Method for reducing arsenic concentration in aqueous solutions

A method of reducing the arsenic concentration in an aqueous solution that comprises arsenic, which method comprises contacting the aqueous solution with a complex of Formula I,

• wherein M1 and M2 are the same or different and are independently selected from V, Mn, Ga, Cu, Ni, Co, Fe or Zn;
• wherein a is 0, or 1, and b is 0, or 1, provided that a+b together must be at least 1;
• Q is a negatively charged counter ion, wherein the negatively charged counter ion is NO3−, ClO4−, AcO−, PF6−, BF4−, Cl−, BPh4− or Br−;
• n is from 1 to 5;
• X1 is OH, O, SH or S;
• L1 is a group selected from -La1-C(O)NR—, -La2-C(O)OR—, -La3-NRC(O)—, La4-OC(O)—, La5-O— or La6-NRO—, wherein La1, La2, La3, La4, La5 and La6 are each C1-6 alkyl, optionally substituted, R is H or C1-6 alkyl optionally substituted;
• Linker is a polyethylene glycol (PEG) chain with from 1 to 10 repeating units, a C1-16 polyamine chain or a C1-16 alkyl chain;
• Z is a solid support;
• L2 to L7 are independently C1-3 alkyl, optionally substituted;
• and
• Het1 to Het4 are independently 5 to 14 membered heteroaryl group having at least one N atom and optionally substituted.