Improved synthesis of 4,4′-bipyridine-2-carboxylic acid and its use in the construction of novel metal and mixed-metal coordination polymers

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An improved synthesis of 4,4′-bipyridine-2-carboxylic acid (ppcaH) has significantly increased the yield and thus enabled the preparation of four new coordination compounds that contain copper, cobalt, and vanadium or molybdenum oxide. Each structure was synthesized solvothermally and characterized by both powder and single-crystal X-ray diffraction. Cu(ppca)2 (1) is a discrete molecular complex that crystallizes in the P21/c space group, a = 5.0749(4) Å, b = 25.442(2) Å, c = 7.2536(6) Å. Co(ppca)(SCN)(H2O) (2) is a H-bonded 2D coordination polymer that crystallizes in the P21/c space group, a = 11.0716(4) Å, b = 11.2327(4) Å, c = 10.2073(4) Å. [Cu(ppca)(Hppca)]2[H2Mo4O14] (3) and Co(ppca)2(V2O6)(H2O) (4) are mixed-metal coordination polymers that crystallize in the P1¯" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">P1¯ and Pbca space groups, respectively. Complex (3) is a 2D framework that contains an H2Mo4O142−anion, a = 8.4019(6) Å, b = 8.6990(6) Å, c = 16.8513(12) Å, while (4) is a highly ordered H-bonded 3D mixed-metal coordination polymer whose vanadatecluster species was generated in situ using a tetramethyl ammonium hydroxide and acetic acid buffer solution, a = 18.0118(8) Å, b = 11.2664(5) Å, c = 25.3385(11) Å.