The second and third tetranuclear mixed-valence platinum(2.25+) blues to be characterized crystallographically are reported. The compound [(en)Pt(C5H4NO)2Pt(en)]2(NO3)5-H2O (1), where en = ethylenediamine and C5H5NO is a-pyridonate, crystallizes in triclinic space group PT Z = 1, with a = 10.652 (1) Å, b = 13.068 (2) Å, c = 9.413 (1) Å, α = 108.65 (2)°, β = 96.63 (1)°, ᵧ = 68.39 (1)°, and V = 1157.1 Å3. The cis-diammineplatinum 1-methyluracilate (C5H5N2O2) analogue [(H3N)2Pt(C5H5-N2O2)2Pt(NH3)2]2(NO3)5-5H2O (2) also crystallizes in PT Z = 2, with a = 10.123 (3) Å, b = 13.084 (4) Å, c = 19.508 (7) Å, a = 92.28 (3)°, β= 101.09 (3)°, ᵧ = 107.49 (2)°, and V= 2405.2 Å3. The Pt-Pt bond lengths in 1, 2.830 (1) and 2.916 (1) Å for the outer and inner pairs of platinum atoms in the linear, zigzag chain, are longer by 0.06 and 0.04 Å, respectively, than comparable distances in cis-diammineplatinum α-pyridone blue, [(H3N)2Pt(C5H4NO)2Pt(NH3)2]2(NO3)5·H2O (3), owing to nonbonded interactions between ethylenediamine chelate rings in adjacent platinum coordination planes. The Pt-Pt distances in 2 are values intermediate between those in 1 and 3. A semiquantitative model based on previous SCF-Xα calculations for 3 is used to correlate energy changes in the visible absorption bands of these three mixed-valence (Pt2.25)4blues with their Pt-Pt distances. Moreover, the lowest energy visible band of 1–3 can be qualitatively rationalized by a model in which the unpaired electron is delocalized in a one-dimensional box, the length of which is determined by the end-to-end Pt-Pt distance in the chain. Magnetic susceptibility studies have also been carried out which establish that 1 and 2 have S =1/2ground states, with μeff=1.94 and 1.89 μBrespectively.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry