Solvothermal synthesis of new metal organic framework structures in the zinc–terephthalic acid–dimethyl formamide system

Abstract

Two new metal organic framework (MOF) structures have been obtained from the Zn–terephthalic acid (H 2BDC)–dimethyl formamide (DMF) system and examined by single-crystal X-ray diffraction: Zn(C 8H 4O 4)(C 3H 7NO), 1, monoclinic C2/ m, a = 11.1369 ( 5 ) , b = 14.0217 ( 7 ) , c = 7.9890 ( 4 ) Å , β = 106.316 ( 1 ) ° , V = 1197.3 ( 1 ) Å 3 , T = 180 ( 2 ) K , Z = 4 , R 1 = 0.060 , w R 2 = 0.169 , S = 1.27 ; Zn(HCO 2) 3(C 2H 8N), 2, trigonal R 3 ¯ c , a = 8.1818 ( 1 ) , c = 22.1235 ( 7 ) Å , V = 1282.57 ( 5 ) Å 3 , T = 180 ( 2 ) K , Z = 6 , R 1 = 0.014 , w R 2 = 0.039 , S = 1.11 . Contrary to previously published structures in the same system, the crystals were obtained by solvothermal synthesis at 381 K. Structure 1 consists of 2-D layers stacked in an offset manner to accommodate DMF moieties coordinated to Zn 2+ within voids in adjacent layers. Structure 2 consists of a 3-D network constructed from Zn 2+ ions bridged by deprotonated formic acid moieties. Over time, the structure of 1 rearranges to Zn(C 8H 4O 4)(C 3H 7NO)(H 2O) [monoclinic P2 1 /n, a = 6.6456 ( 2 ) , b = 15.2232 ( 5 ) , c = 12.6148 ( 4 ) Å , β = 104.110 ( 2 ) ° , V = 1237.70 ( 7 ) Å 3 , T = 100 ( 2 ) K , Z = 4 , R 1 = 0.048 , w R 2 = 0.100 , S = 1.07 ], which is identical to the known MOF-2 structure, obtained by crystallization at ambient conditions. The three structures were determined from crystals with similar crystal habits picked from a single solvothermal synthesis batch. The study demonstrates that MOF syntheses can give not only multiple crystal structures under different conditions, but also that numerous different structures, including some that are metastable, can be formed under identical conditions.