Sc(III), Eu(III), and Gd(III) Complexes with Macrocyclic Cavitand Cucurbit[6]uril: Synthesis and Crystal Structures

Abstract

The studies performed in recent years showed that organic macrocyclic cavitand cucurbit[6]uril (C 36 H 36 N 24 O 12 ), which consists of six glycoluryl fragments bonded by methylene bridges, can form complexes with some oxophillic metals due to its 12 polarized carbonyl groups and act as polydentate ligand [1][2][3][4][5][6][7]. cucurbit [6]uril was found to be efficient as a polydentate ligand used in isolation of the kinetically labile lanthanide(III) complexes from aqueous solutions [8][9][10]. The lanthanide complexes are known to show interesting spectral and magnetic properties. Different compounds of rare-earth metals are widely used as luminescence marks in biology or medicine [11]. In aqueous solutions, cations of f elements form aqua complexes with different coordination numbers and coordination surrounding of a metal. Such complexes are kinetically labile, and therefore, their separation from aqueous solutions into a solid phase is difficult. This difficulty can be successfully overcome by making use of the chelate and macrocyclic effects.It is not infrequent that complexation with polydentate N-and O-donor ligands, such as crown ethers or calixarenes, is used in order to separate lanthanide aqua complexes [12,13]. Data are also available on the separation of aqua complexes of metals, such as yttrium and scandium, in a solid phase using macrocyclic ligands. The following aqua complexes of these metals with crown ethers were synthesized and structurally characterized: [17]. In these compounds, aqua complex is united with microcycle by hydrogen bonds between the water molecules and the O atoms of crown ether.The use of cucurbit[6]uril as a polydentate ligand turned efficient. Cucurbit[6]uril is similar to 18-crown-6 in size, but has a higher negative charge on the donor O atoms of portals, which makes its compounds with the metal cations more stable. Previously, we synthesized and studied the structures of its complexes with L ‡ 3+ , Ce 3+ , Sm 3+ , Gd 3+ , Ho 3+ , Yb 3+ with the metal : cucurbit[6]uril ratios 1 : 1, 2 : 2, and 2 : 3 [8], where the cucurbit[6]uril molecule is coordinated by the lanthanide cations through the O atoms of portals in bi-or tetradentate mode. The yttrium complex with cucurbit[6]uril ( H ) 2 [ Y ( H 2 O ) 8 ] 2 ( NO 3 ) 8 ( C 36 H 36 N 24 O 12 ) · 13 H 2 O, where aqua complex of yttrium is not bonded with the microcyclic ligand, was synthesized and structurally characterized [18]. The aim of this work was to synthesize and study the crystal structure of new Cs(III), Eu(III), and Gd(III) complexes with cucurbit[6]uril: [ Sc ( NO 3 )( H 2 O ) 4 ( C 36 H 36 N 24 O 12 )]( NO 3 ) 2 · 8.5 H 2 O ( I ), [ Eu ( NO 3 )( H 2 O ) 4 ( C 36 H 36 N 24 O 12 )]( NO 3 ) 2 · 6.75 H 2 O ( II ),Abstract -Slow evaporation of solutions of Sc and Eu nitrates with macrocyclic cavitand cucurbit[6]uril gives crystals of isostructural complexes [ Sc ( NO 3 )( H 2 O ) 4 ( C 36 H 36 N 24 O 12 )]( NO 3 ) 2 · 8.5 H 2 O (space group Pna 2 1 , a = 32.0065(18) Å , b = 14.7904(8) Å , c = 11.5774(6) Å, V = 5480.6...

Synthesis, crystal structures, and properties of [Ca(H2O)2(Dmf@CB[6])(Bdc)] · DMF · 4H2O and [Ca(H2O)3(Dmf@CB[6])]Cl2 · 2H2O

“…The distance from the metal atom to the plane of the portal in compound II is 0.53 Å, and that in compound I is 1.04 Å. Similar changes were observed in the mononuclear complexes of lan thanides with CB [6] [23][24][25]. The position of the DMF molecule inside CB [6] differs: in compound I two CH 3 groups are directed to the portal, whereas in compound II one group is directed to the portal and the second CH 3 group is located at the center of the CB [6] cavity.…”

Synthesis and crystal structure of [Na2(μ-H2O)(H2O)CB[5]]Cl2 · 6H2O, [Na3(μ-H2O)4(H2O)4(CNPy@CB[6])]Cl3 · 8H2O, and [Rb2(μ-H2O)2(CNPy@CB[6])]Cl · 8H2O

“…The IR spectra of all compounds show a broad stretching band at 3700-2800 cm -1 corresponding to different types of water molecules that form hydrogen bonds [20]. The bands at 1740-400 cm -1 refer to different vibrations in the cucurbituril molecule [5,6,[21][22][23][24][25][26][27].…”

“…Distortions of the CB [6] molecule were observed for complexes of Al 3+ (Δ CH = 1.29 Å) with inclusion of the pyridine molecule [6], Sm 3+ (Δ CH = 0.71 Å) and Gd 3+ (Δ CH = 0.68 Å); the CB [6] cavity of the latter complex includes also a pyridine molecule [22,25,28]; Ho 3+ (Δ CH = 1.27 and 1.55 Å) with inclusion of isonicoti nate anion [24], Pr 3+ (Δ CH = 1.86 Å) with inclusion of nitrate anion [23]. In the crystals of compounds I-III, the chains are packed in such a way that the narrow segment of one chain is opposed by the wide segment of another chain (Fig.…”

A novel two-dimensional network formed by complexation of cucurbituril with cadmium ions

“…Cucurbit[n]urils [10][11][12] are good ligands because of the two opening portals rimmed with carbonyl groups and are easy to self-assemble with many cationic substances, e.g., metal ions like alkali and alkaline earth ions [12], transition-metal ions [12,13], lanthanide ions [12,[14][15][16] and their complexes or clusters [12,17], to form various supramolecular entities and frameworks.…”