catena-Poly[[bis­(N,N-dimethyl­formamide-κO)nickel(II)]-di-μ-1,5-dicyanamido-κN¹:κN⁵]

In the crystal structure of the title complex, [Ni(C₂N₃)₂(C₃H₇NO)₂]_n or [Ni(dca)₂(DMF)₂]_n, where dca is dicyanamide and DMF is N,N-dimethyl­formamide, each Ni^II atom is six-coordinated in a distorted octa­hedral coordination environment. Four N atoms from four dca ligands fill the equatorial positions, and two O atoms from two DMF ligands fill the axial positions. The structure is isostructural with [Co(dca)₂(DMF)₂]_n but is not isostructural with [Mn(dca)₂(DMF)₂]_n. The Ni^II atom and the dicyanamide bridging ligand occupy special positions of symmetry 2/m and m, respectively. The structure consists of uniform neutral chains where neighbouring Ni^II atoms are connected through two asymmetric end-to-end dca bridges.

Key indicators

• Single-crystal X-ray study
• T = 193 K
• Mean [sigma](N-C) = 0.003 Å
• R factor = 0.023
• wR factor = 0.062
• Data-to-parameter ratio = 11.8

checkCIF/PLATON results

No syntax errors found



Alert level C
PLAT062_ALERT_4_C Rescale T(min) & T(max) by .....................       0.99
PLAT164_ALERT_4_C Nr. of Refined C-H H-Atoms in Heavy-At Struct...          5
PLAT220_ALERT_2_C Large Non-Solvent    C     Ueq(max)/Ueq(min) ...       2.98 Ratio
PLAT380_ALERT_4_C Check Incorrectly? Oriented X(sp2)-Methyl Moiety         C3
PLAT380_ALERT_4_C Check Incorrectly? Oriented X(sp2)-Methyl Moiety         C4
PLAT731_ALERT_1_C Bond    Calc     0.94(2), Rep    0.938(9) ......       2.22 su-Rat
              C4   -H4B     1.555   1.555

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   6 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   0 ALERT type 3 Indicator that the structure quality may be low
   4 ALERT type 4 Improvement, methodology, query or suggestion

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S1. Comment

Dicyanamide (dca), [N(CN)₂]^-, complexes have been studied extensively recently because of their fascinating topologies and interesting magnetic properties (Batten et al., 1998; Miller & Manson 2001; Jensen et al., 2000; Riggio et al., 2001). A number of nickel(II)–dca complexes have been reported (Sun, et al., 2000; Wang et al., 2004; Konor et al., 2005). Our research interest is construction of novel topologies of cyano complexes and studying the magnetic properties (Shen et al., 2004, 2003). In the present work, we report the crystal structure of a one-dimensional chain polymer, viz. [Ni(dca)₂(DMF)₂]_n, (I).

Fig. 1 shows the local coordination about the nickel(II) center in (I). The structure of (I) is isostructural with [Co(dca)₂(DMF)₂]_n (Tong et al., 2003) and not isostructural with [Mn(dca)₂(DMF)₂]_n (Batten et al., 1999). The space group of [Co(dca)₂(DMF)₂]_n reported by Dong et al. (2003) has been described incorrectly in C2; it should be C2/m, as reported by Tong et al. (2003). The structure of (I) consists of uniform neutral chains where neighboring nikel(II) atoms are connected through two asymmetric end-to-end dca bridges. The coordination geometry of the nickel(II) atom is distorted octahedral, being coordinated by four N atoms of four symmetry-related dca ligands in the equatorial plane and two O atoms of two symmetry-related DMF ligands at the axial positions. The N—Ni—N bond angles are in the range 87.84 (6) to 92.16 (6)°, close to 90°. The four Ni—N(dca) bond lengths in (I) are all 2.0733 (11) Å, corresponding to the values reported in the dca-bridged nickel(II) complexes [Ni(apo)(dca)₂] [2.043 (4)–2.096 (4) Å; apo = 2-aminopyridine N-oxide; Sun et al., 2000] and [Ni(tn)₂(dca)](ClO₄) [2.095 (4) and 2.116 (4) Å; tn = trimethylenediamine; Li et al., 2002], and shorter than the Mn—N bond lengths [2.218 (2) and 2.203 (2) Å] in [Mn(dca)₂(DMF)₂]_n (Batten et al., 1999) and the Co—N bond lengths [2.123 (2) Å] in [Co(dca)₂(DMF)₂]_n (Tong et al., 2003); this is what one would expect from the ionic radii (Ni²⁺ < Co²⁺ < Mn²⁺). The two Ni—O (DMF) bond lengths are both 2.0670 (13) Å, corresponding to the values [2.0776 (19) Å] in [Ni(pmbp)₂(DMF)₂] [Hpmbp = 1-phenyl-3-methyl-4-benzoyl-1H-pyrazol-5(4H)-one; Shen & Yuan 2004] and shorter than the M—O bond lengths in [Mn(dca)₂(DMF)₂]_n [Mn—O = 2.199 (2) Å] and in [Co(dca)₂(DMF)₂]_n [Co—O = 2.096 (2) Å].

The dicyanamide (dca) ligand adopts an end-to-end coordination mode. Two dca ions link two nickel(II) atoms to form a 12-membered Ni(dca)₂Ni ring and the neighboring rings share the nickel(II) atoms to form a chain of [Ni(dca)₂]_n. The chains are linear, the Ni(dca)₂Ni rings being in a slight chair conformation.

Free dicyanamide (dca) ligand possesses C_2v symmetry. The dca ligand in (I) also adopts C_2v symmetry with a nitrile C≡ N bond length of 1.1545 (18) Å for N1≡C1, showing the triple-bond character. The bond angle related to the amide N atom, C1—N2—C1(x, 1 - y, z), is 118.61 (16)°, corresponding to an amide N atom with an sp² hybrid orbital; tha related to the nitrile group, N1≡ C1—N2, is 174.95 (13)°, corresponding to N1 and C1 with an sp hybrid orbital.

The chains propagate parallel to the crystallographic b axis, the Ni···Ni distance along the chain being equal to the b cell length 7.3166 (7) Å. The chains interdigate such that each DMF ligand lies between two DMF ligands of an adjacent chain, with a shortest Ni···Ni interchain distance of 7.628 (2) Å (Fig. 3). Adjacent chains are held together by a weak C—H···N hydrogen bond, forming layers parallel to the ab plane (Fig. 2 and Table 2).

S2. Experimental

An aqueous solution (10 ml) of Ni(NO₃)₂·6H₂O (0.146 g, 0.5 mmol) was added to a DMF solution (10 ml) of Na[N(CN)₂] (0.090 g, 1.0 mmol). Slow evaporation of the resulting mixture led to green crystals suitable for X-ray diffraction analysis. Analysis found: C 35.53, H 4.12, N 33.31%; calculated for C₁₀H₁₄N₈NiO₂: C 35.64, H 4.19, N 33.26%.

S3. Refinement

H atoms were found in a difference Fourier map and refined with bond-length restraints of C—H = 0.95 (1) Å for the methyl groups and the H···H distance restrained to 1.50 (1) Å. One of two independent H atoms lies on the mirror plane.

Computing details

Data collection: CrystalClear (Rigaku, 2000); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: the coordinates of the Co structure of Tong et al. (2003) were used; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1998); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The coordination geometry of the Ni^II atom in (I), with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) 1 - x, 1 - y, 1 - z; (ii) 1 - x, y, 1 - z; (iii) x, 1 - y, z.]
	Fig. 2. The packing in (I), showing the C—H···N hydrogen-bond interactions as dashed lines.

catena-Poly[[bis(N,N-dimethylformamide-κO)nickel(II)]-di- µ-1,5-dicyanamido-κN¹:κN⁵]

Crystal data

[Ni(C2N3)2(C3H7NO)2]	F(000) = 348
Mr = 336.98	Dx = 1.535 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2y	Cell parameters from 1804 reflections
a = 13.3866 (17) Å	θ = 3.2–27.5°
b = 7.3166 (7) Å	µ = 1.35 mm^−1
c = 8.0595 (10) Å	T = 193 K
β = 112.503 (3)°	Block, blue
V = 729.28 (15) Å^3	0.40 × 0.21 × 0.20 mm
Z = 2

Data collection

Rigaku Mercury CCD diffractometer	900 independent reflections
Radiation source: fine-focus sealed tube	887 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.018
ω scans	θmax = 27.5°, θmin = 3.2°
Absorption correction: multi-scan (Jacobson, 1998)	h = −17→15
Tmin = 0.646, Tmax = 0.774	k = −8→9
4029 measured reflections	l = −10→10

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)] = 0.023	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.062	H atoms treated by a mixture of independent and constrained refinement
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0436P)^2 + 0.3824P] where P = (Fo^2 + 2Fc^2)/3
900 reflections	(Δ/σ)max < 0.001
76 parameters	Δρmax = 0.15 e Å^−3
9 restraints	Δρmin = −0.47 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
Ni1	0.5000	0.5000	0.5000	0.01621 (13)
O1	0.58082 (11)	0.5000	0.77586 (18)	0.0230 (3)
N1	0.59942 (9)	0.70410 (15)	0.47063 (15)	0.0231 (3)
N2	0.63339 (15)	1.0000	0.3571 (2)	0.0255 (4)
N3	0.73719 (13)	0.5000	1.0204 (2)	0.0256 (4)
C1	0.61394 (9)	0.84635 (18)	0.42201 (16)	0.0181 (3)
C2	0.68128 (15)	0.5000	0.8455 (2)	0.0210 (4)
H2	0.7242 (17)	0.5000	0.774 (3)	0.026 (6)*
C3	0.6836 (2)	0.5000	1.1460 (3)	0.0541 (8)
H3A	0.7060 (14)	0.6031 (7)	1.217 (2)	0.075 (8)*
H3B	0.6084 (9)	0.5000	1.089 (4)	0.073 (11)*
C4	0.85511 (17)	0.5000	1.0956 (3)	0.0320 (5)
H4A	0.8843 (13)	0.6028 (7)	1.1684 (16)	0.044 (6)*
H4B	0.882 (2)	0.5000	1.004 (2)	0.042 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ni1	0.01952 (19)	0.01301 (18)	0.01555 (18)	0.000	0.00610 (13)	0.000
O1	0.0218 (6)	0.0294 (7)	0.0161 (6)	0.000	0.0052 (5)	0.000
N1	0.0268 (6)	0.0182 (5)	0.0264 (6)	−0.0022 (4)	0.0127 (5)	−0.0017 (4)
N2	0.0383 (9)	0.0164 (7)	0.0318 (9)	0.000	0.0245 (8)	0.000
N3	0.0235 (8)	0.0343 (9)	0.0171 (7)	0.000	0.0057 (6)	0.000
C1	0.0173 (6)	0.0192 (6)	0.0190 (6)	0.0000 (5)	0.0084 (5)	−0.0038 (5)
C2	0.0242 (9)	0.0206 (8)	0.0182 (8)	0.000	0.0082 (7)	0.000
C3	0.0369 (13)	0.108 (3)	0.0189 (10)	0.000	0.0127 (9)	0.000
C4	0.0234 (10)	0.0381 (12)	0.0272 (10)	0.000	0.0017 (8)	0.000

Geometric parameters (Å, º)

Ni1—O1	2.0670 (13)	N2—C1	1.3074 (15)
Ni1—O1^i	2.0670 (13)	N3—C2	1.319 (2)
Ni1—N1	2.0733 (11)	N3—C3	1.448 (3)
Ni1—N1^i	2.0733 (11)	N3—C4	1.458 (3)
Ni1—N1^ii	2.0733 (11)	C2—H2	0.954 (10)
Ni1—N1^iii	2.0733 (11)	C3—H3A	0.923 (8)
O1—C2	1.243 (2)	C3—H3B	0.933 (10)
N1—C1	1.1545 (18)	C4—H4A	0.942 (8)
N2—C1^iv	1.3074 (15)	C4—H4B	0.938 (9)
O1—Ni1—O1^i	180.0	C1—N1—Ni1	152.49 (11)
O1—Ni1—N1	91.61 (4)	C1^iv—N2—C1	118.61 (16)
O1^i—Ni1—N1	88.39 (4)	C2—N3—C3	121.12 (18)
O1—Ni1—N1^i	88.39 (4)	C2—N3—C4	121.70 (17)
O1^i—Ni1—N1^i	91.61 (4)	C3—N3—C4	117.18 (18)
N1—Ni1—N1^i	180.0	N1—C1—N2	174.95 (13)
O1—Ni1—N1^ii	91.61 (4)	O1—C2—N3	123.76 (17)
O1^i—Ni1—N1^ii	88.39 (4)	O1—C2—H2	121.7 (15)
N1—Ni1—N1^ii	92.16 (6)	N3—C2—H2	114.6 (15)
N1^i—Ni1—N1^ii	87.84 (6)	N3—C3—H3A	107.4 (14)
O1—Ni1—N1^iii	88.39 (4)	N3—C3—H3B	113 (2)
O1^i—Ni1—N1^iii	91.61 (4)	H3A—C3—H3B	109.9 (11)
N1—Ni1—N1^iii	87.84 (6)	N3—C4—H4A	112.6 (10)
N1^i—Ni1—N1^iii	92.16 (6)	N3—C4—H4B	110.5 (16)
N1^ii—Ni1—N1^iii	180.00 (6)	H4A—C4—H4B	107.4 (10)
C2—O1—Ni1	121.06 (12)
N1—Ni1—O1—C2	−46.10 (3)	N1^ii—Ni1—N1—C1	145.1 (2)
N1^i—Ni1—O1—C2	133.90 (3)	N1^iii—Ni1—N1—C1	−34.9 (2)
N1^ii—Ni1—O1—C2	46.10 (3)	Ni1—O1—C2—N3	180.0
N1^iii—Ni1—O1—C2	−133.90 (3)	C3—N3—C2—O1	0.0
O1—Ni1—N1—C1	−123.3 (2)	C4—N3—C2—O1	180.0
O1^i—Ni1—N1—C1	56.7 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2···N2^v	0.95 (1)	2.51 (1)	3.453 (2)	169 (2)

Symmetry code: (v) −x+3/2, −y+3/2, −z+1.