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A complex of a deprotonated form of metformin with Cu2+, [Cu(C4H10N5)2]·8H2O, was prepared from alkaline aqueous solution. The coordination geometry around the Cu atom is square planar, with four N atoms from two bidentate ligands. The deprotonation of the ligand causes an increase in the π conjugation of the C—N—C system, reducing the bond angle at the central N atom to nearly 120°. The dihedral angle between the two six-membered chelate rings in the complex is 11.31 (5)°. The Cu atom lies on a twofold rotation axis.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802007092/cf6167sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536802007092/cf6167Isup2.hkl
Contains datablock I

CCDC reference: 185754

Key indicators

  • Single-crystal X-ray study
  • T = 173 K
  • Mean [sigma](N-C) = 0.002 Å
  • R factor = 0.026
  • wR factor = 0.051
  • Data-to-parameter ratio = 13.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


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Comment top

Metformin (1,1-dimethylbiguanide) has been introduced as an oral glucose-lowering agent for the treatment of non-insulin dependent diabetes mellitus. Like biguanide, it is a moderately strong base, forming well defined salts and possessing excellent capacity for coordination with transition metals, giving rise to highly colored bidentate chelate complexes. Various metal complexes have been studied, such as [PtCl(C4H11N5)(DMSO)]Cl (Viossat et al., 1995), [PtCl4(C4H11N5)(DMSO)] (Bentefrit et al., 1997), [Co(C4H12N5)Cl3], [CuCl2(C4H11N5)2], [Cu(C4H11N5)2]Cl2·2H2O, [Ni(C4H11N5)2](Cl)(OH) (Lemoine et al., 1996), and [Zn(C4H12N5)Cl3] (Zhu, Lu, Jin & Yang, 2002) (DMSO is dimethyl sulfoxide). The metal complexes of biguanide ligands are usually cationic in nature, and their color varies with the nature of the metal ion and its oxidation state, as well as with the number of ligands in the complex. It has been found that the bidentate ligand can chelate to metals in a square-planar configuration through four N atoms of two ligands. Here, we report the synthesis of a red copper complex of a deprotonated form, (I), of metformin (an anionic ligand) and its crystal structure.

The geometric parameters of (I) are listed in Table 1. The molecular conformation and crystal packing are illustrated in Figs. 1 and 2. The structure can be regarded as a square-planar coordination of the metal ion through the formation of four M—N bonds with two bidentate ligands. The central metal atom lies on a crystallographic twofold rotation axis. The two ligands form a slightly distorted plane with the Cu at the center. The dimethyl groups of the two ligands have a trans configuration.

The Cu—N bond distances in the structure of (I) are worthy of comment. The values 1.9210 (14) and 1.9428 (13) Å are very similar to those of 1.920 (4) and 1.931 (4) Å in [Cu(C4H11N5)2]·2HCO3, and 1.932 (7) and 1.948 (7) Å in [Cu(C4H11N5)2]Cl2·2H2O (Viossat et al., 1995; Lemoine et al., 1996). They are significantly longer than the Ni—N bonds in [Ni(C4H11N5)2] (Zhu, Lu, Yang & Jin, 2002), [1.8478 (17) and 1.8541 (16) Å] and in [Ni(C4H11N5)2](Cl)(OH) (Lemoine et al., 1996) [1.863 (5) and 1.866 (5) Å]. This large difference is considered to be a result of the removal of an unpaired electron from the d(x2-y2) orbital of the d9 configuration of Cu2+ on going to the low-spin d8 configuration of Ni2+, in addition to the small ionic radius difference of Ni2+ (0.55) and Cu2+ (0.57) for all coordination numbers (Shannon, 1976).

Another interesting feature in the ligand geometry is the effect of deprotonation. The C—N bond lengths involving the coordinating N atoms of the deprotonated biguanide moiety are 1.3060 (19) and 1.3125 (19) Å. These show delocalization with the C—N4 bonds of 1.3503 (19) and 1.372 (2) Å. Deprotonation of the ligand produces an increase of the π conjugation, reducing the bond angle at N4 to 121.04 (13)°, compared with 124.9 (8)–127.7 (5)° for neutral ligands (Bentefrit et al., 1997; Lemoine et al., 1996).

The dihedral angle between the two chelate rings in (I) is 11.31 (5)°. This is larger than that in [Ni(C4H11N5)2] (Zhu, Lu, Yang & Jin, 2002) [0.02 (7)°], and may be due to the larger ionic radius of Cu2+. The crystal packing is characterized by 11 intermolecular hydrogen bonds involving N2, N3, and N4 of the metformin as well as all O atoms of solvent water molecules.

Experimental top

1,1-Dimethylbiguanide hydrochloride was purchased from the Wujin Medicine Raw Material Chemical Factory of China. CuCl2·2H2O was a commercial sample from Acros, and was used without further purification. An aqueous solution of CuCl2·2H2O was added dropwise to 0.1 M KOH solution of the ligand with stirring, in the mole ratio 1:2. The red solution was filtered, and the filtrate was left at room temperature. Red crystals were formed after a few days. The elemental analyses results are in agreement with the structural composition of (I).

Refinement top

Methyl H atoms were treated as riding, with C—H = 0.96 Å and Uiso(H) = 1.5Ueq(C). The H atoms on N or O atoms were refined, with Uiso(H) = 0.03 Å2 (0.08 for O); N—H distances are in the range 0.81—0.89 Å and the O—H distances are in the range 0.78–0.84 Å.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: MSC/AFC Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP (Siemens, 1990); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. A view of the molecular structure of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. The packing of the title compound, viewed approximately down the b axis.
Bis(1,1-dimethylbiguanido)copper(II) octahydrate top
Crystal data top
[Cu(C4H10N5)2]·8H2OF(000) = 988
Mr = 464.01Dx = 1.472 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 9440 reflections
a = 23.561 (5) Åθ = 3.1–27.5°
b = 6.952 (1) ŵ = 1.10 mm1
c = 13.297 (3) ÅT = 173 K
β = 105.95 (3)°Block, red
V = 2094.1 (7) Å30.50 × 0.40 × 0.25 mm
Z = 4
Data collection top
Rigaku RAXIS RAPID IP
diffractometer
2381 independent reflections
Radiation source: fine-focus sealed tube1894 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.032
Detector resolution: 100x100 microns pixels mm-1θmax = 27.5°, θmin = 3.1°
ϕ scansh = 3030
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
k = 99
Tmin = 0.596, Tmax = 0.760l = 1716
2381 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.026Hydrogen site location: hydrogen atoms are generated by HFIX instructions
wR(F2) = 0.051H atoms treated by a mixture of independent and constrained refinement
S = 0.90 w = 1/[σ2(Fo2) + (0.0242P)2]
where P = (Fo2 + 2Fc2)/3
2381 reflections(Δ/σ)max = 0.008
173 parametersΔρmax = 0.38 e Å3
0 restraintsΔρmin = 0.21 e Å3
Crystal data top
[Cu(C4H10N5)2]·8H2OV = 2094.1 (7) Å3
Mr = 464.01Z = 4
Monoclinic, C2/cMo Kα radiation
a = 23.561 (5) ŵ = 1.10 mm1
b = 6.952 (1) ÅT = 173 K
c = 13.297 (3) Å0.50 × 0.40 × 0.25 mm
β = 105.95 (3)°
Data collection top
Rigaku RAXIS RAPID IP
diffractometer
2381 independent reflections
Absorption correction: multi-scan
(ABSCOR; Higashi, 1995)
1894 reflections with I > 2σ(I)
Tmin = 0.596, Tmax = 0.760Rint = 0.032
2381 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0260 restraints
wR(F2) = 0.051H atoms treated by a mixture of independent and constrained refinement
S = 0.90Δρmax = 0.38 e Å3
2381 reflectionsΔρmin = 0.21 e Å3
173 parameters
Special details top

Experimental. ABSCOR BY T·Higashi 8 march,1995

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
xyzUiso*/Ueq
Cu10.00000.30656 (4)0.25000.01457 (8)
O10.14695 (5)0.5913 (2)0.01670 (9)0.0259 (3)
O20.17243 (6)0.05680 (19)0.11067 (10)0.0258 (3)
O30.20797 (7)0.7597 (2)0.30342 (12)0.0348 (3)
O40.23114 (7)0.0324 (2)0.46070 (12)0.0359 (3)
N10.00087 (6)0.2977 (2)0.10439 (10)0.0185 (3)
N20.08473 (6)0.3139 (2)0.28720 (10)0.0208 (3)
N30.17916 (6)0.3333 (2)0.26815 (11)0.0213 (3)
N40.10350 (5)0.27755 (18)0.12070 (10)0.0162 (3)
N50.03608 (6)0.2209 (2)0.03835 (10)0.0188 (3)
C10.04526 (7)0.2672 (2)0.06462 (12)0.0153 (3)
C20.11909 (6)0.3060 (2)0.22517 (11)0.0154 (3)
C30.08238 (7)0.2029 (3)0.09095 (12)0.0223 (3)
H3A0.12010.22330.04150.034*
H3B0.07640.29700.14570.034*
H3C0.08120.07640.12040.034*
C40.02361 (7)0.2050 (3)0.10674 (11)0.0218 (3)
H4A0.04780.13620.07130.033*
H4B0.02280.13690.16920.033*
H4C0.03960.33130.12490.033*
H11A0.1491 (9)0.693 (4)0.0484 (17)0.047 (7)*
H11B0.1373 (8)0.505 (4)0.0505 (16)0.044 (7)*
H12A0.1522 (8)0.034 (3)0.1092 (15)0.034 (6)*
H12B0.1924 (10)0.035 (4)0.0722 (18)0.060 (8)*
H13A0.1946 (10)0.817 (3)0.2469 (19)0.052 (7)*
H13B0.1995 (10)0.650 (4)0.2926 (18)0.048 (8)*
H14A0.2680 (11)0.039 (4)0.474 (2)0.076 (9)*
H14B0.2227 (10)0.056 (4)0.4234 (18)0.065 (9)*
H210.0308 (8)0.295 (3)0.0590 (13)0.020 (5)*
H220.1038 (7)0.339 (2)0.3499 (13)0.020 (5)*
H23A0.1995 (8)0.303 (3)0.2326 (14)0.025 (5)*
H23B0.1936 (8)0.285 (3)0.3317 (15)0.027 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cu10.01494 (14)0.01703 (15)0.01244 (14)0.0000.00494 (10)0.000
O10.0337 (7)0.0238 (7)0.0201 (6)0.0062 (6)0.0070 (5)0.0019 (6)
O20.0296 (7)0.0210 (7)0.0290 (7)0.0051 (6)0.0119 (6)0.0012 (6)
O30.0456 (9)0.0294 (9)0.0275 (8)0.0040 (7)0.0068 (6)0.0009 (6)
O40.0325 (8)0.0409 (9)0.0379 (8)0.0080 (7)0.0158 (6)0.0124 (7)
N10.0142 (6)0.0255 (7)0.0147 (6)0.0001 (7)0.0023 (5)0.0003 (6)
N20.0178 (6)0.0312 (8)0.0124 (6)0.0018 (7)0.0027 (5)0.0019 (7)
N30.0155 (7)0.0318 (9)0.0169 (7)0.0000 (6)0.0050 (6)0.0002 (7)
N40.0161 (6)0.0176 (7)0.0151 (6)0.0007 (5)0.0047 (5)0.0007 (5)
N50.0193 (6)0.0240 (8)0.0137 (6)0.0010 (6)0.0056 (5)0.0019 (6)
C10.0199 (7)0.0115 (8)0.0139 (7)0.0004 (6)0.0039 (6)0.0022 (6)
C20.0160 (7)0.0125 (7)0.0170 (7)0.0003 (7)0.0032 (6)0.0019 (7)
C30.0275 (8)0.0244 (9)0.0170 (8)0.0006 (8)0.0092 (6)0.0033 (8)
C40.0233 (8)0.0246 (9)0.0149 (7)0.0006 (8)0.0009 (6)0.0017 (7)
Geometric parameters (Å, º) top
Cu1—N2i1.9210 (14)N2—H220.849 (17)
Cu1—N21.9210 (14)N3—C21.3861 (19)
Cu1—N1i1.9428 (13)N3—H23A0.789 (18)
Cu1—N11.9428 (13)N3—H23B0.886 (19)
O1—H11A0.82 (2)N4—C21.3503 (19)
O1—H11B0.82 (2)N4—C11.372 (2)
O2—H12A0.79 (2)N5—C11.3647 (19)
O2—H12B0.80 (2)N5—C31.4539 (19)
O3—H13A0.83 (2)N5—C41.454 (2)
O3—H13B0.79 (2)C3—H3A0.960
O4—H14A0.84 (2)C3—H3B0.960
O4—H14B0.78 (3)C3—H3C0.960
N1—C11.3125 (19)C4—H4A0.960
N1—H210.820 (18)C4—H4B0.960
N2—C21.3060 (19)C4—H4C0.960
N2i—Cu1—N2176.96 (10)C1—N5—C4120.32 (12)
N2i—Cu1—N1i87.86 (6)C3—N5—C4114.65 (12)
N2—Cu1—N1i92.24 (6)N1—C1—N5121.22 (14)
N2i—Cu1—N192.24 (6)N1—C1—N4124.15 (14)
N2—Cu1—N187.86 (6)N5—C1—N4114.63 (13)
N1i—Cu1—N1176.39 (9)N2—C2—N4127.96 (13)
H11A—O1—H11B110 (2)N2—C2—N3118.28 (14)
H12A—O2—H12B107 (2)N4—C2—N3113.74 (13)
H13A—O3—H13B106 (2)N5—C3—H3A109.5
H14A—O4—H14B104 (2)N5—C3—H3B109.5
C1—N1—Cu1129.38 (11)H3A—C3—H3B109.5
C1—N1—H21111.3 (11)N5—C3—H3C109.5
Cu1—N1—H21118.6 (11)H3A—C3—H3C109.5
C2—N2—Cu1128.10 (11)H3B—C3—H3C109.5
C2—N2—H22112.1 (11)N5—C4—H4A109.5
Cu1—N2—H22119.3 (11)N5—C4—H4B109.5
C2—N3—H23A115.8 (13)H4A—C4—H4B109.5
C2—N3—H23B115.0 (12)N5—C4—H4C109.5
H23A—N3—H23B109.4 (18)H4A—C4—H4C109.5
C2—N4—C1121.04 (13)H4B—C4—H4C109.5
C1—N5—C3124.75 (13)
N2—Cu1—N1—C112.15 (15)C3—N5—C1—N46.5 (2)
N2i—Cu1—N1—C1170.89 (15)C4—N5—C1—N4179.93 (13)
N1i—Cu1—N2—C2174.01 (16)C2—N4—C1—N15.3 (2)
N1—Cu1—N2—C22.37 (16)C2—N4—C1—N5174.39 (14)
Cu1—N1—C1—N5164.27 (12)Cu1—N2—C2—N45.0 (3)
Cu1—N1—C1—N415.4 (2)Cu1—N2—C2—N3173.56 (12)
C3—N5—C1—N1173.82 (15)C1—N4—C2—N25.1 (3)
C4—N5—C1—N10.2 (2)C1—N4—C2—N3173.49 (14)
Symmetry code: (i) x, y, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H11A···O2ii0.82 (2)1.94 (2)2.737 (2)165 (2)
O1—H11B···N40.82 (2)2.10 (2)2.9149 (19)173 (2)
O2—H12A···N40.79 (2)2.08 (2)2.8597 (19)174.3 (19)
O2—H12B···O4iii0.80 (2)1.94 (2)2.727 (2)167 (2)
O3—H13A···O2ii0.83 (2)1.95 (2)2.778 (2)173 (2)
O3—H13B···N30.79 (2)2.26 (3)3.049 (2)177 (2)
O4—H14A···O1iv0.84 (2)2.01 (3)2.834 (2)169 (3)
O4—H14B···O3v0.78 (3)2.00 (3)2.764 (2)166 (2)
N2—H22···O1vi0.849 (17)2.225 (17)3.072 (2)175.5 (15)
N3—H23A···O3iv0.789 (18)2.376 (18)3.103 (2)153.7 (17)
N3—H23B···O40.886 (19)2.444 (19)3.272 (2)155.8 (16)
Symmetry codes: (ii) x, y+1, z; (iii) x, y, z1/2; (iv) x+1/2, y1/2, z+1/2; (v) x, y1, z; (vi) x, y+1, z+1/2.

Experimental details

Crystal data
Chemical formula[Cu(C4H10N5)2]·8H2O
Mr464.01
Crystal system, space groupMonoclinic, C2/c
Temperature (K)173
a, b, c (Å)23.561 (5), 6.952 (1), 13.297 (3)
β (°) 105.95 (3)
V3)2094.1 (7)
Z4
Radiation typeMo Kα
µ (mm1)1.10
Crystal size (mm)0.50 × 0.40 × 0.25
Data collection
DiffractometerRigaku RAXIS RAPID IP
diffractometer
Absorption correctionMulti-scan
(ABSCOR; Higashi, 1995)
Tmin, Tmax0.596, 0.760
No. of measured, independent and
observed [I > 2σ(I)] reflections
2381, 2381, 1894
Rint0.032
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.051, 0.90
No. of reflections2381
No. of parameters173
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.38, 0.21

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1994), MSC/AFC Diffractometer Control Software, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), XP (Siemens, 1990), SHELXL97.

Selected geometric parameters (Å, º) top
Cu1—N21.9210 (14)N3—C21.3861 (19)
Cu1—N11.9428 (13)N4—C21.3503 (19)
N1—C11.3125 (19)N4—C11.372 (2)
N2—C21.3060 (19)N5—C11.3647 (19)
N2—Cu1—N187.86 (6)N1—C1—N4124.15 (14)
C1—N1—Cu1129.38 (11)N5—C1—N4114.63 (13)
C2—N2—Cu1128.10 (11)N2—C2—N4127.96 (13)
C2—N4—C1121.04 (13)N2—C2—N3118.28 (14)
N1—C1—N5121.22 (14)N4—C2—N3113.74 (13)
N2—Cu1—N1—C112.15 (15)C2—N4—C1—N5174.39 (14)
N1—Cu1—N2—C22.37 (16)Cu1—N2—C2—N45.0 (3)
Cu1—N1—C1—N5164.27 (12)Cu1—N2—C2—N3173.56 (12)
Cu1—N1—C1—N415.4 (2)C1—N4—C2—N25.1 (3)
C2—N4—C1—N15.3 (2)C1—N4—C2—N3173.49 (14)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H11A···O2i0.82 (2)1.94 (2)2.737 (2)165 (2)
O1—H11B···N40.82 (2)2.10 (2)2.9149 (19)173 (2)
O2—H12A···N40.79 (2)2.08 (2)2.8597 (19)174.3 (19)
O2—H12B···O4ii0.80 (2)1.94 (2)2.727 (2)167 (2)
O3—H13A···O2i0.83 (2)1.95 (2)2.778 (2)173 (2)
O3—H13B···N30.79 (2)2.26 (3)3.049 (2)177 (2)
O4—H14A···O1iii0.84 (2)2.01 (3)2.834 (2)169 (3)
O4—H14B···O3iv0.78 (3)2.00 (3)2.764 (2)166 (2)
N2—H22···O1v0.849 (17)2.225 (17)3.072 (2)175.5 (15)
N3—H23A···O3iii0.789 (18)2.376 (18)3.103 (2)153.7 (17)
N3—H23B···O40.886 (19)2.444 (19)3.272 (2)155.8 (16)
Symmetry codes: (i) x, y+1, z; (ii) x, y, z1/2; (iii) x+1/2, y1/2, z+1/2; (iv) x, y1, z; (v) x, y+1, z+1/2.
 

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