Single crystals of the title compound, K 2 [Ni(H 2 O) 6 ][ZrF 6 ] 2 , were grown by slow evaporation of a 40% aqueous HF solution in which a stoichiometric mixture of NiCl 2 Á6H 2 O, ZrF 4 and KCl was dissolved. The monoclinic structure is isotypic with its K 2 Cu, K 2 Zn, Cs 2 Zn and Cs 2 Cu analogues. The structure is built up from isolated, slightly elongated octahedral [Ni(H 2 O) 6 ] 2+ complex cations (symmetry 1) and dimeric [Zr 2 F 12 ] 4À complex anions (symmetry 1) that are also isolated from each other. The [Zr 2 F 12 ] 4À anion results from the association of two distorted pentagonal-bipyramidal [ZrF 7 ] coordination polyhedra by sharing an equatorial edge passing through an inversion center of the unit cell. Both isolated [Ni(H 2 O) 6 ] 2+ and [Zr 2 F 12 ] 4À complex ions are situated in planes parallel to (010). They are connected by the eightcoordinated K + ions into a three-dimensional structure. An intricate O-HÁ Á ÁF hydrogen-bonding network consolidates the structure. Related literature For isotypic structures, see: Fischer & Weiss (1973); Bukvetskii et al. (1993); Hitchman et al. (2002). For a review on the stereochemistry of zirconium and hafnium fluorido complexes, see: Davidovich (1998). For background to distortion indices, see: Momma & Izumi (2008). Experimental Crystal data K 2 [Ni(H 2 O) 6 ][ZrF 6 ] 2 M r = 655.45 Monoclinic, P2 1 =n a = 6.6090 (1) Å b = 10.0398 (1) Å c = 11.7843 (1) Å = 95.897 (1) V = 777.79 (2) Å 3 Z = 2 Mo K radiation = 3.20 mm À1 T = 296 K 0.28 Â 0.14 Â 0.09 mm Data collection Bruker APEXII CCD diffractometer Absorption correction: multi-scan (SADABS; Bruker, 2008) T min = 0.613, T max = 0.748 17267 measured reflections 4436 independent reflections 3858 reflections with I > 2(I) R int = 0.028 Refinement R[F 2 > 2(F 2)] = 0.023 wR(F 2) = 0.052 S = 1.06 4436 reflections 131 parameters All H-atom parameters refined Á max = 0.63 e Å À3 Á min = À0.57 e Å À3 inorganic compounds Acta Cryst. (2011). E67, i6-i7 Oudahmane et al. K 2 [Ni(H 2 O) 6 ][ZrF 6 ] 2 i7 supporting information sup-5 Acta Cryst. (2011). E67, i6-i7 supporting information sup-6