AtomConfigElectrons H1s 1 1 He1s 2 2 Li1s 2 2s 1 3 Be1s 2 2s 2 4 B1s 2 2s 2 2p 1 5 C1s 2 2s 2 2p 2 6 N1s 2 2s 2 2p 3 7 O1s 2 2s 2 2p 4 8 F1s 2 2s 2 2p 5 9 Ne1s 2 2s 2 2p 6 10 n = 2 n = 1

Na1s 2 2s 2 2p 6 3s 1 11 Mg1s 2 2s 2 2p 6 3s 2 12 Al1s 2 2s 2 2p 6 3s 2 3p 1 13 Si1s 2 2s 2 2p 6 3s 2 3p 2 14 P1s 2 2s 2 2p 6 3s 2 3p 3 15 S1s 2 2s 2 2p 6 3s 2 3p 4 16 Cl1s 2 2s 2 2p 6 3s 2 3p 5 17 Ar1s 2 2s 2 2p 6 3s 2 3p 6 18 K1s 2 2s 2 2p 6 3s 2 3p 6 3d 0 4s 1 19 Ca1s 2 2s 2 2p 6 3s 2 3p 6 3d 0 4s 2 20 Sc1s 2 2s 2 2p 6 3s 2 3p 6 3d 1 4s 2 21 Ti1s 2 2s 2 2p 6 3s 2 3p 6 3d 2 4s 2 22 V1s 2 2s 2 2p 6 3s 2 3p 6 3d 3 4s 2 23 Cr1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 24 Mn1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2 25 Fe1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2 26 Co1s 2 2s 2 2p 6 3s 2 3p 6 3d 7 4s 2 27 Ni1s 2 2s 2 2p 6 3s 2 3p 6 3d 8 4s 2 28 Cu1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1 29 Zn1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 30 n = 3

3d metals (8 First transition series metals constitute the bulk of essential microminerals to life)

An element in the periodic table characterized by having partially filled d orbitals, created by having the adjoining s orbitals filled before the d. Definition: What is a transition element? Properties: The 3d orbitals are split by ligands resulting in orbitals with higher and lower energy states that supersede the 5 degenerate orbitals. Characterized by Multi-valence states Importance: Resulting complexes take on specific geometrical shapes that relate to binding, color formation, and functionality

Important Definitions Ligand: (Lat: that which ties) A ligand is a charged or neutral molecule that binds to a metal through either coordinate covalent or ionic bonds. Water is a neutral ligand, CN is a charged ligand. Chelator: (Lat. Claw) A chelator is an organic compound that is capable of wrapping around a metal in multiple bonds thus competing with other molecules (e.g., proteins, nucleic acids) for the metal. Orbital Splitting: A process by which d orbitals are split into high and low energy levels in response to the binding of a ligand. Coordination Number: Referring to the number of ligands that attach Multidentate: ( Lat: dentate, teeth) Referring to a molecule that has multiple binding groups within the same chain capable of forming multiple bonds with the metal ion, e.g., bidentate (2) tridentate (3) etc. Coordinate covalent: A type of bond created when a ligand provides the pair of bonding electrons (Lewis base) to share with the metal.

Multi-dentate Ligands Oxalate C  C O O O O CH 2 -CH 2 NH 2 H2NH2N Co 3+ O O O O C - C Cu 2+ Ethylene diamine CH 2 -CH 2 N N OOC COO Ethylenediamine tetraacetic acid (EDTA)

Z Z ZZ Z X X X X X Y YY Y Y d xy d yz d xz d d X 2 -Y 2 Z2Z2 3d orbitals

Octahedral Complex

3 of most common complexes with metal ions are: Octahedral (most common) An 8 sided figure featuring 6 ligands, 4 in one plane and two above and below the plane. Square planar A 4 sided figure with 4 ligands all in the same plane Tetrahedral 4 ligands vectorially positioned to have minimum interaction

FeNi CoMn Cr Transition metals that form octahedral complexes Zn

Transition metals that form tetrahedral complexes ZnCuCo Transition metals that form square planar and 5-coordination complexes CuZnCu

Orbital splitting Take Home: By altering the energy state of electrons in a metal ion, ligands are capable of determining valence, reactivity, and even the color of the complex Insights into the properties of ligands

3d Orbitals dz2dz2 d x 2 -y 2

Fe forms an octahedral (8 sided figure, six ligands) complex by having its 5, 3d orbitals split into two 2 new orbitals, e g and t 2g. xy xzyzx 2 -y 2 z2z2 z2z2 xyxzyz oo egeg t 2g Octahedral Iron Before splitting After splitting Energy difference

z2z2 x 2 -y 2 xyxzyz Ti = z2z2 x 2 -y 2 xyxzyz hv Ground state [Ar]4s 2 3d 2 Ti(II) = [Ar]3d 2 Ti(III) = [Ar]3d 1 t 1 2g Excited state e1ge1g Ti(III) Ti 2+ Ti 3+ Ti L L L L L L One 3d

z2z2 x 2 -y 2 xyxzyz z2z2 x 2 -y 2 xyxzyz Fe o [Ar]4s 2 3d 6 [Fe(H 2 O) 6 ] 2+ t 6 2g Low Spin (Highly energetic) Diamagnetic High Spin (Low energetic) Paramagnetic t 4 2g e 2 g [Fe(CN) 6 ] 4- Fe 2+ [Ar]3d 6 (water as a ligand) CN - as a ligand Ionizes (loses 4s 2 electrons to form Fe 2+ ) Fe(II)

V [Ar]4s 2 3d 3 Cr [Ar]4s 1 3d 5 Mn [Ar]4s 2 3d 5 High Spin Low Spin No low spin possible V(II) Cr(II) Mn(II)

Fe [Ar]4s 2 3d 6 Co [Ar]4s 2 3d 7 Ni [Ar]4s 2 3d 8 No low spin possible Fe(II) Co(II) Ni(II)

Cu [Ar]4s 1 3d 10 Cu [Ar]4s 1 3d 9 Zn [Ar]4s 2 3d 10 Cu(I) Cu(II) No low spin possible Zn(II)

Class Exercise: Draw the electronic configuration of octahedral [Zn(H 2 O) 6 ] 2+ and predict the color. Zn is [Ar]4s 2 3d 10 Solution z2z2 x 2 -y 2 xyxzyz All orbitals are filled, no color is possible Upon ionization, Zn loses its 2, 4s electrons and becomes 3d 10

Common Ligands F - FluorideFluoro Cl - ChlorideChloro Br - BromideBromo I - IodideIodo CN - CyanideCyano NCS - IsothiocyanateIsothiocyanato SCN - ThiocyanateThiocyanato OH - HydroxideHydroxo O 2- OxideOxo ONO - NitriteNitro COCarbon monoxideCarbonyl H 2 OWaterAqua NH 3 AmmoniaAmmine Underline indicates atom bonded to metal LigandNameName as ligand

Ligand Strength and Numbers as a determinant Rule: Ligands differ in the strength of their orbital splitting. The following has been determined experimentally Cl < F - < H 2 O < NH 3 < NO 2 - < CN - < CO Rule: Low spin complexes are created by ligands with strong orbital splitting properties Rule: Octahedral complexes that have 3, 4, 5, or 6 electrons in the t 2g orbital tend to be very stable (inert). All others are labile.

Biological Relevance

Myoglobin Heme group O=O Interfere Spherical- 90%  -helix

O 2 binding to Heme Histidine F8 Ferrous (Fe(II) O 2 binds above the ring plane Histidine binds below the plane of the ring Only Fe(II) will bind O 2 C O A linear carbon monoxide can bind with less interference His E7

COLOR

garnetaquamarine amethyst ruby topaz kyanite

Red Blood vs Blue Blood O 2 binding to the heme ring of hemoglobin is coordinated to iron (II). When O 2 is bound to one of the coordinates, Fe(II) is in a low spin (high energy) state and the light emitted is a red. Without O 2 the iron binds water resulting in high spin (low energy) and takes on a bluish color.  red  blue Hmb 4O 2 red (low spin) Hmb blue (high spin) + 4O 2 Arterial blood Venous blood