The calcium oxotellurate(IV) nitrates Ca5Te4O12(NO3)2(H2O)2 and Ca6Te5O15(NO3)2

Abstract

Single crystals of two novel calcium oxotellurate(IV) nitrates were grown under hydrothermal conditions and were structurally characterized by X-ray diffraction. Ca\(_5\)Te\(_4\text {O}_{12}\)(NO\(_3\))\(_2\)(H\(_2\)O)\(_2\) [\(Cc\), \(Z=4\), \(a=25.258(3)\) A, \(b=5.7289(7)\) A, \(c=17.0066(19)\) A, \(\beta =124.377(2)^{\circ}\), \(R[F^2 > 2\sigma (F^2)]=0.043\), 4083 \(F^2\) data, 281 parameters] can be described as a non-classic order/disorder (OD) structure, which fulfills the basic principle of OD theory, viz. local equivalence of polytypes, but does not strictly follow the vicinity condition (VC) of OD theory. The structure is made up from an alternating stacking of non-polar layers composed of isolated [TeO\(_3\)] units and Ca\(^{2+}\) ions and polar layers containing NO\(_3^-\) ions and water molecules. The electron lone-pairs of the [TeO\(_3\)] units protrude into the free space of the anion/water layers. The crystal under investigation was a non-classic OD-twin of domains of a maximum degree of order (MDO). At the twin plane a fragment of the second MDO polytype is located. The main building blocks of Ca\(_6\)Te\(_5\text {O}_{15}\)(NO\(_3\))\(_2\) [\(P2_1/c\), \(Z=4\), \(a=15.494(2)\) A, \(b=5.6145(7)\) A, \(c=39.338(4)\) A, \(\beta =142.480(5)^{\circ}\), \(R[F^2 > 2\sigma (F^2)]=0.043\), 3026 \(F^2\) data, 307 parameters] are isolated [TeO\(_3\)] units and Ca\(^{2+}\) ions which are connected to a three-dimensional framework perforated by channels in which the N atoms of the nitrate anions are located and the electron lone-pairs of the [TeO\(_3\)] units protrude. The structure can topologically be derived from the structure of Ca\(_5\)Te\(_4\text {O}_{12}\)(NO\(_3\))\(_2\)(H\(_2\)O)\(_2\) by removing the water molecules and connecting the CaTeO\(_3\) layers with additional [TeO\(_3\)] units and Ca\(^{2+}\) ions.