Crystal structure of poly[bis-(μ-2-amino-4,5-di-cyano-imidazolato-κ(2) N (1):N (3))-trans-bis-(N,N'-di-methyl-formamide-κO)cadmium].

In the title structure, [Cd(C5H2N5)2(C3H7NO)2] n or [Cd(adci)2(DMF)2] n , the Cd(2+) ion is located on a twofold rotation axis and is six-coordinated in a CdN4O2 manner by four imidazole N atoms of four symmetry-related 2-amino-4,5-di-cyano-imidazolate (adci) anions in the equatorial plane and by two O atoms of symmetry-related N,N-di-methyl-formamide (DMF) ligands in axial positions. The adci(-) anions bridge adjacent Cd(2+) ions [shortest Cd⋯Cd separation = 6.733 (3) Å] into a layered coordination polymer extending parallel to (001). The primary amino group and the non-coordinating cyano groups of adci(-) anions are involved in hydrogen-bonding inter-actions with DMF ligands to stabilize the crystal structure.

Chemical context

Porous materials such as <span class="Chemical">metaln>-organic frameworks (MOFs) combining advantages of both organic and inorganic components have emerged as a unique class of crystalline solid-state materials today due to their potential applications in gas adsorption and separation (Collins & Zhou, 2007 ▸), catalysis (Gu et al., 2012 ▸) and analytical chemistry (Mondal et al., 2013 ▸). As a branch of MOFs, <span class="Chemical">zeolitic imidazolate frameworks (ZIFs), which are topologically related to inorganic zeolites, commonly reveal high thermal and chemical stability (Eddaoudi et al., 2015 ▸). Bridging N-<span class="Species">donor ligands such as 2-substituted 4,5-di­cyano­imidazole (dci) mol­ecules are often used to synthesize ZIFs (Sava et al., 2009 ▸; Mondal et al., 2014 ▸). In addition, the cyano group of dci can generate carboxyl­ate- (Orcajo et al., 2014 ▸) or tetra­zole-based (Xiong et al., 2002 ▸) ligands by in-situ ligand reactions.

We chose a rigid planar ligand, viz. 2-amino-4,5-di­cyano­imidazole (<span class="Chemical">adcin>), and Cd2+ that exhibits strong coordination capabilities for imidazolates, to prepare new <span class="Chemical">metal-organic <span class="Chemical">polymers and report here the structure of the title compound, [Cd(C5H2N5)2(C3H7NO)2], or [Cd(adci)2(DMF)2] (DMF is di­methyl­formamide), (I).

Structural commentary

Complex (I) is a mononuclear <span class="Chemical">cadmiumn> coordination <span class="Chemical">polymer, in which the central Cd2+ ion exhibits a tetra­gonally distorted octa­hedral coordination environment (Fig. 1 ▸). The asymmetric unit of (I) comprises one Cd2+ ion located on a twofold <span class="Disease">rotation axis, one 2-amino-4,5-di­cyano­imidazolate ion and one DMF ligand, both in general positions. The Cd2+ ion has an N4O2 coordination set defined by four N atoms of four symmetry-related adci− anions in the equatorial plane and by two oxygen atoms of two symmetry-related DMF ligands in axial positions. The Cd—N bond lengths [2.339 (4) and 2.353 (4) Å] and Cd—O bond length [2.322 (4) Å] fall in normal ranges (Groom & Allen, 2014 ▸). Each adci− anion bridges two adjacent Cd2+ ions in a bis-monodentate mode through two imidazole N atoms whereas the DMF mol­ecules serve as terminal ligands. Thus, four Cd2+ ions and four bridging adci− ligands generate a square motif aligned parallel to (001), as shown in Fig. 2 ▸. The Cd⋯Cd distance along the edge of the square is 6.733 (3) Å, which is similar to previously reported structures (Li et al., 2010 ▸; Wang et al., 2010 ▸).

Figure 1

The coordination sphere around Cd2+ in the structure of (I), with displacement ellipsoids drawn at the 30% probability level. H atoms bonded to C and N atoms have been omitted for clarity. [Symmetry code: (A) 2 − x, y,  − z.].

Figure 2

The two-dimensional network in the structure of (I), viewed perpendicular to the ab plane. Colour key: Cd steel, N blue, H grey, C light grey ande O red.

Supra­molecular features

Complex (I) possesses various <span class="Chemical">hydrogenn>-bonding inter­actions (Table 1 ▸). The amino group and the non-coordinating <span class="Chemical">cyano N atoms are involved in <span class="Chemical">hydrogen-bonding inter­actions with DMF ligands to stabilize the crystal structure. In the 2D metal-organic network, inter­molecular N1—H1A⋯O1 hydrogen bonds between the primary amine group of adci− and the O atoms of an DMF ligand as well as C7—H7C⋯N5 inter­actions between the methyl C atoms of DMF and the non-coordinating N atoms of the cyano group of an adci− anion play a crucial role in directing and stabilizing the assembly of the supra­molecular structure (Kim et al., 2015 ▸; Sava et al., 2009 ▸), as shown in Fig. 3 ▸ a. The layers are packed together by weak C7—H7B⋯N4 inter­actions, involving the methyl C atom of DMF and another N atom of a cyano group (Fig. 3 ▸ b). The lengths of these three hydrogen bonds fall in or approach the range (3.2–4.0 Å) of weak hydrogen-bonding inter­actions (Desiraju, 1996 ▸; Steed & Atwood, 2000 ▸).

Table 1

Hydrogen-bond geometry (, )

DHA	DH	HA	D A	DHA
N1H1AO1i	0.86	2.45	3.187(6)	144
C7H7CN5i	0.96	2.68	3.429(12)	135
C7H7BN4ii	0.96	2.65	3.496(11)	148

Symmetry codes: (i) ; (ii) .

Figure 3

(a) View of two kinds of hydrogen bonds in the layers. Dashed lines represent C—H⋯N (green) and N—H⋯O (red) hydrogen bonds, respectively. (b) The crystal packing between the layers in the title structure. C—H⋯N hydrogen-bonding inter­actions are drawn as red dashed lines. [Symmetry codes: (a)  − x, − + y, z; (b)  − x,  + y, z; (c) x, −y, − + z].

Database survey

The cyano groups of the <span class="Chemical">dcin> ligands exhibit a strong electron-withdrawing effect. Consequently, the formation of anionic species is relatively straightforward (Prasad et al., 1999 ▸) and 4,5-di­cyano­imidazoles can be used in the preparation of coordination frameworks with different metal ions. However, reports on systems with 2-amino-4,5-di­cyano­imidazole, a novel rigid planar ligand with five potential coordination sites, are rather scarce. A search in the Cambridge Structural Database (Version 5.27, May 2014; Groom & Allen, 2014 ▸) for 4,5-di­cyano­imidazole revealed eleven complexes with 2-substituted 4,5-imidazole­dicarbo­nitrile ligands. An unprecedented SHG-active silver-containing MOF with a rare 103 topology has been reported (Yang et al., 2013 ▸), as well as the synthesis and fluorescent properties of a 3D hetero<span class="Chemical">metallic polymeric complex {[K[Cd(dci)2(H2O)6]Cl]} (Li et al., 2010 ▸), and of {[Zn2(IMDN)4(H2O)3]·3H2O3} and [Co(IMDN)2(H2O)2] (Hu et al., 2013 ▸) (IMDN is 2H-imidazole-4,5-dicarbo­nitrile) with chain structures. However, the coordination modes of the imidazoles in these complexes are different.

Synthesis and crystallization

Compound (I) was synthesized as follows: <span class="Chemical">adcin> (0.0266 g, 0.2 mmol) and <span class="Chemical">HNO3 (0.2 ml, 3.5 M in <span class="Chemical">DMF) were mixed in 2 ml DMF. After stirring for 0.5 h, Cd(NO3)2·4H2O (0.0308 g, 0.1 mmol) in 6 ml methanol was added dropwise. The mixture was further stirred for another hour and then filtrated. The filtrate was kept at ambient temperature. After about three weeks, yellow block-shaped crystals of (I) suitable for single X-ray diffraction were obtained. Yield: 0.0224 g (43% based on Cd). FT–IR (KBr, cm−1): 3436, 3346, 2930, 2217, 1658, 1525, 1486, 1444, 1385, 1328, 1305, 1115, 675.

Refinement

Crystal data, data collection and refinement details are summarized in Table 2 ▸. <span class="Chemical">Hydrogen atoms of the organic ligands were placed in idealized positions, with d(C—H) = 0.93 Å for sp 2-bound <span class="Disease">H atoms and U iso(H) = 1.2U eq(C), and d(C—H) = 0.96 Å for methyl H atoms and U iso(H) = 1.5U eq(C). <span class="Disease">H atoms of the amino group were located from a difference map and were refined with d(N—H) = 0.86 Å and U iso(H) = 1.2U eq(N).

Table 2

Experimental details

Crystal data
Chemical formula	[Cd(C5H2N5)2(C3H7NO)2]
M r	522.83
Crystal system, space group	Orthorhombic, P b c n
Temperature (K)	296
a, b, c ()	9.8438(2), 9.1897(2), 22.8948(4)
V (3)	2071.10(7)
Z	4
Radiation type	Mo K
(mm1)	1.10
Crystal size (mm)	0.18 0.12 0.10
Data collection
Diffractometer	Bruker SMART APEX CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2008 ▸)
T min, T max	0.854, 0.896
No. of measured, independent and observed [I > 2(I)] reflections	9497, 2386, 1741
R int	0.022
(sin /)max (1)	0.650
Refinement
R[F 2 > 2(F 2)], wR(F 2), S	0.042, 0.159, 1.07
No. of reflections	2353
No. of parameters	143
No. of restraints	96
H-atom treatment	H-atom parameters constrained
max, min (e 3)	1.71, 0.66

Computer programs: SMART and SAINT (Bruker, 2008 ▸), SHELXTL (Sheldrick, 2008 ▸), Mercury (Macrae et al. (2006 ▸) and DIAMOND (Brandenburg, 2006 ▸).

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S2056989015014516/wm5187sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989015014516/wm5187Isup2.hkl

CCDC reference: 1416545

Additional supporting information: crystallographic information; 3D view; checkCIF report

[Cd(C5H2N5)2(C3H7NO)2]	F(000) = 1048
Mr = 522.83	Dx = 1.677 Mg m−3
Orthorhombic, Pbcn	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2ab	θ = 3.5–27.5°
a = 9.8438 (2) Å	µ = 1.10 mm−1
b = 9.1897 (2) Å	T = 296 K
c = 22.8948 (4) Å	Block, yellow
V = 2071.10 (7) Å3	0.18 × 0.12 × 0.10 mm
Z = 4

Bruker SMART APEX CCD area-detector diffractometer	2386 independent reflections
Radiation source: fine-focus sealed tube	1741 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
phi and ω scans	θmax = 27.5°, θmin = 4.1°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −12→11
Tmin = 0.854, Tmax = 0.896	k = −11→11
9497 measured reflections	l = −29→26

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.159	H-atom parameters constrained
S = 1.07	w = 1/[σ2(Fo2) + (0.0999P)2 + 4.109P] where P = (Fo2 + 2Fc2)/3
2353 reflections	(Δ/σ)max < 0.001
143 parameters	Δρmax = 1.71 e Å−3
96 restraints	Δρmin = −0.65 e Å−3

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.

	x	y	z	Uiso*/Ueq
Cd1	1.0000	0.11224 (5)	0.7500	0.0180 (2)
N1	0.8425 (4)	0.4650 (5)	0.71416 (18)	0.0327 (10)
H1A	0.8043	0.5387	0.6978	0.039*
H1B	0.9243	0.4416	0.7050	0.039*
N2	0.8289 (4)	0.2699 (4)	0.78205 (17)	0.0269 (9)
C4	0.7391 (6)	0.1135 (5)	0.8626 (2)	0.0360 (12)
O1	0.9090 (4)	0.1297 (4)	0.65667 (17)	0.0449 (10)
N3	1.1454 (4)	−0.0840 (4)	0.72898 (18)	0.0224 (8)
C1	0.7732 (6)	0.3852 (5)	0.75474 (18)	0.0235 (10)
C2	0.7281 (5)	0.2249 (5)	0.81951 (18)	0.0258 (9)
C3	1.1166 (4)	−0.1874 (5)	0.6876 (2)	0.0234 (9)
N6	0.9069 (5)	0.1975 (7)	0.5616 (2)	0.0516 (13)
N5	0.8982 (5)	−0.2271 (6)	0.6291 (3)	0.0571 (15)
N4	0.7418 (7)	0.0315 (6)	0.9000 (2)	0.0651 (17)
C5	0.9921 (5)	−0.2038 (6)	0.6565 (2)	0.0308 (11)
C6	0.9373 (9)	0.2022 (10)	0.6174 (3)	0.0700 (18)
H6	0.9931	0.2801	0.6272	0.084*
C8	0.9492 (13)	0.3011 (17)	0.5189 (5)	0.122 (3)
H8A	0.9115	0.3947	0.5282	0.183*
H8B	0.9178	0.2711	0.4811	0.183*
H8C	1.0465	0.3073	0.5187	0.183*
C7	0.8193 (12)	0.0771 (13)	0.5425 (5)	0.113 (3)
H7A	0.8668	−0.0134	0.5472	0.169*
H7B	0.7959	0.0902	0.5022	0.169*
H7C	0.7381	0.0758	0.5657	0.169*

	U11	U22	U33	U12	U13	U23
Cd1	0.0143 (3)	0.0181 (3)	0.0217 (3)	0.000	0.00059 (15)	0.000
N1	0.023 (2)	0.032 (2)	0.043 (2)	0.0050 (18)	0.0117 (18)	0.0122 (19)
N2	0.0247 (19)	0.029 (2)	0.027 (2)	0.0072 (17)	0.0029 (15)	0.0036 (16)
C4	0.043 (3)	0.033 (3)	0.032 (2)	0.017 (2)	0.010 (2)	0.0043 (19)
O1	0.048 (2)	0.060 (2)	0.0270 (18)	0.0003 (19)	−0.0062 (17)	0.0052 (16)
N3	0.0155 (18)	0.024 (2)	0.0272 (18)	0.0032 (16)	0.0015 (16)	−0.0037 (17)
C1	0.022 (2)	0.024 (2)	0.024 (2)	0.0054 (17)	−0.0030 (16)	−0.0004 (16)
C2	0.029 (2)	0.026 (2)	0.023 (2)	0.0059 (19)	0.0019 (18)	0.0001 (17)
C3	0.021 (2)	0.021 (2)	0.028 (2)	−0.0009 (17)	0.0007 (18)	−0.0001 (17)
N6	0.052 (3)	0.076 (3)	0.027 (2)	0.014 (3)	−0.006 (2)	0.005 (2)
N5	0.036 (3)	0.069 (4)	0.067 (4)	−0.004 (3)	−0.019 (3)	−0.021 (3)
N4	0.100 (5)	0.054 (3)	0.041 (3)	0.030 (3)	0.022 (3)	0.018 (2)
C5	0.029 (3)	0.028 (3)	0.035 (3)	−0.0021 (19)	0.001 (2)	−0.008 (2)
C6	0.072 (4)	0.084 (4)	0.054 (3)	0.025 (4)	0.004 (3)	0.007 (3)
C8	0.143 (7)	0.138 (8)	0.085 (6)	0.023 (7)	0.016 (6)	0.036 (6)
C7	0.116 (7)	0.130 (7)	0.092 (6)	0.023 (6)	−0.024 (5)	−0.032 (6)

Cd1—O1i	2.322 (4)	C1—N3iii	1.342 (7)
Cd1—O1	2.322 (4)	C2—C3iii	1.371 (6)
Cd1—N2i	2.339 (4)	C3—C2ii	1.371 (6)
Cd1—N2	2.339 (4)	C3—C5	1.426 (6)
Cd1—N3i	2.353 (4)	N6—C6	1.311 (9)
Cd1—N3	2.353 (4)	N6—C8	1.427 (13)
N1—C1	1.366 (6)	N6—C7	1.469 (12)
N1—H1A	0.8600	N5—C5	1.136 (7)
N1—H1B	0.8600	C6—H6	0.9300
N2—C1	1.347 (6)	C8—H8A	0.9600
N2—C2	1.375 (6)	C8—H8B	0.9600
C4—N4	1.141 (6)	C8—H8C	0.9600
C4—C2	1.426 (6)	C7—H7A	0.9600
O1—C6	1.154 (8)	C7—H7B	0.9600
N3—C1ii	1.342 (7)	C7—H7C	0.9600
N3—C3	1.371 (6)
O1i—Cd1—O1	172.1 (2)	N3iii—C1—N1	123.0 (4)
O1i—Cd1—N2i	88.18 (14)	N2—C1—N1	122.3 (5)
O1—Cd1—N2i	86.91 (14)	C3iii—C2—N2	109.1 (4)
O1i—Cd1—N2	86.91 (14)	C3iii—C2—C4	124.4 (4)
O1—Cd1—N2	88.18 (14)	N2—C2—C4	126.3 (4)
N2i—Cd1—N2	103.5 (2)	C2ii—C3—N3	108.9 (4)
O1i—Cd1—N3i	95.71 (15)	C2ii—C3—C5	124.5 (4)
O1—Cd1—N3i	90.38 (15)	N3—C3—C5	126.6 (4)
N2i—Cd1—N3i	167.68 (14)	C6—N6—C8	125.3 (9)
N2—Cd1—N3i	88.42 (14)	C6—N6—C7	116.6 (8)
O1i—Cd1—N3	90.38 (15)	C8—N6—C7	118.0 (8)
O1—Cd1—N3	95.71 (15)	N5—C5—C3	173.8 (6)
N2i—Cd1—N3	88.42 (13)	O1—C6—N6	133.3 (9)
N2—Cd1—N3	167.68 (15)	O1—C6—H6	113.4
N3i—Cd1—N3	79.89 (19)	N6—C6—H6	113.4
C1—N1—H1A	120.0	N6—C8—H8A	109.5
C1—N1—H1B	120.0	N6—C8—H8B	109.5
H1A—N1—H1B	120.0	H8A—C8—H8B	109.5
C1—N2—C2	103.4 (4)	N6—C8—H8C	109.5
C1—N2—Cd1	129.4 (3)	H8A—C8—H8C	109.5
C2—N2—Cd1	122.0 (3)	H8B—C8—H8C	109.5
N4—C4—C2	174.4 (6)	N6—C7—H7A	109.5
C6—O1—Cd1	131.7 (6)	N6—C7—H7B	109.5
C1ii—N3—C3	103.9 (4)	H7A—C7—H7B	109.5
C1ii—N3—Cd1	132.5 (3)	N6—C7—H7C	109.5
C3—N3—Cd1	123.1 (3)	H7A—C7—H7C	109.5
N3iii—C1—N2	114.7 (4)	H7B—C7—H7C	109.5
O1i—Cd1—N2—C1	136.9 (5)	N2i—Cd1—N3—C3	−116.7 (4)
O1—Cd1—N2—C1	−36.8 (5)	N2—Cd1—N3—C3	78.0 (8)
N2i—Cd1—N2—C1	49.6 (4)	N3i—Cd1—N3—C3	59.4 (3)
N3i—Cd1—N2—C1	−127.3 (5)	C2—N2—C1—N3iii	−0.9 (5)
N3—Cd1—N2—C1	−145.5 (6)	Cd1—N2—C1—N3iii	153.2 (3)
O1i—Cd1—N2—C2	−73.1 (4)	C2—N2—C1—N1	178.5 (4)
O1—Cd1—N2—C2	113.1 (4)	Cd1—N2—C1—N1	−27.4 (7)
N2i—Cd1—N2—C2	−160.5 (4)	C1—N2—C2—C3iii	1.1 (5)
N3i—Cd1—N2—C2	22.7 (3)	Cd1—N2—C2—C3iii	−155.5 (3)
N3—Cd1—N2—C2	4.4 (9)	C1—N2—C2—C4	−174.0 (5)
O1i—Cd1—O1—C6	44.5 (6)	Cd1—N2—C2—C4	29.4 (6)
N2i—Cd1—O1—C6	−7.3 (6)	N4—C4—C2—C3iii	−35 (8)
N2—Cd1—O1—C6	96.3 (6)	N4—C4—C2—N2	140 (7)
N3i—Cd1—O1—C6	−175.3 (6)	C1ii—N3—C3—C2ii	−0.4 (5)
N3—Cd1—O1—C6	−95.4 (6)	Cd1—N3—C3—C2ii	172.2 (3)
O1i—Cd1—N3—C1ii	−34.6 (4)	C1ii—N3—C3—C5	179.5 (5)
O1—Cd1—N3—C1ii	140.3 (4)	Cd1—N3—C3—C5	−7.9 (7)
N2i—Cd1—N3—C1ii	53.5 (4)	C2ii—C3—C5—N5	−1 (6)
N2—Cd1—N3—C1ii	−111.8 (7)	N3—C3—C5—N5	179 (100)
N3i—Cd1—N3—C1ii	−130.4 (5)	Cd1—O1—C6—N6	164.9 (6)
O1i—Cd1—N3—C3	155.1 (4)	C8—N6—C6—O1	178.2 (9)
O1—Cd1—N3—C3	−30.0 (4)	C7—N6—C6—O1	−0.2 (13)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1iv	0.86	2.45	3.187 (6)	144
C7—H7C···N5iv	0.96	2.68	3.429 (12)	135
C7—H7B···N4v	0.96	2.65	3.496 (11)	148