Bis­(cyano­guanidine)silver(I) nitrate-cyanoguanidine (1/1)

In the title compound, [Ag(C₂H₄N₄)₂](NO₃)·C₂H₄N₄, the Ag atom is surrounded by three cyano­guanidine (cnge) mol­ecules. Two monodentate cnge mol­ecules form strong covalent Ag-N bonds of 2.210 (7) and 2.266 (6) Å through their nitrile N atoms. The third cnge mol­ecule is located in a vacant crystal site and is only weakly coordinated to the Ag atom as a solvate molecule. Inter- and intramolecular hydrogen bonds play an important role in the crystal packing.

S1. Comment

Cyanoguanidine (cnge; Scheme 1), which is the dimeric form of cyanamide (H₂NCN) and a commercially important compound, is a versatile precursor for the syntheses of organonitrogen compounds; its coordination chemistry has been intensively studied because of its differing functional groups. Cnge readily coordinates to the later transition metals, and the coordination typically occurs through the nitrile N atom. Complexes with copper(II) (Chiesi et al., 1971; Hubberstey et al., 1997, 1993), copper(I) (Hubberstey et al., 1996), zinc(II) (Pickardt & Kühn, 1996; Harrison et al., 2001), cadmium(II) and mercury (II) (Pickardt & Kühn, 1996), and nickel(II) (Meyer et al., 2000) have been reported, but no crystal structure of a silver–cnge complex has been known up to now.

A labelled displacement ellipsoid plot of the coordination motifs of [Ag(C₂H₄N₄)₃]NO₃ is shown in Fig. 1, and bond distances and angles are given in Table 1. The Ag atom is surrounded by three cnge molecules, two of which behave as monodentate ligands through nitrile N atoms. The Ag—N(21) and Ag—N(11) distances are 2.210 (7) and 2.266 (6) Å, respectively, and the N(11)—Ag(1)—N(12) angle is 175.5 (2)°, almost linear, a common geometry in 2-coordinate Ag^I complexes. The interactions of the Ag atom with two N31 atoms, viz. one at 2.596 (7) Å within the asymmetric unit and the other at 2.681 (7) Å (symmetry operator: x, -1 + y, z), are longer than the sum of the covalent distances and much weaker. Thus, the third cnge molecule is almost uncoordinated and essentially located in a vacant crystal site. Typical Ag—N distances are 2.11–2.16 Å for 2-coordinate silver in AgN(CN)₂ (Britton, 1990) and silver-pyzazolate complexes (Mohamed & Fakler Jr., 2002), 2.22 Å for 3-coordinate silver in AgC(CN)₃ (Konnert & Britton, 1966), and 2.23 Å for 4-coordinate silver in AgC(CN)₂NO (Chow & Britton, 1974) and silver 1,10-decanedinitrile complexes (Carlucci et al., 1999). The elongated 2-coordinate Ag—N distances are probably caused by the effects of four further Ag···N interactions [two with N31, as mentioned above, and two with N11, viz. 2.795 (7) and 2.860 (7) Å: symmetry operators 1/2 - x, -1/2 + y, 1/2 - z and 1/2 - x, 1/2 + y, 1/2 - z respectively). The Ag atom is coplanar with the three surrounding N atoms but not with the three cnge molecules. The angles Ag—N11—C12 [140.2 (5)°] and Ag—N21—C22 [167.6 (6)°] are smaller than those expected for a transition metal–nitrile interaction (180°) because of the hydrogen bonding (N16—H···N31 and N35—H···N21; Fig. 2 and Table 2). Such a distortion of the coordination geometry has also been observed in [Cu(OAc)₂(cnge)₂]₂ (Begley et al., 1993).

The hydrogen bonds are listed in Table 2. cnge is a hydrogen-bonding ligand that may act both as a donor (amino, NH₂) and as an acceptor (cyanimino, ═N—C≡N). The N—H donor systems from both amino groups have close contacts to the nitrate anion [Fig. 2; hydrogen bond type (i)], and there is also hydrogen bonding between imino and amino N atoms of neighboring molecules [Fig. 2; hydrogen bond type (ii)]. In addition, there is intramolecular hydrogen bonding between amino and nitrile N atoms [Fig. 2; hydrogen bond type (iii)]. The above- mentioned three hydrogen-bonding modes have been reviewed for cnge coordination compounds by Hubberstey et al. (1997). The overall hydrogen bonding promotes the two-dimensional sheet structure and stabilizes the crystal architecture.

All three cnge molecules are planar within crystallographic resolution, and the maximum distances from the least-squares plane are 0.025 (N11—N16 ligand), 0.008 (N21—N26 ligand) and 0.013 (N31—N36 ligand) Å. The individual coordination does not severely affect the structural parameters of cnge (Fernanda et al., 1993). The shortest Ag—Ag distance along b is 3.648 (1) Å, parallel to the 2₁ axis. The structure as a whole consists of layers stacked along the b direction, which is also the direction of fast crystal growth.

S2. Experimental

[Ag(C₂H₄N₄)₃]NO₃ was prepared by mixing AgNO₃ (34.0 mg, 0.2 mmol) and H₂NCN (cyanamide; Aldrich; 50.4 mg, 1.2 mmol) in diethylether (10 ml), yielding a colorless solution. Slow addition of hexane caused the complex to crystallize as long colorless needles (Scheme 2). These were separated by filtration, washed with diethyl ether and hexane, and dried in a desiccator over P₂O₅. An IR spectrum indicated a nitrile unit (major absorption at 2150 cm^-1) and a series of N—H groups in the range 3200–3450 cm^-1; the elemental analysis agrees with the title composition.

S3. Refinement

All H atoms were found from ΔF maps and were refined freely, with all N—H bond distances restrained to be equal within an effective standard deviation of 0.02 Å (SADI instruction in SHELXL97). H atoms were assigned a common isotropic displacement parameter.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP97 and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 (Sheldrick, 1990).

Figures

	Fig. 1. ORTEP drawing of the title compound, with thermal ellipsoids scaled at the 50% probability level for non-H atoms.
	Fig. 2. Crystal packing for the title compound, showing the inter- and intra-molecular hydrogen bonding and hydrogen-bonding type.

Bis(cyanoguanidine)silver(I) nitrate cyanoguanidine

Crystal data

[Ag(C2H4N4)2](NO3)·C2H4N4	F(000) = 840
Mr = 422.16	Dx = 1.921 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 9648 reflections
a = 15.526 (4) Å	θ = 2.6–28.3°
b = 3.6482 (9) Å	µ = 1.42 mm^−1
c = 25.797 (6) Å	T = 293 K
β = 92.519 (6)°	Needle, colorless
V = 1459.8 (6) Å^3	0.15 × 0.05 × 0.02 mm
Z = 4

Data collection

Bruker AXS Apex CCD diffractometer	3609 independent reflections
Radiation source: fine-focus sealed tube	1818 reflections with I > \2s(I)
Graphite monochromator	Rint = 0.095
ω scans	θmax = 28.3°, θmin = 2.6°
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996)	h = −20→20
Tmin = 0.746, Tmax = 0.989	k = −4→4
9648 measured reflections	l = −34→22

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)] = 0.065	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.206	Only H-atom coordinates refined
S = 0.87	w = 1/[σ^2(Fo^2)] where P = (Fo^2 + 2Fc^2)/3
3609 reflections	(Δ/σ)max < 0.001
245 parameters	Δρmax = 0.78 e Å^−3
66 restraints	Δρmin = −0.53 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
Ag	0.24420 (4)	0.5273 (2)	0.18740 (2)	0.0587 (3)
N11	0.1528 (4)	0.5410 (17)	0.2535 (2)	0.0430 (15)
C12	0.0819 (5)	0.6098 (19)	0.2612 (2)	0.0333 (16)
N13	0.0032 (4)	0.6786 (18)	0.2738 (2)	0.0372 (14)
C14	−0.0483 (5)	0.838 (2)	0.2380 (2)	0.0357 (16)
N15	−0.1313 (4)	0.890 (2)	0.2488 (3)	0.0507 (18)
H11	−0.161 (4)	0.964 (19)	0.225 (2)	0.041 (7)*
H12	−0.149 (4)	0.81 (2)	0.2746 (17)	0.041 (7)*
N16	−0.0243 (4)	0.946 (2)	0.1919 (2)	0.0446 (16)
H13	0.024 (2)	0.91 (2)	0.184 (3)	0.041 (7)*
H14	−0.055 (4)	1.051 (18)	0.172 (3)	0.041 (7)*
N21	0.3415 (4)	0.5045 (19)	0.1275 (3)	0.0537 (18)
C22	0.3969 (4)	0.5540 (19)	0.0996 (3)	0.0347 (16)
N23	0.4531 (4)	0.5967 (16)	0.0641 (2)	0.0365 (14)
C24	0.5302 (4)	0.7412 (19)	0.0769 (2)	0.0296 (14)
N25	0.5549 (4)	0.843 (2)	0.1242 (2)	0.0436 (16)
H21	0.602 (2)	0.916 (19)	0.130 (3)	0.041 (7)*
H22	0.524 (4)	0.86 (2)	0.147 (2)	0.041 (7)*
N26	0.5843 (4)	0.7850 (19)	0.0396 (2)	0.0382 (14)
H23	0.631 (2)	0.868 (19)	0.043 (3)	0.041 (7)*
H24	0.567 (4)	0.76 (2)	0.0107 (13)	0.041 (7)*
N31	0.1501 (4)	1.0103 (18)	0.1374 (2)	0.0491 (17)
C32	0.1228 (5)	1.0517 (19)	0.0959 (3)	0.0370 (16)
N33	0.0854 (4)	1.0975 (17)	0.0493 (2)	0.0399 (15)
C34	0.1290 (4)	1.256 (2)	0.0112 (3)	0.0322 (15)
N35	0.2099 (4)	1.3840 (19)	0.0187 (2)	0.0426 (16)
H31	0.223 (5)	1.473 (18)	−0.0077 (17)	0.041 (7)*
H32	0.229 (5)	1.39 (2)	0.0474 (14)	0.041 (7)*
N36	0.0908 (4)	1.282 (2)	−0.0348 (2)	0.0451 (16)
H33	0.111 (5)	1.36 (2)	−0.0599 (19)	0.041 (7)*
H34	0.045 (3)	1.19 (2)	−0.037 (3)	0.041 (7)*
O1	0.8457 (3)	0.3640 (16)	0.1292 (2)	0.0503 (14)
O2	0.7356 (4)	0.0943 (15)	0.1616 (2)	0.0502 (14)
N	0.7724 (4)	0.2361 (17)	0.1239 (2)	0.0370 (14)
O3	0.7329 (3)	0.2463 (19)	0.08107 (19)	0.0556 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag	0.0399 (4)	0.0991 (7)	0.0378 (4)	0.0049 (4)	0.0106 (2)	0.0029 (3)
N11	0.036 (3)	0.046 (4)	0.048 (4)	0.004 (3)	0.009 (3)	0.013 (3)
C12	0.036 (4)	0.043 (4)	0.021 (3)	−0.011 (3)	−0.005 (3)	0.002 (3)
N13	0.031 (3)	0.050 (4)	0.031 (3)	−0.006 (3)	0.004 (2)	0.007 (3)
C14	0.037 (4)	0.043 (4)	0.027 (3)	−0.002 (3)	0.005 (3)	0.001 (3)
N15	0.034 (3)	0.077 (6)	0.042 (4)	−0.001 (3)	0.005 (3)	0.018 (3)
N16	0.041 (4)	0.063 (5)	0.030 (3)	0.005 (4)	0.007 (3)	0.010 (3)
N21	0.045 (4)	0.065 (5)	0.052 (4)	−0.005 (4)	0.013 (3)	0.000 (3)
C22	0.034 (4)	0.038 (4)	0.031 (3)	−0.005 (3)	−0.003 (3)	−0.001 (3)
N23	0.031 (3)	0.047 (4)	0.032 (3)	−0.010 (3)	0.003 (2)	−0.007 (2)
C24	0.037 (4)	0.028 (4)	0.024 (3)	−0.002 (3)	0.002 (3)	−0.001 (3)
N25	0.035 (4)	0.063 (5)	0.034 (3)	−0.013 (3)	0.007 (3)	−0.014 (3)
N26	0.028 (3)	0.055 (4)	0.031 (3)	−0.010 (3)	0.004 (3)	0.002 (3)
N31	0.050 (4)	0.061 (5)	0.036 (3)	−0.010 (3)	0.002 (3)	0.007 (3)
C32	0.031 (3)	0.034 (4)	0.046 (4)	−0.004 (3)	0.009 (3)	0.004 (3)
N33	0.035 (3)	0.050 (4)	0.034 (3)	−0.011 (3)	0.001 (3)	0.015 (3)
C34	0.031 (3)	0.027 (4)	0.039 (4)	−0.002 (3)	0.004 (3)	−0.005 (3)
N35	0.042 (4)	0.049 (4)	0.037 (3)	−0.009 (3)	0.001 (3)	0.002 (3)
N36	0.040 (4)	0.064 (5)	0.030 (3)	−0.006 (4)	−0.003 (3)	0.008 (3)
O1	0.037 (3)	0.065 (4)	0.048 (3)	−0.015 (3)	−0.006 (2)	0.008 (3)
O2	0.047 (3)	0.063 (4)	0.042 (3)	−0.006 (3)	0.010 (2)	0.013 (2)
N	0.039 (3)	0.037 (4)	0.035 (3)	−0.002 (3)	0.002 (3)	0.007 (3)
O3	0.042 (3)	0.082 (5)	0.042 (3)	−0.022 (3)	−0.009 (3)	0.012 (3)

Geometric parameters (Å, º)

Ag—N21	2.210 (7)	N25—H21	0.79 (2)
Ag—N11	2.266 (6)	N25—H22	0.78 (2)
Ag—N31	2.596 (7)	N26—H23	0.79 (2)
N11—C12	1.155 (9)	N26—H24	0.79 (2)
C12—N13	1.302 (9)	N31—C32	1.144 (9)
N13—C14	1.328 (8)	C32—N33	1.323 (9)
C14—N16	1.322 (9)	N33—C34	1.350 (8)
C14—N15	1.344 (9)	C34—N36	1.307 (9)
N15—H11	0.79 (2)	C34—N35	1.345 (9)
N15—H12	0.79 (2)	N35—H31	0.79 (2)
N16—H13	0.79 (2)	N35—H32	0.79 (2)
N16—H14	0.79 (2)	N36—H33	0.79 (2)
N21—C22	1.159 (9)	N36—H34	0.79 (2)
C22—N23	1.301 (9)	O1—N	1.233 (7)
N23—C24	1.336 (8)	O2—N	1.260 (7)
C24—N26	1.314 (8)	N—O3	1.239 (7)
C24—N25	1.318 (8)
N21—Ag—N11	175.5 (2)	C24—N25—H21	120 (6)
N21—Ag—N31	93.8 (2)	C24—N25—H22	125 (6)
N11—Ag—N31	90.1 (2)	H21—N25—H22	115 (8)
C12—N11—Ag	140.2 (5)	C24—N26—H23	125 (6)
N11—C12—N13	175.4 (7)	C24—N26—H24	118 (5)
C12—N13—C14	117.1 (6)	H23—N26—H24	116 (8)
N16—C14—N13	124.8 (7)	C32—N31—Ag	137.0 (6)
N16—C14—N15	117.1 (7)	N31—C32—N33	175.7 (8)
N13—C14—N15	118.1 (6)	C32—N33—C34	120.2 (6)
C14—N15—H11	115 (6)	N36—C34—N35	119.3 (7)
C14—N15—H12	120 (6)	N36—C34—N33	118.1 (6)
H11—N15—H12	124 (8)	N35—C34—N33	122.6 (6)
C14—N16—H13	119 (6)	C34—N35—H31	107 (6)
C14—N16—H14	123 (6)	C34—N35—H32	118 (6)
H13—N16—H14	118 (8)	H31—N35—H32	134 (8)
C22—N21—Ag	167.6 (6)	C34—N36—H33	126 (6)
N21—C22—N23	173.5 (7)	C34—N36—H34	115 (6)
C22—N23—C24	119.7 (6)	H33—N36—H34	119 (8)
N26—C24—N25	118.3 (6)	O1—N—O3	120.4 (6)
N26—C24—N23	117.5 (6)	O1—N—O2	121.1 (6)
N25—C24—N23	124.1 (6)	O3—N—O2	118.5 (6)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N15—H11···O2^i	0.79 (2)	2.30 (3)	3.079 (9)	169 (8)
N15—H12···O2^ii	0.79 (2)	2.31 (3)	3.075 (8)	165 (7)
N16—H13···N31	0.79 (2)	2.37 (4)	3.113 (9)	157 (7)
N16—H14···O1^i	0.79 (2)	2.18 (3)	2.954 (8)	170 (8)
N25—H21···O2^iii	0.79 (2)	2.29 (3)	3.067 (8)	170 (8)
N25—H21···O3^iii	0.79 (2)	2.72 (5)	3.363 (8)	140 (7)
N25—H22···N13^ii	0.78 (2)	2.39 (5)	3.073 (8)	146 (7)
N26—H23···O3^iii	0.79 (2)	2.29 (4)	3.014 (8)	154 (7)
N26—H24···N23^iv	0.79 (2)	2.34 (5)	3.048 (8)	151 (8)
N35—H31···O3^v	0.79 (2)	2.28 (3)	3.071 (8)	176 (8)
N35—H32···N21^iii	0.79 (2)	2.68 (4)	3.427 (10)	160 (7)
N36—H33···O1^v	0.79 (2)	2.17 (3)	2.962 (8)	173 (8)
N36—H34···N33^vi	0.79 (2)	2.29 (3)	3.075 (9)	176 (8)

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