The Lewis acidic redox-active and photoactive
ruthenium(II) bipyridyl moiety in combination with amide
(CO−NH) groups has been incorporated into acyclic, macrocyclic, and lower
rim calix[4]arene structural frameworks
to produce a new class of anion receptor with the dual capability of
sensing anionic guest species via electrochemical
and optical methodologies. Single-crystal X-ray structures of
(1)Cl and
(11)H2PO4 reveal the
importance of
hydrogen bonding to the overall anion complexation process. In the
former complex, six hydrogen bonds (two
amide and four C−H groups) stabilize the Cl- anion and
three hydrogen bonds (two amide and one
calix[4]arene
hydroxyl) effect H2PO4
-
complexation with 11. Proton NMR titration
investigations in deuterated DMSO solutions
reveal these receptors form strong and, in the case of the macrocyclic
5 and calix[4]arene-containing receptor
11,
highly selective complexes with
H2PO4
-. Cyclic and
square-wave voltammetric studies have demonstrated these
receptors to electrochemically recognize Cl-,
Br-, H2PO4
-,
and HSO4
- anions. The
calix[4]arene anion receptor
11 selectively electrochemically senses
H2PO4
- in the presence of
10-fold excess amounts of HSO4
- and
Cl-.
Fluorescence emission spectral recognition of
H2PO4
- in DMSO solutions is
displayed by 3, 5, and
11.
New neutral ferrocene anion receptors L3, L4, L5 selectively complex, electrochemically recognise and respond t o the dihydrogen phosphate guest anion in the presence of excess amounts of hydrogen sulfate and chloride anions.
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