Coordination Complexes Containing Monosulfonated Catecholate Ligands and Methods for Producing the Same

Abstract

Flow batteries and other electrochemical systems can contain an active material that is a coordination complex having at least one monosulfonated catecholate ligand or a salt thereof bound to a metal center. The monosulfonated catecholate ligand has a structure of More particularly, the coordination complex can be a titanium coordination complex with a formula of D g Ti(L 1 )(L 2 )(L 3 ), in which D is a counterion selected from H, NH 4 + , Li + , Na + , K + , or any combination thereof; g ranges between 3 and 6; and L 1 , L 2 and L 3 are ligands, where at least one of L 1 , L 2 and L 3 is a monosulfonated catecholate ligand. Methods for synthesizing such monosulfonated catecholate ligands can include providing a neat mixture of catechol and up to about 1.3 stoichiometric equivalents of sulfuric acid, and heating the neat mixture at a temperature of about 80° C. or above to form 3,4-dihydroxybenzenesulfonic acid or a salt thereof.

What is claimed is: 
     
         1 . A composition comprising:
 a coordination complex having at least one monosulfonated catecholate ligand or a salt thereof bound to a titanium metal center;   wherein the at least one monosulfonated catecholate ligand has a structure of   
       
         
           
           
               
               
           
         
       
     
     
         2 . The composition of  claim 1 , wherein the coordination complex has a formula of:
   D g Ti(L 1 )(L 2 )(L 3 )   wherein:
 D is a counterion that is H + , NH 4   + , Li + , Na + , K + , or any combination thereof; 
 g ranges between 3 and 6; and 
 L 1 , L 2 , and L 3  are ligands, wherein at least one of L 1 , L 2 , and L 3  is a monosulfonated catecholate ligand. 
   
     
     
         3 . The composition of  claim 2 , wherein each of L 1 , L 2 , and L 3  are monosulfonated catecholate ligands and g is 5 or 6. 
     
     
         4 . The composition of  claim 2 , wherein one of L 1 , L 2 , and L 3  is a monosulfonated catecholate ligand and g is 3 or 4. 
     
     
         5 . The composition of  claim 4 , wherein two of L 1 , L 2 , and L 3  are non-sulfonated catecholate ligands. 
     
     
         6 . The composition of  claim 5 , wherein two of L 1 , L 2 , and L 3  are unsubstituted catecholate ligands. 
     
     
         7 . The composition of  claim 2 , wherein the coordination complex comprises both Na +  and K +  counterions. 
     
     
         8 . The composition of  claim 7 , wherein the coordination complex has a formula of:
   Na x K y Ti(L 1 )(L 2 )(L 3 )   wherein:
 3≤x+y≤6; 
 at least one of L 1 , L 2  and L 3  is a monosulfonated catecholate ligand; and 
 x and y are each greater than 0, and are the same or different. 
   
     
     
         9 . The composition of  claim 8 , wherein comprising substantially equimolar amounts of Na +  and K + . 
     
     
         10 . The composition of  claim 2 , wherein two of L 1 , L 2 , and L 3  are monosulfonated catecholate ligands, one of L 1 , L 2 , and L 3  is a non-sulfonated catecholate ligand, and g is 4 or 5. 
     
     
         11 . The composition of  claim 10 , wherein one of L 1 , L 2 , and L 3  is an unsubstituted catecholate ligand. 
     
     
         12 . The composition of  claim 1  that is an aqueous solution in which the coordination complex is dissolved. 
     
     
         13 . The composition of  claim 12 , wherein the aqueous solution has an alkaline pH. 
     
     
         14 . The composition of  claim 1 , wherein the coordination complex has an overall negative charge and comprises both Na +  and K +  counterions. 
     
     
         15 . The composition of  claim 2  that is an aqueous solution in which the coordination complex is dissolved. 
     
     
         16 . The composition of  claim 15 , wherein the aqueous solution has an alkaline pH. 
     
     
         17 . A flow battery comprising a first half-cell and a second half-cell, wherein the first half-cell contains a first electrolyte solution therein, the first electrolyte solution comprising the composition of  claim 12 . 
     
     
         18 . The flow battery of  claim 17 , wherein the first electrolyte solution comprises the aqueous solution of  claim 15 . 
     
     
         19 . The flow battery of  claim 17 , further comprising a second half-cell having a second electrolyte solution therein, the second electrolyte solution comprising an aqueous solution comprising an iron hexacyanide complex.