Linear trinuclear copper(II)-alkali/alkaline earth metal compounds derived from a compartmental ligand

The work in this investigation deals with syntheses, crystal structures and ESI-MS positive of five compounds of composition [(Cu^IIL)₂Na^I](ClO₄) (1), [(Cu^IIL)₂K^I](ClO₄) (2), [{Cu^IIL(H₂O)}Ca^II(Cu^IIL)](ClO₄)₂ (3), [(Cu^IIL)(µ-ClO₄)Sr^II{Cu^IIL(MeOH)_0.6}](ClO₄)·1.2MeOH (4) and [(Cu^IIL)(µ-ClO₄)Ba^II{Cu^IIL(MeOH)}](ClO₄)·MeOH (5), where H₂L = N,N′-bis(3-ethoxysalicylidene)-1,4-butanediamine. The s-block metal ion in all of these five compounds occupies an O₈ (four phenoxo and four ethoxy) site provided by two L²⁻ ligands. While Na^I, K^I and Ca^II are eight-coordinated, Sr^II and Ba^II are nine-coordinated due to additional coordination by an oxygen atom of a bridging perchlorate ligand. In all of 1–5, the two Cu^II and M^I/II are positioned in almost linear way (Cu^II–M^I/II–Cu^II angle range = 168.24–175.39°). The geometries of the coordination environments have been understood from SHAPE analyses. A disagreement has been observed for the first time between the results of SHAPE analyses and Addison geometric parameter for the pentacoordinated environment. Some interesting structural features regarding composition, metal-ligand bond lengths and twisting of the aromatic rings have been observed. UV-Vis spectra indicates two d-d absorption of copper(II) centers in each of the five compounds. ESI-MS positive reveals the appearance of some tri/di/mononuclear ions.