Syntheses-structures-thermal behaviors relationships in three fumarate MOFs

(1)Benmerad. B., (1)Aliouane. K., (1)N. Rahahlia, (1)Guehria-Laidoudi A., (2)Dahaoui S. and (2)Lecomte C.

(1)Laboratoire de Cristallographie-Thermodynamique, Faculté de Chimie, USTHB, BP 32 El-alia, Bab Ezzouar 16111, Alger;

(2) CRM2-UPRESA 7036, Université Henri Poincaré BP 239, 54506 Vandoeuvre-lès-Nancy, France.

Key-words: coordination polymer, fumarate, rare-earth, metal organic frameworks (MOFs)

Abstract

The use of unsaturated flexible ligands, like the dianion stemming from fumaric acid, with lanthanides seems to be a promising route for modulating coordination polymers or “breathing” MOFs with various architecture and porous properties. The comparative synthesis/structure/relationships concern three hybrid compounds, containing Gd(III), from the intermediate subgroup (Pm,…Dy), Ho(III), which takes place in the heavier one (Ho,…La) and La(III) for lightest (La,…Nd). [M2(C4H2O3)3(H2O)4].3H2O (M= Ho; Gd) are two isostructural compounds, belonging to P 21/n system with a= 9.4149(3)Å; b=14.6460(8)Å ; c=14.6985(11)Å, β=91.005(5)°, and obtained under two different synthesis conditions. However, [La2(C4H2O3)3(H2O)4].2H2O, presents different chemical formula and its cell parameters are a=9.3163(2)Å, b=13.4323(2)2Å, c=8.7550(2)Å, β=115.754(3)° .These three fumarates contain only deprotonated ligands, and four aqua ligands, and their structures, packings, and thermal behaviors are completely different from those exhibiting acid molecule, or hydroxyl ion as ligand, beside the dianion, like:

-  Ln2(C4H2O4)3(C4H4O4)(H2O)2 with Ln=La, Pr, Sm, Ce, Nd [1]

-  Eu4(OH)4(H2O)5(C4H2O4)4.4H2O and Eu5(OH)9(H2O)6(C4H2O4)3.9.5H2O [2].

These three new compounds are three-dimensional frameworks. The lanthanum compound is dihydrated and consists of interpenetrated layers forming infinite La-O-La-O chains, as in some typical MOFs previously studied [3]. Whereas the two isostructural trihydrated compounds are built up from binuclear entities connected into infinite arrays through carbon backbone of two independent ligands, without similar infinite chains. However the structure can be affiliated to MOFs owing to its secondary building units (SBUs), and its empty voids [4].

The single crystal synthesis and crystal structure results highlight very important points:

-  The hydrothermal synthesis doesn’t necessarily lead to compounds with the minimum of water molecules, nor the silica gel process give the polymers with a great number of water molecules.

-  As in the coordination polymers incorporating saturated dicarboxylates, the number of guest or solvent molecules is narrowly linked to the hydrophobicity around the voids formed by the carbon backbone.

-  The lanthanide contraction has no effect on the kind of the resulting packing, but affects the thermal behaviour.

-  Binuclear entities do not allow the extending of the infinite typical M-O-M-O subfeature distinguishing rare earth and earth alkaline dicarboxylates.

This conclusion is based on this study compared to several coordination polymers obtained in the laboratory [3, 5-8].

References

[1] G. Zhang, G. Yang, J. Shima, Crystal Growth & Design, 6, 4, 933, (2006).

[2] C. Serre, F. Pelle, N. Gardant, G. Ferey, Chem. Mater., 16, 1177, (2004).

[3] B. Benmerad, Thèse de Doctorat , USTHB, Alger, (2007).

[4] D.J. Tranchemontagne, J.L. Mendoza-Cortés, M. O’Keeffe, O.M. Yaghi, Chem. Soc. Rev., 38, 1257-1283, (2009).

[5] N Rahahlia, Thèse de Doctorat, USTHB, Alger, (2007).

[6] K. Aliouane, A. Djeghri, A. Guehria-Laidoudi, S. Dahaoui, C. Lecomte, J. of Mol. Struct., 832, 150, (2007).

[7] N. Rahahlia, B. Benmerad, A. Guehria-Laidoudi, S. Dahaoui, C. Lecomte , J. of Mol. Struct., 833, 42, (2007).

[8] A. Djeghri, Thèse de Doctorat, USTHB, Alger, (2010).