Osmium(IV) pyrophosphate: Synthesis, Crystallization, and Ligand‐Field Analysis of the [OsIVO6] Chromophore

Abstract

AbstractTwo polymorphs of burgundy‐red OsP2O7, with cubic (ZrP2O7 structure type, Z=4, a=7.8276(4) Å, 3×3×3 superstructure with a’=3a=23.484(2) Å) and triclinic symmetry (ruby‐red crystals, single‐crystal X‐ray structure determination, GeP2O7 structure type, (no. 2), Z=2, a=4.8072(7) Å, b=6.8993(13) Å, c=8.050(1) Å, α=91.82(2)°, β=92.92(1)°, γ=107.42(2)°, 98 parameters, R1=0.045, wR2=0.144, 3006 unique reflections with |Fo|>4σ(Fo)) have been obtained reducing OsO4 by phosphorus in sealed silica ampoules followed by subsequent chemical vapour transport. Reaction with the wall led to mixed SiIV/OsIV silicophosphates (Os1−xSix)3[Si2O(PO4)6] {x=0.84, pale orange, SiIV3[Si2O(PO4)6] structure type, , Z=3, a=7.893(1) Å, c=24.409(5) Å, 59 parameters, R1=0.058, wR2=0.160, 1311 unique reflections with 1033 |Fo|>4σ(Fo); x=0.47, orange, GeIV3[Si2O(PO4)6] structure type, , Z=2, a=7.9979(3) Å, c=16.4625(5) Å, 59 parameters, R1=0.040, wR2=0.094, 902 unique reflections with 749 |Fo|>4σ(Fo)}. Both structures were refined from single‐crystal data. Above 25 K triclinic OsP2O7 shows temperature independent paramagnetism with a strong temperature dependence of pointing to as electronic ground state for Os4+ (d4) with strong spin‐orbit coupling leading to =0 and the non‐magnetic ground state of the octahedral [OsIVO6] chromophore.. Optical spectra of both polymorphs of OsP2O7 show similar combinations of intense sharp and broad absorption bands typical for dn electronic systems systems with both, spin‐orbit coupling and ligand field splitting, being strong. The observations are consistent with the ligand‐field parameters Δo=20000 cm−1, B=704 cm−1, and ζ=3454 cm−1 for the octahedral [OsIVO6] chromophore.