The ligand 1-(1-(pyridin-2-yl)ethylidene)carbonohydrazide (H 4 L 1) and 1-(pyridin-2-ylmethylene)carbonohydrazide (H 4 L 2) were prepared by reaction of carbonohydrazide with 2-acetylpyridine or pyridine carbaldehyde respectively in a reflux methanol solution. The complexes are prepared by reaction of the ligand with the appropriate metal salt. These complexes are well characterized by elemental analysis, IR and UV spectroscopies and their structure were determined by single X-ray diffraction technic. In the crystal of the dinuclear complex [Mn 2 (H 4 L 1) 2 (H 2 O) 4 ]•Cl 4 , 1) each Mn(II) center is seven coordinated by two nitrogen atom and one carbonyl atom of the one ligand and one nitrogen atom and one carbonyl oxygen atom of another ligand molecule. The coordination sphere is completed by two water molecules. Each of the carbonyl oxygen atom acts as bridge between the two Mn(II) centers. In the mononuclear complex [Co(H 4 L 2)(NO 3)(H 2 O) 2 ]•(NO 3); 2) the Co(II) center is heptacoordinated. The ligand acts in tridentate fashion through two nitrogen atoms and one carbonyl oxygen atom. Two water molecules lie in the apical positions. One nitrate group acts in bidentate manner while the other nitrate group remains uncoordinated. In both complexes the coordination polyhedral are best described as a pentagonal bipyramid. The molecules are linked together in each case by multiple hydrogen bond interaction resulting in a three-dimensional network. The crystallographic data has been deposited in Cambridge Crystallographic Data Centre [CCDC No. 1944387 (complex 1

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The use of N'–(1–(pyridin–2–yl)ethylidene)nicotinohydrazide (HL) in lanthanide(III) chemistry has yielded one mononuclear and one dinuclear complexes. The 1:1 Nd(NO3)3.6H2O or Pr(CH3COO)3.6H2O/HL in methanol afforded the complexes [Nd (HL)2(NO3)2(H2O)2].(NO3) (1) and {[Pr(L)(h2–OOCCH3)(H2O)](h1:h2:m–OOCCH3)2[Pr (L)(h2–OOCCH3)(H2O)]} (2). The structures of the complexes were solved by single crystal X–ray crystallography. In the mononuclear complex, the Nd3+ atom is coordinated by two neutral molecules of ligand acting in tridentate fashion, two nitrate anions acting in bidentate manner and two coordinated water molecules yielding a twelve–coordinated Nd atom. In the complex (2) the Pr3+ atoms are doubly bridged by two acetates anions and each metal ion is coordinated by one tridentate monodeprotonated molecule ligand, one bidentate acetate group and one coordinated water molecule. Each Pr3+ atom is nine–coordinated with an environment best described as a tricapped prismatic geometry. Complex 1 crystallizes in the monoclinic space group C2/c with the following parameters: a = 22.7657(8) Å, b = 8.4276(3) Å, c = 18.0831(7) Å, b = 114.851(2)°, V = 3148.2(2) Å3, Z = 4, R1 = 0.032, wR2 = 0.098. Complex 2 crystallizes in the monoclinic space group P21/n with the following parameters: a = 11.5388(6) Å, b = 14.1087(8) Å, c = 12.2833(6) Å, b = 102.211(2)°, V = 1954.45(18) Å3, Z = 2, R1 = 0.029, wR2 = 0.066. The supramolecular structures are consolidated by multiple hydrogen bonds.

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