Disclosed herein are host or receptor compounds that bind targets of interest. In one embodiment the compounds bind ions, such as metal ions.A compound, or a protonate or salt thereof, having the formula of: Formula IIa wherein R6 is an aminoalkoxy, alkylamino, nitro or —NH2; n is 1 or 2; each R2 is independently selected from an optionally substituted alkyl, halogen, optionally substituted alkoxy, optionally substituted carboxyl, or amide; a is 0 to 4.