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

Vandavasi Koteswara Rao; Matthias Zeller; Sherri R Lovelace-Cameron

doi:10.1107/S1600536812038949

. 2012 Sep 22;68(Pt 10):m1291–m1292. doi: 10.1107/S1600536812038949

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

Vandavasi Koteswara Rao ^a, Matthias Zeller ^a, Sherri R Lovelace-Cameron ^a,^*

PMCID: PMC3470164 PMID: 23125608

Abstract

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 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 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.

Related literature

For background information on Mg- and Zn-bdc metal-organic frameworks, see: Mallick et al. (2011 ▶); Burrows et al. (2005 ▶); Edgar et al. (2001 ▶); Grzesiak et al. (2006 ▶); Rood et al. (2006 ▶); Davies et al. (2007 ▶); Williams et al. (2005 ▶).

Experimental

Crystal data

[Mg₃(C₈H₄O₄)₃(C₃H₇NO)₄]
M _r = 857.65
Monoclinic,
a = 18.158 (2) Å
b = 9.5046 (13) Å
c = 24.066 (3) Å
β = 100.825 (2)°
V = 4079.6 (10) Å³
Z = 4
Mo Kα radiation
μ = 0.15 mm⁻¹
T = 100 K
0.34 × 0.20 × 0.05 mm

Data collection

Bruker SMART APEX CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2011 ▶) T _min = 0.619, T _max = 0.746
21816 measured reflections
10014 independent reflections
7598 reflections with I > 2σ(I)
R _int = 0.039

Refinement

R[F ² > 2σ(F ²)] = 0.066
wR(F ²) = 0.149
S = 1.12
10014 reflections
574 parameters
33 restraints
H-atom parameters constrained
Δρ_max = 0.46 e Å⁻³
Δρ_min = −0.35 e Å⁻³

Data collection: APEX2 (Bruker, 2011 ▶); cell refinement: SAINT (Bruker, 2011 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXLE (Hübschle et al., 2011 ▶) and SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: DIAMOND (Brandenburg, 2001 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812038949/tk5144sup1.cif

e-68-m1291-sup1.cif^{(57KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812038949/tk5144Isup2.hkl

e-68-m1291-Isup2.hkl^{(489.7KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

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.

supplementary crystallographic information

Comment

The construction of metal-organic frameworks (MOFs) with light building blocks has been the subject of intense research during the past few years (Mallick et al., 2011). A suitable metal for construction of lightweight frameworks is magnesium. In the present study, the title compound, [Mg₃(bdc)₃(DMF)₄]_n, was obtained during part of our investigations into the solvothermal synthesis of lightweight metal organic frameworks. Reaction of magnesium nitrate with terephthalic acid (bdcH₂) and 1,3-bis(4-pyridyl)propane (tmdpyr) at 373 K (100 °C) in dimethyl formamide (DMF) yielded the title 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 two-dimensional layered 3⁶-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, Mg₃(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).

Experimental

The compound was synthesized under solvothermal conditions. In a typical synthesis, Mg(NO₃)₂.6H₂O (0.129 g, 1.0 mmol) and terepthalic acid (0.169 g, 2.0 mmol) were dissolved in DMF (5.0 ml). Then, 1,3-bis(4-pyridyl)propane (0.101 g, 1.0 mmol) was added to the reaction mixture and stirred for one hour before transferring the mixture into a glass vial. 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 solvent loss and decompose rapidly once taken out of solution.