Potassium carbamoyldi­cyano­methanide

The crystal structure of the title compound, K[(CN)₂CC(O)NH₂)] or K⁺·C₄H₂N₃O^-, conventionally abbreviated as Kcdm, where cdm is carbamoyldi­cyano­methanide, is described. The bond lengths and angles of the cdm cation are comparable to those reported previously for [M(cdm)₂(H₂O)₄]·2H₂O (M = Ni, Mn and Co). The K atoms are coordinated to four nitrile N atoms and two carbonyl O atoms in a distorted trigonal prismatic fashion, with two further N atoms semicoordinated through the centers of two prism side faces. This coordination leads to the formation of mixed anion-cation sheets parallel to the ab plane, which are joined together via hydrogen-bonding interactions. The cdm anion is potentially useful for the formation of transition metal coordination polymers, in which magnetic superexchange could occur through a bidentate cdm bridge. Kcdm provides a model compound by which the molecular geometry of the cdm anion can be analyzed.

S1. Comment

The structural and magnetic properties of coordination polymers containing cyano-based anions have been increasingly studied over the past decade. The dicyanamide (dca) anion, N(CN)₂⁻, has been shown to be an effective magnetic superexchange ligand, with Ni(dca)₂ exhibiting ferromagnetism at 21 K (Kurmoo & Kepert, 1998). A logical extension of this research is to include cyanocarbon anions as molecular building blocks for the construction of magnetic solids. Tricyanomethanide (tcm), C(CN)₃⁻, is one of simplest cyanocarbon anions that is capable of forming polymeric structures. The M(tcm)₂ (M = Cu, Mn and Zn) crystal structures are characterized by the interpenetration of two identical rutile-like lattices, in which the tcm anion is µ₃-bonded to three M^II ions (Batten et al., 1991; Manson et al., 1998; Hoshino et al., 1999). The carbamoyldicyanomethanide (cdm) anion, (CN)₂CC(O)NH₂⁻, is a derivative of tcm in which one nitrile group is replaced with C(O)NH₂. Cdm is therefore a candidate for forming coordination polymers (Trofimenko et al., 1962). Unfortunately, structures where the cdm anion bridges transition metal centers are yet unknown. Single crystal X-ray diffraction studies have revealed that Ni (Shi et al., 2001), Co (Shi, Yin et al., 2002) and Mn (Schlueter et al., 2003) form isomorphous mononuclear complexes, [M(cdm)₂(H₂O)₄]·2H₂O, in which the metal atom is octahedrally coordinated by the nitrile N atoms of two cdm anions and the O atoms of four water molecules. In this study, the crystal structure of Kcdm was examined in an attempt to understand why tcm has a tendency to form polymeric networks while cdm preferentially forms molecular species.

The geometry of the cdm anion in the Kcdm salt is essentially identical to that found in [M(cdm)₂(H₂O)₄]·2H₂O. The anion is very nearly planar (r.m.s. deviation 0.009 Å), with the greatest deviation from planarity being 0.017 (1) Å me thanide atom C3 (Fig. 1). As expected, the C—C—C angles about the methanide C atom [117.6 (1), 120.2 (1) and 122.2 (1)°] sum to 360.0°, indicating nearly complete sp² hybridization. A distorted trigonal prismatic inner coordination sphere exists about the potassium cation, consisting of two carbonyl O atoms and four nitrile N atoms of six different cdm anions. The outer coordination sphere of potassium contains one amide and one nitrile N atom whose K—N distances are about 0.4 Å longer than the inner-sphere K—N bond lengths.

The plane of the cdm ligand lies at an angle of 26.79 (2)° with respect to the ac plane. The angle between cdm molecular planes related by the screw axis is twice as large. The potassium coordination links the cdm anions into bi-bridged sheets parallel to the ab plane (Fig. 2). Intersheet hydrogen bonding is observed between amine atom H3A and the carbonyl O atoms. The second amine H atom, H3B, has a significantly weaker hydrogen-bonding interaction because of the lack of good acceptor sites, with the nearest acceptor being nitrile atom N2.

The geometry of the dicyanomethanide moiety of the cdm anion is essentially identical to that observed in Ktcm (Witt & Britton, 1971). The reason that the cdm anion has not formed polymeric structures with transition metals through bidentate bridging of the nitrile groups may simply be a result of the subtle steric effects related to the carbamoyl moiety. It is noted that cdm forms a two-dimensional polymeric stucture with europium (Shi, Xu et al., 2002), but in this case, the bridge is completed through the bonding of the carbonyl O atom to the oxophilic rare earth atom. Crystallization in non-aquous solvents may be necessary to form polymeric transition metal complexes with cdm because the formation of [M(cdm)₂(H₂O)₄]·2H₂O compounds appears to be thermodynamically favorable as a result of cdm having a better hydrogen-bonding capability than tcm.

S2. Experimental

Potassium carbamoyldicyanomethanide was prepared by a modification of the procedure described by Trofimenko et al. (1962). Malononitrile (6.6 g, 0.1 mol, Aldrich) was added to a slurry containing powdered potassium cyanate (8.1 g, 0.1 mol, Aldrich) in N,N-dimethylformamide (150 ml). After heating at reflux for 1 h, the resulting red–orange solution was filtered while hot. The solution was cooled to 273 K overnight. Diethyl ether (100 ml) was added to precipitate a yellow powder that was recovered by filtration. The crude product was recrystallized by dissolution in warm methanol (1.5 l) followed by precipitation with hexane (1 l). Crystals of Kcdm were formed while attempting to crystallize an adduct of [Mn(cdm)₂(H₂O)₄]·2H₂O in which the coordinated water molecules would be replaced with pyrimidine. Pyrimidine (340 mg, 4 mmol, Aldrich) was added to a solution of Kcdm (588 mg, 4 mmol) in water (20 ml). This solution was layered on top of a solution of manganese(II) nitrate (2 mmol, 358 mg, Aldrich) in water (10 ml). After one month, colorless rod-like crystals of Kcdm were collected, and after these were removed, crystals of [Mn(cdm)₂(H₂O)₄]·2H₂O formed from the filtrate (Schlueter et al., 2003).

S3. Refinement

H atoms were placed geometrically and refined with a riding model, with U_iso(H) values constrained to be 1.2U_eq of the carrier atom.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. A view of the molecular structure of Kcdm, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probablility level, and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram for Kcdm, projected approximately along the b axis. Displacement ellipsoids are drawn at the 20% probability level. Intersheet hydrogen bonds are depicted as dashed lines.

Potassium carbamoyldicyanomethanide

Crystal data

K^+·C4H2N3O^−	F(000) = 296
Mr = 147.19	Dx = 1.600 Mg m^−3
Monoclinic, P21/c	Melting point: 550 K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 8.2495 (3) Å	Cell parameters from 1719 reflections
b = 3.8591 (1) Å	θ = 3.4–28.1°
c = 19.2181 (6) Å	µ = 0.78 mm^−1
β = 93.168 (1)°	T = 298 K
V = 610.89 (3) Å^3	Rod, colorless
Z = 4	0.50 × 0.08 × 0.06 mm

Data collection

Siemens SMART CCD area detector diffractometer	1448 independent reflections
Radiation source: fine-focus sealed tube	1286 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.027
area detector ω scans	θmax = 28.3°, θmin = 2.1°
Absorption correction: integration (Sheldrick, 2001)	h = −10→10
Tmin = 0.801, Tmax = 0.958	k = −5→5
5795 measured reflections	l = −25→25

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.027	H-atom parameters constrained
wR(F^2) = 0.072	w = 1/[σ^2(Fo^2) + (0.0328P)^2 + 0.1783P] where P = (Fo^2 + 2Fc^2)/3
S = 1.10	(Δ/σ)max = 0.020
1448 reflections	Δρmax = 0.27 e Å^−3
83 parameters	Δρmin = −0.20 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.038 (4)

Special details

Experimental. The data collection nominally covered over a hemisphere of reciprocal space, by a combination of four sets of exposures; each set had a different ϕ angle for the crystal and each exposure covered 0.3° in ω. The crystal-to-detector distance was 4.97 cm. Coverage of the unique set was over 96% complete to at least 28° in θ and greater than 99% complete to at least 27° in θ. Crystal decay was monitored by repeating the initial 50 frames at the end of data collection and analyzing the duplicate reflections. Decay was found to be less than 1%, and no decay correction was therefore applied.

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
K1	0.65764 (4)	0.83397 (8)	0.09807 (2)	0.03234 (14)
O1	0.48284 (11)	0.3237 (3)	0.16159 (5)	0.0311 (2)
C1	0.25917 (17)	0.5604 (4)	0.06215 (7)	0.0291 (3)
C2	0.04523 (17)	0.3646 (4)	0.13496 (7)	0.0302 (3)
C3	0.21060 (16)	0.4062 (4)	0.12382 (7)	0.0261 (3)
C4	0.33595 (16)	0.2848 (3)	0.17294 (7)	0.0241 (3)
N1	0.30456 (19)	0.6841 (4)	0.01222 (7)	0.0431 (3)
N2	−0.08969 (17)	0.3260 (4)	0.14582 (8)	0.0462 (4)
N3	0.29245 (15)	0.1317 (3)	0.23191 (6)	0.0337 (3)
H3A	0.3657	0.0598	0.2621	0.040*
H3B	0.1914	0.1056	0.2395	0.051*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K1	0.0333 (2)	0.0285 (2)	0.0358 (2)	−0.00062 (12)	0.00734 (13)	0.00153 (12)
O1	0.0216 (5)	0.0415 (6)	0.0304 (5)	−0.0005 (4)	0.0023 (4)	−0.0011 (4)
C1	0.0301 (7)	0.0293 (7)	0.0278 (7)	0.0005 (6)	−0.0004 (5)	−0.0015 (5)
C2	0.0289 (7)	0.0334 (7)	0.0280 (7)	0.0017 (6)	−0.0015 (5)	0.0003 (5)
C3	0.0237 (6)	0.0304 (7)	0.0240 (6)	−0.0003 (5)	0.0004 (5)	0.0005 (5)
C4	0.0239 (6)	0.0257 (6)	0.0228 (6)	0.0002 (5)	0.0019 (5)	−0.0041 (5)
N1	0.0541 (9)	0.0440 (8)	0.0316 (7)	−0.0003 (7)	0.0065 (6)	0.0060 (6)
N2	0.0270 (7)	0.0606 (10)	0.0511 (8)	0.0003 (6)	0.0032 (6)	0.0038 (7)
N3	0.0271 (6)	0.0469 (8)	0.0272 (6)	0.0007 (5)	0.0015 (5)	0.0087 (5)

Geometric parameters (Å, º)

K1—O1^i	2.7084 (11)	C1—C3	1.4043 (19)
K1—O1	2.7645 (11)	C2—N2	1.153 (2)
K1—N1^ii	2.8499 (13)	C2—C3	1.4017 (19)
K1—N2^iii	2.9294 (15)	C3—C4	1.4396 (18)
K1—N1^iv	2.9426 (14)	C4—N3	1.3443 (18)
K1—N2^v	2.9696 (15)	N3—H3A	0.8600
O1—C4	1.2521 (16)	N3—H3B	0.8600
C1—N1	1.1525 (19)
K1···N1	3.3180 (16)	K1···N3^vi	3.3626 (12)
O1^i—K1—O1	89.67 (3)	C3—C1—K1^iv	129.10 (9)
O1^i—K1—N1^ii	87.86 (4)	N2—C2—C3	178.14 (16)
O1—K1—N1^ii	150.99 (4)	C2—C3—C1	120.20 (12)
O1^i—K1—N2^iii	78.10 (4)	C2—C3—C4	122.17 (12)
O1—K1—N2^iii	134.66 (4)	C1—C3—C4	117.60 (12)
N1^ii—K1—N2^iii	72.83 (4)	O1—C4—N3	120.38 (12)
O1^i—K1—N1^iv	151.51 (4)	O1—C4—C3	120.91 (12)
O1—K1—N1^iv	84.99 (4)	N3—C4—C3	118.71 (12)
N1^ii—K1—N1^iv	83.54 (4)	C1—N1—K1^ii	160.62 (13)
N2^iii—K1—N1^iv	124.34 (4)	C1—N1—K1^iv	111.75 (11)
O1^i—K1—N2^v	134.70 (4)	K1^ii—N1—K1^iv	83.54 (4)
O1—K1—N2^v	76.56 (4)	C1—N1—K1	88.56 (10)
N1^ii—K1—N2^v	123.84 (4)	K1^ii—N1—K1	97.29 (4)
N2^iii—K1—N2^v	81.71 (4)	K1^iv—N1—K1	110.58 (5)
N1^iv—K1—N2^v	70.95 (4)	C2—N2—K1^viii	134.76 (13)
C4—O1—K1^vii	122.65 (9)	C2—N2—K1^ix	121.78 (12)
C4—O1—K1	134.09 (9)	K1^viii—N2—K1^ix	81.71 (4)
K1^vii—O1—K1	89.67 (3)	C4—N3—H3A	120.0
N1—C1—C3	177.61 (16)	C4—N3—H3B	120.0
N1—C1—K1^iv	50.62 (9)	H3A—N3—H3B	120.0
K1^vii—O1—C4—N3	87.96 (14)	C1—C3—C4—O1	1.7 (2)
K1—O1—C4—N3	−144.36 (11)	C2—C3—C4—N3	−1.1 (2)
K1^vii—O1—C4—C3	−92.81 (13)	C1—C3—C4—N3	−179.05 (13)
K1—O1—C4—C3	34.87 (19)	K1^iv—C1—N1—K1^ii	140.3 (4)
C2—C3—C4—O1	179.66 (13)	K1^iv—C1—N1—K1	−111.63 (8)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3A···O1^x	0.86	2.08	2.9358 (15)	171
N3—H3B···N2^xi	0.86	2.63	3.185 (2)	123

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