Ligand-Modulated Nuclearity and Geometry in Nickel(II) Hydrazone Complexes: From Mononuclear Complexes to Acetato- and/or Phenoxido-Bridged Clusters

Abstract

The propensity of 4-hydroxybenzhydrazone-related ligands derived from 3-methoxysalicylaldehyde (H2L3OMe), 4-methoxysalicylaldehyde (H2L4OMe), and salicylaldehyde (H2LH) to act as chelating and/or bridging ligands in Ni(II) complexes was investigated. Three clusters of different nuclearities, [Ni3(L3OMe)2(OAc)2(MeOH)2]∙2MeOH∙MeCN (1∙2MeOH∙MeCN), [Ni2(HL4OMe)(L4OMe)(OAc)(MeOH)2]∙4.7MeOH (2∙4.7MeOH), and [Ni4(HLH)2(LH)2(OAc)2]∙4MeOH·0.63H2O·0.5MeCN·HOAc (3∙4MeOH·0.63H2O·0.5MeCN·HOAc), were prepared from Ni(OAc)2∙4H2O and the corresponding ligand in the presence of Et3N. The hydrazones in these acetato- and phenoxido-bridged clusters acted as singly or doubly deprotonated ligands. When pyridine was used, mononuclear complexes with the square-planar geometry seemed to be favoured, as found for complexes [Ni(L3OMe)(py)] (4), [Ni(L4Ome)(py)] (5) and [Ni(LH)(py)] (6). Ligand substituent effects and the stability of square-planar complexes were investigated and quantified by extensive quantum chemical analysis. Obtained results showed that standard Gibbs energies of binding were lower for square-planar than for octahedral complexes. Starting from [MoO2(L)(EtOH)] complexes as precursors and applying the metal-exchange procedure, the mononuclear complexes [Ni(HL3OMe)2]∙MeOH (7∙MeOH) and [Ni(HLH)]∙2MeOH (9∙2MeOH) and hybrid organic–inorganic compound [Ni2(HL4OMe)2(CH3OH)4][Mo4O10(OCH3)6] (10) were achieved. The octahedral complexes [Ni(HL)2] (7–9) can also be obtained by the direct synthesis from Ni(Oac)2∙4H2O and the appropriate ligand under specific reaction conditions. Crystal and molecular structures of 1∙2MeOH∙MeCN, 2∙4.7MeOH, 3∙4MeOH∙0.63H2O∙0.5MeCN∙HOAc, 4, 5, 9∙2MeOH, and 10 were determined by the single-crystal X-ray diffraction method.

Evaluation of vanadium coordination compounds derived from simple acetic acid hydrazide as non-conventional semiconductors

“…In this complex the (L 1 ) 2À ion coordinates in its hydrazidato tautomeric form (ESI, † Scheme S2) which is evident from the relevant bond lengths. 43,44 The packing of molecules in the solid state is dictated by the presence of non-coordinated methanol molecules, which connect complexes via O-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds with the R 4 4 ( 14) motif into supramolecular dimers which further associate in the crystal structure via C-HÁ Á ÁO interactions (ESI, † Fig. S15).…”

“…The structure of this complex is comparable with that of the [VO(L 2 )(OMe)(MeOH)] (3) (ESI, † Scheme S1). Namely, the complex displays the distorted octahedral geometry with the L 2À ion coordinated in the hydrazidato tautomeric form via ONO donor atoms, 43,44 along with a methoxo moiety and a methanol molecule. In the crystal structure molecules associate into complex O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen-bonded network (ESI, † Table S5 and Fig.…”

“…4) has a molecular structure quite similar to that of [VO(L 2 )(OMe)(MeOH)] (3). Here as well complex displays the distorted octahedral geometry with the L 2À ion coordinated in the hydrazidato tautomeric form via ONO donor atoms, 43,44 alongside a methoxo moiety and a methanol molecule. Complexes form through O-HÁ Á ÁN hydrogen bonds of the R 2 2 (10) motif supramolecular dimers that further associate via C-HÁ Á ÁO interactions in the crystal structure (ESI, † Table S7 and Fig.…”