Structures and Spectroscopy Studies of Two M(II)-Phosphonate Coordination Polymers Based on Alkaline Earth Metals (M = Ba, Mg)

Abstract

The two examples of alkaline-earth M(II)-phosphonate coordination polymers, [Ba2(L)(H2O)9]·3H2O (1) and [Mg1.5(H2O)9]·(L-H2)1.5·6H2O (2) (H4L = H2O3PCH2N(C4H8)NCH2PO3H2),N,N′-piperazinebis(methylenephosphonic acid), (L-H2= O3PH2CHN(C4H8)NHCH2PO3) have been hydrothermally synthesized and characterized by elemental analysis, FT-IR, PXRD, TG-DSC, and single-crystal X-ray diffraction. Compound1possesses a 2D inorganic-organic alternate arrangement layer structure built from 1D inorganic chains through the piperazine bridge, in which the ligand L−4shows two types of coordination modes reported rarely at the same time. In1, both crystallographic distinct Ba(1) and Ba(2) ions adopt 8-coordination two caps and 9-coordination three caps triangular prism geometry structures, respectively. Compound2possesses a zero-dimensional mononuclear structure with two crystallographic distinct Mg(II) ions. Free metal cations [MgO6]n2+and uncoordinated anions(L-H2)n2-are joined together by static electric force. Results of photoluminescent measurement indicate three main emission bands centered at 300 nm, 378.5 nm, and 433 nm for1and 302 nm, 378 nm, and 434.5 nm for2(λex=235 nm), respectively. The high energy emissions could be derived from the intraligandπ∗-ntransition stations ofH4L(310 nm and 382 nm,λex=235 nm), while the low energy emission (>400 nm) of1-2may be due to the coordination effect with metal(II) ions.