A layered vanadium arsenate network decorated with the directly coordinated organonitrogen ligands: [V₄O₇(HAsO₄)₂(o-phen)₂] (o-phen=o-phenanthroline)

Abstract

A novel layered vanadium arsenate [V₄O₇(HAsO₄)₂(o-phen)₂] 1 (o-phen=o-phenanthroline) was synthesized by the hydrothermal reaction of V₂O₅, ZnCl₂, Na₂HAsO₄·7H₂O, o-phenanthroline (o-phen) and water. Its structure was determined by elemental analyses, ESR spectrum, XPS spectrum, TG analysis, IR spectrum and the single-crystal X-ray diffraction. Compound 1 crystallizes in monoclinic system, space group P2/c, a=10.122(2) Å, b=9.867(2) Å, c=15.367(3) Å, β=102.83(3)°, V=1496.4(5) Å³, Z=1, λ(MoKα)=0.71073 Å, (R(F)=0.0397 for 3422 reflections). Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 2.06°<θ<27.48°. The title compound contains an unusual two-dimensional (2D) As–V–O layer with four-, six- and eight-membered rings. The chelating o-phen ligands project perpendicularly above and below the undulating layer. 1 represents the first example of 2D inorganic vanadium arsenate backbone grafted with the directly coordinated organic ligands. Furthermore, the 3D supermolecular architecture is formed by π–π stacking interactions of the o-phen groups between adjacent layers.

Introduction

Polyoxovanadates have been attracting extensive interest in solid state materials chemistry owing to their interesting structural features and various potential applications in catalysis, electron conductivity, magnetism and photochemistry [1], [2], [3], [4]. In this field, an important advance recently is the modification of inorganic vanadium oxides with various organic ligands and transition metal complexes or fragments. Based on this strategy, a large number of new compounds have been synthesized and structurally characterized in the V–P–O system [5], [6], [7], [8], [9], [10]. They exhibit varieties of novel frameworks and have potential applications in catalysis and materials science [11], [12]. In contrast to abundant compounds in the {V/P/O} system, the {V/As/O} system remains relatively undeveloped. In the past years, reports have been concentrated on the discrete vanadium arsenate clusters [13], [14], [15], for example, the K₆[As₆V₁₅O₄₂(H₂O)]·8H₂O [13] and anionic porous skeletons such as MVOAsO₄ (M=Na, Li, NH₄) [16] and [Cs₃(VO)₂(V₂O₃)(AsO₄)(HAsO₄)₂] [17]. Recently, the introduction of hydrothermal technique and the use of organic templating agents have led to the production of some vanadium arsenate phases with two-dimensional (2D) layer-like and 3D porous structures, such as [H₂NC₄H₈NH₂][(VO)₂(HAsO₄)₂(H₂AsO₄)₂] [18] and [AsV^IV₈V^V₂O₂₆(H₂O)]·8H₂O [19], in which the organic templates act as counter cations or structural filling agents. To the best of our knowledge, vanadium arsenate complexes containing organic components functioning as ligands coordinated directly to the vanadium arsenate backbone or to the secondary metal centers are rare. Since vanadium-oxide-phosphates system exhibits extensive coordination chemistry with the organic ligands, the solids constructed from {V/As/O} system may also have the feasibility for the incorporation of appropriate organic ligand moieties. This offers opportunities for preparing novel organic–inorganic hybrid materials containing inorganic {V/As/O} scaffoldings decorated with organic ligand functional units.

In this work we report on the hydrothermal synthesis and crystal structure of a novel organic–inorganic hybrid vanadium arsenate, [V₄O₇(HAsO₄)₂(o-phen)₂] 1 (o-phen=o-phenanthroline). Compound 1 contains an unusual 2D {V/As/O} skeleton with the o-phen fragments coordinated directly to the inorganic layer. To the best of our knowledge, 1 represents the first example of 2D inorganic vanadium arsenate backbone decorated with the directly coordinated organic ligands.