New supramolecular trigonal prisms from zinc(II)– 1,4,7,10-tetraazacyclododecane (cyclen) complexes and trithiocyanurate in aqueous solution

Abstract

The multiple bonding between multinuclear zinc(II)-1,4,7,10-tetraazacyclododecane (cyclen, a 12-membered tetraamine) complexes and multidentate ligands is an effective method for constructing supramolecular complexes having well defined and distinct structures in aqueous solution. Herein we present examples of supramolecular D 3h prisms formed by self-assembly of linearly dimeric or trimeric zinc(II)-cyclen complexes with a potentially trianionic C 3 subunit trithiocyanuric acid (TCA 3؊ ), wherein Zn 2؉ OS ؊ or Zn 2؉ ON ؊ coordination bonds and hydrogen bonds are responsible for stability of the multicomponent architectures in aqueous solution at neutral pH.A rtificial supramolecular hosts with stable and well defined structures formed by spontaneous self-assembly of molecular building blocks in organic solvents have shown great potential for inclusion phenomena, molecular recognition, or catalysis (1-12). However, supramolecular complexes that operate in aqueous solution are rare (10)(11)(12)(13)(14). While working on molecular recognition of imide functions by zinc(II) complexes of 12-membered tetraamine [Zn 2ϩ -1,4,7,10-tetraazacyclododecane (cyclen)] in aqueous solution (15-28), we tested interaction of cyanuric acid (CA) containing C 3 -symmetric three-imide functions with a C 3 -symmetric trinuclear zinc(II)-cyclen, Tris(Zn 2ϩ -cyclen) 1 [Zn 3 L 1 ; L 1 ϭ 1,3,5-Tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene]. We have discovered quantitative formation of a 2:3 1-dianionic CA (CA 2Ϫ ) complex at neutral pH that is represented schematically as a trigonal prism 2 ( Fig. 1; ref. 29). More interestingly, we accidentally isolated a 4:4 assembly [(Zn 3 L 1 ) 4 -(CA 3Ϫ ) 4 ] from basic aqueous solution. The x-ray crystal structure showed four sets of completely deprotonated CA (CA 3Ϫ ) binding to three Zn 2ϩ -cyclen units from three different Zn 3 L 1 at each N Ϫ rim (29). Its outer shape may be viewed as a cuboctahedron 3a with 12 vertices occupied by Zn 2ϩ and its inner shell as a truncated tetrahedron 4a. It was unfortunate, however, to find that this 4:4 cuboctahedral complex collapsed in neutral H 2 O, possibly because of the extremely high pK a value of the third imide proton of CA. More recently (30), this problem was overcome by replacing CA for TCA, the thioimide functions of which possess lower pK a values [5.12 (pK 1 ), 8.24 (pK 2 ), and 11.69 (pK 3 )] than those of CA [6.85 (pK 1 ), 10.91 (pK 2 ), and Ͼ12 (pK 3 )]. As anticipated, TCA acted as a tridentate donor for three Zn 3 L 1 at neutral pH to yield a similar type of the 4:4 self-assembling supercomplex 3b, in which the deprotonated TCA 3Ϫ in an aromatic 1,3,5-triazine bound to 1 through Zn 2ϩ OS Ϫ (exocyclic) coordination bonds, and thus the 4:4 assembly is a chiral, twisted cuboctahedron. More interestingly, 3b [(Zn 3 L 1 ) 4 -(TCA 3Ϫ ) 4 ] encapsulates various sizematched and hydrophobic guest molecules such as adamantane in its inner cavity, which is represented as a twisted, truncated tetrahedron 4b. Thus, we discovered an approach to de...

Polyhedral structures with an odd number of vertices: nine-atom clusters and supramolecular architectures

“…Four pending pyridyl groups at each porphyrin hold the Pd atoms in place, forming the upper and lower face ot the bioctahedron. 59 The same architecture is found in a Cu 9 compound prepared by Fenske and coworkers. The triangular column that results from the stacking of Pt 3 (CO) 6 triangles in the world of clusters, is also reproduced in the supramolecular world by a core of nine Zn atoms held together through bridging ligands.…”

Trithiocyanurate Complexes of Iron, Manganese and Nickel and Their Anticholinesterase Activity

“…The complex Ni 2 (L 2 )(ttcH)(ClO 4 ) 2 ·6H 2 O·EtOH ( 3 ) was studied by ESI − mass spectroscopy and a molecular peak was found. Macrocyclic ligands form very stable complexes as it can be demonstrated on multinuclear zinc cyclen (1,4,7,10-tetraazacyclododecane) complexes with ttc bridges, which are stable in water at neutral pH [39]. In this case of 3 , the biological activity is caused either by a combined effect of macrocyclic complex and ttc anion or by complex with coordinated ttc ligand.…”

The Synthesis of a Bis(thiosemicarbazone) Macrocyclic Ligand and the Mn(II), Co(II), Zn(II) and 68Ga(III) Complexes

“…A trigonal prismatic geometry can be forced upon Co 2+ complexes by sterically constrained pendant arms, whereas two discrete ligands can give trigonal prismatic com-plexes with Mn 2+ and Zn 2+ , including the formation of a Mn 2+ complex with an N 4 S 2 donor sphere [72,73,76,77]. Only two N 5 S cyclen-based complexes have been previously reported with Co 2+ and Zn 2+ , both with octahedral geometry [79,80]. H 2 L is the first example of an azamacrocyclic N 5 S donor for Mn 2+ .…”