Intermetallic borides are characterized by a great variety of crystal structures and bonding interactions, however, a comprehensive rationalisation of the electronic structure is missing. A more general interpretation will be targeted towards comparing several boride phases of one particular transition metal on one hand side, but also isostructural borides of various metals at the other side. Finally, a concise model should result from a detailed analysis of excellent data both from experimental charge density analysis and quantum chemical methods. Ultimate target is a transferability model based on typical building blocks. Experimental investigations of the electron density derived from diffraction data are very rare for intermetallic compounds. One of the main reasons is that the suitability of such compounds for charge density analysis is estimated to be relatively low as compared to organic compounds. In the present work, X-ray single crystal diffraction measurements up to high resolution were carried out for TiB2, VB2, V3B4, and VB crystals. The respective experimental electron densities were reconstructed using the multipole model introduced by Hansen and Coppens [1]. The topological aspects of the experimental electron density were analysed on the basis of the multipole parameters using Bader’s Quantum Theory, Atoms in Molecules [2] and compared with theoretical calculations. References [1] Hansen, N.K.; Coppens, P. Acta Crystallogr. 1978, A34, 909 [2] Bader, R.F.W. Atoms in Molecules─A Quantum Theory; Oxford University Press: Oxford, 1990

Low valent nickel (less than +1) complexes are rare in nature, however they are regularly encountered in nitridonickelate chemistry. Ternary alkaline earth nitridonickelates exhibit a variety of interesting crystal structures with respect to their covalently bonded nitridonickelate anionic framework. The coordination geometry of low valent nickel in these compounds presents a unique structural feature with nickel being in linear coordination by nitrogen atoms. The nitridonickelate frameworks of compounds investigated in this work are: Ba2[Ni3N2]: The first ternary alkaline earth nitridonickelates with 2D Ni-N anionic network. The formal oxidation state of Ni is +0.67. Ba2(Ba6N)[NiN]6: The structure is made of o1D helical Ni-N anionic chains. Also, the structural stability of this compound´s structure type was found to occur over a wide range of substitution of Ba by Ca and Sr; a max. of 70 percent Ba could be successfully replaced by Sr and Ca atoms retaining the same structure type. The formal oxidation state of Ni is +0.83. Ba[NiN] and the solid solution series Ba[CuxNi1-xN]: The structure is made of 1D zig-zag Ni-N chains. The solid-solution series is isostructural to Ba[NiN] at lower content of Cu while, at higher content it resembles Ba[CoN] structure type, however at very high Cu content it again transforms to Ba[NiN] structure type. The formal oxidation state of Ni is +1.0. Sr2[Ni(CN)N]: The structure consists of N-Ni-(CN) dumbbells. The compound is the first example of cyano-nitridonickelate. The formal oxidation state of Ni is 0. The handling of the ternary alkaline earth nitridonickelates in specific and also of the other nitridometalates in general suffers greatly due to their being air and moisture sensitive. This requires synthetic methods suitable for air and moisture sensitive samples and also the respective instrumental setup for the measurement of their physical properties under inert atmosphere. Up to now no comprehensive investigation of the physical properties of the ternary alkaline earth nitridonickelates has been made. In this work an emphasis was given to systematically investigate the physical properties of the ternary alkaline earth nitridonickelates and to understand their structure specific physical properties. The common features of the investigated ternary alkaline earth nitridonickelates are: 1. the low valency of nickel. 2. the linear coordination of Ni and octahedral coordination of N. During this investigation the low valent character of nickel was experimentally confirmed with the help of X-ray absorption spectroscopy and the interpretation of magnetic susceptibility data where the magnetic moments of the nickel atoms were always consistent with that of a low valent nickel species. The results obtained from the magnetic measurements and electrical conductivity shows that the alkaline earth nitridonickelates order antiferromagnetically at low temperatures and show temperature dependent metallic conductivity whereas the cyano-nitridonickelate Sr2[Ni(CN)N] does not order at low temperature, is paramagnetic, and exhibits semiconducting behaviour. This investigation has provided a better understanding of ternary alkaline earth nitridonickelates with respect to the different structure they exhibit and their associated physical properties. This work motivates to extend the investigations of the physical properties of other nitridometalates. These also exhibit different crystal structures with respect to their nitridometalate anionic framework and thus, structure specific physical properties are also to be expected.