supplementary materials

In the past few years, much attention has been put into the design and construction of multi-functional materials (Zhou et al., 2012). Octacyanometallates [M(CN)₈]^n- (M = Mo, W; n = 3, 4) with flexible coordination modes and lower symmetries have been aggressively studied recently (Nowicka et al., 2012), because these building blocks can adopt various geometries, e.g., square antiprismatic, dodecahedral or bicapped trigonal prismatic, depending on the external environments. The combination of the [M(CN)₈]^n- precusors and the second metal centers has produced various dimensional molecular structures and the resulting materials have displayed intriguing properties (Sieklucka et al., 2011). However, the development of octacyano- and lanthanide-based assemblies has been somewhat hampered by the tendency of the lanthanide ions to adopt higher coordination numbers, their ability to easily adapt to a given environment, and in the absence of design strategies for 4f-4d/5d networks. Recently, we used [Mo^V(CN)₈]^3- as building block to react with the lanthanide ion Ce³⁺ and dpe ligand (dpe = 1,2-di(pyridin-4-yl)ethylene), in order to obtain new octacyanide-based 4f/4 d compound with open structure. Unfortunately, a new ion-pair compound without Ce³⁺ ions was isolated. The asymmetric unit of the title compound contains 4,4'-ethene-1,2-diyldipyridinium, [H₂dpe]²⁺, and 4-(2-(pyridin-4-yl)ethenyl)pyridinium, [Hdpe]⁺, cations, one [Mo(CN)₈]^3- anion, and four crystallized water molecules (Fig. 1). Both the [H₂dpe]²⁺ and [Hdpe]⁺ cations are disordered over the same site. The eight-coordinated [Mo(CN)₈] unit exhibits a distorted slightly square antiprismatic geometry, typical of octacyanometalates (Prins et al., 2007; Tanase et al., 2008). The average distances of Mo1—C and C—N bonds are 2.1682 and 1.156 Å, respectively, while the Mo1—CN bonds are almost linear with the maximum deviation from linearity of 3.8°.

In the structure, [H₂dpe]²⁺ cation, [Hdpe]⁺ cation and [Mo(CN)₈]^3- unit are arranged alternatively through N3—H3X···O1 and O1—H1B···N2^v (symmetric code: (v) -x + 1/2, -y, z) hydrogen bonds (Table 1) to generate a two-dimensional layer. These layers are further interlinked through O1—H1A···N1^iv (symmetric code: (iv) x + 1, y - 1/2, -z) hydrogen bonds, forming a three-dimensional supramolecular network (Fig. 2). This structural feature has also been observed in related octacyanide-based compounds (C₁₀H₁₀N₄)(C₁₀H₉N₄)[M(CN)₈].nH₂O (M = Mo, W) (Qian et al., 2009; Liu et al., 2008).