Unique seven-node rare-earth octacyanomolybdate(IV) three-dimensional molecular frameworks: {[Er(H2O)5(Er(H2O)4)3][Mo(CN)8]3·11H2O}n and {[Eu(H2O)5(Eu(H2O)4)3][Mo(CN)8]3·11H2O}n

The crystal structure analyses of {[Er(H2O)5(Er(H2O)4)3][Mo(CN)8]3·11H2O}n (1) and {[Eu(H2O)5(Eu(H2O)4)3][Mo(CN)8]3·11H2O}n (2), show that they are not only new neutral three-dimensional rare-earth octacyanomolybdate(IV) molecular frameworks, but that they also belong to an unknown structure type having seven different nodes. To the best of our knowledge this is different to any other known molybdenum(IV) octacyanide complexes published to date. Both compounds crystallize in the triclinic system, space group P-1, and are isostructural and isotypic. The coordination polyhedra of the molybdenum atoms in the three different [Mo(CN)8]4− anions are trigonal prisms, with two additional atoms. A new bridging mode for octacyanometallates is also observed with five of the eight cyanide groups involved in bridging either three or four rare-earth atoms, while the three remaining cyanide groups are terminal and are involved in hydrogen bonding. The four rare-earth atoms in 1 and 2 have different coordination polyhedra in the form of trigonal prisms with two additional atoms. The three-dimensional structures are made up of infinite two-dimensional slabs linked by one of the rare-earth metal atoms. In both compounds, apart from the 17 coordinated water molecules, there are 11 lattice water molecules of crystallization present in the cavities of the three-dimensional frameworks. The 28 water molecules and the terminal CN− groups are involved in an extensive O–H⋯O and O–H⋯N hydrogen bonding network.

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► Two new neutral three-dimensional rare-earth octacyanomolybdate(IV) molecular frameworks.
► They belong to an unknown structure type having seven different nodes.
► Infinite two-dimensional slabs linked by one of the rare-earth metal atoms.
► A new bridging mode for octacyanometallates.
► 11 Lattice water molecules of crystallization present in the cavities.