A two-dimensional copper(II) coordination polymer based on 2-propyl-1H-imidazole-4,5-di­carb­oxy­lic acid

Single-crystal X-ray diffraction analysis of poly[bis­(μ₂-5-carb­oxy-2-propyl-1H-imidazole-4-carboxyl­ato-κ³N³,O⁴:O⁵)copper(II)], [Cu(C₈H₉N₂O₄)₂)]_n, indicates that one carb­oxy­lic acid group of the 2-propyl-1H-imidazole-4,5-di­carb­oxy­lic acid (H₃PDI) ligand is deprotonated. The resulting H₂PDI⁻ anion, acting as a bridge, connects the Cu^II cations to form a two-dimensional (4,4)-connected layer. Adjacent layers are further linked through inter­layer hydrogen-bond inter­actions, resulting in a three-dimensional supra­molecular structure.

S1. Introduction

During the past decade, the design and synthesis of coordination polymers have attracted considerable attention because of their intuitive architectures and potential applications (Bourrelly et al., 2010; Kurmoo, 2009; Lu et al., 2006). One important factor that determines the structures and functions of the resulting crystal materials is the organic ligand. To date, organic ligands such as carb­oxy­lic acid, N-heterocyclic aromatic and N-heterocyclic carb­oxy­lic acid ligands have been utilized extensively as building blocks for the construction of functional complex materials (Blake et al., 1999; Sun et al., 2006). 2-Propyl-1H-imidazole-4,5-di­carb­oxy­lic acid (H₃PDI) is a nitro­gen heterocycle carboxyl­ate ditopic ligand, with one imidazole ring and two carboxyl­ate groups. In the past few years, H₃PDI, with its strong coordination ability and diverse coordination modes, has attracted inter­est in the field of coordination chemistry (Chen & Liu, 2012; Deng et al., 2012; Deng, Zhong, Luo et al., 2013; Deng, Zhong, Mei et al., 2013; Deng, Zhong, Wang et al., 2013; Fan et al., 2012; Feng et al., 2010; Li et al., 2009, 2011; Zhai et al., 2013). However, based on investigations of the reported complexes of H₃PDI, we have found that, due to the steric hindrance of the propyl group in the imidazole ring, most of the H₃PDI-based complexes are mononuclear or one-dimensional chain structures. We report here the synthesis and structure of a two-dimensional Cu^II coordination polymer based on H₃PDI.

S2. Experimental

S2.1. Synthesis and crystallization

A mixture of Cu(NO₃)₂.3H₂ (0.5 mmol, 0.121 g), H₃PD (0.5 mmol, 0.099 g), NaOH (1 mmol, 0.040 g) and H₂O (10 ml) was heated at 433 K for 72 h under autogeneous pressure in a sealed 20 ml Teflon-lined stainless steel vessel. After the autoclave had been cooled over a period of 16 h at a rate of 5 K h^-1, green block-shaped crystals of (I) were isolated by filtration, washed with water and dried in air [yield 0.098 g, 42.8% (based on Cu)].

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The disorder of the propyl group of the H₂PDI^- anion was treated by assuming half-occupancies initially, which finally refined to 0.58. The displacement parameters of the C7/C7' and C8/C8' atoms were restricted by an EADP instruction [Please rephrase using non-software-specific terms]. To obtain a reasonable structure, the C—C bond lengths of the disordered part were constrained to 1.54 Å using a DFIX instruction [Please rephrase using non-software-specific terms]. H atoms attached to C and N atoms were placed geometrically and refined isotropically in riding mode, with C—H = 0.98–0.99 Å and N—H = 0.88 Å, and with U_iso(H) = 1.2U_eq(C,N), or 1.5U_eq(C) for methyl H [Added text OK?]. O-bound H atoms were positioned from a difference Fourier synthesis and refined with O—H = 0.84 Å, and with U_iso(H) = 1.5U_eq(O).

S3. Results and discussion

Under hydro­thermal conditions, the reaction of Cu(NO₃)₂.3H₂O with H₃PDI leads to the formation of [Cu(H₂PDI)₂]_n, (I). Single-crystal X-ray diffraction analysis indicates that there is one crystallographically independent Cu^II cation in the asymmetric unit of (I). Atom Cu1 coordinates with two N atoms and four O atoms from four separate anionic H₂PDI^- ligands, resulting in a slightly distorted o­cta­hedral geometry (Fig. 1). The Cu—N and Cu—O bond lengths are 1.9689 (17) and 2.0081 (15) Å, respectively (Table 2).

The H₂PDI^- ligand, with one carb­oxy­lic acid group deprotonated, acts as a bridge, connecting Cu^II cations to form a two-dimensional (4,4)-connected layer (Fig. 2). Adjacent layers are further linked through inter­layer hydrogen-bond inter­actions [N2—H2···O2 = 2.818 (2) Å], generating a three-dimensional supra­molecular structure (Table 3 and Fig. 3).

To the best of our knowledge, (I) is one of the few higher-dimensional compounds of H₃PDI (Deng et al., 2012) to have been reported.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART (Bruker, 1998); data reduction: SAINT (Bruker, 1998); 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).

Figures

	Fig. 1. The coordination evironment of the Cu^II cation and coordination mode of the H2PDI^- anion of (I), showing the atom-numbering scheme. The disordered parts of the propyl groups have been omitted for clarity. [Symmetry codes: (i) -x + 2, -y + 2, -z + 2; (ii) x - 1/2, -y + 3/2, z + 1/2; (iii) -x + 5/2, y + 1/2, -z + 3/2.] [Section Editors: Would you prefer an ellipsoid plot here?]
	Fig. 2. The two-dimensional layer structure of (I). The disordered parts of the propyl groups have been omitted for clarity.
	Fig. 3. The three-dimensional supramolecular structure of (I). The disordered parts of the propyl groups have been omitted for clarity.

Poly[bis(µ₂-5-carboxy-2-propyl-1H-imidazole-4-carboxylato-κ³N³,O⁴:O⁵)copper(II)]

Crystal data

[Cu(C8H9N2O4)2]	F(000) = 470
Mr = 457.88	Dx = 1.640 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 2043 reflections
a = 8.344 (2) Å	θ = 2.7–27.0°
b = 9.859 (2) Å	µ = 1.23 mm^−1
c = 11.273 (3) Å	T = 113 K
β = 91.493 (4)°	Block, green
V = 927.1 (4) Å^3	0.42 × 0.38 × 0.36 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer	1596 independent reflections
Radiation source: fine-focus sealed tube	1460 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
ϕ and ω scans	θmax = 25.0°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Bruker, 1998)	h = −9→9
Tmin = 0.626, Tmax = 0.665	k = −11→8
3356 measured reflections	l = −13→3

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)] = 0.028	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.077	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0445P)^2 + 0.6951P] where P = (Fo^2 + 2Fc^2)/3
1596 reflections	(Δ/σ)max < 0.001
149 parameters	Δρmax = 0.39 e Å^−3
4 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	Occ. (<1)
Cu1	1.0000	0.5000	0.5000	0.01328 (15)
C1	1.1622 (2)	0.6684 (2)	0.35120 (17)	0.0142 (4)
C2	1.2676 (2)	0.6557 (2)	0.45887 (17)	0.0150 (4)
C3	1.1771 (2)	0.7318 (2)	0.24368 (17)	0.0142 (4)
C4	1.3128 (2)	0.8036 (2)	0.19022 (17)	0.0163 (4)
C5	0.9326 (2)	0.6456 (2)	0.25646 (17)	0.0145 (4)
C6	0.7619 (3)	0.6138 (2)	0.22620 (18)	0.0202 (5)
H6A	0.7072	0.6963	0.1956	0.024*
H6B	0.7068	0.5839	0.2984	0.024*
N1	1.01103 (19)	0.61440 (18)	0.35728 (14)	0.0133 (4)
N2	1.0311 (2)	0.71573 (18)	0.18578 (14)	0.0144 (4)
H2	1.0060	0.7462	0.1143	0.017*
O1	1.20673 (17)	0.59358 (15)	0.54441 (11)	0.0161 (3)
O2	1.40414 (17)	0.71056 (16)	0.46081 (12)	0.0189 (3)
O3	1.44205 (17)	0.82022 (17)	0.25872 (13)	0.0222 (4)
H3	1.4287	0.7818	0.3242	0.033*
O4	1.30496 (18)	0.84384 (16)	0.08848 (12)	0.0211 (4)
C7	0.7519 (8)	0.4985 (7)	0.1295 (6)	0.0222 (12)	0.483 (5)
H7A	0.8192	0.5231	0.0617	0.027*	0.483 (5)
H7B	0.7932	0.4125	0.1637	0.027*	0.483 (5)
C8	0.5759 (6)	0.4791 (6)	0.0857 (5)	0.0324 (14)	0.483 (5)
H8A	0.5083	0.4611	0.1537	0.049*	0.483 (5)
H8B	0.5694	0.4023	0.0306	0.049*	0.483 (5)
H8C	0.5386	0.5616	0.0451	0.049*	0.483 (5)
C7'	0.7247 (8)	0.4788 (6)	0.1721 (5)	0.0222 (12)	0.517 (5)
H7'1	0.6072	0.4686	0.1616	0.027*	0.517 (5)
H7'2	0.7639	0.4060	0.2260	0.027*	0.517 (5)
C8'	0.8032 (6)	0.4650 (5)	0.0532 (4)	0.0271 (12)	0.517 (5)
H8'1	0.7657	0.5380	0.0004	0.041*	0.517 (5)
H8'2	0.7749	0.3771	0.0179	0.041*	0.517 (5)
H8'3	0.9199	0.4710	0.0642	0.041*	0.517 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cu1	0.0130 (2)	0.0181 (2)	0.0086 (2)	−0.00297 (14)	−0.00112 (13)	0.00286 (13)
C1	0.0140 (10)	0.0158 (11)	0.0128 (10)	−0.0026 (8)	0.0000 (7)	−0.0020 (8)
C2	0.0160 (10)	0.0176 (11)	0.0114 (10)	−0.0002 (9)	0.0000 (8)	−0.0009 (8)
C3	0.0147 (10)	0.0168 (11)	0.0110 (9)	−0.0008 (8)	−0.0010 (7)	−0.0002 (8)
C4	0.0160 (10)	0.0174 (11)	0.0153 (11)	−0.0016 (9)	0.0004 (8)	−0.0012 (8)
C5	0.0161 (10)	0.0152 (11)	0.0122 (9)	−0.0004 (8)	−0.0010 (8)	0.0003 (8)
C6	0.0132 (10)	0.0261 (12)	0.0211 (11)	−0.0027 (9)	−0.0036 (8)	0.0085 (9)
N1	0.0126 (8)	0.0160 (9)	0.0114 (8)	−0.0015 (7)	0.0001 (6)	0.0002 (7)
N2	0.0149 (8)	0.0191 (10)	0.0092 (8)	−0.0014 (7)	−0.0017 (6)	0.0026 (7)
O1	0.0171 (7)	0.0206 (8)	0.0106 (7)	−0.0037 (6)	−0.0011 (5)	0.0017 (6)
O2	0.0162 (7)	0.0283 (9)	0.0121 (7)	−0.0072 (7)	−0.0030 (5)	0.0019 (6)
O3	0.0163 (8)	0.0344 (10)	0.0157 (7)	−0.0085 (7)	−0.0012 (6)	0.0058 (7)
O4	0.0218 (8)	0.0279 (9)	0.0135 (8)	−0.0058 (7)	0.0007 (6)	0.0047 (6)
C7	0.014 (2)	0.021 (2)	0.031 (4)	−0.0068 (16)	−0.002 (3)	0.007 (2)
C8	0.023 (3)	0.034 (3)	0.039 (3)	−0.008 (2)	−0.016 (2)	0.001 (2)
C7'	0.014 (2)	0.021 (2)	0.031 (4)	−0.0068 (16)	−0.002 (3)	0.007 (2)
C8'	0.023 (2)	0.030 (3)	0.029 (3)	−0.005 (2)	−0.007 (2)	−0.001 (2)

Geometric parameters (Å, º)

Cu1—O1	2.0081 (15)	C6—C7'	1.493 (6)
Cu1—N1	1.9690 (17)	C6—C7	1.576 (7)
Cu1—O4^i	2.4695 (16)	C6—H6A	0.9900
Cu1—O1^ii	2.0081 (15)	C6—H6B	0.9900
Cu1—N1^ii	1.9690 (17)	N2—H2	0.8800
Cu1—O4^iii	2.4695 (16)	O3—H3	0.8400
C1—N1	1.372 (3)	C7—C8	1.549 (7)
C1—C3	1.372 (3)	C7—H7A	0.9900
C1—C2	1.486 (3)	C7—H7B	0.9900
C2—O1	1.260 (2)	C8—H8A	0.9800
C2—O2	1.261 (3)	C8—H8B	0.9800
C3—N2	1.376 (3)	C8—H8C	0.9800
C3—C4	1.478 (3)	C7'—C8'	1.514 (6)
C4—O4	1.214 (3)	C7'—H7'1	0.9900
C4—O3	1.320 (3)	C7'—H7'2	0.9900
C5—N1	1.332 (3)	C8'—H8'1	0.9800
C5—N2	1.350 (3)	C8'—H8'2	0.9800
C5—C6	1.490 (3)	C8'—H8'3	0.9800
O1—Cu1—N1	83.25 (6)	C5—C6—H6A	109.6
O1—Cu1—O4^i	79.41 (5)	C7'—C6—H6A	120.1
O1—Cu1—O1^ii	180.00	C7—C6—H6A	109.6
O1—Cu1—N1^ii	96.75 (6)	C5—C6—H6B	109.6
O1—Cu1—O4^iii	100.59 (5)	C7'—C6—H6B	88.5
O4^i—Cu1—N1	88.96 (6)	C7—C6—H6B	109.6
O1^ii—Cu1—N1	96.75 (6)	H6A—C6—H6B	108.2
N1—Cu1—N1^ii	180.00	C5—N1—C1	107.43 (16)
O4^iii—Cu1—N1	91.05 (6)	C5—N1—Cu1	142.82 (14)
O1^ii—Cu1—O4^i	100.59 (5)	C1—N1—Cu1	109.00 (13)
O4^i—Cu1—N1^ii	91.05 (6)	C5—N2—C3	108.91 (16)
O4^i—Cu1—O4^iii	180.00	C5—N2—H2	125.5
O1^ii—Cu1—N1^ii	83.25 (6)	C3—N2—H2	125.5
O1^ii—Cu1—O4^iii	79.41 (5)	C2—O1—Cu1	113.16 (13)
O4^iii—Cu1—N1^ii	88.96 (6)	C4—O3—H3	109.5
N1—C1—C3	109.00 (17)	C8—C7—C6	110.0 (5)
N1—C1—C2	116.88 (17)	C8—C7—H7A	109.7
C3—C1—C2	133.98 (19)	C6—C7—H7A	109.7
O1—C2—O2	125.28 (18)	C8—C7—H7B	109.7
O1—C2—C1	115.08 (18)	C6—C7—H7B	109.7
O2—C2—C1	119.57 (18)	H7A—C7—H7B	108.2
C1—C3—N2	105.48 (17)	C6—C7'—C8'	110.6 (4)
C1—C3—C4	131.82 (18)	C6—C7'—H7'1	109.5
N2—C3—C4	122.70 (17)	C8'—C7'—H7'1	109.5
O4—C4—O3	122.39 (19)	C6—C7'—H7'2	109.5
O4—C4—C3	121.25 (18)	C8'—C7'—H7'2	109.5
O3—C4—C3	116.35 (17)	H7'1—C7'—H7'2	108.1
N1—C5—N2	109.18 (17)	C7'—C8'—H8'1	109.5
N1—C5—C6	126.32 (18)	C7'—C8'—H8'2	109.5
N2—C5—C6	124.46 (18)	H8'1—C8'—H8'2	109.5
C5—C6—C7'	117.9 (3)	C7'—C8'—H8'3	109.5
C5—C6—C7	110.1 (3)	H8'1—C8'—H8'3	109.5
C7'—C6—C7	21.2 (2)	H8'2—C8'—H8'3	109.5

Symmetry codes: (i) −x+5/2, y−1/2, −z+1/2; (ii) −x+2, −y+1, −z+1; (iii) x−3/2, −y+1/2, z−1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O2^iv	0.88	1.96	2.818 (2)	167
O3—H3···O2	0.84	1.71	2.549 (2)	177

Symmetry code: (iv) x−1/2, −y+3/2, z−1/2.