FULL PAPER DOI: 10.1002/ejic.200800152 The Use of Liquid–Liquid Interface (Biphasic) for the Preparation of Benzenetricarboxylate Complexes of Cobalt and Nickel Abhishek Banerjee, [a] Partha Mahata, [a] and Srinivasan Natarajan* [a] Keywords: Metal–organic frameworks / Cobalt / Nickel/ Biphasic synthesis method New metal–organic frameworks (MOFs) [Ni(C 12 N 2 H 10 )- (H 2 O)][C 6 H 3 (COO) 2 (COOH)] (I), [Co 2 (H 2 O) 6 ][C 6 H 3 (COO) 3 ] 2 · (C 4 N 2 H 12 )(H 2 O) 2 (II), [Ni 2 (H 2 O) 6 ][C 6 H 3 (COO) 3 ] 2 ·(C 4 N 2 H 12 )- (H 2 O) 2 (III), [Ni(C 13 N 2 H 14 )(H 2 O)][C 6 H 3 (COO) 2 (COOH)] (IV), [Ni 3 (H 2 O) 8 ][C 6 H 3 (COO) 3 ](V) and [Co(C 4 N 2 H 4 )(H 2 O)][C 6 H 3 - (COO) 3 ](VI) {C 6 H 3 (COOH) 3 = trimesic acid, C 12 N 2 H 10 = 1,10-phenanthroline, C 4 N 2 H 12 = piperazine dication, C 13 N 2 H 14 = 1,3-bis(4-pyridyl)propane and C 4 N 2 H 4 = pyrazine} have been synthesized by using an interface be- tween two immiscible solvents, water and cyclohexanol. The compounds are constructed from the connectivity between the octahedral M 2+ (M = Ni, Co) ions coordinated by oxygen atoms of carboxylate groups and water molecules and/or by Introduction Metal–organic frameworks (MOFs) have been in the forefront of research for their applications in the areas of adsorption, [1] separation and catalysis. [2] Additionally, the ability to incorporate almost all the elements of the periodic table along with the possibility of introducing functionality through the organic linkers provide the added impetus for the continuing interest. [3] Of the many MOFs that have been synthesized, [4] those with transition metals are impor- tant. [5] The transition elements, with their varied oxidation states and coordination preferences, present an excellent op- portunity to correlate magnetic, spectroscopic and related properties with the framework structure. [6] The organic lin- kers, with varying lengths and functionalities, can form MOFs with adjustable channels and impart chemical reac- tivity and in some cases chirality. [7] A detailed study of the available literature clearly reveals that the number of metal–organic framework compounds formed by aromatic carboxylates is far more than that formed by aliphatic ones. [4e,8] Of the many aromatic carb- oxylic acid based MOFs, those of trimesic acid [9,10] (ben- [a] Framework Solids Laboratory, Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, India E-mail: snatarajan@sscu.iisc.ernet.in Supporting information for this article is available on the WWW under http://www.eurjic.org or from the author. Eur. J. Inorg. Chem. 2008, 3501–3514 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3501 nitrogen atoms of the ligand amines and the carboxylate units to form a variety of structures of different dimensional- ity. Strong hydrogen bonds of the type O–H···O are present in all the compounds, which give rise to supramolecularly organized higher-dimensional structures. In some cases π···π interactions are also observed. Magnetic studies indicate weak ferromagnetic interactions in I, IV and V and weak antiferromagnetic interactions in the other compounds (II, III and VI). All the compounds have been characterized by a variety of techniques. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) zene-1,3,5-tricarboxylic acid, H 3 tma) form the largest number of high-symmetry structures. [10] Most of these com- pounds are prepared by using a mild hydrothermal reaction between a metal salt, trimesic acid and a base. [10a,10b,10d] Recently, there have been many attempts to modify the syn- thesis conditions, which has given rise to newer approaches, such as the biphasic solvothermal method [12] and those that use ionic liquids, [11] etc. Of these, the biphasic approach ap- pears to have distinct advantages. In biphasic reactions, the metal salt is generally in aqueous medium and the organic acid is in an organic solvent, which is usually immiscible with water (cyclohexanol). The formation of the product phase is usually at or near the interface between the two liquids. This approach has been employed profitably for the preparation of many inorganic–organic hybrid compounds by Cheetham and co-workers. [12] Recently, the liquid–liquid interface has also been employed for the synthesis of nano- particles, nanocrystals, etc. [13] The biphasic synthesis is advantageous while working with metals that have low reduction potentials, i.e. metals that are easily reducible – as is the case for Cu 2+ ions. [12b] It also offers the possibility to work with organic solvents that may be unstable under hydrothermal conditions. Yaghi and co-workers employed a modified approach for the preparation of MOFs of aromatic dicarboxylates by em- ploying two different solvents. Thus, Zn(NO 3 ) 2 ·6H 2 O and naphthalene-2,6-dicarboxylic acid were dissolved in a mix-