Poly[diaqua­([mu]₄-benzene-1,2-di­car­boxyl­ato)(isonicotinato-[kappa]²O,O')gadolinium(III)]

The title neutral polymer, [Gd(C₆H₄NO₂)(C₈H₄O₄)(H₂O)₂]_n, contains an extended two-dimensional wave-like lanthanide carboxyl­ate layer decorated by isonicotinate (IN) ligands. The Gd^II atom is eight-coordinated by four carboxyl­ate O atoms from four benzene-1,2-dicarboxyl­ate (1,2-bdc) ligands, two 1,2-bdc carboxyl­ate O atoms from one chelating IN ligand and two terminal water mol­ecules, forming a bicapped trigonal-prismatic coordination geometry. The wave-like layers are stacked in an ...ABAB... packing mode along the c-axis direction. Strong hydrogen-bonding inter­actions further stabilize the structure of the title compound.

S1. Comment

Considerable attention has been paid to the design of multi-dimensional metal–organic frameworks (MOFs), owing to their intriguing structural topological properties and potential magnetism (Noro et al., 2000; Banfi et al., 2004). The rational choice of appropriate metal ions and organic linkers is an important issue for the design and synthesis of predictable MOFs. The lanthanide ions are good candidates for the construction of MOFs, because of their high coordination number with variable coordination geometries and their unique magnetism and luminescent properties. The aromatic polycarboxylate ligands, possessing multi-dentate functional groups and versatile coordination modes, have been demonstrated as useful organic linkers for the construction of MOFs (Fan et al., 2003; Wang et al., 2004). Many infinite one-, two- and three-dimensional coordination compounds have been reported to be assembled by the three isomeric benzenedicarboxylate (bdc) ligands (Groenman et al., 1998; Chen et al., 2007). Among them, the 1,2-bdc ligand, when used as the sole organic linker, often forms zero-dimensional isolated structures or one-dimensional chains (Ma et al., 2004; Wang et al., 2007), but occasionally results in a higher dimensionality metal–carboxylate framework as demonstrated by several reports concerning two-dimensional layers in metal-carboxylate coordination polymers (Natarajan & Thirumurugan, 2005; Wang et al., 2003). We present here a new two-dimensional MOF assembled by Gd^III atoms and 1,2-bdc ligands in the presence of isonicotinate (IN) ligands, in which 1,2-bdc acts as the only organic linker.

The title compound, (I), consists of an infinite two-dimensional wave-like lanthanide carboxylate layer decorated by the isonicotinate ligands. The asymmetric unit (Fig. 1) contains one gadolinium(III) ion, one bdc ligand, one IN ligand and two aqua ligands. Each Gd^III ion is eight-coordinated with a bicapped trigonal–prismatic coordination geometry consisting of four carboxylate O atoms (O_COO) from four bdc ligands, two O_COO atoms from one chelating IN ligand and two terminal water molecules. The Gd—O bond lengths range from 2.310 (3) to 2.499 (3) Å (Table 1), comparable to those of other gadolinium(III)–carboxylate complexes (Natarajan & Thirumurugan, 2005).

Although abundant and versatile coordination modes have been found in IN and bdc ligands, only a single bidentate chelating (for IN) and a unique tetradentate bridging (for bdc) mode are adopted in the crystal structure of the title compound. This suggests a high cooperativity between the IN and bdc ligands (Wang et al., 2007) in the formation of the framework.

The Gd^III centers are bridged by carboxylate groups of bdc ligands so as to form eight-membered rings (Fig. 2, rings A and B). Such rings are further connected to one another by sharing common Gd atoms, and form an infinite wave-like chain propagating approximately along the a-axis direction. The Gd···Gd distances between neighboring Gd atoms, bridged by C7OO and C8OO groups, are 5.530 (12) and 4.846 (12) Å, respectively. The phenyl rings of the bdc ligands link neighboring one-dimensional wave-like chains to construct a two-dimensional undulating layer in the ab plane and form two 14-membered rings with dimensions of 5.896 (12) × 7.457 (12) Ų (ring C) and 7.520 (7) × 7.014 (26) Ų (ring D).

The IN ligand in the title compound does not serve as an organic linker or raise the dimensionality of the structure, but only decorates the two-dimensional layer, owing to its coordination mode chelating a single Gd center. Each of the two coordinated water molecules on the Gd atom forms two O—H···O hydrogen bonds (Table 2) with neighboring carboxylate atoms. These hydrogen-bonding interactions help to consolidate the layer structure. The undulating layers are stacked together in an ABAB packing mode along the c-axis direction, with the pyridyl rings of the IN ligands projecting into the interlamellar region (Fig. 3).

Compound [H₂PIP][Gd₂(H₂O)₂(bdc)₂] (PIP is piperazine; Natarajan & Thirumurugan, 2005) is another example of a two-dimensional network constructed from Gd^III ions linked by a single organic linker, 1,2-bdc, in the presence of piperazine. In this compound, the Gd atom is eight-coordinated by five bdc anions and one aqua ligand, while the Gd atom in the title compound is eight-coordinated by four bdc ligands, one IN anion and two aqua ligands. The two carboxylate units of the bdc ligand in [H₂PIP][Gd₂(H₂O)₂(bdc)₂] have three coordination modes, namely chelating to one Gd atom, bridging two Gd atoms and monodentate connecting to only one Gd atom. The H₂PIP ligands are isolated and located in the voids within the sheet. By contrast, both carboxylate groups of 1,2-bdc in the title compound bridge two Gd atoms, and the IN ligands are covalently connected to the two-dimensional lanthanide carboxylate framework.

Related literature

For related literature, see: Banfi et al. (2004); Chen et al. (2007); Fan et al. (2003); Groenman et al. (1998); Ma et al. (2004); Natarajan & Thirumurugan (2005); Noro et al. (2000); Wang et al. (2003, 2004, 2007).

S2. Experimental

A mixture of Gd₂O₃ (0.036 g, 0.1 mmol), benzene-1,2-dicarboxylic acid (0.135 g, 0.8 mmol), isonicotinic acid (0.098 g, 0.8 mmol) and water (8 ml) was placed in an 18 ml Teflon-lined Parr acid digestion bomb. The pH value of the reaction mixture was adjusted to ca 5.0 with 10% sodium hydroxide. The mixture was then heated for 4 d at 443 K under autogenous pressure. Slow cooling of the reaction mixture to room temperature gave colorless prismatic crystals (yield ca 42%, based on Gd).

S3. Refinement

The water H atoms were located in difference Fourier maps and fixed in refinement [with O—H = 0.82 Å and U_iso(H) = 1.2U_eq(O)]. Other H atoms were placed geometrically and refined as riding [with C—H = 0.93 Å and U_iso(H) = 1.2 U_eq(C)].

Computing details

Data collection: CrystalClear (Rigaku, 2002); cell refinement: CrystalClear (Rigaku, 2002); data reduction: CrystalClear (Rigaku, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXL97 (Sheldrick, 2008) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. A view of molecular structure of title compound. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) -x, -y + 3, -z; (ii) -x, -y + 2, -z; (iii) x + 1/2, y - 1/2, z; (iv) x - 1/2, y + 1/2, z.]
	Fig. 2. A perspective view of the two-dimensional layer structure. The pyridyl C and N atoms of the IN ligands and all H atoms have been omitted for clarity.
	Fig. 3. A view along the b axis showing the stacking of layers in the c-axis direction. All H atoms have been omitted for clarity.

Poly[diaqua(µ₄-benzene-1,2-dicarboxylato)(isonicotinato- κ²O,O')gadolinium(III)]

Crystal data

[Gd(C8H4O4)(C6H4NO2)(H2O)2]	F(000) = 1848
Mr = 479.50	Dx = 2.039 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 3574 reflections
a = 16.6086 (15) Å	θ = 3.1–27.5°
b = 6.1031 (3) Å	µ = 4.29 mm^−1
c = 31.450 (3) Å	T = 298 K
β = 101.495 (6)°	Prism, colorless
V = 3123.9 (4) Å^3	0.10 × 0.10 × 0.05 mm
Z = 8

Data collection

Rigaku Mercury CCD diffractometer	3566 independent reflections
Radiation source: fine-focus sealed tube	3308 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.031
Detector resolution: 14.6306 pixels mm^-1	θmax = 27.5°, θmin = 2.5°
ω scan	h = −21→18
Absorption correction: multi-scan (CrystalClear; Rigaku, 2002)	k = −7→7
Tmin = 0.673, Tmax = 0.814	l = −40→40
11364 measured reflections

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)] = 0.033	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.073	H-atom parameters constrained
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0333P)^2 + 14.8145P] where P = (Fo^2 + 2Fc^2)/3
3566 reflections	(Δ/σ)max < 0.001
217 parameters	Δρmax = 1.20 e Å^−3
6 restraints	Δρmin = −0.97 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
Gd1	0.139846 (11)	1.22196 (3)	0.039941 (6)	0.01722 (8)
O1	0.00523 (18)	1.1186 (6)	0.03770 (12)	0.0358 (9)
O2	−0.12825 (17)	1.0591 (5)	0.01584 (10)	0.0229 (6)
O3	−0.10121 (18)	1.5870 (5)	0.02786 (10)	0.0240 (7)
O4	−0.22583 (18)	1.6064 (5)	0.04302 (11)	0.0298 (7)
O5	0.1478 (2)	0.8926 (5)	0.08780 (10)	0.0314 (7)
O6	0.1722 (2)	1.2159 (5)	0.11810 (11)	0.0312 (8)
O7	0.06391 (18)	1.5307 (5)	0.05751 (11)	0.0293 (7)
H7A	0.0807	1.6547	0.0645	0.035*
H7B	0.0142	1.5347	0.0480	0.035*
O8	0.22841 (18)	1.5367 (5)	0.05215 (11)	0.0319 (8)
H8A	0.2736	1.5274	0.0456	0.038*
H8B	0.2244	1.6677	0.0574	0.038*
N1	0.1300 (6)	0.7787 (12)	0.2444 (2)	0.091 (2)
C1	−0.0810 (2)	1.2045 (7)	0.08639 (14)	0.0191 (8)
C2	−0.1237 (2)	1.3977 (7)	0.09020 (13)	0.0198 (8)
C3	−0.1383 (3)	1.4600 (8)	0.13042 (15)	0.0317 (11)
H3	−0.1675	1.5876	0.1330	0.038*
C4	−0.1095 (4)	1.3327 (11)	0.16656 (18)	0.0473 (15)
H4	−0.1187	1.3758	0.1936	0.057*
C5	−0.0672 (4)	1.1416 (11)	0.16258 (18)	0.0499 (15)
H5	−0.0481	1.0551	0.1868	0.060*
C6	−0.0532 (3)	1.0793 (9)	0.12232 (16)	0.0361 (12)
H6	−0.0246	0.9506	0.1197	0.043*
C7	−0.0664 (2)	1.1242 (7)	0.04312 (14)	0.0200 (8)
C8	−0.1530 (2)	1.5409 (7)	0.05133 (14)	0.0199 (8)
C9	0.1530 (3)	0.9233 (8)	0.16459 (16)	0.0301 (10)
C10	0.1742 (4)	1.0557 (10)	0.20058 (18)	0.0478 (14)
H10	0.1953	1.1949	0.1977	0.057*
C11	0.1646 (5)	0.9840 (13)	0.2410 (2)	0.0636 (18)
H11	0.1809	1.0714	0.2654	0.076*
C12	0.1099 (5)	0.6447 (12)	0.2087 (2)	0.064 (2)
H12	0.0883	0.5060	0.2115	0.077*
C13	0.1218 (4)	0.7160 (9)	0.1690 (2)	0.0448 (14)
H13	0.1088	0.6245	0.1450	0.054*
C14	0.1590 (3)	1.0145 (8)	0.12102 (15)	0.0268 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Gd1	0.01152 (11)	0.01725 (12)	0.02367 (13)	0.00141 (7)	0.00537 (8)	−0.00047 (8)
O1	0.0143 (16)	0.047 (2)	0.049 (2)	−0.0095 (15)	0.0147 (14)	−0.0264 (17)
O2	0.0157 (15)	0.0219 (16)	0.0321 (17)	0.0000 (12)	0.0071 (12)	−0.0050 (13)
O3	0.0194 (15)	0.0254 (16)	0.0288 (17)	0.0031 (12)	0.0084 (13)	0.0065 (13)
O4	0.0140 (15)	0.0352 (19)	0.0398 (19)	0.0116 (13)	0.0047 (13)	−0.0007 (15)
O5	0.040 (2)	0.0256 (17)	0.0284 (18)	−0.0060 (15)	0.0067 (14)	−0.0037 (14)
O6	0.040 (2)	0.0230 (17)	0.0308 (18)	−0.0030 (14)	0.0068 (15)	−0.0009 (13)
O7	0.0154 (15)	0.0196 (16)	0.054 (2)	0.0015 (12)	0.0085 (14)	−0.0093 (15)
O8	0.0178 (16)	0.0243 (17)	0.057 (2)	−0.0047 (13)	0.0154 (15)	−0.0133 (15)
N1	0.128 (7)	0.093 (5)	0.060 (4)	0.025 (5)	0.036 (4)	0.023 (4)
C1	0.0138 (19)	0.018 (2)	0.026 (2)	0.0016 (16)	0.0057 (16)	−0.0015 (16)
C2	0.0116 (19)	0.024 (2)	0.024 (2)	0.0009 (16)	0.0052 (16)	−0.0005 (17)
C3	0.034 (3)	0.035 (3)	0.027 (2)	0.001 (2)	0.010 (2)	−0.006 (2)
C4	0.060 (4)	0.060 (4)	0.026 (3)	0.011 (3)	0.018 (3)	0.000 (3)
C5	0.061 (4)	0.056 (4)	0.033 (3)	0.014 (3)	0.011 (3)	0.019 (3)
C6	0.035 (3)	0.037 (3)	0.037 (3)	0.007 (2)	0.009 (2)	0.010 (2)
C7	0.017 (2)	0.0135 (19)	0.031 (2)	0.0001 (16)	0.0091 (17)	−0.0001 (16)
C8	0.015 (2)	0.017 (2)	0.028 (2)	0.0011 (16)	0.0058 (17)	−0.0059 (16)
C9	0.031 (3)	0.030 (3)	0.031 (3)	0.009 (2)	0.009 (2)	0.007 (2)
C10	0.067 (4)	0.040 (3)	0.037 (3)	0.003 (3)	0.013 (3)	−0.001 (2)
C11	0.083 (4)	0.064 (3)	0.045 (3)	0.005 (3)	0.016 (3)	−0.001 (3)
C12	0.102 (6)	0.045 (4)	0.053 (4)	0.003 (4)	0.035 (4)	0.017 (3)
C13	0.057 (4)	0.036 (3)	0.042 (3)	0.004 (3)	0.013 (3)	0.011 (2)
C14	0.023 (2)	0.026 (2)	0.030 (2)	0.0010 (18)	0.0036 (18)	0.0018 (19)

Geometric parameters (Å, º)

Gd1—O1	2.310 (3)	C1—C6	1.366 (6)
Gd1—O2^i	2.434 (3)	C1—C2	1.393 (6)
Gd1—O3^ii	2.402 (3)	C1—C7	1.511 (6)
Gd1—O4^iii	2.323 (3)	C2—C3	1.388 (6)
Gd1—O5	2.499 (3)	C2—C8	1.503 (6)
Gd1—O6	2.410 (3)	C3—C4	1.381 (7)
Gd1—O7	2.393 (3)	C3—H3	0.9300
Gd1—O8	2.403 (3)	C4—C5	1.380 (8)
Gd1—C14	2.808 (5)	C4—H4	0.9300
O1—C7	1.236 (5)	C5—C6	1.385 (7)
O2—C7	1.264 (5)	C5—H5	0.9300
O3—C8	1.272 (5)	C6—H6	0.9300
O4—C8	1.251 (5)	C9—C10	1.378 (7)
O5—C14	1.266 (5)	C9—C13	1.385 (7)
O6—C14	1.255 (5)	C9—C14	1.501 (6)
O7—H7A	0.8210	C10—C11	1.382 (8)
O7—H7B	0.8205	C10—H10	0.9300
O8—H8A	0.8188	C11—H11	0.9300
O8—H8B	0.8211	C12—C13	1.373 (8)
N1—C12	1.375 (10)	C12—H12	0.9300
N1—C11	1.392 (10)	C13—H13	0.9300
O1—Gd1—O2^i	81.29 (10)	H8A—O8—H8B	103.5
O1—Gd1—O3^ii	91.13 (12)	C12—N1—C11	120.5 (6)
O1—Gd1—O4^iii	146.48 (13)	C6—C1—C2	119.7 (4)
O1—Gd1—O5	74.53 (13)	C6—C1—C7	118.4 (4)
O1—Gd1—O6	92.58 (12)	C2—C1—C7	121.8 (4)
O1—Gd1—O7	70.77 (11)	C3—C2—C1	119.6 (4)
O1—Gd1—O8	141.33 (11)	C3—C2—C8	119.7 (4)
O4^iii—Gd1—O7	140.84 (11)	C1—C2—C8	120.7 (4)
O4^iii—Gd1—O3^ii	105.58 (10)	C4—C3—C2	120.1 (5)
O7—Gd1—O3^ii	76.29 (11)	C4—C3—H3	119.9
O4^iii—Gd1—O8	71.58 (11)	C2—C3—H3	119.9
O7—Gd1—O8	70.58 (10)	C5—C4—C3	120.0 (5)
O3^ii—Gd1—O8	78.50 (11)	C5—C4—H4	120.0
O4^iii—Gd1—O6	86.30 (12)	C3—C4—H4	120.0
O7—Gd1—O6	78.31 (11)	C4—C5—C6	119.7 (5)
O3^ii—Gd1—O6	151.49 (11)	C4—C5—H5	120.1
O8—Gd1—O6	81.04 (11)	C6—C5—H5	120.1
O4^iii—Gd1—O2^i	75.72 (11)	C1—C6—C5	120.8 (5)
O7—Gd1—O2^i	138.76 (11)	C1—C6—H6	119.6
O3^ii—Gd1—O2^i	74.54 (10)	C5—C6—H6	119.6
O8—Gd1—O2^i	129.53 (10)	O1—C7—O2	124.9 (4)
O6—Gd1—O2^i	133.95 (10)	O1—C7—C1	117.7 (4)
O4^iii—Gd1—O5	78.22 (11)	O2—C7—C1	117.3 (3)
O7—Gd1—O5	117.47 (11)	O4—C8—O3	123.1 (4)
O3^ii—Gd1—O5	153.84 (11)	O4—C8—C2	120.0 (4)
O8—Gd1—O5	126.13 (11)	O3—C8—C2	117.0 (3)
O6—Gd1—O5	53.05 (10)	C10—C9—C13	119.5 (5)
O2^i—Gd1—O5	81.63 (10)	C10—C9—C14	118.7 (5)
O1—Gd1—C14	80.70 (13)	C13—C9—C14	121.7 (5)
O4^iii—Gd1—C14	83.76 (12)	C9—C10—C11	120.7 (6)
O7—Gd1—C14	96.60 (12)	C9—C10—H10	119.6
O3^ii—Gd1—C14	170.65 (11)	C11—C10—H10	119.6
O8—Gd1—C14	105.10 (13)	C10—C11—N1	118.9 (7)
O6—Gd1—C14	26.46 (12)	C10—C11—H11	120.6
O2^i—Gd1—C14	108.37 (12)	N1—C11—H11	120.6
O5—Gd1—C14	26.79 (12)	C13—C12—N1	119.9 (7)
C7—O1—Gd1	160.2 (3)	C13—C12—H12	120.0
C7—O2—Gd1^i	130.4 (3)	N1—C12—H12	120.0
C8—O3—Gd1^ii	122.0 (3)	C12—C13—C9	120.4 (6)
C8—O4—Gd1^iv	170.4 (3)	C12—C13—H13	119.8
C14—O5—Gd1	90.3 (3)	C9—C13—H13	119.8
C14—O6—Gd1	94.7 (3)	O6—C14—O5	121.0 (4)
Gd1—O7—H7A	128.4	O6—C14—C9	118.3 (4)
Gd1—O7—H7B	118.5	O5—C14—C9	120.7 (4)
H7A—O7—H7B	109.5	O6—C14—Gd1	58.8 (2)
Gd1—O8—H8A	117.8	O5—C14—Gd1	62.9 (2)
Gd1—O8—H8B	137.6	C9—C14—Gd1	168.7 (3)

Symmetry codes: (i) −x, −y+2, −z; (ii) −x, −y+3, −z; (iii) x+1/2, y−1/2, z; (iv) x−1/2, y+1/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O7—H7A···O5^v	0.82	1.89	2.682 (4)	163
O7—H7B···O3	0.82	1.92	2.737 (4)	172
O8—H8A···O2^vi	0.82	2.04	2.841 (4)	165
O8—H8B···O5^v	0.82	2.21	2.893 (4)	140

Symmetry codes: (v) x, y+1, z; (vi) x+1/2, y+1/2, z.