Three pyridyl modified Cu(II)/Cd(II)-diphosphonates: Syntheses, crystal structures and properties

Three examples of M(II)-diphosphonates, [Cu-3(H3L H)(4)center dot 2(OH)center dot 2H(2)O 1, [Cu-3(H2L)(2)(H2O)(2)] 2, and [Cd(H2L H)]center dot H2O 3 based on 1-hydroxy-2-(3-pyridyl)ethylidene-1,1-diphosphonic acid (HxL/HxL-H: x = 0-5, H5L = (H4C5N)CH2C(OH)(PO3H2)(2), H5L-H = (H4C5N-H)CH2C(OH)(PO3H2)(2)), have been hydro thermally obtained and characterized by powder X-ray diffraction, elemental analysis, TG-DSC and IR. The single-crystal X-ray diffractions reveal that compounds 1 and 3 are one-dimensional chain structures (linear for 1 and ladderlike for 3) constructed by binuclear units [M2O2](n), simultaneously organic pyridine-ring suspending both sides, and compound 2 shows a two-dimensional inorganic-organic alternate arrangement layer built from 1-D ladderlike inorganic chain with trinuclear units [Cu-3(OPO)(4)](n), via pyridine-ring linker. The results of electrochemical measurements indicate that both 2 and 3 are significant negatively shifted by 0.17 V and 0.13 V (0.33 V for 2 and 0.37 V for 3), respectively, while I was red-shifted by 0.87 V (137 V), compared with the ligand H5L (0.50 V). Moreover fluorescent measurements reveal that compounds 1-3 display fluorescent emission bands, 383 nm and 425 nm for 1, 382 nm and 425 nm for 2 and 311 nm, 378 nm and 422.5 nm for 3 (lambda(ex),, = 235 nm), caused by intraligand pi* - pi emission state of the ligand H5L = 233 nm). Magnetic data indicate that compound 1 exhibits weak ferromagnetic interactions within 1-D linear chain, but compound 2 gives an antiferrornagnetic behavior within 1-D ladderlike chain. The energy levels of the frontier molecular orbitals of 1-3 are obtained from DFT calculations (Enomo 1: -15.23 eV, 2: = -9.74 eV, 3: -11.5 eV), and the low HOMO-LUMO gaps of 1 (0.38 eV), 2 (020 eV) and 3 (038 eV) mean that high chemical reactivity for three compounds. (C) 2017 Elsevier B.V. All rights reserved.