A copper(II) azide compound of pyrazinic acid containing a new dinuclear complex anion [Cu-2(N-3)(6)](2-). Synthesis, spectral and structural study of KCu2(pyrazinato)(N-3)(4)

A new complex of copper(II) azide with pyrazinic acid, of general formula KCu2(pyrazinato)(N-3)(4) has been synthesized and characterized by spectroscopic and crystallographic methods. The structure of the complex consists of a new dinuclear complex anion [Cu-2(N-3)(6)](2-), potassium cations and neutral polymeric complex [Cu(pyrazinato)(N-3)]. Each distorted square-planar copper centre [Cu(l)] in the complex anion is coordinated to four nitrogen atoms from two terminal and two mu-(1,1) bridging azido ligands [Cu-N distances 1.940(6)-2.011(5) Angstrom]. In the polymeric complex, each copper atom, Cu(2), is coordinated to N(41) of a terminal azido group and N(61), N(62) and O(31) from pyrazinato anions to form infinite, ''neutral'' chains of polyhedra with orientations along [010]. The potassium cations are located in broad channels which are a consequence of stacking of the copper complexes. The IR spectrum confirms the presence of different asymmetric azido ligands. The absorption frequencies of diagnostic values are given and discussed. The electronic spectrum displays three absorption bands associated with N-3-Cu-II charge transfer transitions. The EPR spectrum of the solid complex suggests an axial structure with non-coupled copper(II) atoms. Copyright (C) 1996 Elsevier Science Ltd