Cu(II) vs. Cu(I): Properties, Oxidation, and Stabilization of Copper Ions, Exercises of Chemistry

Download Cu(II) vs. Cu(I): Properties, Oxidation, and Stabilization of Copper Ions and more Exercises Chemistry in PDF only on Docsity! Cu(II) vs. Cu(I) ! Cu(II) is the stable state of copper. i Configuration 3d 9 with one unpaired electron makes Cu(II) compounds paramagnetic. i Incomplete 3d subshell permits d-d state-to-state electronic transitions, which causes color (typically blue or green). ! Cu(I) is an unstable state of copper. i Configuration 3d 10 with no unpaired electrons makes Cu(I) diamagnetic. i Complete 3d subshell precludes d-d state-to-state transitions, so Cu(I) is colorless like isoelectonic Zn(II). º Cu(I) compounds may be colored with certain anions CuI(s) — pale yellow Cu2O(s) — brick red i Fehling's solution, an alkaline solution of Cu2+ with sodium tartrate, reacts with reducing sugars such as glucose to give brick red Cu2O. Oxidation of Cu(I) ! In aqueous solution, Cu(I) is readily oxidized to Cu(II) in the presence of oxygen: 4(Cu+ º Cu2+ + e–) –Eo = –0.153 V O2 + 4H+ + 4 e– º 2H2O Eo = +1.229 V 4Cu+ + O2 + 4H+ º 4Cu2+ + 2H2O Eo cell = 1.076 V ! Cu(I) undergoes spontaneous disproportionation (autoredox): Cu+ º Cu2+ + e– –Eo = –0.153 V Cu+ + e– º Cu Eo = +0.521 V 2 Cu+ º Cu + Cu2+ Eo cell = +0.368 V i Thus ∆G is negative (spontaneous) for disproportionation. Stability of Cu+ vs. Cu2+ Complexes L Position of the 2Cu+ º Cu2+ + Cu0 equilibrium in the presence of complexing ligands depends on the relative stability of the Cu+ complex relative to the Cu2+ complex. ! Anions or bridging ligands that form complexes with Cu+ may stabilize Cu+ so long as they do not form more stable complexes with Cu2+. ! In the synthesis, formation of [CuCl2] –(aq) effectively removes Cu+ from the solution, thereby driving the equilibrium to the left (LeChatelier’s Principle). ! When CuCl(s) is treated with the chelating ligand ethylenediamine Cu+ is oxidized to Cu2+, because the bis-ethylenediamine copper(II) complex is more stable than the copper(I) complex: 2 CuCl(s) + 2 en º [Cu(en)2] 2+(aq) + Cu(s) + 2 Cl–(aq) ! With non-chelating ligands such as NH3 and pentamethylenediamine [H2N-(CH2)5-NH2] the copper(I) complex is favored. [Cu(NH3)4] 2+(aq) + Cu(s) º 2 [Cu(NH3)2] +(aq) Copper(I) Iodide ! Copper(I) iodide precipitates when any Cu(II) salt is added to a KI(aq) solution. 2Cu2+(aq) + 4I–(aq) º 2CuI(s) + I2 ! I–(aq) is a strong enough reducing agent to reduce Cu2+(aq) to CuI(s). 2I– º I2 + 2e– –Eo = –0.54 V 2(Cu2+ + I– + e– º CuI) Eo = +0.88 V 2Cu2+ + 4I– º 2CuI + I2 Eo cell = +0.34 V Cu+ in Acetonitrile ! CuCl is soluble in actonitrile, CH3CN. i Cu(I) is effectively solvated by CH3CN. i Cu(I) is actually more stable than Cu(II) in acetonitrile. i Tetrahedral ion [Cu(CH3CN)4] + can be isolated in salts with large anions such as ClO4 – and PF6 –.