Beyond Oxides: Nitride as a Ligand in a Neutral Ir^IXNO₃ Molecule Bearing a Transition Metal at High Oxidation State

Abstract

This work commemorates the 150th anniversary of Mendeleyev's Periodic Table of Elements.Abstract: Theoretical calculations utilizingr elativistic ZORA Hamiltonian point to the conceivable existence of an IrNO 3 molecule in C 3v geometry.T his minimum is shown to correspond to genuine nonavalent iridium nitride trioxide, whichi saneutrala nalogue of cationic [IrO 4 ] + speciesd etected recently.D espite the presence of nitride anion,the molecule is protected by substantial barriers exceeding 200 kJ mol À1 against transformations leading, for example, to global minimum (O=) 2 IrÀNO, which contains metal at al ower formal oxidation state.In recent years, some unusualf ormal oxidation states of metals,t hat is, Hg IV , [1,2] Cs V , [3][4][5] and Pu VIII[6] or U XII[7] were studied theoretically,and some wereestablishede xperimentally.Anoctavalents tate has traditionally been considered the highest achievableo xidation state of chemicale lements, as exemplified by Ru VIII , [8][9][10] Os VIII , [8][9][10] or Xe VIII[11] in their tetraoxides,a nd other relateds toichiometries. Exactly half ac entury ago Jørgensen pointed out that, if the formal oxidation state + IX existed, it would be in ac ompound of iridium. [12] Because IrO 4 has one unpaired valencee lectron in the d-shell, ar elated [IrO 4 ] + monocation became the naturalc andidate for investigations. Indeed, in 1996 Kiselev and co-workerss howed that the minimum potential energy surfacef or this cation corresponded to the isomeric form of [IrO4] + in which the metal atom has af ormal oxidation state of + IX. [13,14] In 2010, the thermochemical stability of oxidation level + IX in an [IrO 4 ] + cation was theoretically predicted by Himmel et al. using electronic structure calculations. [15] Four years later,t he abovementioned cation was reliably detected using time-of-flight photodissociation spectroscopy. [16] It is worth mentioning that much earlier,i n1 969, Rother et al. provided Mçssbauer isomer [a] Dr.

The high covalence of metal-ligand bonds as stability limiting factor: the case of Rh(IX)O4+ and Rh(IX)NO3

“…1) and (η 1 -O 2 )MO 2 states (minimum E OO ), while rendering the isomerization an "energy uphill" process by 141.5 kJ/mol and 281.0 kJ/mol, respectively. The first of those, which governs energetic stability of the tetrahedral minimum, is, however, smaller than that for OsO 4 of 428 kJ/mol with M06-L/ ZORA approach [5] (cf. 380.7 kJ/mol at B3LYP/ECP level [39]).…”

“…380.7 kJ/mol at B3LYP/ECP level [39]). The transition state (B OO ) on the pathway of O 2 elimination from ruthenium tetraoxide resembles the transition state in the case of osmium tetraoxide [5,39], and it corresponds to O-O bond formation during isomerization process:…”

“…Recall that the high kinetic stability of tetraoxide complexes with metal on +8 oxidation state is secured in OsO 4 with the huge barrier of 406.3 kJ/mol on singlet PES and the corresponding barrier on the triplet PES of 334.4 kJ/mol [5] (cf. 394.3 kJ/mol in [39]).…”

“…Experimental data for OsO 4 and RuO 4 are from gas phase (ED) [36,37]; data for CsOsNO 3 are from crystal structure (XRD) [38]. Interatomic distances and bond indices come from M06-L/ ZORA computations, T 1 parameter values were calculated at CCSD(T)/ DKH2 for M06-L/DKH2 equilibrium structures minimum of interest was found to be surrounded by two comparable energy barriers of about 208 kJ/mol [5]. In the case of its rhodium analogue, RhNO 3 , the (η 2 -O 2 ) RhNO state is lower by − 33.8 kJ/mol from the quasi-tetrahedral Rh(IX)NO 3 , and the associated singlet-triplet crossing which creates a barrier is about 35% smaller than for the Ir complex but still quite large (~154 kJ/mol, Fig.…”

“…The well-known group 8 complexes are represented by stable yet largely covalent Os (VIII)O 4 and the less stable and highly reactive Ru (VIII)O 4 while related Fe (VIII)O 4 has never been observed but it has been predicted to be metastable [4]. Moving to the right in the periodic table, in group 9, only the observed [IrO 4 ] + cation and the recently predicted neutral molecule IrNO 3 (nitride trioxide) [5] feature genuine nonavalent transition metal center. Similar to Fe (VIII)O 4 , Ir (IX)NO 3 has been predicted to be mildly metastable with respect to (η 2 -NO)IrO 2 and (η 1 -NO)IrO 2 but elimination of NO is predicted to be protected by considerable barriers thus leaving some hope that Ir (IX)NO 3 might be observed experimentally.…”