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Magnetic Susceptibility Synthesis of Mn(acac)3 Synthesis 12 Reasons for Determining Number of Unpaired Electrons • Related to the oxidation state of the metal. • Helpful in assigning geometry. • Information provided about metal-metal bonding. • Information provided about the bonding between the metal and its ligands. Octahedral Metal Complexes • Crystal field theory predicts that the five d orbitals split. – 3 orbitals of low energy, t2g – 2 orbitals of high energy, eg • The energy ‘gap’ between the two sets of orbitals depends on the ligands. – I-<Br-<Cl-<F-<OH-<H2O<NH3<NO2<PPh3<CH3-<CN-<CO (the spectrochemical series) Octahedral Metal Complexes • For octahedral complexes that possess between 4 and 7 d electrons, there are two different ways to distribute the electrons. – Depends on the energy ‘gap’. – Illustrate for Fe(H2O)63+ (five electrons). • High-spin versus low-spin. – If the energy gap is large enough, all the electrons will be placed in the t2g (low-spin). – If the energy gap is small, five electrons will be paired in each orbital first (low-spin and high-spin). Obtaining the Mass Susceptibility • Packing the sample tube – Page 7 in the instruction manual • Operating the balance – Pages 8 and 9 in the instruction manual. • Calibration of the instrument, CBal – Use the MKI standard to do this (Sherwood Scientific printout). • Obtain the magnetic susceptibility (mass) of your sample(s) Magnetic Susceptibility g C Bal l (R R o ) 109 m Mass susceptibility l = sample length (cm) m = sample mass (g) R = reading for tube place sample Ro = empty tube reading CBal = balance calibration constant M g MW Molar susceptibility M M' M (metal core electrons ) M (ligands ) M (other ) 1 T n(n 2) 8 ' M