Crystal structure of catena-poly[[[trans-bis(aceto-nitrile-κN)diaquacobalt(II)]-μ-pyrazine-κ(2) N:N'] dinitrate].

The central structural motif of the title coordination polymer, [Co(NO3)2(C4H4N2)(CH3CN)2(H2O)2] n , is a chain composed of Co(II) ions linked by bis-monodentate bridging pyrazine ligands through their N atoms. The Co(II) ion is located on an inversion center and is additionally coordinated by two O atoms of water mol-ecules and two N atoms of aceto-nitrile mol-ecules. The resultant N4O2 coordination sphere is distorted octa-hedral. The linear cationic chains extend parallel to the a axis and are aligned into layers parallel to the ac plane. Nitrate anions are situated in the space between the Co(II) chains and form O-H⋯O hydrogen bonds with the coordinating water mol-ecules, leading to a three-dimensional network structure. Weak C-H⋯O hydrogen bonds are also present between pyrazine or aceto-nitrile mol-ecules and the nitrate anions.

Chemical context

In the design of coordination polymers, the choice of bridging ligands between metal atoms plays an important role in the formation of the final structure and the resulting properties. During our investigations of the preparation conditions and magnetic properties of compounds with ladder-like structures, we have used pyrazine as a bis-monodentate bridging ligand to link paramagnetic metal cations. From the point of view of mediating magnetic inter­actions, the pyrazine mol­ecule offers some advantages compared to other bidentate bridging ligands such as 4,4′-bi­pyridine. In some of the structures with the latter ligand, the two pyridine rings are not co-planar and therefore can magnetically isolate metal atoms (Losier & Zaworotko, 1996 ▸; Ruan et al., 2009 ▸; Seidel et al., 2011 ▸; Lehleh et al., 2013 ▸).

We herein report the preparation and structure of a pyrazine-bridged chain structure obtained by reacting pyrazine and cobalt(II) nitrate hexa­hydrate using aceto­nitrile as the solvent.

Structural commentary

The asymmetric unit of the title compound, [Co(C4H4N2)(CH3CN)2(H2O)2(NO3)2], contains one CoII cation located on an inversion center, one water mol­ecule, one aceto­nitrile mol­ecule, one nitrate anion, and one half of a pyrazine mol­ecule, the latter being completed by inversion symmetry. The CoII cation exhibits an N4O2 coordination set defined by two O atoms [O1, O1ii; symmetry code: (ii) −3 − x, 1 − y, −z] of two coordinating water mol­ecules, two N atoms (N2, N2ii) of two coordinating aceto­nitrile mol­ecules, and two nitro­gen atoms (N1, N1ii) of two bridging pyrazine mol­ecules (Fig. 1 ▸). The two Co—Owater bonds have a length of 2.0315 (8) Å, considerably shorter than the two Co—Naceto­nitrile bonds of 2.1263 (9) Å, and the two Co—Npyrazine bonds of 2.1493 (10) Å. The resulting coordination sphere is compressed octa­hedral with all bond lengths in good agreement with similar structures (Choudhury et al., 2002 ▸; Holman et al., 2005 ▸; Aşkin et al., 2015 ▸). In contrast to the N2O4 coordination spheres observed more frequently in the structures of other Co-containing compounds (Choudhury et al., 2002 ▸; Holman et al., 2005 ▸; Hyun et al., 2011 ▸; Aşkin et al., 2015 ▸), the title structure exhibits an N4O2 coordination sphere due to the inclusion of the solvent aceto­nitrile mol­ecules in the coordination sphere of CoII. The bridging bis-monodentate pyrazine mol­ecules link the CoII ions, forming linear chains extending parallel to the a axis. The distance between two symmetry-related CoII ions within a chain (symmetry code: 1 + x, y, z) is 7.0798 (3) Å, in good agreement with those reported for similar structures (Choudhury et al., 2002 ▸; Holman et al., 2005 ▸; Aşkin et al., 2015 ▸).

Figure 1

A fragment of the one-dimensional chain structure of the title compound with displacement ellipsoids drawn at the 50% probability level. [Symmetry codes: (i) 1 + x, y, z; (ii) −3 − x, 1 − y, −z; (iii) −4 − x, 1 − y, −z.]

Supra­molecular features

In the crystal, the cationic chains are arranged to form sheets parallel to the ac plane, and neighboring sheets are related by a glide plane. Nitrate ions are sandwiched in the space between the sheets and form columns parallel to the a axis. Each CoII chain is surrounded by six columns of nitrate ions that are related by the inversion centers located along the cationic chains. Each cationic chain is further surrounded by six other chains. This structural motif with alternating layers has been observed in similar structures (Choudhury et al., 2002 ▸; Yang et al., 2003 ▸; Holman et al., 2005 ▸; Aşkin et al., 2015 ▸). CoII chains in neighboring sheets inter­act through nitrate ions by forming O—H⋯O hydrogen bonds where the donor O—H groups are provided by the coordinating water mol­ecules and the acceptor oxygen provided by the nitrate ions. One of those hydrogen bonds is bifurcated. For numerical values and symmetry operators, see Table 1 ▸. Weak C—H⋯O hydrogen bonds are also present between the C—H groups of bridging pyrazine and coordinating aceto­nitrile mol­ecules, and the oxygen atoms of nitrate ions, linking CoII chains both within the same sheet and to adjacent sheets (Table 1 ▸, Fig. 2 ▸).

Table 1

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1Y⋯O13i	0.83 (2)	1.85 (2)	2.6819 (12)	173.5 (18)
O1—H1X⋯O12ii	0.80 (2)	1.99 (2)	2.7869 (12)	174.1 (19)
O1—H1X⋯O13ii	0.80 (2)	2.562 (19)	3.0912 (12)	125.3 (17)
C1—H1A⋯O11iii	0.95	2.54	3.1572 (14)	123
C2—H2A⋯O13iv	0.95	2.59	3.4644 (14)	153
C4—H4A⋯O13v	0.98	2.49	3.2785 (17)	138
C4—H4B⋯O11vi	0.98	2.49	3.2823 (17)	138

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Figure 2

Crystal packing of the title compound, showing hydrogen bonds as dashed lines.

Synthesis and crystallization

The title compound was obtained by a slow diffusion method in an U-shaped glass tube. The tube was first partially filled with aceto­nitrile. An aceto­nitrile solution of 0.333 mmol (97.0 mg) of Co(NO3)2·6H2O was then placed in one arm of the tube. Another aceto­nitrile solution of 0.500 mmol (40.0 mg) of pyrazine was placed in the other arm of the tube. The slow diffusion of the two solutions in the tube produced pink needle–shaped crystals within one day. The crystals were collected by filtration and washed with fresh aceto­nitrile and kept under inert atmosphere (yield 31.5%). Selected IR bands (KBr, cm−1): 3273 (O—H), 2283 (C N), 1633, 1413, 1384 (N=O), 479 (bridging pyrazine).

Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. C-bound H atoms were calculated in geometrically idealized positions and refined riding on their parent atoms, with U iso(H) = 1.2U eq(C) (aromatic) and 1.5U eq(C) (meth­yl), and with C—H = 0.95 Å (aromatic) and 0.98 Å (meth­yl). The methyl H atoms were allowed to rotate around the corresponding C—C bond. H atoms bound to water mol­ecules were found in a difference map and were freely refined.

Table 2

Experimental details

Crystal data
Chemical formula	[Co(NO3)2(C4H4N2)(C2H3N)2(H2O)2]
M r	381.18
Crystal system, space group	Monoclinic, P21/c
Temperature (K)	100
a, b, c (Å)	7.0798 (3), 15.0376 (6), 7.9329 (3)
β (°)	110.8803 (6)
V (Å3)	789.10 (5)
Z	2
Radiation type	Mo Kα
μ (mm−1)	1.14
Crystal size (mm)	0.29 × 0.11 × 0.08
Data collection
Diffractometer	Bruker APEXII DUO CCD
Absorption correction	Analytical based on measured indexed crystal faces using SHELXTL2014 (Sheldrick, 2015b ▸)
T min, T max	0.735, 0.904
No. of measured, independent and observed [I > 2σ(I)] reflections	21292, 1811, 1687
R int	0.022
(sin θ/λ)max (Å−1)	0.650
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.019, 0.055, 1.07
No. of reflections	1811
No. of parameters	115
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.34, −0.31

Computer programs: APEX2 and SAINT (Bruker, 2014 ▸), SHELXLT (Sheldrick, 2015a ▸), SHELXL2014/7 (Sheldrick, 2015b ▸), XP in SHELXTL-Plus (Sheldrick, 2008 ▸), ORTEP-3 for Windows (Farrugia, 2012 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989016000220/wm5260sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989016000220/wm5260Isup2.hkl

CCDC reference: 1445438

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

[Co(NO3)2(C4H4N2)(C2H3N)2(H2O)2]	F(000) = 390
Mr = 381.18	Dx = 1.604 Mg m−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.0798 (3) Å	Cell parameters from 9896 reflections
b = 15.0376 (6) Å	θ = 2.0–28.0°
c = 7.9329 (3) Å	µ = 1.14 mm−1
β = 110.8803 (6)°	T = 100 K
V = 789.10 (5) Å3	Needle, pink
Z = 2	0.29 × 0.11 × 0.08 mm

Bruker APEXII DUO CCD diffractometer	1687 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.022
φ– and ω–scans	θmax = 27.5°, θmin = 2.7°
Absorption correction: analytical based on measured indexed crystal faces using SHELXTL2014 (Sheldrick, 2015b)	h = −9→9
Tmin = 0.735, Tmax = 0.904	k = −19→19
21292 measured reflections	l = −10→10
1811 independent reflections

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.019	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.055	w = 1/[σ2(Fo2) + (0.0316P)2 + 0.2947P] where P = (Fo2 + 2Fc2)/3
S = 1.07	(Δ/σ)max < 0.001
1811 reflections	Δρmax = 0.34 e Å−3
115 parameters	Δρmin = −0.31 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.

	x	y	z	Uiso*/Ueq
Co1	0.5000	0.5000	0.0000	0.00977 (8)
O1	0.45432 (12)	0.38331 (6)	−0.13782 (12)	0.01522 (17)
H1Y	0.431 (3)	0.3365 (13)	−0.092 (2)	0.035 (5)*
H1X	0.391 (3)	0.3842 (13)	−0.243 (3)	0.036 (5)*
N1	0.19570 (15)	0.49931 (6)	−0.00181 (13)	0.01163 (19)
N2	0.39794 (14)	0.56807 (6)	−0.25144 (13)	0.01470 (19)
C1	0.07744 (16)	0.57128 (7)	−0.05354 (15)	0.0134 (2)
H1A	0.1283	0.6228	−0.0923	0.016*
C2	−0.11795 (16)	0.57209 (7)	−0.05167 (14)	0.0131 (2)
H2A	−0.1981	0.6242	−0.0889	0.016*
C3	0.31802 (17)	0.58923 (8)	−0.39744 (16)	0.0158 (2)
C4	0.2144 (2)	0.61342 (10)	−0.58544 (17)	0.0278 (3)
H4A	0.3122	0.6380	−0.6346	0.042*
H4B	0.1106	0.6580	−0.5939	0.042*
H4C	0.1508	0.5605	−0.6545	0.042*
N11	0.23020 (15)	0.30295 (7)	0.44860 (13)	0.0172 (2)
O11	0.09637 (15)	0.26787 (6)	0.31960 (13)	0.0295 (2)
O12	0.21017 (14)	0.38082 (6)	0.49826 (12)	0.0228 (2)
O13	0.39023 (13)	0.26094 (6)	0.53329 (12)	0.0230 (2)

	U11	U22	U33	U12	U13	U23
Co1	0.00857 (12)	0.01064 (12)	0.01028 (12)	−0.00011 (7)	0.00357 (8)	0.00023 (7)
O1	0.0187 (4)	0.0130 (4)	0.0136 (4)	−0.0023 (3)	0.0053 (3)	−0.0011 (3)
N1	0.0107 (4)	0.0130 (5)	0.0112 (4)	0.0000 (3)	0.0038 (3)	−0.0005 (3)
N2	0.0142 (4)	0.0151 (5)	0.0151 (5)	0.0002 (4)	0.0056 (4)	0.0010 (4)
C1	0.0135 (5)	0.0125 (5)	0.0144 (5)	−0.0006 (4)	0.0051 (4)	0.0011 (4)
C2	0.0128 (5)	0.0127 (5)	0.0138 (5)	0.0012 (4)	0.0045 (4)	0.0013 (4)
C3	0.0144 (5)	0.0164 (5)	0.0178 (6)	−0.0005 (4)	0.0072 (4)	0.0008 (4)
C4	0.0215 (6)	0.0426 (8)	0.0162 (6)	0.0002 (6)	0.0029 (5)	0.0093 (5)
N11	0.0222 (5)	0.0137 (5)	0.0149 (4)	−0.0015 (4)	0.0057 (4)	0.0004 (4)
O11	0.0319 (5)	0.0190 (5)	0.0236 (5)	−0.0026 (4)	−0.0073 (4)	−0.0018 (4)
O12	0.0315 (5)	0.0134 (4)	0.0213 (4)	0.0030 (4)	0.0067 (4)	−0.0024 (3)
O13	0.0207 (4)	0.0198 (4)	0.0232 (5)	0.0041 (3)	0.0012 (3)	−0.0054 (3)

Co1—O1	2.0315 (8)	C1—C2	1.3888 (15)
Co1—O1i	2.0315 (8)	C1—H1A	0.9500
Co1—N2i	2.1263 (9)	C2—N1ii	1.3425 (14)
Co1—N2	2.1263 (9)	C2—H2A	0.9500
Co1—N1i	2.1493 (10)	C3—C4	1.4542 (16)
Co1—N1	2.1493 (10)	C4—H4A	0.9800
O1—H1Y	0.83 (2)	C4—H4B	0.9800
O1—H1X	0.80 (2)	C4—H4C	0.9800
N1—C1	1.3401 (14)	N11—O11	1.2378 (13)
N1—C2ii	1.3425 (14)	N11—O12	1.2595 (13)
N2—C3	1.1383 (15)	N11—O13	1.2616 (13)
O1—Co1—O1i	180.0	C1—N1—Co1	120.89 (7)
O1—Co1—N2i	91.42 (4)	C2ii—N1—Co1	121.65 (7)
O1i—Co1—N2i	88.58 (4)	C3—N2—Co1	165.59 (9)
O1—Co1—N2	88.58 (4)	N1—C1—C2	121.32 (10)
O1i—Co1—N2	91.42 (4)	N1—C1—H1A	119.3
N2i—Co1—N2	180.0	C2—C1—H1A	119.3
O1—Co1—N1i	88.55 (3)	N1ii—C2—C1	121.23 (10)
O1i—Co1—N1i	91.45 (3)	N1ii—C2—H2A	119.4
N2i—Co1—N1i	89.51 (4)	C1—C2—H2A	119.4
N2—Co1—N1i	90.49 (4)	N2—C3—C4	178.24 (13)
O1—Co1—N1	91.45 (3)	C3—C4—H4A	109.5
O1i—Co1—N1	88.55 (3)	C3—C4—H4B	109.5
N2i—Co1—N1	90.49 (4)	H4A—C4—H4B	109.5
N2—Co1—N1	89.51 (4)	C3—C4—H4C	109.5
N1i—Co1—N1	180.0	H4A—C4—H4C	109.5
Co1—O1—H1Y	121.0 (12)	H4B—C4—H4C	109.5
Co1—O1—H1X	118.3 (14)	O11—N11—O12	121.09 (10)
H1Y—O1—H1X	110.2 (18)	O11—N11—O13	120.29 (10)
C1—N1—C2ii	117.45 (10)	O12—N11—O13	118.61 (10)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1Y···O13iii	0.83 (2)	1.85 (2)	2.6819 (12)	173.5 (18)
O1—H1X···O12iv	0.80 (2)	1.99 (2)	2.7869 (12)	174.1 (19)
O1—H1X···O13iv	0.80 (2)	2.562 (19)	3.0912 (12)	125.3 (17)
C1—H1A···O11ii	0.95	2.54	3.1572 (14)	123
C2—H2A···O13v	0.95	2.59	3.4644 (14)	153
C4—H4A···O13i	0.98	2.49	3.2785 (17)	138
C4—H4B···O11vi	0.98	2.49	3.2823 (17)	138