The design and construction of coordination polymers have been an area of explosive growth in recent years (Kitagawa et al., 2004). Some active pharmaceutical ingredients (APIs), which contain carboxylic group, N-containing ring in the structures, have also utilized for constructing specific functional coordination polymers (Zhao et al., 2008). The hydrophilic or hydrophobic groups in drug molecules may play an important role in the structures and properties of final metal- organic frameworks.

Ozagrel, (E)-3-[4-(1H-imidiazol-1-ylmethyl)phenyl]-2-propenic acid, is a selective thromboxane A2-synthetase inhibitor which is used for treating cerebrovascular disease (Kato et al., 1997). It has a carboxylic group and an imidazole ring in the structure. The molecule is an ideal building block for constructing coordination polymers with specific structures. In this contribution, we report a Cu(I)-olefin coordination polymer of ozagrel, [(C₁₃H₁₁N₂O₂)Cu(I)] (I), which was obtained under solvothermal reaction conditions. In the structure, conjugated olefinic and carboxylic groups of ozagrel link metal centers into a 3-fold helical chain which is linked into a three-dimensional framework structure by metal- imidazole coordination interactions.

Compound I crystallizes in the space group P31 with a deprotonated ozagrel anion and a Cu(I) cation in the asymmetric unit (Fig.1). There exist obvious interactions between Cu(I) center and C═C moiety of the olefin of ozagrel (Cu1—C2, Cu1—C3, Table 1). The C═C bond distance (1.381 Å) of the coordinated olefin is longer than that in free ozagrel (1.324 Å) (Wang et al., 2007). The lengthening of the C═C distance is typical for ethylene that is η²-bonded to low-valent, electron-rich, transition metals such as copper(I) (Young et al., 1998). Cu(I) ion is nearly centered in a trigonal planar geometry, which is defined by C═C moiety, imidazole N atom and carboxylic O atom from three different ozagrel molecules. Interestingly, carboxylic group of ozagrel doesn't serve as bidentate moiety as does it in [Cu(3-PYA)]n reported previously (Zhang et al., 2001). But, conjugated olefinic and carboxylic groups as bidentate spacer link Cu(I) centers into a 3-fold helical chain along c axis (Fig.2). Cu(I)-imidazole interactions further link the one-dimensional helical chain into a three-dimensional framework structure (Fig.3). Thus, ozagrel anion acting as a tridentate linker is coordinated to Cu(I) ion generating a three-dimensional coordination polymer based on one-dimensional helical chain of Cu(I) centers.

Since Schultz synthesized the first air-stable Cu(I)-olefin coordination polymer based on fumarate ligand under hydrothermal conditions (Young et al., 1998), some Cu(I)-olefin complexes with extended framework structures have been prepared by crystal engineering strategies (Wang et al., 2005). Impressively, two luminescent two-dimensional layered copper(I)-olefin coordination polymers were constructed by the use of 3(2)-pyridylacrylic acid as tetradentate linkers (Zhang et al., 2001). Therein, acrylic acid anions linked Cu(I) centers into a one-dimensional chain which was further linked into two-dimensional coordination layers by coordinated pyridyl rings. Otherwise from that in pyridylacrylic acid, the acrylic acid anion in ozagrel acts as a bidentate spacer and links Cu(I) centers into a 3-fold helical chain which is further linked into a three-dimensional framework structure by coordinated imidazole ring. In other words, rigid 3(2)-pyridylacrylic acid resulted in two-dimensional coordination layers by metal coordination to Cu(I) ion while more flexible ozagrel gave rise to a three-dimensional coordination framework. The flexible molecular structure of ozagrel could play the subtle role in the final extended structure.

In conclusion, a Cu(I)-olefin coordination polymer based on ozagrel ligand was synthesized under solvothermal conditions. Conjugated olefinic and carboxylic groups of ozagrel as bidentate spacer link Cu(I) centers into a 3-fold helical chain which is linked into a three-dimensional framework structure by metal-imidazole coordination interactions.

Ozagrel (228 mg, 1 mmol) and Cu(NO₃)₂.3H₂O (240 mg, 1 mmol) were suspended in 10 ml me thanol and a few drops of triethylamine were added. The mixture was placed in a 23 ml Teflon-lined autoclave, sealed, and placed in a furnace at 130 °C for 2 days. Yellow block crystals were isolated. Element analysis for C₁₃H₁₁N₂O₂ Cu₁ (%), Calcd: C, 53.65; H, 3.22; N, 9.63; Found: C, 53.57; H, 3.89; N, 9.66.

H atoms were located geometrically (C—H = 0.95–1.00 Å) with U_iso(H) = 1.2 U_eq(C).

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