Structures And Chromogenic Ion-Pair Recognition Of A Catechol-Functionalized 1,8-Anthraquinone Macrocycle In Dimethyl Sulfoxide

A lariat anthraquinone macrocycle functionalized with catechol (H2L) was synthesized via the Mannich reaction. The Mannich base H2L can be partially decomposed into L1 center dot 3H(2)O and HL1 center dot NO3 center dot 2H(2)O in the presence of tetrabutylammonium hydroxide/Al(NO3)(3)center dot 9H(2)O in dimethyl sulfoxide (DMSO). Free L1 center dot 3H(2)O is essentially coplanar, while protonated HL1 center dot NO3 center dot 2H(2)O is highly distorted. Dark-green FeCl3 center dot H2L center dot 2H(2)O powder and Fe2(HL)(2)Cl-4 crystal can be isolated from ethanol (C2H5OH) in high/low H2L concentration. Anthraquinone in H2L is essentially coplanar but distorted in Fe2(HL)2Cl4. The Fe(III) ion in Fe2(HL)(2)Cl-4 adopts a less common fivecoordination with three catecholate O and two Cl atoms in the dimer. The distortion of inbound C.O is much higher than that of outbound C.O in anthraquinone in all of these compounds. H2L responds to chlorides of Li+, Na+, K+, Cs+, Mg-2(+), Ca-2(+), Sr-2(+), Ba-2(+), Fe3+, Cu-2(+), Zn2+, and Al3+ in a DMSO solution, which can be observed by differential pulse voltammetry, UV-vis, and 1H NMR. All of these metal ions shift Ep of anthraquinone to positive, especially the second reduction peak of anthraquinone. Fe-3(+), Zn-2(+), and Al-3(+) change the reduction of catechol fundamentally. H2L (0.50 mM) shows a chromogenic response to FeCl3 and Fe(NO3) 3 to form uncommon 2:1 and 3:2 (H2L/Fe) complexes, both peaking at 748 nm in DMSO. In the presence of 2 equiv of sodium hydroxide (NaOH), the 748 nm absorbance shifts to 777 nm, identical with Fe-2(HL)(2)Cl-4 in DMSO. Different from the fast reaction between H2L and FeCl3, Fe(NO3) 3 reacts with H2L rather slowly in DMSO. Catechol can coordinate to FeCl3 without any deprotonation in C2H5OH and DMSO. H2L also shows a chromogenic response to fluorides and hydroxides, which peak at 670 and 684 nm, respectively, in DMSO. The binding ratio between H2L and F-/OH- is 1:2. In a higher concentration of hydroxides, a 684 nm greenish-blue 1:2 complex forms immediately, which gradually transforms to a red complex and peaks at similar to 530 nm in minutes at room temperature. No color change can be observed in an C2H5OH solution in the presence of OH-.