At the moment, over 1100 borate crystal structures are listed in the Inorganic Crystal Structure Database ICSD. High-pressure investigations are rare and have been mainly performed from a geological point of view. Starting in 1999, systematic high-pressure experiments up to maximum pressures of 16 GPa have been carried out in our group. In the context of these investigations into the high-pressure / high-temperature syntheses of new rare-earth and transition metal oxoborates, several new high-pressure polymorphs of known compositions, e.g. β-MB₄O₇ (M = Ca, Zn, Hg), χ-REBO₃ (RE = Dy, Er), ν-DyBO₃, γ-RE(BO₂)₃ (RE = La–Nd), δ-RE(BO₂)₃ (RE = La, Ce), and δ-BiB₃O₆ [1] were discovered. These investigations led to fundamental insights into the structural behaviour of oxoborates under high-pressure conditions. Especially the coordination of the boron and rare-earth atoms were of special interest in our investigations. Next to the synthesis of new modifications, new compositions were realized in our group. For example, all attempts to produce rare-earth metal(III) oxoborates with the ratio RE₂O₃:B₂O₃ = 2:3, 1:2, and 3:5 failed under normal-pressure conditions. In contrast, the corresponding high-pressure experiments led in most cases to phase pure rare-earth metal(III) oxoborates RE₄B₆O₁₅ (RE = Dy, Ho)[2] and α-RE₂B₄O₉ (RE = Sm–Ho), exhibiting the new and rare structural unit of edge-sharing tetrahedra. Our latest experiments yielded in a third compound, exhibiting edge-sharing tetrahedra. The special feature of the compound HP-NiB₂O₄ [3] is that in contrast to the first two compounds all tetrahedra are linked to each other via one common edge and two common corners. With the synthesis of β–HfB₂O₅ and β–SnB₄O₇ [4], we were able to synthesize the first crystalline compounds in the ternary systems Hf–B–O and Sn–B–O, respectively. Normally, these systems form glasses at ambient pressure conditions. No crystalline compounds were known in these systems. Now, the parameter pressure induces crystallization, which leads to defined crystalline compounds in both systems.The talk will introduce into several examples, which impressively underline the importance of the parameter pressure for the synthesis of new materials in solid state and materials chemistry.[1]J. S. Knyrim, P. Becker, D. Johrendt, H. Huppertz, Angew. Chem., Int. Ed. Engl. 2006, 45, 8239.[2]H. Huppertz, B. von der Eltz, J. Am. Chem. Soc. 2002, 124, 9376.[3]J. S. Knyrim, F. Roessner, S. Jakob, D. Johrendt, I. Kinski, R. Glaum, H. Huppertz, Angew. Chem., Int. Ed. Engl. 2007, 46, 9097.[4]J. S. Knyrim, F. M. Schappacher, R. Pöttgen, J. Schmedt auf der Günne, D. Johrendt, H. Huppertz, Chem. Mater. 2007, 19, 254.

Solid state materials can be prepared by a large number of different preparative methods. Variable temperature and pressure, solvent-free or solvent assisted methods such as sol-gel, hydrothermal and high temperature flux methods etc. provide a rich product variety. Solvent free solid state reactions are attractive due to their simplicity, the minimization of impurities and the elimination of costly product workups. In an attempt to manipulate properties of materials we explore the reaction pathways of ceramic preparation methods. Using variable pressure and variable temperature in conjunction with controlled reaction atmospheres a large variety of products can be manipulated at different stages during the synthesis. Cycling through pressure and temperature treatments adds additional degrees of freedom to structure modifications. Our in-situ methods have lead to the synthesis of a considerable number of novel intermediates at ambient pressure. Those intermediates and metastable products often lend themselves to high pressure conversions resulting in controlled cation and/or anion ordering processes. The highly strained products often exhibit unique physical properties. Recent experiments indicate that high pressure phases can in turn act as particularly intriguing intermediates for structural manipulations. Reaction pathways, preparative strategies, structural transitions and physical properties of some of these materials will be discussed.

Some members of the Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) type layered perovskites can undergo structural modifications via topochemical manipulations. DJ perovskites, and select RP phases, are receptive to ion exchange and/or intercalation reactions. In some instances, one can use these methodologies to build new metal-halide and metal-oxide layers within receptive hosts, while in others, one can readily manipulate and control valence. Here we will present our recent results in the modification of layered perovskites. Efforts with both DJ and RP phases will be highlighted and new compounds, as well as effective single- and multi-step topochemical strategies, will be presented.

The metallic flux is a powerful synthetic medium for the exploration of complex intermetallics. Just as the solubility of molecules in other molecules (i.e. solvents) enhances reactivity and reaction kinetics to produce new compounds, the solubility of metals in liquid metals (i.e. fluxes) results in analogous benefits. Well formed crystals of materials with complex and difficult to predict compositions often form in metallic fluxes. In this talk I will report on our recent results on the use of group 13 fluxes such as Al, Ga and In to discover several interesting intermetallics of ytterbium. The reactivity of rare earth elements including Yb and transition metals differs significantly in liquid Al, Ga and In. The structures and physical properties of the compounds YbFe4Al9Si6, RECoGa3Ge, Yb4MGe8 (M=Mn, Fe, Co, Ni), YbAuIn, and Yb3AuGe2In3 will be presented. In these phases, mixed-valency in the Yb atoms and magnetism in the transition metal atoms interact in complex ways to give rise to unusual phenomena ranging from unique valence instabilities to extended charge density waves.

LiNb6Cl15 is a crystalline solid whose structure (S.G. Ia -3 d) is built up from octahedral niobium clusters. The twelve edges of octahedra are occupied by chlorine. Three additional chlorines are located in apical position acting as Cl-bridges between Nb6 clusters. Lithium is occupying 1/3 of the 48f position [1]. The number of electrons available for bonding indicates that 16 electrons are located in M-M bonding state. However, the number of electrons can be modified by electrochemical lithium intercalation. Note that because the occupancy of lithium crystallographic position is only 33%, both insertion and extraction of lithium ions may be possible. In such a case it has to be accompanied by the injection or extraction of electrons respectively. We have already reported the synthesis of new clusters by this method but only to fill the bonding states up. This was the case of Ta6Cl15 , a 15 e- cluster that could be reduced to LiTa6Cl15, a new 16 e- cluster [2] in which all the bonding states are fully occupied. Attempts to prepare “Li1+xTa6Cl15” failed. The reaction of lithium with LiTa6Cl15 produces the irreversible reduction of Ta6Cl5. In this case the occupation of anti-bonding states, eg*, with the additional electrons may be at the origin of the observed decomposition.However, we report now a different behaviour found for the 16 e- niobium cluster LiNb6Cl15. It can be inserted with two more lithium ions. Hence, it seems that 2 electrons can be driven, likely, to eg*, by electrochemical reaction. Besides, the formation of Li3Nb6Cl15 is reversible showing that lithium electrochemical intercalation can be used to tune the number of electrons of the cluster. In this connection, we have found that lithium can be also reversibly extracted from LiNb6Cl15 to form Nb6Cl15, a 15 e- cluster similar to Ta6Cl15. Therefore, a complete and reversible path from the 15 to the 18 e- cluster seems to exist.The characteristics of the complete reaction:Nb6Cl15 + x Li ↔LixNb6Cl15 (0≤x≤3)have been analysed by using electrochemical techniques. Results indicate that, besides LixNb6Cl15 with x=0, 1 and 3, other intermediate phase, at x=1.5, seems to exist. The existence of all these phases may be explained as due to different ordering of Li in the 48f positions. References[1] B. Bajan, G. Balzer, H. J. Meyer, Zeitschrift Fur Anorganische Und Allgemeine Chemie 1997, 623, 1723.[2] A. Kuhn, S. Dill, H.-J. Meyer, Zeitschrift Fur Anorganische Und Allgemeine Chemie 2005, 631, 1565.

The rational design and development of synthetic methodologies toward the assembly of complex crystalline solids with topologies that can to a certain extent be predicted from the structure of the molecular building blocks has achieved tremendous success in different fields of materials chemistry.[1] The approach has been widely applied to the assembly of cyano-bridged materials with diverse structural and physical properties.[2] Among these compounds, the most widely investigated are Prussian blue and its analogues, which constitute a family of complex-based magnetic materials with properties that can be affected through the judicious choice of their molecular building blocks component