Face-Driven Corner-Linked Octahedral Nanocages:  M₆L₈ Cages Formed by C₃-Symmetric Triangular Facial Ligands Linked via C₄-Symmetric Square Tetratopic Pd^II Ions at Truncated Octahedron Corners

Abstract

The face-driven corner-linked truncated octahedral nanocages, [Pd6L8]12+ (1, L1 = N,N',N' '-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide; 2, L2 = N,N',N' '-tris(4-pyridinylmethyl)-1,3,5-benzenetricarboxamide), were prepared with eight C3-symmetric tridentate ligands and six square planar tetratopic palladium(II) ions. The combination of the nitrogen donor atom at a approximately 120 degrees kink position of the carboxamido pyridinyl group and the tilted pyridyl versus the facial plane of the ligands can provide the needed curvature for the formation of octahedral cages. The nitrogen atoms can coordinate to the square planar palladium(II) ions to form kinks with approximately 120 degrees angles at the C4-symmetric square planar corners of the truncated octahedron. Depending on the conformation of the ligand, L1, two different truncated octahedral cages of around 2.4 nm in diameters were formed. The major form of 1 with syn-conformational ligands has a cavity volume of approximately 1600 A3. The cage has 12 ports (3.4 x 3.5 A2) at all edges of the octahedron. The minor form of cage 1 with anti-conformational ligands has a slightly increased cavity volume ( approximately 1900 A3) and port size (3.3 x 8.0 A2). The insertion of a methylene group in L2 has not only increased the cavity volume of 2 to approximately 2200 A3 but also enlarged the port size to 4.1 x 8.0 A2. However, an atomic force microscopy (AFM) study of cage 2 showed that the cages had a height of 1.8 +/- 0.1 nm. This value is about 30% smaller than the calculated size of 2.6 nm from the crystal structure. This tip-induced decrease in height in cage 2 suggests the nonrigidity of cage 2.

Star‐Burst Prisms with Cyclotriveratrylene‐Type Ligands: A [Pd6L8]12+ Stella Octangular Structure

“…Molecular entities with stellated structures have rarely been identified; and the only self-assembled example is a pentanuclear silver complex reported by Constable et al [14] The overall size of the assembly in complex 1 is roughly 3.1 nm, as measured from the centers of the basal hydrogen atoms of the -(CH 2 ) 3 -planes for diametrically opposed ligands. The surface of the structure is not fully enclosed, and there are eight windows (Figure 1 b) [15][16][17][18][19] In all these cases the ligands are achiral and based on a 1,3,5-tris-substituted benzene core, which leads to structures of considerably less spiked aspect than seen in the [Pd 6 (L1) 8 ] 12+ structure of 1, and have either truncated octahedral or octahedral geometry. The largest of these structures, of around 3 nm in size, is formed with a variety of divalent transition-metal ions and a disclike ligand with a hexaphenylenebenzene core, but does not contain any significant windows.…”

Novel Single‐Crystal‐to‐Single‐Crystal Anion Exchange and Self‐Assembly of Luminescent d10 Metal (CdII, ZnII, and CuI) Complexes Containing C3‐Symmetrical Ligands

“…The 3D pores containing tripyridylamide moieties as functional units in the channels are particularly attractive for guest uptake and/or ion-exchange studies, thus making such 3D coordination polymers potentially attractive as molecular materials. In this context, the exchange process was carried out in aqueous solution, and hence the voids were successfully filled with ClO 4 À anions (two, of which one is regularly arranged and the other is disordered) and a large number of water molecules (17 water molecules in an asymmetric unit), which are involved in hydrogen-bonding with the ClO 4 À anions, the amide groups, and even the water molecules themselves in the 3D channels (the hydrogen-bond data are [8] in 1 c, 2, and 3.…”

“…In addition, a systematic change in the coordination geometries of the metal ions from tetrahedral (four-coordinate) Cu I ions to trigonal-bipyramidal (five-coordinate) Zn II ions to octahedral (six-coordinate) Cd II ions has been observed, leading to the different structural frameworks. [8] 1 c N(2)ÀH(2A)···O (7) [a] 0.88 2.164 2.937 (7) 146.5 O(6)ÀH(6A)···O (7) 0.89 1.893 2.756 (9) 162.6 O(7)ÀH(7A)···O (2) 0.88 2.555 3.303 (7) 143.4 O(8)ÀH(8A)···O (9) 0.90 1.877 2.680(18) 147.1 2 N(2)ÀH(2A)···O (13) 0.88 2.302 3.152 (7) 162.9 N(2)ÀH(2A)···O (14) 0.88 2.434 3.088 (8) 131.6 N(4)ÀH(4A)···O (22) 0.88 2.100 2.968 (8) 168.8 N(6)ÀH(6B)···O(23) [b] 0.88 2.053 2.908 (8) 164.1 N(10)ÀHA C H T U N G T R E N N U N G (10A)···O (5) 0.88 2.186 3.005 (8) 154.9 N(12)ÀHA C H T U N G T R E N N U N G (12A)···O (24) 0.88 1.960 2.824 (7) 166.5 N(14)ÀHA C H T U N G T R E N N U N G (14A)···O (20) 0.88 1.989 2.838 (7) 161.6 O(16)ÀHA C H T U N G T R E N N U N G (16A)···O(10) [c] 0.90 1.881 2.741 (7) 159.8 O(16)ÀHA C H T U N G T R E N N U N G (16B) ···O(27) 0.90 1.768 2.641 (8) 162.8 O(27)ÀH(27)···O (17) 0.90 1.910 2.802 (10) 170.1 O(27)ÀHA C H T U N G T R E N N U N G (27')···O(26) [d] 0.90 1.851 2.743(11) 170.9 3 N(2)ÀH(2)···O(1) [e] 0.88 2.379 3.129(17) 143.5…”

“…[7] Simulation of the pseudo-trigonal-bipyramidal cages with an MM2 force field showed the cavity diameter to be about 1.9 nm. Later, Lah and co-workers also reported two novel singlecrystal structures of the truncated octahedral cages [Pd 6 L1' 8 ] 12 + and [Pd 6 L2 8 ] 12 + (L2 = N,N',N''-tris(4-pyridinyl)-1,3,5-benzenetricarboxamide), [8] and these face-driven corner-linker nanocages were found to have 12 ports at the edge of the truncated octahedron. Lahs work highlights that both the cavity size and the port size of the cage may be controlled by the size of the facial ligands.…”

“…Surprisingly, different trigonal-bipyramidal Zn II ions propagate in their respective sheet structures, with A ( Figure 2a) and B (Figure 2b) packed in an A-B-A-B manner in the crystal lattice. The A and B sheets are hydrogen-bonded through coordinated NO 3 À ···amide interactions [N(10)···O (5) 3.005 (8) , and (doubly) N(2)···O(13) 3.152 (7) and N(2)···O (14) 3.088 (8) ]. The dimeric sheet structures shown in Figure 2c are further hydrogen-bonded through coordinated water···- (10) 2.741 (7) ] to give a 3D extended framework, as shown in Figure 2d.…”