Synthesis, structural, spectroscopic and magnetic studies of tetranuclear Ni(II) and Co(II) clusters based on cyclobutyl and cyclopentyl-substituted analogues of zoledronic acid

Abstract

Three discrete tetranuclear coordination compounds with formulae (H3O)+[M4(HL)3(H2O)6]–·xH2O where M = Ni(II), HL = HcbtZol3– (1a), M = Ni(II)/Co(II), HL = HcptZol3– (2a/2b) and x = 13.8, 16.8 or 10.5 for 1a, 2a and 2b, respectively, (H4cbtZol = 1-hydroxy-2-[1-(1H-imidazol-1-yl)cyclobutyl]ethylidene-1,1-diphosphonic acid, H4cptZol = 1-hydroxy-2-[1-(1H-imidazol-1-yl)cyclopentyl]ethylidene-1,1-diphosphonic acid) were hydrothermally prepared and characterized by single crystal X-ray diffraction, IR, UV-Vis-NIR, thermal analysis and magnetic studies. All the compounds crystallize in the trigonal R3¯ space group and show a propeller-shaped {M1IIM2II3O6} cores with M cations arranged into trigonal pyramid, in which the M1 ion is located in the apex while three peripheral M2 ions occupy the vertices of a triangle base. Both M1 and M2 are six-coordinate with M1 coordination octahedron slightly contracted along the 3-fold axis towards trigonal antiprism and peripheral M2 octahedrons slightly rotated towards trigonal prism. Discrete [M4(HL)3(H2O)6]– coordination units are assembled by O–H···O interactions involving hydroxyl O atom and coordinated water molecules as proton donors. Multiple lattice water molecules additionally stabilize the crystal structure through O–H···O interactions.All the compounds reveal thermal stability up to ca. 90 °C above which lattice water starts to be released. The architecture of [M4(HL)3(H2O)6]– cores remains intact up to ca. 130–140 °C.Qualitative analysis of potential paths of magnetic interactions in tetranuclear cores suggests ferromagnetic exchange with antiferromagnetic admixture.