Anion Dependent Coordination Polymers of Different Copper Salts with Mixed Organic Ligands (bis(4‐Nitrophenyl)phosphoric Acid and 4,4′‐Bipyridine)

Abstract

AbstractDifferent coordination polymers that are prepared by using various copper salts with diverse counter ions (perchlorate/ nitrate/ acetate/ iodide) along with bis(4‐nitrophenyl)phosphoric acid (BNPP) and 4,4′‐bipyridine (bpy) have been reported. In each case, two distinct coloured crystals (royal and cyan blue) are observed, concomitantly. The composition and structural features of royal blue crystals are the same in all structures irrespective of counter ions employed, yielding a distorted square pyramid structure with each copper metal ion coordinated to one BNPP and four bpy molecules along with six water molecules in the lattice. However, the compositions of the cyan blue crystals are different depending on the counter ions used. Thus, copper metal ion was found in distinct coordination spheres in each structure. For example, perchlorate anion produces a mixed geometry structure {[Cu(BNPP)2(bpy)2(H2O)][Cu(bpy)2(H2O)2]}ClO4 containing two Cu(II) metal ions with independent square pyramid and square planar geometries along with an uncoordinated perchlorate anion. In addition, it also gives a structure with a molecular formula [Cu2(BNPP)5(bpy)3], devoid of perchlorate ions, having two different Cu(II) coordination spheres (square pyramid and square planar), which are connected together. In contrast, with nitrate ions, cyan blue crystals form a square pyramidal geometry with the formula [Cu(BNPP)2(bpy)2(NO3)], in which the anion is coordinated to Cu(II) ions. Furthermore, with acetate ion, two different complexes having formulae [Cu(BNPP)2(bpy)2] ⋅ 2H2O and [Cu(bpy)2(acetate)2](H2O)2(nitrophenol) are observed, with the latter complex is formed possibly due to the facile hydrolysis of BNPP molecules yielding a nitrophenol. In both the complexes Cu(II) projects a square planar geometry. However, in the case of iodide anion, a complex [Cu2(BNPP)5(bpy)3] ⋅ 2H2O is formed, without any anion, in which two distinct Cu metal ions with tetra‐ and penta‐coordinated spheres are connected together through bpy molecules and yield square planar and square pyramid geometries. The structures of these coordination polymers are thoroughly characterised by single crystal X‐ray diffraction and spectroscopic methods (IR, solid state UV and photoluminescence).