Ligand negative charge Is repelled by d electrons, d orbital energy goes up . a. Ag(CN)2 − b. Cu(H 2O)4 + c. Mn(C2O4)2 2− d. Pt(NH 3)4 2+ e. Fe(EDTA)−; note: EDTA has an overall 4! - calledcharge transfer transitions since an electron is transferred from the metal to the ligand or vice versa - very intense transitions since they are … The absorptions that arise from this process are called ligand-to-metal charge-transfer bands … In this case: the phosphines and chloride are all 2 e- … ;1960, pg. n = Valence of neutral metal – charge on the metal Rh(0) has 9 valence electrons, so Rh(I) has (9-1= 8) Rh(I) has 8 d-electrons and is said to be d8 d Total electron count d The total electron count at the metal is given by: (metal electrons + ligand electrons). If the ligand molecular orbitals are full, charge transfer may occur from the ligand molecular orbitals to the empty or partially filled metal d-orbitals. This is indeed the case and, as we shall see in carbonyl complexes, the rule is seldom violated in stable covalent complexes with π-acceptor ligands (Table 1). Ligand charge transfer (MLCT) like in [Fe(bpy) 3] 2+. •π-donor ligands are ligands with one or more lone pairs of electrons in p orbitals on the donor atom that can donate to empty orbitals on the metal. In this complex the charge transfer occurs from Fe(II) to the empty π* orbitals of bpy ligand. ligand π-symmetry orbitals results in an effective increase in the HOMO-LUMO gap (∆o in Fig. Charge Transfer Transitions In addition to transitions between d-orbitals, transitions between ligand-based orbitals and metal d-orbitals are possible. For example, [PtCl6] 2-is a complex ion formed from one Pt4+ and six Cl-, which results in a net charge of 2-. LMCT: Ligand to Metal Charge Transfer σL or πL d* very intense, generally in UV or near UV h h Rydberg: localized MO high energy, highly delocalized, deep UV MLCT: h Metal to Ligand Charge Transfer d* πL very intense ( ~ 100 – 10,000) needs π-acceptor Ligand (CO, CN –, … Ligand to Ligand πL πL* The nature of the metal ligand π interaction is dependent on the type of ligand. The result is that the actual charge on the metal is not accurately reflected in its formal oxidation state” - Pauling ; The Nature of the Chemical Bond, 3rd Ed. Below is a table that shows typical ε values for different types of transitions. 172. For the following complex ions, see Table 19.13 if you don’t know the formula, the charge, or the number of bonds the ligands form. from the difference between the charge of the metal ion and the anion. Ligand field theory; Orbital Splitting and Electron Spin The position of the metal in the periodic table Second and third transition series form low-spin more easily than metals form the first transition series-The greater overlap between the larger 4d and 5d orbitals and the ligand orbitals-A decreased pairing energy due to the • preferred for metals with high oxidation states and low d electron count (d0-d3) charge. Ligands will interact with some d orbitals more than others Depends on relative orientation of orbital and ligand Ligands point right at lobes . In a case where the ligand does not carry a formal charge, such as NH3, an ammonia complex carries the charge of the metal ion, for example [Cu(NH3)4] Stable M-L bond formation generally reduces the positive charge on the metal as well as the negative charge and/or e-density on the ligand. 6 6-11 Octahedral Ti(III) Complexes Br– Cl– (H2N)2C=O NCS– F– H2O CN– 11,400 13,000 17,550 18,400 18,900 20,100 22,300 Ligand DO/cm–1 • Ti(III) is a d1 complex and exhibits ONE absorption in its electronic spectrum due to transition of the electron from the t2g orbitals to the eg orbitals. charge and is a six coordinate ligand. In these orbitals, the ligands are between the lobes 3a) and we would expect the 18 electron rule to hold best for these types of complexes.

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