Selective Anion Recognition by a Dynamic Quadruple Helicate

Abstract

An M L quadruple helicate, formed by wrapping four molecules of 1,4-bis(3-pyridyloxy)benzene (L ) about two palladium(II) centers, is shown to bind anions within its internal cavity. H NMR exchange experiments provide a quantitative measure of anion selectivity and reveal a preference for ClO over the other tetrahedral anions BF and ReO and the octahedral anion PF . X-ray crystal structures of [Pd (L ) ] helicates containing ClO , BF and I reveal that the cavity size can dynamically change in response to the size of the guest.

Bifurcation of self-assembly pathways to sheet or cage controlled by kinetic template effect

“…Micrometer-sized sheet formation on the off-pathway. The selfassembly of the helical [Pd 2 1 4 ] 4+ cage was reported by Steel and McMorran 35,36 . Due to the high flexibility of the ditopic ligand 1, the resulting cage can bind a variety of anionic species (PF 6 − , BF 4 − , ClO 4 − , ReO 4 − , and I − ) in its cavity, whose size can be changed by twisting the helix in an induced-fit manner.…”

“…Due to the high flexibility of the ditopic ligand 1, the resulting cage can bind a variety of anionic species (PF 6 − , BF 4 − , ClO 4 − , ReO 4 − , and I − ) in its cavity, whose size can be changed by twisting the helix in an induced-fit manner. The order of the binding strength for anions is ClO 4 − > BF 4 − > ReO 4 − > PF 6 − , which suggests that smaller anions are more strongly bound in the cage with the exception that ClO 4 − (62.5 Å 3 ) is a better guest than BF 4 − (49.3 Å 3 ) 36 . The self-assembly of the cage from 1 and [PdPy* 4 ](OTf) 2 in CD 3 NO 2 at 298 K was carried out to investigate the intermediates produced during the selfassembly by QASAP (quantitative analysis of self-assembly process) [37][38][39] .…”

“…We then carried out the self-assembly from 1 and [PdPy* 4 ](OTf) 2 in the presence of n-Bu 4 NNO 3 to prevent the formation of the sheet during the self-assembly ( Fig. 2 .442 Å) 36 . The NO 3 − anion in the cage was disordered between two sites with each occupancy of 50% at the Wyckoff position of 4a on the C 2 axis, lying on a plane perpendicular to the helix axis of the cage.…”

Innovative Multipodal Ligands Derived from Tröger's Bases for the Sensitization of Lanthanide(III) Luminescence

“…Even though the general stoichiometry of these coordination compounds is 2:2, Lützen and co‐workers proposed structures with two transition‐metal ions and three TB ligands, showing that a 2:4 structure could also be obtained from a steric point of view [49, 50] . Similar 2:4 structures have been reported for other self‐assembled metallosupramolecular cages, including with lanthanide(III) ions [58–66] …”

Dynamic Open Coordination Cage from Nonsymmetrical Imidazole–Pyridine Ditopic Ligands for Turn‐On/Off Anion Binding

“…TheN MR-based structure determination of (Pd 2+ ) 2 (1) 4 and (Pd 2+ ) 2 (1 S ) 4 suggests an open cage (Figure 4a)t hat can bind with anions (G À = BF 4 À ,P F 6 À ,C lO 4 À ,R eO 4 À ,a nd SbF 6 À ). [19][20][21] Figure 4e shows 1 HNMR titration experiments of (Pd 2+ ) 2 (1 S ) 4 with successive additions of NBu 4 ReO 4 , wherein particularly,w eobserved an otable downfield shift of the pyridine proton H b (blue triangle) and ac oncomitant upfield shift of the carbazole proton H d (green square). The NMR titration data can be fitted by nonlinear fitting based on the 1:1host-guest binding model (Figure 4c), [10c] which yields an association constant (K a )o f( 7.6 AE 0.8) 10 2 m À1 (see also Figures S14-S17).…”