{FeNO}⁷‐Type Halogenido Nitrosyl Ferrates: Syntheses, Bonding, and Photoinduced Linkage Isomerism

Abstract

Mononitrosyl-iron compounds (MNICs) of the Enemark-Feltham {FeNO} 7 type can be divided into ad oublet (S = 1/2) and aq uartet (S = 3/2) spin variant. The latter relies on weak-field co-ligands such as amine carboxylates. Aquaonly co-ligation appears to exist in the long-known "brownring" [Fe(H 2 O) 5 (NO)] 2 + cation, whichw as preparedo riginally from ferrous salts and NO in sulfuric acid. Ac hloride variant of this species, the green [FeCl 3 (NO)] À ion, was first prepared analoguosly by using hydrochloric instead of sulfuric acid. As at etrahedral species, it is the simple prototypeo fs ulfurbonded {FeNO} 7 (S = 3/2) MNICs of biological significance. Although it has been investigated form ore than ac entury, neitherc lean preparative routes nor reliable structuralp arameters were available for the [FeCl 3 (NO)] À ion and related speciess uch as the [FeCl 2 (NO) 2 ] À ion, ap rototypical dinitrosylirons pecies( a" DNIC"). In this work, both issues have been resolved. In addition, we report on ac omputational study on the ground-and excited-state properties including an assignment of the chromophoric transitions. Photoinduced metastable isomersw ere characterisedi nacombined experimental and computational approacht hat resulted in the confirmation of as ingle photoinduced linkage isomer of the paramagnetic nitrosyl-metal coordination entity.

Four‐Coordinate Copper Halonitrosyl {CuNO}10 Complexes

“…The discrepancy between CCSD and CCSD(T) results suggests that multiple electron configurations may be necessary to describe the {CuNO} 10 system. Multiconfigurational ground states have been explored for {FeNO} 7 , {CoNO} 9 , {NiNO} 10 , and {CuNO} 11 compounds using the complete active space self‐consistent field (CASSCF) method, but such an investigation of {CuNO} 10 electronic structure has not been explicitly documented.…”

Four‐Coordinate Copper Halonitrosyl {CuNO}10 Complexes

“…1208 8). [33] Together,computational and experimental results support am ulticonfigurational, open-shell singlet Cu II -NOC electronic structure,g iving insight into how facile capture and release of NOC from copper(II) ions is achieved electronically. Interestingly, aC ASSCF (9,13) calculation of the related iron halonitrosyl compound [Cl 3 FeNO] À reveals striking similarities.I nt his case,t he Fe-NO p bonding and antibonding orbitals exhibit populations of 1.73 and 0.27 electrons,r espectively,a nd the leading S = 3/2 electronic configuration contributes 65 %t o the ground state.…”

“…Interestingly, aC ASSCF (9,13) calculation of the related iron halonitrosyl compound [Cl 3 FeNO] À reveals striking similarities.I nt his case,t he Fe-NO p bonding and antibonding orbitals exhibit populations of 1.73 and 0.27 electrons,r espectively,a nd the leading S = 3/2 electronic configuration contributes 65 %t o the ground state. [33] Together,computational and experimental results support am ulticonfigurational, open-shell singlet Cu II -NOC electronic structure,g iving insight into how facile capture and release of NOC from copper(II) ions is achieved electronically.…”

“…However,u sing the CCSD(T) geometry,the singlet-triplet energy gap computed by CCSD and CCSD(T) is 4.1 and 19.3 kcal mol À1 ,r espectively.T he discrepancy between CCSD and CCSD(T) results suggests that multiple electron configurations may be necessary to describe the {CuNO} 10 system. Multiconfigurational ground states have been explored for {FeNO} 7 ,{ CoNO} 9 , {NiNO} 10 ,a nd {CuNO} 11 compounds using the complete active space self-consistent field (CASSCF) method, [31,33] but such an investigation of {CuNO} 10 electronic structure has not been explicitly documented.…”

“…While the CCSD method improves the description of bond angles,the CuÀNbond distance is underestimated by nearly 0.07 (Table 1). Multiconfigurational ground states have been explored for {FeNO} 7 ,{ CoNO} 9 , {NiNO} 10 ,a nd {CuNO} 11 compounds using the complete active space self-consistent field (CASSCF) method, [31,33] but such an investigation of {CuNO} 10 electronic structure has not been explicitly documented. However,u sing the CCSD(T) geometry,the singlet-triplet energy gap computed by CCSD and CCSD(T) is 4.1 and 19.3 kcal mol À1 ,r espectively.T he discrepancy between CCSD and CCSD(T) results suggests that multiple electron configurations may be necessary to describe the {CuNO} 10 system.…”