New organic–inorganic frameworks incorporating iso‐ and heteropolymolybdate units and a 3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1 H ‐pyrazole‐2,2′‐diium multiple hydrogen‐bond donor

Poly[bis(3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1 H ‐pyrazole‐2,2′‐diium) γ‐octamolybdate(VI) dihydrate], {(C 10 H 16 N 4 ) 2 [Mo 8 O 26 ]·2H 2 O} n , (I), and bis(3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1 H ‐pyrazole‐2,2′‐diium) α‐dodecamolybdo(VI)silicate tetrahydrate, (C 10 H 16 N 4 ) 2 [SiMo 12 O 40 ]·4H 2 O, (II), display intense hydrogen bonding between the cationic pyrazolium species and the metal oxide anions. In (I), the asymmetric unit contains half a centrosymmetric γ‐type [Mo 8 O 26 ] 4− anion, which produces a one‐dimensional polymeric chain by corner‐sharing, one cation and one water molecule. Three‐centre bonding with 3,3′,5,5′‐tetramethyl‐4,4′‐bi‐1 H ‐pyrazole‐2,2′‐diium, denoted [H 2 Me 4 bpz] 2+ [N...O = 2.770 (4)–3.146 (4) Å], generates two‐dimensional layers that are further linked by hydrogen bonds involving water molecules [O...O = 2.902 (4) and 3.010 (4) Å]. In (II), each of the four independent [H 2 Me 4 bpz] 2+ cations lies across a twofold axis. They link layers of [SiMo 12 O 40 ] 4− anions into a three‐dimensional framework, and the preferred sites for pyrazolium/anion hydrogen bonding are the terminal oxide atoms [N...O = 2.866 (6)–2.999 (6) Å], while anion/aqua interactions occur preferentially via μ 2 ‐O sites [O...O = 2.910 (6)–3.151 (6) Å].