Poly[[μ₃-2-(carboxyl­atometh­yl)­benzoato-κ³O¹:O²:O²]bis­(1H-imidazole-κN³)copper(II)]

In the title polymeric compound, [Cu(C₉H₆O₄)(C₃H₄N₂)₂]_n, the copper(II) cation occupies an N₂O₃ coordination sphere defined by two 1H-imidazole (imid) ligands in trans positions and three carboxyl­ate O atoms from three different 2-(car­boxyl­atometh­yl)benzoate (hpt²⁻) dianions. The geometry is that of a square pyramid with one of the O atoms at the apex, bridging neighbouring metal centres into an [–ON₂CuO₂CuN₂O–] dinuclear unit. These units are in turn connected by hpt anions into a reticular mesh topologically characterized by two types of loops, viz. a four-membered Cu₂O₂ diamond motif and a 32-membered Cu₄O₈C₂₀ ring. The imid groups do not take part in the formation of the two-dimensional structure, but take part in the N—H...O interactions. These arise only within individual planes, inter­planar inter­actions being only of the van der Waals type.

S1. Comment

The study of organic–inorganic hybrid coordination frameworks is a key point in [an important part of?] modern structural chemistry, mainly due to the potential properties [of these materials] with which many of these materials are adorned. In these `prediction, design, synthesis and structural analysis' exercises, the ligands usually preferred are those characterized by versatility, coordination capabilities and, eventually, a large number of possible coordination modes (Archer, 2001). Benzenecarboxylic acids of flexible structure, such as homophthalic acid (H₂hpt), the ligand of interest to us, comply with many of these requisites and have largely proven to be useful in constructing complex frameworks with varied topology (He et al., 2006; Cavellec et al., 2003; Pan et al., 2003; Wan et al., 2003).

Interest in these types of materials, and in hpt-based materials, as representatives has been explosive in the last few years, as assessed by inspection of the distribution along the years of structural studies on hpt complexes [Cambridge Structural Database (CSD), Version 5.32; Allen, 2002]: the first report appeared in 2001 (Cotton et al., 2001) and in the following five years only two more followed (Burrows et al., 2003, 2004). But in the equivalent five-year-period following 2006, 18 new structures have appeared, confirming this fast-growing trend.

In these reported structures, the hpt ligand showed its varied binding capabilities by displaying nine different coordination modes. We refer the interested reader to Atria et al. (2011) for a comprehensive review of the ways in which the ligand has shown to bind to metal centres. In this same report, two new isomorphous hpt structures were presented, namely M[(Hdap)(hpt)(H₂O)]₂.4H₂O (where dap is 2,6-diaminopurine and M is Ni^II or Co^II); in these structures, the hpt anion displayed an unusual (and at the time unreported) µ-κ¹O coordination mode.

In pursuit of our interest in the different architectures to which the hpt ligand can give rise, we present herein a new copper(II) complex poly[[µ₃-2-(carboxylatomethyl)benzoato]bis(1H-imidazole)copper(II)], (I), incorporating a fully deprotonated 2-(carboxylatomethyl)benzoate (hpt^2-) dianion and 1H-imidazole (imid) as an ancillary ligand. In this structure, again, a new bridging coordination mode for the hpt^2- anion is found.

Fig. 1 presents an ellipsoid plot of the (extended) asymmetric unit of (I), showing the complete coordination environment of the copper(II) cation and the dimeric unit it gives rise to: two independent imid groups are in trans positions and three symmetry-related hpt^2- anions complete a CuN₂O₂+O square-pyramidal arrangement, with a rather regular base [Cu—L distance range = 1.9643 (18)–2.0060 (18) Å and L—Cu—L cis angle range = 88.60 (8)–91.39 (8)°; L = basal N, O], and an apical bond tilted by 16.2 (2)° from the vertrical to the mean basal plane. The µ₃κ²-O:O':O' mode displayed by hpt^2- is novel and should be added to those listed in Atria et al. (2011). The imidazole ligands coordinate trans to each other [N—Cu—N = 169.82 (9)°] and only interact with the rest of the structure via nonbonding interactions (see below). The hpt^2- anions, instead, play a leading role in the spatial arrangement: via the sharing of atom O43 with two different coordination polyhedra they define a dimeric substructure, linking adjacent moieties into dinuclear entities ("A" in Figs. 1 and 2), with a Cu1···Cu1ⁱⁱ distance of 3.5710 (8) Å [symmetry code: (ii) -x+2, -y+1, -z+1]. The resulting Cu₂O₂ loops, in turn, appear as the nodes of much larger macrocycles determined by the stretched out hpt^2- carboxylato and methylcarboxylato arms, ending up in large Cu₄O₈C₂₀ loops [or (CuO₂C₅)₄, "B" in Fig. 2]. The final structure can be envisaged as the concatenation into a two-dimensional mesh of these two kinds of small and large loops. Even if imid ligands pend [bend?] outwards, with no direct intervention in the mesh formation, they collaborate [contribute?] to the mesh stability through two strong N—H···O hydrogen bonds described in Table 2 and shown in Fig 1. In these contacts, the donor atoms are the protonated imid N atoms, while the acceptors are the two carboxylate O atoms not involved in coordination. These contacts, as well as the remaining (though weaker) interactions of the C—H···O and C—H···π types shown in Table 2, are internal to the two-dimensional structures and do not mix adjacent planes, [for what] interplanar stability appears [to be] achieved through van der Waals forces only.

Fig. 3 shows two lateral views of these planes, depicting this lack of close contacts. The reader should note that the views in Fig. 3 might be deceptive in suggesting some kind of π–π interaction between benzene hpt^2- groups; this is just a perspective artifact since the centroids of neighbouring hpt groups in contiguous planes lie more than 5.5 Å apart and the rings they belong to are far from parallel.

Large loops like the (CuO₂C₅)₄ one herein, or, more generally, (M—L)₄, with M being any transition metal and L being the `looping' ligand, are not uncommon in three-dimensional structures. Sometimes they appear embracing smaller, embedded loops and in this context the larger loops are not so relevant from a structural point of view. However, browsing through the CSD (Allen, 2002) we spotted a few cases presenting rings of a similar size as in (I) which also constituted primary building units in the crystal architecture. Surprisingly, in most of them, the L ligand was a close relative in the benzylcarboxylate family. Some examples, given in a sequence of the type [CSD refcode: M—L (reference)] are: ATORIK: Zn–isophthalohydrazide (He et al., 2004); FUDHOC, FUDHUI, FUHYAJ, FUHYAJ01, FUHYEN01, FUHYIR: Cu–trimesic acid (Ene et al., 2009); SOMLUC: Ni–pyrazole-3,5-dicarboxylate (Bai et al., 2008); TIGLAW: Co–pyrazole-3,5-dicarboxylate (Pan et al., 2001); TUHFIM: Co–5-tert-butylisophalate (Du et al., 2009).

Many of these examples display free open loops where solvents of different kinds and shapes (water or pyridylmethanol) reside. In the present case of (I), instead, the bulky hpt^2- and imid groups lean towards the loop centre, thus limiting the hosting capability of the compound.

Related literature

For related literature, see: Allen (2002); Archer (2001); Atria et al. (2011); Bai et al. (2008); Burrows et al. (2003, 2004); Cavellec et al. (2003); Cotton et al. (2001); Du et al. (2009); Ene et al. (2009); He et al. (2004, 2006); Pan et al. (2001, 2003); Wan et al. (2003).

S2. Experimental

Complex (I) was synthesized by adding an aqueous solution (80 ml) of copper acetate monohydrate (1 mmol) to an aqueous solution containing homophthalic acid (0.5 mmol) and NaOH (1 mmol). The mixture was heated under reflux for 20 min. An ethanolic solution (30 ml) containing imidazole (0.5 mmol) was added slowly and the final solution was maintained under reflux for 4 h. Single crystals suitable for X-ray diffraction studies were obtained by slow concentration of the solution.

S3. Refinement

All the H atoms were clearly seen in a difference Fourier map but they were treated differently in the refinement. H atoms on C atoms were repositioned at their expected locations and allowed to ride both with respect to their coordinates (C—H = 0.93–0.97 Å) and their isotropic displacement parameters [U_iso(H) = 1.2U_eq(C)]. H atoms attached to N atoms were refined freely.

Computing details

Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of (I). Displacement ellipsoids are drawn at the 40% probability level, with independent (symmetry-related) atoms in heavy (hollow) bonds and filled (empty) ellipsoids. Hydrogen bonds are shown as dashed lines. [Symmetry codes: (i) -x+2, y+1/2, -z+1/2; (ii) -x+2, -y+1, -z+1; (iii) x, y+1, z; (iv) -x+2, y-1/2, -z+1/2; (v) -x+2, y-1/2, -z+1/2.]
	Fig. 2. A packing view of (I), along the [100] direction, showing the (100) two-dimensional mesh and the elementary loops (A and B) from which it is constructed. Imidazole rings and H atoms have been omitted for clarity.
	Fig. 3. Two different side views of the (100) planes, viz. (a) projected down [010] and (b) projected down [001], drawn in different line density for clarity. H atoms have been omitted for clarity

Poly[[µ₃-2-(carboxylatomethyl)benzoato- κ³O¹:O²:O²]-bis(1H-imidazole- κN³)copper(II)]

Crystal data

[Cu(C9H6O4)(C3H4N2)2]	F(000) = 772
Mr = 377.84	Dx = 1.532 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5662 reflections
a = 11.817 (3) Å	θ = 3.0–21.6°
b = 9.871 (2) Å	µ = 1.36 mm^−1
c = 14.106 (3) Å	T = 298 K
β = 95.305 (4)°	Prisms, blue
V = 1638.2 (6) Å^3	0.37 × 0.16 × 0.12 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	3654 independent reflections
Radiation source: fine-focus sealed tube	2886 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.029
CCD rotation images, thin slices scans	θmax = 27.8°, θmin = 1.7°
Absorption correction: multi-scan (SADABS in SAINT; Bruker, 2002)	h = −15→15
Tmin = 0.79, Tmax = 0.89	k = −13→12
13360 measured reflections	l = −18→18

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)] = 0.042	Hydrogen site location: difference Fourier map
wR(F^2) = 0.109	H atoms treated by a mixture of independent and constrained refinement
S = 1.06	w = 1/[σ^2(Fo^2) + (0.0572P)^2 + 0.267P] where P = (Fo^2 + 2Fc^2)/3
3654 reflections	(Δ/σ)max = 0.001
225 parameters	Δρmax = 0.66 e Å^−3
0 restraints	Δρmin = −0.20 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cu1	1.05825 (2)	0.59104 (3)	0.40651 (2)	0.03833 (13)
N11	0.96321 (18)	0.7580 (2)	0.41391 (15)	0.0418 (5)
C21	0.9890 (3)	0.8781 (3)	0.3788 (2)	0.0517 (7)
H21	1.0590	0.8988	0.3573	0.062*
N31	0.9034 (2)	0.9647 (3)	0.37823 (19)	0.0596 (7)
H31	0.896 (3)	1.041 (4)	0.352 (3)	0.076 (11)*
C41	0.8157 (3)	0.8987 (3)	0.4145 (3)	0.0679 (9)
H41	0.7441	0.9336	0.4227	0.081*
C51	0.8535 (3)	0.7724 (3)	0.4360 (2)	0.0570 (8)
H51	0.8111	0.7049	0.4621	0.068*
N12	1.15042 (19)	0.4320 (2)	0.37451 (15)	0.0420 (5)
C22	1.1126 (2)	0.3139 (3)	0.33940 (19)	0.0470 (6)
H22	1.0362	0.2918	0.3269	0.056*
N32	1.1981 (2)	0.2314 (3)	0.32436 (18)	0.0544 (6)
H32	1.185 (3)	0.151 (4)	0.301 (3)	0.087 (12)*
C42	1.2966 (3)	0.2978 (3)	0.3501 (2)	0.0580 (8)
H42	1.3700	0.2650	0.3470	0.070*
C52	1.2672 (2)	0.4207 (3)	0.3811 (2)	0.0499 (7)
H52	1.3179	0.4879	0.4036	0.060*
O13	0.80892 (15)	0.20647 (18)	0.10750 (13)	0.0448 (4)
O23	0.84169 (16)	0.19392 (19)	0.26526 (14)	0.0518 (5)
O33	0.87450 (15)	0.50886 (18)	0.27440 (12)	0.0434 (4)
O43	0.92502 (15)	0.47182 (18)	0.42644 (12)	0.0419 (4)
C13	0.6796 (2)	0.3174 (3)	0.19749 (18)	0.0406 (6)
C23	0.6009 (2)	0.3237 (3)	0.1178 (2)	0.0593 (8)
H23	0.6139	0.2740	0.0638	0.071*
C33	0.5048 (3)	0.4014 (4)	0.1169 (3)	0.0785 (12)
H33	0.4530	0.4031	0.0632	0.094*
C43	0.4849 (3)	0.4770 (4)	0.1958 (3)	0.0802 (11)
H43	0.4202	0.5307	0.1953	0.096*
C53	0.5620 (2)	0.4722 (4)	0.2756 (2)	0.0627 (9)
H53	0.5482	0.5238	0.3285	0.075*
C63	0.6591 (2)	0.3933 (3)	0.2793 (2)	0.0434 (6)
C73	0.7848 (2)	0.2324 (2)	0.19216 (19)	0.0399 (6)
C83	0.7409 (2)	0.3985 (3)	0.36755 (19)	0.0439 (6)
H83A	0.7545	0.3069	0.3907	0.053*
H83B	0.7058	0.4483	0.4163	0.053*
C93	0.8542 (2)	0.4638 (2)	0.35329 (17)	0.0370 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0382 (2)	0.0381 (2)	0.0385 (2)	−0.00455 (13)	0.00284 (14)	0.00193 (12)
N11	0.0442 (12)	0.0430 (12)	0.0387 (12)	−0.0004 (10)	0.0057 (9)	0.0015 (9)
C21	0.0555 (18)	0.0453 (16)	0.0558 (18)	0.0002 (13)	0.0131 (14)	0.0052 (13)
N31	0.0705 (18)	0.0467 (15)	0.0622 (17)	0.0093 (14)	0.0094 (14)	0.0163 (13)
C41	0.0527 (19)	0.066 (2)	0.085 (3)	0.0152 (16)	0.0101 (17)	0.0169 (18)
C51	0.0509 (17)	0.0559 (18)	0.065 (2)	0.0012 (14)	0.0092 (14)	0.0158 (15)
N12	0.0444 (13)	0.0420 (12)	0.0396 (12)	−0.0014 (10)	0.0047 (10)	0.0016 (9)
C22	0.0504 (16)	0.0464 (15)	0.0433 (15)	−0.0050 (13)	−0.0008 (12)	−0.0001 (12)
N32	0.0658 (17)	0.0441 (14)	0.0534 (15)	−0.0004 (12)	0.0062 (12)	−0.0110 (12)
C42	0.0519 (18)	0.0572 (18)	0.066 (2)	0.0035 (15)	0.0107 (15)	−0.0064 (15)
C52	0.0434 (16)	0.0510 (17)	0.0553 (18)	−0.0041 (12)	0.0058 (13)	−0.0054 (13)
O13	0.0420 (10)	0.0456 (10)	0.0468 (11)	0.0080 (8)	0.0053 (8)	−0.0008 (8)
O23	0.0532 (12)	0.0471 (11)	0.0527 (12)	0.0113 (9)	−0.0077 (9)	0.0033 (9)
O33	0.0455 (10)	0.0467 (11)	0.0381 (10)	−0.0021 (8)	0.0045 (8)	0.0035 (8)
O43	0.0407 (10)	0.0485 (10)	0.0355 (10)	−0.0078 (8)	−0.0020 (8)	0.0035 (8)
C13	0.0324 (12)	0.0470 (15)	0.0424 (14)	−0.0007 (11)	0.0037 (11)	−0.0015 (11)
C23	0.0437 (16)	0.086 (2)	0.0470 (17)	0.0089 (15)	−0.0032 (13)	−0.0107 (16)
C33	0.0441 (18)	0.131 (4)	0.057 (2)	0.0293 (19)	−0.0109 (15)	−0.009 (2)
C43	0.0455 (19)	0.112 (3)	0.082 (3)	0.030 (2)	−0.0011 (18)	−0.011 (2)
C53	0.0408 (16)	0.083 (2)	0.065 (2)	0.0072 (16)	0.0103 (15)	−0.0178 (18)
C63	0.0342 (13)	0.0527 (16)	0.0434 (15)	−0.0044 (11)	0.0047 (11)	−0.0020 (12)
C73	0.0386 (13)	0.0321 (12)	0.0486 (16)	−0.0002 (10)	0.0016 (12)	−0.0004 (11)
C83	0.0377 (14)	0.0567 (17)	0.0378 (14)	−0.0074 (12)	0.0069 (11)	−0.0040 (12)
C93	0.0403 (14)	0.0338 (12)	0.0368 (14)	−0.0002 (10)	0.0033 (11)	−0.0026 (10)

Geometric parameters (Å, º)

Cu1—O13^i	1.9643 (18)	C52—H52	0.9300
Cu1—N12	1.987 (2)	O13—C73	1.279 (3)
Cu1—N11	2.003 (2)	O13—Cu1^iii	1.9643 (17)
Cu1—O43	2.0060 (18)	O23—C73	1.237 (3)
Cu1—O43^ii	2.4269 (17)	O33—C93	1.242 (3)
N11—C21	1.331 (3)	O43—C93	1.269 (3)
N11—C51	1.368 (4)	O43—Cu1^ii	2.4269 (17)
C21—N31	1.324 (4)	C13—C23	1.393 (4)
C21—H21	0.9300	C13—C63	1.415 (4)
N31—C41	1.363 (4)	C13—C73	1.507 (3)
N31—H31	0.84 (4)	C23—C33	1.369 (4)
C41—C51	1.349 (4)	C23—H23	0.9300
C41—H41	0.9300	C33—C43	1.377 (5)
C51—H51	0.9300	C33—H33	0.9300
N12—C22	1.327 (3)	C43—C53	1.382 (5)
N12—C52	1.379 (4)	C43—H43	0.9300
C22—N32	1.330 (4)	C53—C63	1.384 (4)
C22—H22	0.9300	C53—H53	0.9300
N32—C42	1.356 (4)	C63—C83	1.505 (4)
N32—H32	0.87 (4)	C83—C93	1.516 (3)
C42—C52	1.346 (4)	C83—H83A	0.9700
C42—H42	0.9300	C83—H83B	0.9700
O13^i—Cu1—N12	88.60 (8)	C42—C52—N12	109.7 (3)
O13^i—Cu1—N11	89.15 (8)	C42—C52—H52	125.1
N12—Cu1—N11	169.82 (9)	N12—C52—H52	125.1
O13^i—Cu1—O43	177.64 (7)	C73—O13—Cu1^iii	117.34 (16)
N12—Cu1—O43	91.26 (8)	C93—O43—Cu1	112.92 (15)
N11—Cu1—O43	91.39 (8)	C93—O43—Cu1^ii	139.61 (16)
O13^i—Cu1—O43^ii	104.59 (7)	Cu1—O43—Cu1^ii	106.95 (7)
N12—Cu1—O43^ii	91.22 (7)	C23—C13—C63	118.8 (2)
N11—Cu1—O43^ii	98.95 (7)	C23—C13—C73	118.5 (2)
O43—Cu1—O43^ii	73.05 (7)	C63—C13—C73	122.7 (2)
C21—N11—C51	104.3 (2)	C33—C23—C13	121.6 (3)
C21—N11—Cu1	124.41 (19)	C33—C23—H23	119.2
C51—N11—Cu1	130.2 (2)	C13—C23—H23	119.2
N31—C21—N11	112.1 (3)	C23—C33—C43	120.0 (3)
N31—C21—H21	123.9	C23—C33—H33	120.0
N11—C21—H21	123.9	C43—C33—H33	120.0
C21—N31—C41	107.2 (3)	C33—C43—C53	119.4 (3)
C21—N31—H31	129 (2)	C33—C43—H43	120.3
C41—N31—H31	123 (3)	C53—C43—H43	120.3
C51—C41—N31	106.2 (3)	C43—C53—C63	122.1 (3)
C51—C41—H41	126.9	C43—C53—H53	118.9
N31—C41—H41	126.9	C63—C53—H53	118.9
C41—C51—N11	110.2 (3)	C53—C63—C13	118.2 (3)
C41—C51—H51	124.9	C53—C63—C83	118.6 (3)
N11—C51—H51	124.9	C13—C63—C83	123.2 (2)
C22—N12—C52	104.8 (2)	O23—C73—O13	124.4 (2)
C22—N12—Cu1	127.28 (19)	O23—C73—C13	121.1 (2)
C52—N12—Cu1	127.92 (19)	O13—C73—C13	114.5 (2)
N12—C22—N32	111.2 (3)	C63—C83—C93	114.4 (2)
N12—C22—H22	124.4	C63—C83—H83A	108.7
N32—C22—H22	124.4	C93—C83—H83A	108.7
C22—N32—C42	107.9 (2)	C63—C83—H83B	108.7
C22—N32—H32	121 (3)	C93—C83—H83B	108.7
C42—N32—H32	131 (3)	H83A—C83—H83B	107.6
C52—C42—N32	106.3 (3)	O33—C93—O43	122.6 (2)
C52—C42—H42	126.8	O33—C93—C83	121.1 (2)
N32—C42—H42	126.8	O43—C93—C83	116.3 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N31—H31···O23^iv	0.84 (4)	2.01 (4)	2.824 (3)	163 (4)
N32—H32···O33^iii	0.87 (4)	1.85 (4)	2.699 (3)	162 (4)
C21—H21···O33^i	0.93	2.35	3.096 (4)	137
C22—H22···O23	0.93	2.57	3.482 (3)	167
C51—H51···Cg2^ii	0.93	2.66	3.294 (3)	126

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