73449-93-1Relevant academic research and scientific papers
Control of molecular architecture by steric factors: Mononuclear vs polynuclear manganese(iii) compounds with tetradentate N2O 2 donor Schiff bases
Bhowmik, Prasanta,Nayek, Hari Pada,Corbella, Montserrat,Aliaga-Alcalde, Nuria,Chattopadhyay, Shouvik
, p. 7916 - 7926 (2011)
Three manganese(iii) compounds, [MnIII(vanoph)(DMF)(H 2O)]ClO4 (1), [MnIII(vanoph)(N 3)(H2O)]·2H2O (2) and [Mn III(saloph)(μ1,3-N3)]n (3), where H2vanoph = N,N′-(1,2-phenylene)-bis(3- methoxysalicylideneimine), H2saloph = N,N′-(1,2-phenylene)- bis(salicylideneamine) are tetradentate N2O2 ligands and DMF = N,N-dimethylformamide, have been prepared and characterised by elemental analysis, IR and UV-Vis spectroscopy and single-crystal X-ray diffraction studies. Compounds 1 and 2 are monomeric but compound 3 consists of a chain system with the repeating unit [MnIII(saloph)(N3)] bridged by μ-1,3 azide. Compound 1 crystallises in monoclinic space group P2 1/n with cell dimensions of a = 11.1430(2), b = 16.3594(3), c = 15.4001(3) A, β = 108.417(1), Z = 4 whereas compounds 2 and 3 crystallise in orthorhombic space groups Pbca and Pna21, respectively, with cell dimensions of a = 16.069(3), b = 15.616(3), c = 18.099(4) A, Z = 8 (for 2) and a = 18.760(9), b = 13.356(5), c = 6.616(3) A, Z = 4 (for 3). In all the compounds, Mn(iii) has a six-coordinated pseudo-octahedral geometry in which O(2), O(3), N(1) and N(2) atoms of the deprotonated di-Schiff base constitute the equatorial plane. In both compounds 1 and 2, water molecules are present in the fifth coordination sites in the apical positions. The sixth coordination sites are occupied by one O atom of a solvent DMF in compound 1 and an N atom of azide in compound 2. The coordinated water initiates hydrogen-bonded networks in both compounds 1 and 2 to form well-isolated supramolecular dimers. At room temperature the χMT values for the compounds 1 and 2 remain almost constant until 30 K. Below this temperature, the χMT values drastically drop to 0.72 cm 3 mol-1 K for 1 and 0.52 cm3 mol-1 K for 2. The best fits were obtained with J = -0.92 cm-1, D = 2.05 cm-1, g = 2.0 and R = 8.1 × 10-4 for 1 and J = -1.16 cm-1, D = 2.05 cm-1, g = 2.0 and R = 1.2 × 10 -3 for 2. However, in compound 3, two axial positions are occupied by the azide ions. The Mn...Mn repeating distance is 6.616 A along the chain. Magnetic characterisation shows that the μ1,3-bridging azide ion mainly transmits an antiferromagnetic interaction (J = -6.36 cm -1) between Mn(iii) ions. The presence of two methoxy groups increases the steric crowding in the H2vanoph moiety and thereby inhibits the formation of a polynuclear compound with this ligand.
