Single Crystals of a 2-Dimensional Metal Coordination Polymer Containing Pendant Carbazole Groups

Abstract

Coordination polymers consisting of metal cations and organic linkers are widely used in fundamental supramolecular approaches as well as various other practical applications. [1][2][3][4] There are various types of metal-organic coordinated structures 2,5,6 such as linear-shaped 1-dimensional (1D), 7,8 sheet-shaped 2-dimensional (2D) 9,10 and networkshaped 3-dimensional (3D) 11,12 structures.Such coordinated structures are dependent on the substituents that are present on the organic linkers. For example, the organic linker H 2 BDC (benzene-1,4-dicarboxylic acid or terephthalic acid) formed a 3D metal-organic framework (MOF) structure with a well-defined cavity, with zinc cations. 11 H 2 BDC analogues that had small substituents (e.g., Br, NH 2, and short alkoxy chains) with volumes that are smaller than the cavity volume, also formed similar 3D MOF structures. 13,14 In contrast, the presence of more bulky substituents results in the formation of 3D MOF or 1D coordinated structures. For example, 2,5-disubstituted H 2 BDC analogues, in which the substituents were long alkoxy chains-like octyloxy chains, first formed a 3D MOF structure that then transferred to a 1D coordinated structure. [15][16][17] When more bulky substituents such as 3-(9H-carbazol-9-yl)octyloxy groups were introduced on a H 2 BDC linker, only 1D coordinated structure was obtained. 18 In this work, we studied a novel metal coordination polymer based on an organic H 2 BDC analogue, in order to determine the influence of the substituents of the organic linker on metal coordinated structure. In contrast to previous reports, 15,18 the organic linker 2,5-bis(3-(9H-carbazol-9-yl)-propoxy)benzene-1,4-dicarboxylic acid (CZ3-acid, see Figure 1) having bulky carbazole groups formed single crystals resulting from sheet-shaped 2D metal coordinated structure. Therefore, the coordinated structure was strongly dependent on the size of the substituents on the H 2 BDC linkers.Our novel metal coordination polymer was composed of zinc cations and a H 2 BDC analogue. Figure 1 shows the chemical structure of the organic linker CZ3-acid, which is a H 2 BDC analogue having 2,5-disubstituted groups. The bulky non-polar carbazole groups are connected by propyloxy spacers. The metal coordination polymer of CZ3-acid with zinc nitrate [Zn(NO 3 ) 2 ·6H 2 O] was synthesized by a solvothermal reaction in dimethylformamide (DMF). As shown in Figure 1, transparent single crystals of the metal coordination polymer were obtained directly from the solvothermal reaction.In order to understand the coordinated structure of the single crystals, we analyzed the crystal structure of the metal coordination polymer by X-ray single crystal structure analysis. The metal coordination polymer exhibited triclinic P-1 space group symmetry with high crystal quality as described in the Experimental section. The solvent DMF also participated in the crystal structure. These crystals are henceforth denoted as "[Zn(CZ3)(DMF)]".In general, many metal coordination polymers that contain solvents exhi...