Sesquicaesium hemisodium tetracyanidoplatinate(II) sesquihydrate

The title compound, Cs1.5Na0.5[Pt(CN)4]·1.5H2O, was isolated from solution as a salt. The tetracyanidoplatinate (TCP) anions are stacked in a linear quasi-one-dimensional arrangement along the b axis, with Pt⋯Pt interactions of 3.6321 (5) Å. The mixed alkali metal TCP contains three distinct alkali metal positions in the structure that do not show any mixed occupancy: Cs1 (site symmetry 2), Cs2 (general position) and Na1 (site symmetry ). The Na+ ion contains an octahedral coordination environment composed of two water molecules and four N-terminal cyanides, which serve to bridge TCP anions. The Cs+ cations contain mono- and bicapped square-prismatic environments, where the square prisms are formed from cyanide N atoms with water molecules capping the faces. The 1.5 water molecules per formula unit are a result of two fully occupied sites, one on a general position and one on a twofold rotation axis. Weak hydrogen-bonding interactions are observed between one water molecule and terminal N-atom acceptors from TCP, while the second water molecule is not involved in hydrogen bonding.

The title compound, Cs 1.5 Na 0.5 [Pt(CN) 4 ]Á1.5H 2 O, was isolated from solution as a salt. The tetracyanidoplatinate (TCP) anions are stacked in a linear quasi-one-dimensional arrangement along the b axis, with PtÁ Á ÁPt interactions of 3.6321 (5) Å . The mixed alkali metal TCP contains three distinct alkali metal positions in the structure that do not show any mixed occupancy: Cs1 (site symmetry 2), Cs2 (general position) and Na1 (site symmetry 1). The Na + ion contains an octahedral coordination environment composed of two water molecules and four N-terminal cyanides, which serve to bridge TCP anions. The Cs + cations contain mono-and bicapped square-prismatic environments, where the square prisms are formed from cyanide N atoms with water molecules capping the faces. The 1.5 water molecules per formula unit are a result of two fully occupied sites, one on a general position and one on a twofold rotation axis. Weak hydrogen-bonding interactions are observed between one water molecule and terminal N-atom acceptors from TCP, while the second water molecule is not involved in hydrogen bonding.

Related literature
Crystalline TCP systems have been studied extensively for their interesting structural and spectroscopic, especially photoluminescent, properties (Holzapfel et al., 1981;Gliemann & Yersin, 1985;Stojanovic et al., 2010). An intrinsic factor affecting the optical properties and arrangement of TCP chains is the identity of the cations involved, and much work has been done in the systematic study of various combinations of alkali metal cations involved (Holzapfel et al., 1981). However, only one known reference of a caesium/ sodium mixed alkali metal TCP, viz. NaCs[Pt(CN) 4 ]Á1.5H 2 O, exists (Bergsoe et al., 1962), which notes the synthesis and scintillation properties for the compound, but not any structural information.  Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1 2 ; y À 1 2 ; Àz þ 1 2 ; (ii) Àx; Ày þ 1; Àz. The title compound, Cs 1.5 Na 0.5 Pt(CN) 4 .1.5H 2 O, was obtained as an unexpected product from a reaction that was an attempt to prepare a heterometallic cyanidometalate complex containing Eu(III), TCP, and dicyanidoaurate moieties. A number of related mixed-metal cation (alkali, alkaline-earth) TCPs have been reported (Holzapfel et al., 1981;Gliemann & Yersin, 1985). However, only one known reference of a caesium/ sodium mixed-alkali metal TCP (NaCsPt(CN) 4 .1.5H 2 O) exists (Bergsoe et al., 1962), which notes the synthesis and scintillation properties for the compound, but not any structural information.

Experimental
The structure of the title compound consists of pseudo one-dimensional chains of square-planar TCP anions tethered by Pt···Pt interactions of 3.6321 (5) Å. The platinate chains run parallel to the b axis and are bridged by ionic interactions among Cs + and Na + ions with the N atoms of the cyanidoplatinate, and show a loose packing of water molecules within that space.
The water molecules feature weak H-bonding interactions with the N atoms of the platinate as well (Table 1). The Na + ion contains a nearly regular octahedral coordination environment composed of two trans water molecules and four cyanido N atoms. Cs1 and Cs2 contain mono-and bi-capped square prismatic environments, respectively, where the slightly distorted square prisms are formed from cyanido N atoms and the capping positions are occupied by water molecules. As per each discrete TCP anion, the empirical structure of the compound contains an equivalency of 1.5 Cs + as a result of the Cs1 site residing on a twofold rotation axis and Cs2 occupying a general position, 1.5 H 2 O molecules due to O1 residing on a general position and the presence of O2 on a twofold rotation axis, and 0.5 Na + as a result of Na1 residing on an inversion center.
The N1 and N3 sites, trans to one another on the TCP anion, are involved in H-bonding interactions to the water molecule containing O1, while the other trans pair of cyanide groups containing N2 and N4 are involved in interactions with Na + (2.527 (4) and 2.541 (4) Å, respectively). The O2 water molecule interacts with Cs1 at a distance of 3.103 (6) Å, but does not engage in any meaningful H-bonding interactions.

Refinement
All H-atoms on the water molecules were located in a difference map and restrained with O-H distances of 0.85 Å, H···H separations of 1.39 Å, and U iso (H) = 1.5U eq (O). Fig. 1. The asymmetric unit of Cs 1.5 Na 0.5 Pt(CN) 4 .1.5H 2 O with the atom-numbering scheme. Displacement ellipsoids for non-hydrogen atoms are drawn at the 50% probability level.

Special details
Geometry. All e.s. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.