Poly[[diaqua­bis[[mu]₂-2-(4-pyridinio)propane-1,3-dionato-[kappa]²O:O']cobalt(II)] dinitrate]

The title compound, {[Co(C₈H₇NO₂)₂(H₂O)₂](NO₃)₂}_n, is the first d-metal ion complex involving bidentate bridging of a [beta]-­dialdehyde group. The Co²⁺ ion is situated on an inversion centre and adopts an octa­hedral coordination with four equatorial aldehyde O atoms [Co-O = 2.0910 (14) and 2.1083 (14) Å] and two axial aqua ligands [Co-O = 2.0631 (13) Å]. The title compound has a two-dimensional square-grid framework structure supported by propane-1,3-dionate O:O'-bridges between the metal ions. The organic ligand itself possesses a zwitterionic structure, involving conjugated anionic propane-1,3-dionate and cationic pyrid­in­ium fragments. Hydrogen bonding between coordinated water mol­ecules, the pyridinium NH group and the nitrate anions [O...O = 2.749 (2) and 2.766 (3) Å, and N...O = 2.864 (3) Å] is essential for the crystal packing.

S1. Comment

In view of providing pathways for magnetic coupling between bridged paramagnetic metal centres, formate complexes (Wang et al., 2005) bear a close resemblance to common azide systems (Cabrero et al., 2003). To sustain long-range magnetic coupling, extended conjugated O-donor bridges M—O—CH═CH—CH═O—M may be formally related to formate compounds as vinylogues. However, this coordination mode of 1,3-propanedionates towards d-metal ions is entirely unknown and the formation of such coordination bridges is difficult to predict. Unlike the thoroughly explored chemistry of 1,3-diketones, one of the most common ligand systems, structural information on 1,3-dialdehydes and their metal complexes is extremely scarce. In the anionic magnesium complex NMe₄[Mg{C(CHO)₃}₃], the triformylmethanide group behaves as a chelate O,O'-donor (Groth, 1987), while the 2-phenylpropane-1,3-dionate anion is monodentate, or O,O'-bridging as in the tetraphenylantimony(V) and triphenyltin(IV) compounds (Perrin & Kim, 2000). In two reported d-metal complexes, chromium(III) tris-1,3-propanedionate (Glick et al., 1975) and the tris-complex of Co^II with the 2-nitromalonic aldehyde anion (Albertin et al., 1981), the ligands are bidentate-chelates, similar to the 1,3-diketonate analogues. We suppose that the O,O'-bridging coordination of the dialdehyde frame may be more characteristic in the case of formally neutral ligands, while significant conjugation within the bis(formyl)methylide site is possible under deprotonation and therefore the appropriate ligand pattern may be best provided by a zwitterion. Some such charge-separated species cocrystallize even with alkali metal salts (Kolehmainen et al., 1989) and may be viewed as promising ligands for the synthesis of coordination polymers. In this context, we have examined the cobalt(II) nitrate complex with 4-pyridyl-substituted malonic aldehyde, a representative amphoteric ligand possessing relatively strong basic and acidic sites.

In the title compound, (I), the organic ligand exists as a zwitterion and the molecular framework involves charge-separated anionic 1,3-dionate and cationic 4-pyridinium fragments. The Co²⁺ ion is situated on an inversion centre and adopts a typical sixfold CoO₆ coordination, with a slightly distorted octahedral geometry (Fig. 1). This involves four aldehyde O atoms in the equatorial plane [Co—O = 2.0910 (14) and 2.1083 (14) Å] and two water molecules [Co—O = 2.0631 (13) Å] in the axial positions (Table 1). Thus, the bond lengths with the axial aqua ligands are even shorter than those formed with the organic donors. The latter act as O,O'-bidentate bridges between two Co²⁺ ions, separated by 8.26 Å [symmetry code: -x, y - 1/2, -z + 1/2], allowing propagation of the coordination geometry and assembly of a flat four-connected network (`square-grid net') (Fig. 2). It is interesting to note that the topology and shape of the network are very similar to those observed in the 3d-metal (Co, Ni) formate complexes with urea (Koyano et al., 1992) and formamide (Domasevitch et al., 2002). This also suggests close structural resemblance of the formate and 1,3-dionate (as the vinylogous formate anion) groups as bridging blocks for the design of polymeric coordination compounds. The space inside the square meshes of the framework is populated with a pair of pyridinium groups of the ligands that show characteristic slipped π–π stacking (Fig. 2). These two heterocycles are related by inversion (-x, 1 - y, -z) and are situated parallel to one another with a relatively long centroid-to-centroid distance of 3.705 (2) Å [interplanar distance = 3.482 (2) Å; slippage angle of the interacting groups = 29.92 (2)°] (Janiak, 2000).

The non-coordinated nitrate anions are involved in the overall three-dimensional supramolecular structure of (I) as acceptors of three strong hydrogen bonds with water molecules and pyridinium NH-donors (Table 2). Two coordinated water molecules and two NO₃^- anions assemble into typical centrosymmetric aqua-anion dimers (Fig. 3). Such modes of interaction between the components were also observed in the diaquanickel dinitrate complex with a substituted phenanthroline ligand (Freire et al., 2002). The third O atom of the nitrate anion accepts a hydrogen bond from a pyridinium NH group [N1···O4ⁱⁱⁱ = 2.864 (3) Å; symmetry code: (iii) 1 - x, 1 - y, -z]. This interaction is slightly weaker than that present in pyridinium nitrate itself (N···O = 2.70 Å; Batsanov, 2004). In total, these hydrogen-bond interactions provide cross-linking of successive coordination layers, which are related by translation along the a axis (interlayer separation 7.57 Å).

The molecular structure of the ligand is planar, with the dihedral angle between the mean planes through the heterocyclic and dialdehyde fragments being 7.6 (2)°. Bond lengths indicate effective delocalization of the π-electron density, since both pairs of C—C [1.418 (3) and 1.422 (2) Å] and C—O [1.240 (2) and 1.249 (2) Å] bonds in the dionate fragment are practically uniform (Table 1). This is consistent with the geometry of the conjugated phenylmalonic dialdehyde anion in its triethylammonium salt and in the triphenyltin(IV) complex (Perrin & Kim, 2000), the only known structural precedent for O,O'-bridging coordination of dialdehyde. However, monodentate coordination of the latter ligand led to localization of the single and double bonds (i.e. C—O 1.288 and 1.218 Å). The C3—C6 bond between the pyridinium and methylide fragments is also suggestive of conjugation and is shorter than in the structure of the phenyl analogue [1.455 (3) versus 1.485–1.493 Å; Semmingsen, 1977]. The O1—C1—C3—C2—O2 chain adopts a trans–trans configuration (see torsion angles in Table 1), which is the most characteristic arrangement for dialdehyde fragments in crystal structures. It is unlikely to be influenced by possible intramolecular weak C—H···O hydrogen bonding [e.g. C7···O1 = 2.848 (3) Å and C7—H7···O1 = 127°], since a similar configuration was retained even in related molecules with orthogonal disposition of the aromatic and bis(formyl)methylide fragments (Mueller et al., 2001), and in the aliphatic trimethylammonium diformylmethylide (Kolehmainen et al., 1989).

In conclusion, compound (I) provides a first example of O,O'-diformylmethylide bridges between transition metal ions and it suggests the utility of zwitterionic dialdehydes as highly conjugated ligands for coordination compounds. This may find further application in the developement of metal–organic systems with long-range magnetic coupling between paramagnetic metal centres.

Related literature

For related literature, see: Albertin et al. (1981); Arnold (1963); Batsanov (2004); Cabrero et al. (2003); Domasevitch et al. (2002); Freire et al. (2002); Glick et al. (1975); Groth (1987); Janiak (2000); Kolehmainen et al. (1989); Koyano et al. (1992); Mueller et al. (2001); Perrin & Kim (2000); Semmingsen (1977); Wang et al. (2005).

S2. Experimental

The 2-(4-pyridyl)-1,3-propanedione ligand was prepared by Vilsmeyer–Haack formylation of 4-methylpyridine (Arnold, 1963). For the synthesis of compound (I), the ligand (0.148 g, 1.0 mmol) and Co(NO₃)₂·6H₂O (0.145 g, 0.5 mmol) were dissolved in methanol (20 ml). Slow evaporation of the solution at room temperature led to crystallization of yellow prisms of (I) (yield 70%, 0.18 g).

S3. Refinement

The H atoms were located in difference Fourier maps and were then treated as riding atoms, with O—H = 0.85 Å, N—H = 0.87 Å and C—H = 0.94 Å, and with U_iso(H) = 1.2U_eq(C) or U_iso(H) = 1.5U_eq (O,N).

Computing details

Data collection: SMART-NT (Bruker, 1998); cell refinement: SAINT-NT (Bruker, 1999); data reduction: SAINT-NT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Version 1.700.00; Farrugia, 1999).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 40% probability level and H atoms are shown as small spheres of arbitrary radii. Dashed lines indicate hydrogen bonds. [Please check added text] [Symmetry codes: (i) -x, y - 1/2, -z + 1/2; (iv) -x, -y, -z.]
	Fig. 2. A view of the square-grid network in the structure of (I), showing the bridging coordination of the diformylmethylide fragment and the slipped π–π interaction of the heterocyclic groups situated inside the rectangular cages (projection on the bc plane). H atoms have been omitted for clarity, and O and N atoms are shaded grey. [Symmetry codes: (i) -x, y - 1/2, -z + 1/2; (v) -x, y + 1/2, -z + 1/2.]
	Fig. 3. A view of the interconnection of the coordination layers in (I) via hydrogen-bonded nitrate anions. Dashed lines indicate hydrogen bonds. [Please check added text] Note the formation of the characteristic aqua–anion dimers. C-bound H atoms have been omitted for clarity, and O and N atoms are shaded grey. [Symmetry codes: (ii) -x + 1, -y, -z; (iii) -x + 1, -y + 1, -z.]

poly[[diaquabis[µ₂-2-(4-pyridinio)propane-1,3-dionato-κ²O:O']cobalt(II)] dinitrate]

Crystal data

[Co(C8H7NO2)2(H2O)2]·(NO3)2	F(000) = 530
Mr = 517.27	Dx = 1.663 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 7.6156 (8) Å	Cell parameters from 3557 reflections
b = 11.5530 (9) Å	θ = 2.7–27.1°
c = 11.8140 (11) Å	µ = 0.91 mm^−1
β = 96.258 (2)°	T = 213 K
V = 1033.24 (17) Å^3	Prism, yellow
Z = 2	0.24 × 0.20 × 0.20 mm

Data collection

Siemens SMART CCD area-detector diffractometer	2235 independent reflections
Radiation source: fine-focus sealed tube	1908 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ω scans	θmax = 27.1°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −9→9
Tmin = 0.812, Tmax = 0.840	k = −4→14
3557 measured reflections	l = −9→15

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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.109	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0772P)^2 + 0.2103P] where P = (Fo^2 + 2Fc^2)/3
2235 reflections	(Δ/σ)max < 0.001
151 parameters	Δρmax = 0.56 e Å^−3
0 restraints	Δρmin = −0.30 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
Co1	0.0000	0.0000	0.0000	0.02161 (15)
O1	0.0451 (2)	0.17324 (12)	0.05126 (13)	0.0281 (3)
O2	0.0662 (2)	0.46112 (12)	0.33708 (12)	0.0289 (3)
O3	0.25944 (12)	−0.03977 (9)	0.05493 (9)	0.0371 (4)
H1W	0.3127	−0.0682	0.0018	0.056*
H2W	0.3159	0.0189	0.0830	0.056*
O4	0.5699 (3)	0.28319 (17)	0.21289 (18)	0.0577 (6)
O5	0.5362 (3)	0.19342 (17)	0.05350 (18)	0.0526 (5)
O6	0.4292 (3)	0.12116 (16)	0.19933 (16)	0.0454 (5)
N1	0.3100 (3)	0.57216 (16)	−0.04011 (16)	0.0310 (4)
H1N	0.3502	0.6224	−0.0858	0.046*
N2	0.5120 (3)	0.19878 (16)	0.15639 (18)	0.0350 (4)
C1	0.0320 (3)	0.22185 (16)	0.14350 (17)	0.0233 (4)
H1	−0.0192	0.1778	0.1982	0.028*
C2	0.0399 (3)	0.36688 (16)	0.28623 (17)	0.0250 (4)
H2	−0.0166	0.3093	0.3253	0.030*
C3	0.0847 (3)	0.33603 (15)	0.17682 (17)	0.0216 (4)
C4	0.2981 (3)	0.60096 (18)	0.0684 (2)	0.0316 (5)
H4	0.3362	0.6745	0.0949	0.038*
C5	0.2310 (3)	0.52484 (18)	0.1415 (2)	0.0294 (5)
H5	0.2263	0.5460	0.2180	0.035*
C6	0.1689 (2)	0.41503 (15)	0.10341 (16)	0.0202 (4)
C7	0.1931 (3)	0.38758 (18)	−0.01014 (18)	0.0284 (5)
H7	0.1623	0.3135	−0.0387	0.034*
C8	0.2609 (3)	0.4672 (2)	−0.0793 (2)	0.0331 (5)
H8	0.2732	0.4479	−0.1553	0.040*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Co1	0.0368 (3)	0.0123 (2)	0.0163 (2)	−0.00083 (13)	0.00542 (15)	−0.00004 (12)
O1	0.0451 (9)	0.0173 (6)	0.0224 (8)	−0.0036 (6)	0.0053 (6)	−0.0034 (5)
O2	0.0495 (9)	0.0177 (6)	0.0209 (7)	−0.0017 (6)	0.0094 (6)	−0.0029 (5)
O3	0.0396 (9)	0.0331 (8)	0.0383 (9)	0.0013 (7)	0.0024 (7)	−0.0075 (7)
O4	0.0770 (15)	0.0457 (10)	0.0476 (12)	−0.0277 (10)	−0.0060 (10)	0.0037 (9)
O5	0.0713 (14)	0.0419 (10)	0.0494 (13)	0.0053 (9)	0.0280 (10)	0.0036 (9)
O6	0.0494 (11)	0.0460 (10)	0.0400 (10)	−0.0192 (8)	0.0016 (8)	0.0127 (8)
N1	0.0309 (10)	0.0294 (9)	0.0340 (10)	−0.0034 (7)	0.0096 (8)	0.0073 (8)
N2	0.0346 (10)	0.0287 (9)	0.0425 (12)	0.0001 (7)	0.0079 (9)	0.0068 (8)
C1	0.0303 (11)	0.0180 (8)	0.0218 (10)	−0.0011 (7)	0.0036 (8)	−0.0007 (7)
C2	0.0360 (11)	0.0172 (8)	0.0226 (10)	0.0005 (7)	0.0064 (8)	0.0016 (7)
C3	0.0276 (10)	0.0171 (8)	0.0200 (10)	0.0006 (7)	0.0017 (7)	−0.0016 (7)
C4	0.0357 (12)	0.0244 (10)	0.0353 (12)	−0.0070 (8)	0.0072 (9)	−0.0016 (9)
C5	0.0385 (12)	0.0234 (9)	0.0270 (11)	−0.0071 (8)	0.0069 (9)	−0.0056 (8)
C6	0.0191 (9)	0.0193 (9)	0.0219 (10)	0.0018 (7)	0.0001 (7)	−0.0011 (7)
C7	0.0355 (12)	0.0253 (10)	0.0249 (11)	−0.0045 (8)	0.0056 (9)	−0.0049 (8)
C8	0.0395 (13)	0.0359 (11)	0.0250 (11)	−0.0051 (10)	0.0087 (9)	−0.0037 (9)

Geometric parameters (Å, º)

Co1—O3^i	2.0631 (13)	N1—C4	1.338 (3)
Co1—O1	2.1083 (14)	N1—H1N	0.8700
Co1—O2^ii	2.0910 (14)	C1—C3	1.422 (2)
Co1—O3	2.0631 (13)	C1—H1	0.9400
Co1—O2^iii	2.0910 (14)	C2—C3	1.418 (3)
Co1—O1^i	2.1083 (14)	C2—H2	0.9400
O1—C1	1.240 (2)	C3—C6	1.455 (3)
O2—C2	1.249 (2)	C4—C5	1.370 (3)
O2—Co1^iv	2.0910 (14)	C4—H4	0.9400
O3—H1W	0.8500	C5—C6	1.411 (3)
O3—H2W	0.8500	C5—H5	0.9400
O4—N2	1.236 (3)	C6—C7	1.410 (3)
O5—N2	1.251 (3)	C7—C8	1.369 (3)
O6—N2	1.237 (2)	C7—H7	0.9400
N1—C8	1.336 (3)	C8—H8	0.9400
O3^i—Co1—O3	180.00 (11)	O6—N2—O5	119.9 (2)
O3^i—Co1—O2^ii	91.06 (5)	O1—C1—C3	128.04 (19)
O3^i—Co1—O2^iii	88.94 (5)	O1—C1—H1	116.0
O3—Co1—O2^iii	91.06 (5)	C3—C1—H1	116.0
O2^ii—Co1—O2^iii	180.00 (8)	O2—C2—C3	127.99 (18)
O3^i—Co1—O1^i	90.04 (5)	O2—C2—H2	116.0
O3—Co1—O1^i	89.96 (5)	C3—C2—H2	116.0
O2^ii—Co1—O1^i	90.71 (6)	C2—C3—C1	113.37 (17)
O2^iii—Co1—O1^i	89.29 (6)	C2—C3—C6	123.44 (16)
O3^i—Co1—O1	89.96 (5)	C1—C3—C6	123.12 (18)
O2^ii—Co1—O1	89.29 (6)	N1—C4—C5	120.9 (2)
O3—Co1—O1	90.04 (5)	N1—C4—H4	119.5
O3—Co1—O2^ii	88.94 (5)	C5—C4—H4	119.5
O2^iii—Co1—O1	90.71 (6)	C4—C5—C6	120.8 (2)
O1^i—Co1—O1	180.00 (8)	C4—C5—H5	119.6
C1—O1—Co1	131.02 (13)	C6—C5—H5	119.6
C2—O2—Co1^iv	126.00 (13)	C7—C6—C5	115.59 (18)
Co1—O3—H1W	111.8	C7—C6—C3	122.54 (17)
Co1—O3—H2W	111.8	C5—C6—C3	121.87 (18)
H1W—O3—H2W	109.6	C8—C7—C6	120.93 (19)
C8—N1—C4	120.82 (18)	C8—C7—H7	119.5
C8—N1—H1N	119.6	C6—C7—H7	119.5
C4—N1—H1N	119.6	N1—C8—C7	120.8 (2)
O4—N2—O6	121.2 (2)	N1—C8—H8	119.6
O4—N2—O5	118.9 (2)	C7—C8—H8	119.6
O3^i—Co1—O1—C1	90.76 (19)	N1—C4—C5—C6	−1.5 (4)
O3—Co1—O1—C1	−89.24 (19)	C4—C5—C6—C7	4.5 (3)
O2^ii—Co1—O1—C1	−0.31 (19)	C4—C5—C6—C3	−175.2 (2)
O2^iii—Co1—O1—C1	179.69 (19)	C2—C3—C6—C7	−172.17 (19)
Co1—O1—C1—C3	171.70 (15)	C1—C3—C6—C7	4.8 (3)
Co1^iv—O2—C2—C3	−178.97 (16)	C2—C3—C6—C5	7.5 (3)
O1—C1—C3—C2	176.1 (2)	C1—C3—C6—C5	−175.5 (2)
O2—C2—C3—C1	−178.7 (2)	C5—C6—C7—C8	−4.6 (3)
O2—C2—C3—C6	−1.5 (4)	C3—C6—C7—C8	175.1 (2)
O1—C1—C3—C6	−1.2 (3)	C4—N1—C8—C7	1.7 (4)
C8—N1—C4—C5	−1.7 (4)	C6—C7—C8—N1	1.7 (4)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H1W···O5^v	0.85	2.00	2.766 (2)	149
O3—H2W···O6	0.85	1.94	2.749 (2)	158
N1—H1N···O4^vi	0.87	2.00	2.864 (3)	170

Symmetry codes: (v) −x+1, −y, −z; (vi) −x+1, −y+1, −z.