2D Porous Honeycomb Polymers versus Discrete Nanocubes from Trigonal Trinuclear Complexes and Ligands with Variable Topology

Abstract

Trinuclear building block {Fe(2)NiO(Piv)(6)} (Piv = pivalate), which possessed pseudo-D(3h) symmetry, was linked by two ligands, pseudo-D(3h) ligand tris-(4-pyridyl)pyridine (L1) and C(2v) ligand 4-(N,N-dimethylamino)phenyl-2,6-bis(4-pyridyl)pyridine (L2) into two products with different topologies: 2D coordination polymer [Fe(2)NiO(Piv)(6)(L1)](n) (1), and discrete molecule [{Fe(2)NiO(Piv)(6)}(8) {L2}(12)], which had a nanocube structure (2). In compound 1, trinuclear {Fe(2)NiO(Piv)(6)} blocks were linked through ligand L1 into layers with honeycomb topology. In compound 2, eight trinuclear blocks were located in the vertices of the nanocube, with each L2 ligand linked to two {Fe(2)NiO(Piv)(6)} units. In the crystal structure, these nanocubes formed infinite catenated chains. Analysis of possible structures that could be assembled from these building blocks showed that compounds 1 and 2 corresponded to their respective predicted topologies. Compound [1⋅solvent] possessed a porous structure, in which the voids were filled by solvent molecules (DMF or DMSO). This structure was retained following desolvation, and compound 1 absorbed significant quantities of N(2) and H(2) at 78 K (S(BET) = 730 m(2) g(-1), H(2) sorption capacity: 0.9 % by weight at 865 Torr). Desolvation of [2⋅solvent] led to disorder of its crystal structure, and compound 2 only adsorbed negligible quantities of N(2) but adsorbed 0.27 % H(2) (by weight) at 855 Torr and 78 K. The magnetic properties of these complexes (temperature dependence of molar magnetic susceptibility) were governed by the magnetic properties of the trinuclear "building block".

Influence of morphology and defects in crystals of porous coordination polymers on the sorption characteristics

“…Compound I is built of parallel 2D polymer layers according to the honeycomb type. Three pyridine fragments of three L 1 molecules are coordinated to the trigonal fragments {Fe 2 NiO(Piv) 6 } at an angle of 120° in each 2D layer (Fig. 3).…”

“…3). In turn, each ligand L 1 binds three metal ions of three fragments {Fe 2 NiO(Piv) 6 at the same angle. Thus, the topology of 2D layers in structure I is deter mined by the symmetry of components of the building fragments.…”

“…The differences in sizes, crystal shapes, and order ing (crystallinity) of the [Fe 2 MO(Piv) 6 and L 2 ) samples obtained from different solvents can be explained by different crystallization rates. In turn, the crystallization rate affects the closeness of crystal lization to the idealized equilibrium state.…”

“…We have previously described a series of porous coordination polymers of the composition [Fe 2 MO(Piv) 6 (L) x ] n (L is a ligand of the bipyridine or tripyridine series; х = 1.5 or 1, respectively) [6][7][8]. Among these compounds, complex [Fe 2 MO(Piv) 6 (L 1 )] n is characterized by the highest Brunauer-Emmett-Teller (BET) surface area S BET = 730 m 2 /g and a pore volume of 0.28 cm 3 /g (the porous coordination polymer sorbs 0.91% Н 2 at 1 atm and 78 K) [6].…”

“…We have previously described a series of porous coordination polymers of the composition [Fe 2 MO(Piv) 6 (L) x ] n (L is a ligand of the bipyridine or tripyridine series; х = 1.5 or 1, respectively) [6][7][8]. Among these compounds, complex [Fe 2 MO(Piv) 6 (L 1 )] n is characterized by the highest Brunauer-Emmett-Teller (BET) surface area S BET = 730 m 2 /g and a pore volume of 0.28 cm 3 /g (the porous coordination polymer sorbs 0.91% Н 2 at 1 atm and 78 K) [6]. In addition to the high sorption characteris tics, the crystal lattice of this porous coordination polymer is conformationally rigid and the pore size and sorption characteristics of the complex are inde pendent of the substrate nature (unlike the porous coordination polymers with conformationally labile crystal lattices [7,8]).…”