Mnemonic 1 — Spectrochemical Series (Weak → Strong):

Full series: $I^{-}$ < $Br^{-}$ < $Cl^{-}$ < $F^{-}$ < $OH^{-}$ < $H_{2}O$ < $NH_{3}$ < en < $NO_{2}^{-}$ < $CN^{-}$ < CO

Memory sentence:

"I Bring Chlorine For Our House, Now Every Night Can Open." I(^{-}) Br(^{-}) Cl(^{-}) F(^{-}) O($H^{-}$) H(_{2}O) N($H_{3}$) E(n) N($O_{2}^{-}$) C($N^{-}$) O(CO)

Breakdown by field strength:

• Weak field (high spin): $I^{-}$, $Br^{-}$, $Cl^{-}$, $F^{-}$, $OH^{-}$, $H_{2}O$
• Strong field (low spin): $NH_{3}$, en, $NO_{2}^{-}$, $CN^{-}$, CO

Mnemonic 2 — IUPAC Naming "LANCE":

• Ligands named first (alphabetical, ignoring multiplying prefixes)
• Anionic ligands end in -o (chloro, cyano, oxalato, hydroxo)
• Neutral ligands: exceptions — aqua ($H_{2}O$), ammine ($NH_{3}$), carbonyl (CO), nitrosyl (NO)
• Charge of metal in Roman numerals in parentheses
• External anion/cation named separately — cation first, then anion

Mnemonic 3 — $KMnO_{4}$ Products by Colour:

"ABC-Colour Rule":

• Acidic → colourless ($Mn^{2+}$)
• Basic → green ($MnO_{4}^{2-}$)
• Centre (neutral) → brown ($MnO_{2}$)

Electrons gained: A = 5, C = 3, B = 1 (counts down 5→3→1 as acidity decreases)

Mnemonic 4 — Biological Coordination Compounds:

"Fe-Mg-Co-Zn, Blood-Plant-B12-Brain"

• $Fe^{2+}$ → Hemoglobin → Blood ($O_{2}$ transport)
• $Mg^{2+}$ → Chlorophyll → Plant (photosynthesis)
• $Co^{3+}$ → Vitamin $B_{12}$ → B12 (cobalamin)
• $Zn^{2+}$ → Carbonic anhydrase → Enzyme in C$O_{2}$/$H_{2}O$ equilibrium