Coordination Chemistry of Polyoxometalates: Rational Synthesis of the Mixed Organosilyl Derivatives of Trivacant Polyoxotungstates α‐A‐[PW9O34(tBuSiO)3 (RSi)]3− and α‐B‐[AsW9O33(tBuSiO)3(HSi)]3−

Trivacant polyoxotungstates such as α-A-[PW9O34]9− ions react with tBuSiCl3 to afford the anion 1. This can react further with other trichlorosilanes to give α-A-[PW9O34(tBuSiO)3(RSi)]3− ions (R = H, Me, Et, CHCH2, CH2CH2CH2Cl). Similar arsenic compounds are also reported.