Trichloro(1,1-dimethylbiguanidium-κN³)zinc(II)

The title compound, [ZnCl₃(C₄H₁₂N₅)], was prepared from aqueous solution and its structure determined. The coordination geometry around the Zn atom is a tetrahedron, with the central Zn atom bound to three Cl atoms and to one N atom of the biguanide ligand. The dihedral angle between the two guanidine groups is 67.86 (1)°.

S1. Comment

An N-substituted derivative of biguanide, metformin (N,N-dimethylbiguanide), is a powerful oral antihyperglycaemic drug that has been used in many countries for over 30 years for treating diabetic patients with non-insulin-dependent diabetes mellitus. As an N-donor monodentate and bidentate ligand, it also forms complexes with many metal ions (Baily, 1992; Ray, 1961). Zinc is considered as an important inorganic chemical element involved in biological processes. It exists in many organs, such as the liver, kidney, brain and pancreas, and it plays an important role and function within proteins, enzymes and so on.

From a chemical point of view, biguanide and its N-substituted derivatives are considered to be a good type of chelating ligand, with abundant chemical properties. There are structural differences between monodentate and bidentate ligands when they coordinate to different metal ions, with the former normally forming a tetrahedron and the latter a square-planar configuration, e.g. the bidentate biguanide derivative complexes of Co^II, Tc^V, Rh^V, Ag^III and Cu^II all have a square-planar geometry (Lemoine et al., 1996; Marchi et al., 1999; Ghosh et al., 1994; Hota & Saha, 1984). In addition, the planar angle between the two guanidine groups differs between complexes with monodentate or bidentate coordinated ligands. In the light of this, the title compound, (I), with a monodentate biguanide ligand, has been crystallized, and its structure is presented here. \sch

The geometric parameters of (I) are listed in Table 1 and the molecular structure is illustrated in Fig. 1. The structure can be viewed as two parts, namely C₄H₁₂N₅⁺ and ZnCl₃^-. These two parts are connected by the Zn²⁺ cation through the formation of a Zn—N coordination bond of 2.0611 Å.

In the structure of (I), each Zn²⁺ cation is coordinated by one N atom of the biguanide ligand and three Cl^- ions, in a slightly distorted tetrahedral configuration. The Cl—Zn bond distances are almost equal, in the range 2.2568 (7)–2.2728 (6) Å, with a mean of 2.2622 Å. These values are compatible with the Co—Cl bond lengths in [Co(C₄H₁₂N₅)Cl₃] [2.250 (1)–2.264 (1) Å; Lemoine et al., 1996]. The Cl—Zn distances in (I) are also in agreement with those found in a morpholine biguanide-coordinated Zn complex, [Zn(C₆H₁₄N₅O)Cl₃] (Yang & Zhu, 1991, 1992), in which the Cl—Zn bond distances [2.245 (1)–2.258 (1) Å] are slightly shorter than those in (I).

The Cl—Zn—Cl angles in (I) are in the range 109.82 (3)–116.50 (3)°, and the Cl—Zn—N angles are in the range 104.43 (4)–108.45 (4)°, close to the theoretical tetrahedral value of 109.5°.

In the crystal structure of metformin hydrochloride, Hariharan et al. (1989) pointed out that the C—N bond distances in the two guanide groups are intermediate between single and double bonds, in the range 1.330 (4)–1.348 (3) Å. A similar conclusion can be drawn for the C—N bond characterization in (I), with C—N bond lengths in the range 1.314 (2)–1.382 (2) Å. The standard single and double C—N bond lengths are 1.474 and 1.265 Å, respectively (reference?).

The two halves of the biguanide residue in (I) are planar, with atom C1 0.03260 Å out of the N1/N2/N5 plane and atom C2 0.04194 Å out of the N2/N3/N4 plane. The two planes of the different halves have a dihedral angle of 67.86° in (I); dihedral angles of 77.58 and 67.9 (1)° were found in [Zn(C₆H₁₄N₅O)Cl₃] (Yang & Zhu, 1992) and metformin hydrochloride (Hariharan et al., 1989), respectively. Thus, the dihedral angle in (I) is very close to that of the uncomplexed biguanide. It is noted that the different N-substituted group within the ligand is the main reason for the dihedral angle to differ: the dihedral angle in the morpholine-substituted complex is approximately 9.72° larger than that in the dimethyl-substituted complex.

S2. Experimental

Crystals of (I) were grown from an aqueous solution of zinc dichloride dihydrate (1.0 mmol) and N,N-dimethylbiguanide hydrochloride (1.0 mmol). The solution was left at room temperature and crystals were formed in the bottom of the flask after one to three months. The elemental analysis result was completely in agreement with the structural composition of (I).

S3. Refinement

The H atoms on C atom were treated as riding with C—H=0.96 Å and U_iso(H)= 1.5U_e.g of the parent atom. The H atoms on N atom were refined with U_iso(H)=0.08 and N—H distances in the range 0.78–0.92 Å·The final electron density maximum and minimum were +0.621 and -0.516 e Å^-3, respectively.

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

Computing details

Data collection: Please provide missing details; cell refinement: Please provide missing details; data reduction: Please provide missing details; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing details; software used to prepare material for publication: Please provide missing details.

Figures

	Fig. 1. A view of the molecular structure of (I) with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram of (I) viewed along the b axis.

Trichloro(1,1-dimethylbiguanidium-κN³)zinc(II)

Crystal data

[Zn(C4H12N5)Cl3]	F(000) = 608
Mr = 301.91	Dx = 1.774 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.5040 (7) Å	Cell parameters from 10407 reflections
b = 7.5170 (5) Å	θ = 3.1–27.5°
c = 13.0894 (5) Å	µ = 2.85 mm^−1
β = 113.237 (3)°	T = 173 K
V = 1130.5 (1) Å^3	Block, colourless
Z = 4	0.4 × 0.3 × 0.2 mm

Data collection

Rigaku R-AXIS RAPID image-plate diffractometer	2574 independent reflections
Radiation source: fine-focus sealed tube	2107 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
Detector resolution: 100 × 100 microns pixels mm^-1	θmax = 27.5°, θmin = 3.1°
oscillation scans	h = −16→16
Absorption correction: empirical (using intensity measurements) (ABSCOR; Higashi, 1995)	k = −9→9
Tmin = 0.402, Tmax = 0.566	l = −16→15
10407 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.022	H-atom parameters constrained
wR(F^2) = 0.048	Calculated w = 1/[σ^2(Fo^2) + (0.0243P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.94	(Δ/σ)max = 0.001
2574 reflections	Δρmax = 0.36 e Å^−3
138 parameters	Δρmin = −0.56 e Å^−3
0 restraints

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
Zn1	0.282952 (17)	0.13965 (3)	0.297150 (16)	0.01607 (6)
Cl2	0.13650 (4)	0.15467 (6)	0.12736 (3)	0.02258 (11)
Cl3	0.46377 (4)	0.10263 (6)	0.30140 (4)	0.02117 (10)
Cl4	0.24484 (4)	−0.07610 (6)	0.39974 (4)	0.02573 (11)
N1	0.37182 (15)	0.5511 (2)	0.53957 (14)	0.0223 (4)
N2	0.28448 (12)	0.37208 (18)	0.38125 (11)	0.0151 (3)
N3	0.17053 (12)	0.5575 (2)	0.23638 (12)	0.0181 (3)
N4	0.11663 (14)	0.5076 (2)	0.38315 (14)	0.0210 (3)
N5	0.41223 (15)	0.2538 (2)	0.54696 (13)	0.0236 (4)
C1	0.35440 (14)	0.3930 (2)	0.49044 (14)	0.0156 (3)
C2	0.19093 (14)	0.4857 (2)	0.33386 (13)	0.0144 (3)
C3	0.05951 (18)	0.6452 (3)	0.17234 (17)	0.0310 (5)
H3A	−0.0031	0.5759	0.1765	0.047*
H3B	0.0499	0.6557	0.0961	0.047*
H3C	0.0590	0.7615	0.2024	0.047*
C4	0.26062 (18)	0.5749 (3)	0.19237 (16)	0.0280 (4)
H4A	0.3297	0.5144	0.2405	0.042*
H4B	0.2777	0.6985	0.1882	0.042*
H4C	0.2337	0.5233	0.1194	0.042*
H11A	0.408 (3)	0.560 (4)	0.612 (3)	0.080*
H11B	0.349 (3)	0.641 (4)	0.508 (3)	0.080*
H14A	0.130 (3)	0.455 (4)	0.443 (3)	0.080*
H14B	0.071 (3)	0.590 (4)	0.363 (3)	0.080*
H15A	0.393 (3)	0.157 (4)	0.521 (3)	0.080*
H15B	0.464 (3)	0.268 (4)	0.619 (2)	0.080*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.01686 (11)	0.01453 (11)	0.01636 (11)	0.00090 (8)	0.00607 (8)	−0.00130 (8)
Cl2	0.0184 (2)	0.0303 (3)	0.0166 (2)	−0.00188 (19)	0.00421 (17)	−0.00273 (18)
Cl3	0.0171 (2)	0.0266 (2)	0.0195 (2)	0.00454 (18)	0.00692 (16)	0.00075 (18)
Cl4	0.0347 (3)	0.0171 (2)	0.0251 (2)	−0.0039 (2)	0.0115 (2)	0.00226 (18)
N1	0.0289 (9)	0.0171 (8)	0.0167 (8)	−0.0012 (7)	0.0045 (7)	−0.0016 (6)
N2	0.0179 (7)	0.0116 (7)	0.0135 (7)	0.0021 (6)	0.0038 (6)	0.0001 (6)
N3	0.0199 (7)	0.0158 (8)	0.0166 (7)	0.0025 (6)	0.0052 (6)	0.0029 (6)
N4	0.0196 (8)	0.0235 (9)	0.0222 (8)	0.0015 (7)	0.0110 (7)	0.0011 (7)
N5	0.0286 (9)	0.0198 (9)	0.0167 (8)	0.0066 (7)	0.0028 (7)	0.0020 (7)
C1	0.0143 (8)	0.0182 (9)	0.0146 (8)	0.0000 (7)	0.0060 (6)	0.0009 (7)
C2	0.0141 (8)	0.0100 (8)	0.0179 (8)	−0.0029 (7)	0.0050 (7)	−0.0025 (7)
C3	0.0276 (11)	0.0291 (11)	0.0278 (11)	0.0085 (9)	0.0018 (8)	0.0081 (9)
C4	0.0353 (11)	0.0290 (11)	0.0267 (10)	0.0001 (9)	0.0197 (9)	0.0063 (9)

Geometric parameters (Å, º)

Zn1—N2	2.0611 (14)	N1—H11A	0.88 (3)
Zn1—Cl3	2.2568 (7)	N1—H11B	0.78 (3)
Zn1—Cl2	2.2570 (5)	N4—H14A	0.83 (3)
Zn1—Cl4	2.2728 (6)	N4—H14B	0.81 (3)
N1—C1	1.328 (2)	N5—H15A	0.80 (3)
N2—C1	1.359 (2)	N5—H15B	0.92 (3)
N2—C2	1.382 (2)	C3—H3A	0.9600
N3—C2	1.314 (2)	C3—H3B	0.9600
N3—C4	1.459 (2)	C3—H3C	0.9600
N3—C3	1.465 (2)	C4—H4A	0.9600
N4—C2	1.334 (2)	C4—H4B	0.9600
N5—C1	1.320 (2)	C4—H4C	0.9600
N2—Zn1—Cl3	107.05 (4)	H11A—N1—H11B	116 (3)
N2—Zn1—Cl2	108.45 (4)	C2—N4—H14A	118 (2)
Cl3—Zn1—Cl2	116.50 (3)	C2—N4—H14B	118 (2)
N2—Zn1—Cl4	104.43 (4)	H14A—N4—H14B	122 (3)
Cl3—Zn1—Cl4	109.82 (3)	C1—N5—H15A	118 (2)
Cl2—Zn1—Cl4	109.86 (2)	C1—N5—H15B	120 (2)
C1—N2—C2	118.68 (14)	H15A—N5—H15B	121 (3)
C1—N2—Zn1	121.78 (11)	N3—C3—H3A	109.5
C2—N2—Zn1	117.15 (11)	N3—C3—H3B	109.5
C2—N3—C4	122.38 (15)	H3A—C3—H3B	109.5
C2—N3—C3	121.16 (16)	N3—C3—H3C	109.5
C4—N3—C3	116.02 (15)	H3A—C3—H3C	109.5
N5—C1—N1	119.29 (16)	H3B—C3—H3C	109.5
N5—C1—N2	118.71 (16)	N3—C4—H4A	109.5
N1—C1—N2	121.86 (15)	N3—C4—H4B	109.5
N3—C2—N4	120.89 (16)	H4A—C4—H4B	109.5
N3—C2—N2	119.69 (15)	N3—C4—H4C	109.5
N4—C2—N2	119.13 (15)	H4A—C4—H4C	109.5
C1—N1—H11A	121 (2)	H4B—C4—H4C	109.5
C1—N1—H11B	124 (2)
Zn1—N2—C1—N5	−8.2 (2)	C4—N3—C2—N4	164.46 (17)
Zn1—N2—C1—N1	167.41 (13)	C3—N3—C2—N4	−7.6 (3)
Zn1—N2—C2—N4	111.06 (16)	N3—C2—N2—C1	134.46 (17)
Zn1—N2—C2—N3	−62.77 (19)	N1—C1—N2—C2	−30.7 (2)
Cl4—Zn1—N2—C2	−107.20 (12)	N5—C1—N2—C2	153.77 (16)
Cl2—Zn1—N2—C2	9.91 (13)	N3—C2—N4—N2	173.8 (3)
Cl3—Zn1—N2—C2	136.37 (11)	N2—C1—N1—N5	−175.5 (3)