound is composed of discrete coordinated Cu^II monomers which are centrosymmetric, the copper ions being located at inversion centers in the unit cell. The copper ion is square-planar coordinated by two chloride ions and two glycocyamine O atoms. Both bond distances lie within the range of reported average values (Orpen et al., 1989). The angle Cl—Cu—O1 is close to 90°. Although the Cu···O2 distance [2.782 (2) Å] is significantly shorter than the usual non-bonding contact distance between Cu and O, which may indicate a weak interaction between these atoms, this interaction does not appear to have much influence on the geometry of the other coordination interactions with Cu.

The glycocyamine molecule exists as a zwitterion, the proton from the carboxyl group being transferred to the guanidinium group. Pure glycocyamine has also been found to exist in a zwitterionic form (Guha, 1973; Berthou et al., 1976), but a protonated molecule has also been found in the presence of a stronger acid (Roy et al., 1967; Majumdar et al., 1977). The difference between the two C–O bond lengths [1.278 (2) and 1.226 (2) Å] may be attributed to the fact that only one of the oxygen atoms is coordinating to the copper ion. The guanidinium group is planar, with the sum of the valence angles around C3 equal to 359.99 (19)°. The C3–N distances are very similar, their average value [1.322 (3) Å] is close to the expected value for the delocalized C≐N bond in guanidinium compounds (1.328 Å; Allen et al., 1987). The C_sp3–N bond length between atoms N1 and C2 [1.447 (3) Å] is also similar to that found in pure glycocyamine [1.455 (3) Å].

The geometry of the glycocyamine molecule can be defined in terms of two planes, one containing the carboxylic group (O1, O2, C1, C2), the other the amine group (N1, N2, N3, C3), the angle between these least-squares planes being 25.52 (12)°. This angle is much larger than that found in the pure glycocyamine (3.99°; Berthou et al., 1976), but equal within error to that found in the protonated molecule, (22.6°; Roy et al., 1967).

A three-dimensional network of H atoms bonds links the monomers and stabilizes the structure. The guanidyl N2 atom donates its hydrogen atoms to each of the chlorine atoms of a neighbouring complex. The H atom bonded to N1 is oriented towards the carboxy O2 atom of a third monomer. N3 establishes an intermolecular hydrogen bond to a neighbouring O1, and has its other hydrogen atom shared in a bifurcated bond to neighbouring O2 and Cl atoms, the latter bond being somewhat long [3.512 (2) Å].

The shortest Cu—Cu distance is 7.047 (4) Å which excludes the possibility of a direct magnetic interaction between the transition metal atoms. We are currently trying to synthesize new coordination compounds of glycocyamine and Cu^II in an attempt to obtain dimers or polymeric chains with the metal ions chelated via the carboxy bonds in which low-dimensional magnetic interactions might be observed.

S2. Experimental

Crystals were prepared by adding guanidineacetic acid (99.9%, Aldrich) to an aqueous solution of CuCl₂ hydrated (98% purity, Aldrich) in stoichiometric proportion. Slow evaporation afforded the title compound in polycrystalline form. Good quality, blue single crystals were obtained by recrystallization from acetone. A few of them were tested using photographic methods and the best specimen was chosen for data collection.

S3. Refinement

The H atoms were placed at calculated positions and refined as riding using the SHELXL97 (Sheldrick, 1997) defaults.

Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice. All calculations were performed on a Pentium 330 MHz PC running LINUX.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% level.
	Fig. 2. Packing of the molecules projected along a. The dashed lines represent hydrogen bonds.

bis(glycocyamine-O) dichloro copper(II)

Crystal data

[CuCl2(C3H7N3O2)2]	F(000) = 374
Mr = 368.67	Dx = 1.868 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.047 (4) Å	Cell parameters from 25 reflections
b = 12.9533 (13) Å	θ = 9.7–15.5°
c = 7.297 (2) Å	µ = 2.09 mm^−1
β = 100.250 (16)°	T = 293 K
V = 655.5 (4) Å^3	Plate, translucent intense blue
Z = 2	0.28 × 0.27 × 0.12 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	1047 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.011
Graphite monochromator	θmax = 25.1°, θmin = 3.2°
profile data from ω–2θ scans	h = 0→8
Absorption correction: ψ scan North et al. (1968)	k = 0→15
Tmin = 0.619, Tmax = 0.778	l = −8→8
1259 measured reflections	3 standard reflections every 180 min
1162 independent reflections	intensity decay: 6.1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.060	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0348P)^2 + 0.3768P] where P = (Fo^2 + 2Fc^2)/3
1162 reflections	(Δ/σ)max < 0.001
88 parameters	Δρmax = 0.36 e Å^−3
0 restraints	Δρmin = −0.40 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
Cu	0.0000	0.0000	0.0000	0.02235 (13)
Cl	−0.18966 (8)	0.04752 (4)	0.20643 (7)	0.03314 (16)
O1	0.0831 (2)	−0.11914 (10)	0.1560 (2)	0.0275 (3)
N3	0.7952 (3)	−0.21300 (15)	0.6562 (3)	0.0374 (5)
H3A	0.8253	−0.1490	0.6738	0.045*
H3B	0.8782	−0.2602	0.6957	0.045*
N1	0.4941 (2)	−0.16589 (14)	0.5078 (2)	0.0298 (4)
H1	0.5281	−0.1028	0.5311	0.036*
C3	0.6203 (3)	−0.23896 (15)	0.5679 (3)	0.0246 (4)
O2	0.3029 (2)	−0.01013 (10)	0.3013 (2)	0.0312 (4)
C1	0.2278 (3)	−0.09569 (15)	0.2810 (3)	0.0228 (4)
N2	0.5746 (3)	−0.33750 (14)	0.5446 (3)	0.0339 (4)
H2A	0.4610	−0.3550	0.4894	0.041*
H2B	0.6585	−0.3842	0.5845	0.041*
C2	0.3020 (3)	−0.18534 (15)	0.4053 (3)	0.0266 (4)
H2C	0.2153	−0.1978	0.4923	0.032*
H2D	0.3039	−0.2469	0.3300	0.032*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu	0.0223 (2)	0.0158 (2)	0.0256 (2)	0.00103 (12)	−0.00466 (13)	0.00223 (12)
Cl	0.0335 (3)	0.0281 (3)	0.0374 (3)	0.0033 (2)	0.0050 (2)	−0.0027 (2)
O1	0.0267 (7)	0.0202 (7)	0.0309 (7)	0.0005 (6)	−0.0071 (6)	0.0036 (6)
N3	0.0285 (10)	0.0264 (9)	0.0511 (12)	0.0061 (8)	−0.0100 (8)	−0.0045 (9)
N1	0.0288 (9)	0.0177 (9)	0.0366 (10)	0.0027 (7)	−0.0114 (8)	0.0002 (7)
C3	0.0265 (10)	0.0229 (10)	0.0233 (9)	0.0037 (8)	0.0016 (8)	0.0001 (8)
O2	0.0314 (8)	0.0175 (7)	0.0406 (8)	−0.0023 (6)	−0.0046 (6)	0.0014 (6)
C1	0.0225 (10)	0.0200 (10)	0.0251 (10)	0.0034 (8)	0.0024 (8)	0.0004 (8)
N2	0.0296 (9)	0.0205 (9)	0.0480 (11)	0.0047 (8)	−0.0033 (8)	0.0036 (8)
C2	0.0265 (10)	0.0211 (10)	0.0281 (10)	−0.0002 (8)	−0.0056 (8)	0.0046 (8)

Geometric parameters (Å, º)

Cu—O1^i	1.9449 (13)	N1—C2	1.447 (3)
Cu—O1	1.9449 (13)	N1—H1	0.8600
Cu—Cl^i	2.2695 (8)	C3—N2	1.320 (3)
Cu—Cl	2.2696 (8)	O2—C1	1.226 (2)
O1—C1	1.278 (2)	C1—C2	1.509 (3)
N3—C3	1.328 (3)	N2—H2A	0.8600
N3—H3A	0.8600	N2—H2B	0.8600
N3—H3B	0.8600	C2—H2C	0.9700
N1—C3	1.319 (3)	C2—H2D	0.9700
O1^i—Cu—O1	180.0	N1—C3—N3	119.46 (19)
O1^i—Cu—Cl^i	88.76 (5)	N2—C3—N3	119.43 (19)
O1—Cu—Cl^i	91.24 (5)	O2—C1—O1	125.01 (19)
O1^i—Cu—Cl	91.24 (5)	O2—C1—C2	121.81 (18)
O1—Cu—Cl	88.76 (5)	O1—C1—C2	113.17 (17)
Cl^i—Cu—Cl	180.0	C3—N2—H2A	120.0
C1—O1—Cu	110.37 (12)	C3—N2—H2B	120.0
C3—N3—H3A	120.0	H2A—N2—H2B	120.0
C3—N3—H3B	120.0	N1—C2—C1	111.66 (16)
H3A—N3—H3B	120.0	N1—C2—H2C	109.3
C3—N1—C2	124.05 (18)	C1—C2—H2C	109.3
C3—N1—H1	118.0	N1—C2—H2D	109.3
C2—N1—H1	118.0	C1—C2—H2D	109.3
N1—C3—N2	121.10 (19)	H2C—C2—H2D	107.9
O1^i—Cu—O1—C1	−19 (2)	Cu—O1—C1—O2	0.7 (3)
Cl^i—Cu—O1—C1	92.53 (13)	Cu—O1—C1—C2	−179.03 (13)
Cl—Cu—O1—C1	−87.47 (13)	C3—N1—C2—C1	−153.06 (19)
C2—N1—C3—N2	−3.1 (3)	O2—C1—C2—N1	−16.2 (3)
C2—N1—C3—N3	178.04 (19)	O1—C1—C2—N1	163.49 (17)

Symmetry code: (i) −x, −y, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3A···O2^ii	0.86	2.27	3.001 (2)	143
N3—H3A···Cl^ii	0.86	2.88	3.512 (2)	132
N3—H3B···O1^iii	0.86	2.18	2.974 (2)	153
N1—H1···O2^ii	0.86	2.13	2.911 (2)	151
N2—H2A···Cl^iv	0.86	2.51	3.341 (2)	162
N2—H2B···Cl^iii	0.86	2.46	3.2950 (19)	163

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