Ligand Aspect Ratio as a Decisive Factor for the Self-Assembly of Coordination Cages

Abstract

It is possible to control the geometry and the composition of metallasupramolecular assemblies via the aspect ratio of their ligands. This point is demonstrated for a series of iron- and palladium-based coordination cages. Functionalized clathrochelate complexes with variable aspect ratios were used as rod-like metalloligands. A cubic Fe(II)8L12 cage was obtained from a metalloligand with an intermediate aspect ratio. By increasing the length or by decreasing the width of the ligand, the self-assembly process resulted in the clean formation of tetrahedral Fe(II)4L6 cages instead of cubic cages. In a related fashion, it was possible to control the geometry of Pd(II)-based coordination cages. A metalloligand with a large aspect ratio gave an entropically favored tetrahedral Pd(II)4L8 assembly, whereas an octahedral Pd(II)6L12 cage was formed with a ligand of the same length but with an increased width. The aspect ratio can also be used to control the composition of dynamic mixtures of Pd(II) cages. Out of two metalloligands with only marginally different aspect ratios, one gave rise to a self-sorted collection of Pd(II)4L8 and Pd(II)6L12 cages, whereas the other did not.

Template Synthesis and X-Ray Structure of the First Cobalt(II) Glyoximate Clathrochelate with Terminal Formyl Groups

“…[9] According to the calculations the origin of paramagnetic shifts is different for various protons in a molecule: glyoxime protons are characterized by significant contact shifts (~90 ppm) owing its nearness to the paramagnetic cobalt(II) ion while paramagnetic shifts of Molecular structure of the complex CoGm 3 (B4-C 6 H 4 CHO) 2 is shown in Figure 2; the main geometrical parameters of its clathrochelate framework as well as those for its iron(II)-encapsulating analogue FeGm 3 (B4-C 6 H 4 CHO) 2 are listed in Table 1.…”

“…Like its iron(II)-encapsulating analog [7] 4-formylphenylboron-capped cobalt(II) clathrochelate CoGm 3 (B4-C 6 H 4 CHO) 2 was obtained in moderate yield under vigorous reaction conditions (in boiling nitromethane as a solvent) by Scheme 1 using direct template cross-linking of three molecules of glyoxime with 4-formylphenylboronic acid on a cobalt(II) ion as a matrix. [9] Despite that an iron(II) ion is known in literature to be the most efficient template for such self-assembly than a cobalt(II) ion, [10] the yields of these clathrochelate derivatives of the same caging ligand were almost the same (65 vs. 62 %, respectively).…”

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Cobalt(II) tris-glyoximate clathrochelate CoGm 3 (B4-CКлючевые слова: Макроциклические соединения, клатрохелаты, темплатная конденсация.Mono-and binuclear clathrochelate complexes with functionalizing apical and ribbed substituents containing terminal donor groups such as pyridine, carboxylic or cyano groups as prospective rigid and robust macrobicyclic ligands towards transition and main groups metal ions are reported in [1][2][3][4][5][6] allowing to obtain a wide range of nanosized heterometallic clathrochelate-based metallomacrocycles, coordination polymers and cages. On the other hand, the formyl-terminated clathrochelates seems to be suitable ligand synthones or monomers for the design and synthesis of the imine coordination cages and coordination polymers and their amine derivatives as well.

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“…As a result, the geometries of FeN 6 -coordination polyhedra in the two polymorphs of FeGm 3 (B4-C 6 H 4 CHO) 2 were found in [7] to be intermediate between a TP and a TAP (φ=12.2 and 18.8° at the heights h of these TP-TAP polyhedra of 2.36 and of 2.37 Å, respectively), while CoN 6 -coordination polyhedron of an encapsulated cobalt(II) ion in the molecule CoGm 3 (B4-C 6 H 4 CHO) 2 possesses an almost TP geometry (φ=1.2° at h=2.44 Å, Table 1).…”

“…Such low-spin state of the cobalt(II) clathrochelates can be stabilized by the crystal packing effects. [11][12][13] In the crystal CoGm 3 (B4-C 6 H 4 CHO) 2 ·0.5CH 2 Cl 2 , the observed π...π stacking between N=C-C=N chelate fragments of its neighboring macrobicyclic molecules, forming a clathrochelate dimer (Figure 3), cause the shortening of the corresponding coordination Co-N bonds, while the third ribbed chelate fragment of these interacting macrobicyclic molecules of CoGm 3 (B4-C 6 H 4 CHO) 2 , showing the greatest Co-N distances, is not included in such bonding. The reagents used, anhydrous CoCl 2 , 4-formylphenylboronic acid, sorbents and organic solvents were obtained commercially (Sigma-Aldrich).…”