Transition‐Metal Complexes with the Novel Poly (1,2,4‐triazolyl)borate Ligands [H n B(C 2 H 2 N 3 ) 4 − n ] − ( n = 1 and 2): Synthesis and Characterization of Metal Complexes of Dihydrobis(1,2,4‐triazolyl)borate as One‐ or Two‐Dimensional Coordination Polymers with Six‐Membered Ring Water Substructures and the Structure of Two‐Dimensional Liquid and Solid Water

Abstract

AbstractThe 1:2 manganese (5), nickel (6), and copper complex (7) with the novel dihydrobis(1,2,4‐triazolyl)borate ligand (2) were synthesized and structurally characterized. Single‐crystal X‐ray studies reveal the formation of highly solvated coordination polymers of the formula {[M(H2O)2{μ‐H2B(C2H2N3)2}2] · n H2O}∞ for M = Mn and Cu. In 5 (M = Mn; n = 4) a two‐dimensional metal‐ligand framework is built by means of the bridging action of 2. These metal‐ligand grid sheets sandwich water layers which comprise individual six‐membered rings. Compound 7 (M = Cu; n = 6) can be described as a linear metal‐ligand chain with two borate ligands bridging two copper centers. These one‐dimensional coordination polymers are separated by one‐dimensional arrays of water molecules in the form of edge‐sharing six‐membered rings. In both structures the water of crystallization is held in place both by hydrogen bonding from the aqua ligands and by hydrogen bonding to the nitrogen atoms of the borate ligand. Bis[hydrotris(1,2,4‐triazolyl)borato]nickel, [Ni{HB(C2H2N3)3}2] (8), was obtained from NiCl2 and the potassium salt of [HB(C2H2N3)3]− (1). Single‐crystal X‐ray structures of the solvate 8 · 6 H2O were determined at 293 and 160 K. The water molecules are arranged in two‐dimensional layers with only weak (hydrogen bonding) interactions to the adjacent layers of the complex molecules. The room temperature structure (orthorhombic, space group Cmca) shows a highly disordered water structure being indicative of a dynamic equilibrium between small conglomerates and free molecules. Upon cooling an ordering occurs in the water layer leading to a phase transition in the crystal, and in the low‐temperature structure at 160 K (orthorhombic, space group Pmnb) the hydrogen atoms and bonding network of the water structure could be determined. This structure is best described as being composed of individual rings or chain segments. The material surface morphology after loss of the water of crystallization was studied by scanning electron microscopy and the structural pattern correlated with the crystal packing.