ORIGINAL PAPER Expanded Prussian Blue Analogue Based on Octahedral {Nb 6 } Clusters and {K 2 } Dimers as Nodes Jian-Jun Zhang Æ Jochen Glaser Æ Sergio Aaro ´n Gamboa Æ Abdessadek Lachgar Received: 19 February 2008 / Accepted: 9 May 2008 / Published online: 30 May 2008 Ó Springer Science+Business Media, LLC 2008 Abstract The preparation, structures, and characteriza- tion of two new compounds containing octahedral niobium cyanochloride clusters as building units and (Et 4 N) + as cation are reported. The reaction between Nb 6 Cl 14  8H 2 O, KCN and (Et 4 N)Cl led to the formation of (Et 4 N) 4 [Nb 6 Cl 12 (CN) 6 ]  2.67H 2 O(1) which crystallizes in triclinic P-1 space group (No. 2) with a = 12.552(2), b = 12.818(2), c = 12.919(2) A ˚ , a = 105.157(3)°, b = 104.188(3)°, c = 117.390(2)°, V = 1611.7(5) A ˚ 3 and Z = 1. 1 has a 2D hydrogen-bonded layer structure based on [Nb 6 Cl 12 (CN) 6 ] 4- units connected through hydrogen bonding between cyanide ligands and solvent water molecules. In the presence of large excess of K + ions, similar reaction leads to formation of K 2 (Et 4 N) 2 [Nb 6 Cl 12 (CN) 6 ] (2) which crystallizes in the tetragonal I4/m space group (No. 87) with a = b = 10.9597(3), c = 19.178(1) A ˚ , V = 2303.6(2) A ˚ 3 and Z = 2. Its 3D structure is based on [Nb 6 Cl 12 ] 2+ and [K 2 ] 2+ nodes bridged by cyanide ligands to form an expanded Prussian blue type framework with (Et 4 N) + acting as charge compensating ions Keywords Coordination polymer  Cluster compound  Expanded prussian blue  Niobium Introduction Cyanometallates are extensively used as molecular build- ing blocks for a variety of cyano-bridged assemblies that display rich structural diversity ranging from discrete polynuclear complexes to fascinating poly-dimensional polymers. Many of these cyanometallate based materials are characterized by interesting magnetic, magneto-optical and optoelectronic properties [1]. Octahedral metal clusters with terminal cyanide ligands such as [Re 6 X 8 (CN) 6 ] n- (X = chalcide) or [Nb 6 X 12 (CN) 6 ] n- (X = Cl, Br) can be treated as expanded analogues of mononuclear hexacy- anometallates and are characterized by their large size (*1 nm) and remarkable physical properties arisen from the presence of metal–metal bonds [2]. These cluster units are being actively investigated as molecular building blocks to construct extended inorganic polymers with the aim of investigating their potential use in applications such as molecular sieves, chemical sensors, or ion-exchange materials [3]. For instance, the cluster [Re 6 X 8 (CN) 6 ] 4- has been used instead of the anion [Fe(CN) 6 ] 4- to synthesize a series of compounds that can be considered as a direct expansion of Prussian blue [4, 5]. Other examples include the isotropic expansion of the compounds Na 2 Zn 3 [Fe(CN) 6 ]  9H 2 O and Ba 3 [Cr(CN) 6 ] 2  20H 2 O which lead to the formation of several cluster-based compounds with the formula of A 2 Zn 3 [Re 6 Se 8 (CN) 6 ]  nH 2 O [6] and A 2 M 3 [Re 6 Se 8 (CN) 6 ]  nH 2 O[7] (A = Na + , Cs + , [H 3 O] + ; M = Mn 2+ , Co 2+ , Ni 2+ , Cd 2+ ) respectively. A number of other cluster-base 3D frameworks have been reported [8, 9]. We have been actively investigating the use of the octahedral metal cluster anion [Nb 6 Cl 12 (CN) 6 ] 4- and metal ions or complexes as building blocks for coordination polymers with the goal of making materials in which Electronic supplementary material The online version of this article (doi:10.1007/s10870-008-9423-x) contains supplementary material, which is available to authorized users. J.-J. Zhang  J. Glaser  S. A. Gamboa  A. Lachgar (&) Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA e-mail: lachgar@wfu.edu 123 J Chem Crystallogr (2009) 39:1–8 DOI 10.1007/s10870-008-9423-x