The mixed‐valent 10‐manganese(III/IV)‐containing 36‐tungsto‐4‐arsenate(V), [Mn III 6 Mn IV 4 O 4 (OH) 12 (H 2 O) 12 ( A ‐β‐AsW 9 O 34 ) 4 ] 22−

Interaction of the mixed‐valent 12‐manganese coordination complex [Mn III 8 Mn IV 4 O 12 (CH 3 COO) 16 (H 2 O) 4 ] with the lacunary 9‐tungstoarsenate(V) [ A ‐α‐AsW 9 O 34 ] 9− resulted in the 10‐manganese(III/IV)‐containing 36‐tungsto‐4‐arsenate(V), [Mn III 6 Mn IV 4 O 4 (OH) 12 (H 2 O) 12 ( A ‐β‐AsW 9 O 34 ) 4 ] 22− ( 1 ). Polyanion 1 was isolated as a hydrated mixed potassium–sodium salt, K 14 Na 8 [Mn III 6 Mn IV 4 O 4 (OH) 12 (H 2 O) 12 ( A ‐β‐AsW 9 O 34 ) 4 ]·104H 2 O, which crystallizes in the orthorhombic space group Pbcn and was characterized by FT–IR spectroscopy and single‐crystal X‐ray diffraction, as well as elemental and thermogravimetric analyses. The title polyanion contains a unique [Mn III 6 Mn IV 4 O 4 (OH) 12 (H 2 O) 12 ] 14+ core stabilized within the 36‐tungsto‐4‐arsenate(V) framework.