New Developments in Nitridometalates and Cyanamides: Chemical, Structural and Physical Properties

In the course of these investigations altogether 18 different compounds have been synthesized and their chemical, structural and physical properties were characterized (XRD, XANES, IR, Raman spectrum, magnetic susceptibility, electrical resistivity, low temperature and TG/DTA). Up to now only nitridonickelates and nitridocuprates were known to exhibit exclusively low oxidation states of the transition metals between 0 and +2. In this work it has been presented that also nitridocobaltates belong to this group. We have proved that “Ca3CoIIIN3” do not exist and the real chemical formula can be regarded as Ca5[CoIN2]2. In the thesis another seven new nitridocobaltates(I) have been described, these add to four already known structures. Among novel phases only Ba9Ca[Co2N3]3 may indicate higher valency state for cobalt with the [Co2N3]5- complexes. The XANES data supporting CoII state by comparison with other compounds possess this oxidation state. The crystal structure of Ba9Ca[Co2N3]3 is related to the perovskite type structure. The remarkable structural features of Sr2[CoN2]0.72[CN2]0.28 ≈ Sr6[CoN2]2[CN2] nitridocobaltates [CoIN2]5- ions partially substituted by carbodiimides [N=C=N]2- ions. Up to now in the crystal structure no indications for a homogeneity range could be observed. Both crystal structures of (Sr6N)[CoN2][CN2]2 and Sr6[CoN2]2[CN2] encompass nitridocobaltate [CoN2]5- and carbodiimide [N=C=N]2- ions. In the structures distorted rocksalt motif based on Sr-N partial structure can be distinguished. Up to now in the system AE-Fe-N-(C) only four crystal structures were reported and in the thesis three new were refined Sr8[FeIIIN3]2[FeIIN2], Sr3[FeN3] and (Sr6N)[FeN2][CN2]2 and their physical properties were characterized. The system AE-Mn-N-(C) via this work was extended by Sr8[MnN3]3 and Sr4[MnN3][CN2]. Up to date the only nitridometalate containing different transition elements is Ba[Ni1-xCuxN]. In this work one more mixed nitridometalate has been described Sr8[MnIIIN3]2[FeIIN2]. The crystal structure of Sr4[MnN3][CN2] revealed some weak diffuse scattering lines. The general formula of Sr4[MnN3][CN2] can be written as Sr4[Mn0.96N2.90][C0.96N2] to emphasize possible homogeneity range. Any explanation of the phenomena and establishment of possible homogeneity range are still a challenge. The structures of Sr8[MIIIN3]2[FeIIN2] (M = Mn, Fe) are related to Sr8[MnIVN3]2[MnIIIN3]. All these compounds are first mixed-valency compounds for respective systems and exhibit close relation to crystal structures of Sr3[MN3] (M = Mn, Fe). From the XANES data alike behaviour of all structures containing Mn was observed. Due to some possible degree of Mn/Fe mixing in the crystal structure of Sr8[MIIIN3]2[FeIIN2] the chemical formula might be written as Sr8[MnN3]2-x[FeN3]x[FeN2]. This needs to be investigate in details. Up to now in the literature the only crystallographic data of nitridometalates contain [NCN]2- ions include two compounds. In this work four novel nitridometalate carbodiimides and cyanamides Sr4[MnN3][CN2], (Sr6N)[MN2][CN2]2 (M = Co, Fe) and Sr6[CoN2]2[CN2] have been synthesized. Predominant magnetic properties in the investigated nitridometalates are connected to some antiferromagnetic M-M interactions supported by AFM ordering. The electrical resistivity often shows at some semi-conducting character of these compounds. XANES spectroscopy provided many useful data about valency states of the transition elements, coordination environment around absorbing atoms and electronic structure. The influence of different parameters on the transition metals K-edges was studied in details. IR and Raman give general data about [NCN]2- ions