Comment

The construction of inorganic-organic hybrid frameworks containing d-block transition metal ions and ligands with 4-pyridyl donor groups has developed significantly in recent years (see, for example, Batten & Robson, 1998; Moulton & Zaworotko, 2001). We are interested in the synthesis of novel hybrid compounds which contain not only 4-pyridyl but also carboxylate groups in the crystal structure (Almeida Paz, Khimyak et al., 2002). Recently, we also reported a novel one-dimensional Co²⁺ coordination polymer containing 1,2-bis(4-pyridyl)ethane (BPE), CUmof-4 (Almeida Paz, Bond et al., 2002).

Just as for CUmof-4, the title compound, [Co(BPY)₂(H₂O)₄](NDC).2H₂O, CUmof-6, (I), was synthesized under mild hydrothermal conditions and contains only one crystallographically unique Co²⁺ centre, occupying a centre of symmetry in P. The metal ion shows an almost regular octahedral chemical environment, composed of four water molecules (forming the equatorial plane) and two trans-coordinated 4-pyridyl N atoms (from BPY) at the apical positions (Table 1 and Fig. 1). Individual [Co(BPY)₂(H₂O)₄]²⁺ complex cations stack in an offset manner along the a direction through close BPY contacts. The average distance between adjacent aromatic rings is ca 3.5 Å (Fig. 2). Interestingly, and unlike the situation in CUmof-4, the NDC^2- ions do not participate in these interactions. This is explained by the fact that the metal-to-metal distance imposed by a BPY spacer is not sufficient to accommodate the NDC^2- anions. This may also account for the presence of extra water of crystallization. Compound (I) can be further described by the alternation along the b direction of layers of the complex cations with layers of NDC^2- (Fig. 2). O-HO^- and O-HN hydrogen bonds between the NDC^2- ions and the uncoordinated 4-pyridyl group with the water molecules give rise to a three-dimensional network (Table 2 and Fig. 3).

Figure 1 The asymmetric unit of (I), CUmof-6, represented with displacement ellipsoids at the 50% probability level and showing the labelling scheme for non-H atoms. Unlabelled ball-and-stick atoms were generated by symmetry [Symmetry codes: (for BPY) -x, -y, -z and (for NDC2-) -x, 1 - y, 1 - z].

Figure 2 Perspective view of CUmof-6 along the a direction. Co2+ centres are represented as octahedra, BPY ligands with hollow bonds, NDC2- with filled bonds, and water of crystallization in blue.

Figure 3 Perspective view of CUmof-6 along the c direction, showing the hydrogen-bonding network (dashed lines). H atoms have been omitted for clarity.

Experimental

All chemicals were obtained from commercial sources and were used as received. To a solution of Co(NO₃)₂·6H₂O (0.243 g, Aldrich) in distilled water (6.41 g), 4,4'-bipyridyl (BPY, 0.164 g, Aldrich), 2,6-naphthalenedicarboxylic acid (H₂NDC, 0.218 g, Aldrich) and triethylamine (TEA, 0208 g, Avocado) were added and the mixture was stirred thoroughly for 1 h at ambient temperature. The suspension, with a H₂NDC:Co²⁺:BPY:TEA:H₂O composition ratio of 1.00:1.01:1.04:2.04:353, was placed inside a Parr stainless steel Teflon-lined reaction vessel (8 ml, 70% full). The reaction was performed under autogeneous pressure and static conditions in a pre-heated oven at 418 K for 3 h. The vessel was then cooled slowly inside the oven to 298 K at a rate of 5 K h^-1 before opening. The crystalline product was collected by vacuum filtration and crystals of (I) were manually separated and preserved in a portion of the reaction vessel solution.

Crystal data

C20H24CoN4O4·C12H6O4·2H2O Mr = 693.56 Triclinic,  a = 6.9856 (5) Å b = 9.2926 (11) Å c = 12.3538 (14) Å = 78.585 (5)° = 84.015 (7)° = 73.740 (7)° V = 753.62 (13) Å3 Z = 1 Dx = 1.528 Mg m-3 Mo K radiation Cell parameters from 5738 reflections = 1.0-25.0° = 0.64 mm-1 T = 180 (2) K Needle, colourless 0.10 × 0.05 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer Thin-slice and scans Absorption correction: multi-scan (SORTAV; Blessing, 1995) Tmin = 0.839, Tmax = 0.955 5657 measured reflections 2574 independent reflections 2083 reflections with I > 2(I) Rint = 0.059 max = 24.9° h = -7 8 k = -10 10 l = -13 14

Refinement

Refinement on F2 R[F2 > 2(F2)] = 0.046 wR(F2) = 0.121 S = 1.10 2574 reflections 234 parameters H atoms treated by a mixture of independent and constrained refinement w = 1/[2(Fo2) + (0.0493P)2 + 0.2073P] where P = (Fo2 + 2Fc2)/3 (/)max = 0.009 max = 0.34 e Å-3 min = -0.64 e Å-3

Table 1 Selected geometric parameters (Å, °) Co1-O12 2.070 (2) Co1-O11 2.124 (2) Co1-N21 2.153 (3) O12-Co1-O11 91.04 (9) O12i-Co1-O11 88.96 (9) O12-Co1-N21 89.34 (9) O12i-Co1-N21 90.66 (9) O11-Co1-N21 87.41 (9) O11i-Co1-N21 92.59 (9) Symmetry code: (i) -x,-y,-z.

Table 2 Hydrogen-bonding geometry (Å, °) D-HA D-H HA DA D-HA O11-H11AO4W 0.837 (17) 1.958 (19) 2.785 (3) 169 (3) O11-H11BO311ii 0.835 (17) 1.920 (18) 2.754 (3) 175 (4) O12-H12AO4Wiii 0.832 (17) 2.00 (2) 2.798 (3) 162 (3) O12-H12BN22iv 0.829 (18) 1.951 (19) 2.772 (4) 170 (4) O4W-H4AO312v 0.833 (18) 1.946 (19) 2.767 (3) 169 (4) O4W-H4BO311 0.828 (18) 1.932 (19) 2.750 (3) 170 (4) Symmetry codes: (ii) -x,1-y,-z; (iii) x-1,y,z; (iv) x,y,z-1; (v) 1-x,1-y,-z.

Water H atoms were located in difference Fourier maps and refined with a single isotropic displacement parameter common to all H atoms. O-H and HH distances were restrained to ensure a reasonable geometry for the water molecules. H atoms bound to carbon were placed in calculated positions and allowed to ride during subsequent refinement, with U_iso(H) = 1.2U_eq(C).

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: SHELXTL (Bruker, 2001); molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.