Redox flow battery having ligand-metal complex

1. A nonaqueous electrolyte composition for use in a redox flow battery system, comprising:

a nonaqueous supporting electrolyte; and

an electrochemically active component of formula II:

wherein X is an alkanediyl, a substituted alkanediyl, a cycloalkanediyl, a substituted cycloalkanediyl, an aryldiyl, a substituted aryldiyl, a heteroaryldiyl, or a substituted heteroaryldiyl;

each R 1 -R 4 is independently H, alkyl, substituted alkyl, alkoxy, substituted alkoxy, halogen, acyl, substituted carboxyl or ester; and

Z is a metal.

2. The composition of claim 1 , wherein X is a C 1 -C 6 alkanediyl, or a C 1 -C 6 substituted alkanediyl.

3. The composition of claim 1 , wherein the alkanediyl may be a branched alkanediyl or the substituted alkanediyl may be a substituted branched alkanediyl.

4. The composition of claim 1 , wherein X is —CH 2 —CH 2 —, —CH 2 —CH 2 —CH 2 —, —CH 2 —CH 2 —CH 2 —CH 2 —, —CH 2 —CH 2 —CH(CH 2 CH 3 )—, —CH 2 —C(CH 3 )(CH 3 )—CH 2 , cyclohexanediyl, phenyldiyl, or naphthyldiyl.

5. The composition of claim 1 , wherein at least one of R 1 -R 4 is an alkyl or an alkoxy.

6. The composition of claim 1 , wherein at least one of R 1 -R 4 is a C 1 -C 6 alkyl or C 1 -C 6 alkoxy.

7. The composition of claim 1 , wherein R 1 or R 4 is an alkyl or an alkoxy.

8. The composition of claim 1 , wherein R 2 is an alkyl or an alkoxy.

9. The composition of claim 1 , wherein at least one of R 1 -R 4 is not a H.

10. The composition of claim 1 , wherein Z is selected from scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, or zinc.

11. The composition of claim 1 , wherein Z is nickel, iron, cobalt, chromium or zinc.

12. The composition of claim 1 , wherein Z is nickel.

13. The composition of claim 1 , wherein Z is iron.

14. The composition of claim 1 , wherein each of R 1 -R 4 is H.

15. The composition of claim 1 , wherein the electrochemically active component of formula II is:

16. A redox flow battery system, comprising:

the nonaqueous electrolyte composition of claim 1 ; and

an ion-exchange membrane or porous separator.

17. The system of claim 16 , wherein X is —CH 2 —CH 2 —CH(CH 2 CH 3 )—.

18. The system of claim 16 , wherein the electrochemically active component of formula II is:

19. A redox flow battery system, comprising:

a nonaqueous electrolyte composition comprising an electrochemically active component of formula II:

wherein X is an alkanediyl, a substituted alkanediyl, a cycloalkanediyl, a substituted cycloalkanediyl, an aryldiyl, a substituted aryldiyl, a heteroaryldiyl, or a substituted heteroaryldiyl;

each R 1 -R 4 is independently H, alkyl, substituted alkyl, alkoxy, substituted alkoxy, halogen, acyl, substituted carboxyl or ester; and

Z is a metal; and

an ion-exchange membrane or porous separator.

20. A ligand metal complex of formula II:

wherein X is an alkanediyl, a substituted alkanediyl, a cycloalkanediyl, a substituted cycloalkanediyl, an aryldiyl, a substituted aryldiyl, a heteroaryldiyl, or a substituted heteroaryldiyl;

each R 1 -R 4 is independently H, alkyl, substituted alkyl, alkoxy, substituted alkoxy, halogen, acyl, substituted carboxyl or ester; and

Z is a metal,

provided that X is not —CH 2 —CH 2 —CH 2 —, or at least one of R 1 -R 4 is not a H.

21. The complex of claim 20 , wherein the complex is:

22. The composition of claim 1 , wherein the electrochemically active component of formula II is present in the electrolyte composition in an amount of at least 1 M.

23. The composition of claim 1 , wherein the electrochemically active component of formula II is present in the electrolyte composition in an amount of at least 5 mM.

24. The system of claim 16 , wherein the electrochemically active component of formula II is present in the electrolyte composition in an amount of at least 1 M.

25. The system of claim 16 , wherein the electrochemically active component of formula II is present in the electrolyte composition in an amount of at least 5 mM.