The room temperature reaction of Hg(NO3)2 · H2O, cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) and K8{Nb6O19} · 16 H2O in a mixture of H2O and DMSO led to crystallization of the novel compound {[Hg(cyclam)]6Nb6O19}(NO3)4 · 14 H2O, which is the first mercury containing polyoxoniobate. The structure consists of a {Nb6O19}8− cluster core which is expanded by six [Hg(cyclam)]2+ complexes via Hg–μ2-O–Nb bond formation. The title compound contains a positively charged polyoxoniobate cluster. The crystal water molecules form small aggregates by O–H · · · O hydrogen bonding which are joined into larger aggregates by N–O · · · H–O hydrogen bonding integrating the nitrate anions.

The new compound {[Fe(cyclam)]3Nb7O22}· ≈ 19 H2O (I) was synthesized at room temperature reacting aqueous solutions of K8{Nb6O19}·16 H2O, Fe(NO3)3·9 H2O and cyclam (1,4,8,11‐tetraazacyclotetradecane). In the crystal structure the heptaniobate {Nb7O22}9– anion is observed which is expanded by three [Fe(cyclam)]3+ complexes, thus suppressing further condensations into larger aggregates. The complexes are solely bound to the three terminal O2– anions of the NbO6 octahedron which expands the hexaniobate {Nb6O19}8– anion to form the heptaniobate cluster. The two O atoms in the FeN4O2 octahedron are in cis position leading to a severe distortion of the cyclam ligand with one of the CH2–CH2–CH2–N–CH2–CH2 fragments being rotated by about 90°. The {[Fe(cyclam)]3Nb7O22} units are arranged to form channels which host the crystal water molecules. The crystal water molecules can be removed by thermal treatment. Storing the sample on air the pristine sample is recovered.

The new compound {[Cu(phen)] 2 [Cu(phen) 2 ] 2 Nb 6 O 19 }•24H 2 O (I) (phen = 1,10-phenanthroline) was prepared under ambient conditions. The crystal structure is composed of the [Nb 6 O 19 ] 6− anion which is expanded by two different Cu 2+ centered complexes via Cu−O bonds to form a charge neutral compound. One polyhedron around Cu 2+ is a slightly distorted square pyramid, while the second polyhedron is between square pyramidal and trigonal bipyramidal. The distortion of the polyhedra is reflected in the EPR spectrum. The molecules are arranged in a layer-like fashion with the crystal water molecules forming a cluster being located between the layers. The crystal water molecules can thermally be removed, and water sorption experiments show a steplike water uptake, leading to full recovering of the crystal structure. The steplike behavior is explained by the differing strengths of hydrogen bonding interactions. A room temperature in situ X-ray diffraction experiment demonstrates that the pristine material loses water, forming first an intermediate compound and finally a waterdeficient crystalline sample. Luminescence measurements demonstrate a weak red glow.

AbstractSyntheses were performed at room temperature using Ni(NO3)2·6H2O, cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) and the precursors Li8[Nb6O19]· ≈22H2O or Na7[HNb6O19]·15H2O in a DMSO-H2O mixture. Yellow crystals of the new compound {[Ni(cyclam)]2H4Nb6O19}·12H2O could be obtained after one week applying the Li+ or Na+ salt as starting materials. The crystal structure is unique in polyoxoniobate (PONb) chemistry and displays two interpenetrating three-dimensional (3D) networks. The [Nb6O19]8– anion is expanded by four Ni2+ centered complexes via Ni–O bonds to terminal O2− anions of the hexaniobate anion. The 3D networks are generated by further Ni–O bond formation between neighboring [Nb6O19]8− anions. The remaining void space is occupied by H2O molecules which form a water cluster.

Mixing an aqueous solution of K8[Nb6O19]⋅16H2O with a DMSO/H2O solution of Cu(ClO4)2 · 6 H2O and cyclen at room temperature afforded crystallization of blue crystals of [(Cu(cyclen))6Nb6O19]⋅[ClO4]4·≈4H2O after slow evaporation of the solvents. The crystal structure contains the Lindqvist anion [Nb6O19]8– which is covalently expanded by six symmetry-related [Cu(cyclen)]2+ complexes via Nb-μ 2-O-Cu bridges yielding the positively charged [(Cu(cyclen))6Nb6O19]4+ cluster shell. The ClO4 − anions and crystal water molecules reside in the empty spaces of the packed clusters. The compound shows two electronic d-d transitions at energetic positions explaining the blue color.