Poly[tetrakis(dimethylformamide)tris(μ4-terephthalato)trimagnesium]

The title framework compound, [Mg3(C8H4O4)3(C3H7NO)4]n or [Mg3(bdc)3(DMF)4]n, was obtained as a side product of the solvothermal reaction of magnesium nitrate, terephthalic acid (bdcH2), and 1,3-bis(4-pyridyl)propane in a 1:2:1 ratio in dimethylformamide (DMF). The asymmetric unit consists of three MgII cations, three terephthalate anions, and four coordinating DMF molecules. One of the four DMF molecules was refined as disordered over two mutually exclusive positions, with an occupancy rate for the major moiety of 0.923 (4). The three MgII cations possess distorted octahedral coordination geometries that form linear Mg trimers. Of the three MgII cations, the central MgII is octahedrally coordinated by six different carboxylate O atoms. The terminal MgII cations are bonded to four O atoms of three bdc linkers and to two O atoms of coordinating DMF molecules. The compound has a two-dimensional 36-network structure parallel to (001) that is formed by connection of the Mg trimers as distorted octahedral nodes to the bdc ligands as linkers.

The title framework compound, [Mg 3 (C 8 H 4 O 4 ) 3 (C 3 H 7 NO) 4 ] n or [Mg 3 (bdc) 3 (DMF) 4 ] n , was obtained as a side product of the solvothermal reaction of magnesium nitrate, terephthalic acid (bdcH 2 ), and 1,3-bis(4-pyridyl)propane in a 1:2:1 ratio in dimethylformamide (DMF). The asymmetric unit consists of three Mg II cations, three terephthalate anions, and four coordinating DMF molecules. One of the four DMF molecules was refined as disordered over two mutually exclusive positions, with an occupancy rate for the major moiety of 0.923 (4). The three Mg II cations possess distorted octahedral coordination geometries that form linear Mg trimers. Of the three Mg II cations, the central Mg II is octahedrally coordinated by six different carboxylate O atoms. The terminal Mg II cations are bonded to four O atoms of three bdc linkers and to two O atoms of coordinating DMF molecules. The compound has a two-dimensional 3 6 -network structure parallel to (001) that is formed by connection of the Mg trimers as distorted octahedral nodes to the bdc ligands as linkers.
We thank the Department of Energy (DOE), USA, for financial support (grant CDP-3.10). The X-ray diffractometer was funded by the National Science Foundation (grant 0087210), Ohio Board of Regents (grant CAP-491), and by Youngstown State University.
compound as a minor product along with an unidentified white powder. The crystals of the title compound are sensitive towards solvent loss and decompose rapidly once taken out of solution.
The asymmetric unit of the title framework consists of three magnesium cations, and three anionic bdc units, and four coordinated DMF molecules, respectively (Fig. 1). One of the four DMF molecules was refined as disordered over two mutually exclusive positions with an occupancy ratio of 0.923 (4) to 0.077 (4).
The three magnesium cations in the structure form secondary building units (SBUs) that each possesses a chain of three magnesium ions bridged by six bdc linkers and coordinated by four terminal DMF molecules (Fig. 2). There are two types of magnesium coordination environments in the structure. The terminal ions, Mg1 and Mg3, in the SBU exhibit distorted octahedral geometries. Of the six bonds, four are from O atoms of three different bdc linkers (one bdc linker binds with magnesium in a chelating mode) and the other two are from DMF O atoms. The central ion, Mg2, is also distorted octahedrally coordinated, but it binds to six different carboxylate O atoms (four of them are in bidentate mode and two are in chelation mode). O-Mg-O angles vary between 60.35 (7) and 178.54 (9)°, with the unusually small angle of 60.35 (7)° being associated with the bdc linker in chelation mode. The three distorted octahedral trimeric magnesiums together act as a node that is connected with other nodes through the bdc linkers to give rise to a twodimensional layered 3 6 -network (Fig. 3). The layers in the structure are stacked atop of one another, with terminal DMF molecules that are projecting into the inter-lamellar space (Fig. 4). The structure is isoreticular to previously reported magnesium and bdc based framework compounds, Mg 3 (bdc) 3 (X) 4 [X = DMSO, Rood et al., 2006;DMA, Davies et al., 2007] in which the terminal solvent molecules, DMSO and DMA, project in to the inter-lamellar spaces. Similar layered structures have also been reported with zinc-bdc based frameworks (Edgar et al., 2001;Burrows et al., 2005;Williams et al., 2005;Grzesiak et al., 2006).
The final mixture was heated to 373 K for 24 h. The vial was then slowly cooled to room temperature yielding colorless plates of the title compound as a minor product along with an unidentified white powder. Crystals are sensitive towards supplementary materials sup-2 Acta Cryst. (2012). E68, m1291-m1292 solvent loss and decompose rapidly once taken out of solution.

Refinement
Reflections 1 1 0, 0 1 1 and 1 0 2 were partially obstructed by the beam stop and were omitted from the refinement.
One of the DMF molecules was refined as disordered over two mutually exclusive positions. The minor moiety was restrained to have a similar geometry as the major moiety, the overlapping O and N atoms were each constrained to have ADPs identical to that in the major moiety, and the ADPs of the C, N and O atoms of the minor moiety were restrained to be similar to each other. The occupancy ratios for the two moieties refined to 0.923 (4) to 0.077 (4).
Carbon-bound hydrogen atoms were placed in calculated positions with C-H bond distances of 0.95 Å (aromatic H and carbonyl H of DMF) and 0.98 Å (methyl H). Methyl group H atoms were allowed to rotate around the C-C bond to best fit the experimental electron density. U iso (H) values for all H atoms were constrained to a multiple of U eq of their respective carrier atom (1.2 times for aromatic and carbonyl H atoms, and 1.5 times for methyl H atoms).

Figure 1
View of the title framework compound with the atom numbering scheme and 50% probability displacement ellipsoids.

Figure 4
View of the arrangement of layers parallel to the [100] direction.