Accessing sodium ferrate complexes containing neutral and anionic N-heterocyclic carbene ligands: structural, synthetic, and magnetic insights

This study reports the synthesis and single-crystal X-ray crystallographic, NMR spectroscopic, and magnetic characterization of a series of sodium ferrates using bis(amide) Fe(HMDS)2 as a precursor (HMDS = 1,1,1,3,3,3- hexamethyldisilazide). Reaction with sodium reagents NaHMDS and NaCH2SiMe3 in hexane afforded donor-solvent-free sodium ferrates [{NaFe(HMDS)3}∞] (1) and [{NaFe(HMDS)2(CH2SiMe3)}∞] (2), respectively, which exhibit contacted ion pair structures, giving rise to new polymeric chain arrangements made up of a combination of inter- and intramolecular Na··· Me(HMDS) electrostatic interactions. Addition of the unsaturated NHC IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene) to 1 and 2 caused deaggregation of their polymeric structures to form discrete NHC-stabilized solvent-separated ion pairs [Na(IPr)2]+[Fe(HMDS)3]− (3) and [(THF)3·NaIPr]+[Fe(HMDS)2CH2SiMe3]− (4), where in both cases, the NHC ligand coordinates preferentially to Na. In contrast, when IPr is sequentially reacted with the single-metal reagents NaCH2SiMe3 and Fe(HMDS)2, the novel heteroleptic ferrate (THF)3Na[:C{[N(2,6-iPr2C6H3)]2CHCFe(HMDS)2}] (5) is obtained. This contains an anionic NHC ligand acting as an unsymmetrical bridge between the two metals, coordinating through its abnormal C4 position to Fe and its normal C2 position to Na. The formation of 5 can be described as an indirect ferration process where IPr is first metalated at the C4 position by the polar sodium alkyl reagent, which in turn undergoes transmetalation to the more electronegative Fe(HMDS)2 fragment. Treatment of 5 with 1 molar equiv of methyl triflate (MeOTf) led to the isolation and structural elucidation of the neutral abnormal NHC (aNHC) tricoordinate iron complex [CH3C{[N(2,6-iPr2C6H3)]2CHCFe- (HMDS)2}] (6) with the subsequent elimination of NaOTf, disclosing the selectivity of complex 5 to react with this electrophile via its C2 position, leaving its Fe−C4 and Fe−N bonds intact. The magnetic susceptibility properties of compounds 1−6 have been examined. This study revealed a drastic change of magnetic susceptibility in replacing a pure σ donor from an idealized trigonal coordination environment by an NHC π donating character

Synthetic, structural and magnetic implications of introducing 2,2'-dipyridylamide to sodium-ferrate complexes

Using a transamination approach to access novel Fe(II) complexes, this study presents the synthesis, X-ray crystallographic and magnetic characterisation of a series of new iron complexes containing the multifunctional 2,2-dipyridylamide (DPA) ligand using iron bis(amide) [{Fe(HMDS)2}2] and sodium ferrate [{NaFe (HMDS)3}∞] (1) as precursors (HMDS = 1,1,1,3,3,3-hexamethyldisilazide). Reactions of DPA(H) with 1 show exceptionally good stoichiometric control, allowing access to heteroleptic [(THF)2·NaFe(DPA)(HMDS)2] (3) and homoleptic [{THF·NaFe(DPA)3}∞] (4) by using 1 and 3 equivalents of DPA(H) respectively. Linking this methodology and co-complexation, which is a more widely used approach to prepare heterobimetallic complexes, 3 can also be prepared by combining NaHMDS with heteroleptic [{Fe(DPA)(HMDS)}2] (2). In turn, 2 has been also synthesised and structurally defined by reacting [{Fe(HMDS)2}2] with two equivalents of DPA(H). Structural studies demonstrate the coordination flexibility of the N-bridged bis(heterocycle) ligand DPA, with 2 and 3 exhibiting discrete monomeric motifs, whereas 4 displays a much more intricate supramolecular structure, with one of its DPA ligands coordinating in an anti/anti fashion (as opposed to 2 and 3 where DPA shows a syn/syn conformation), which facilitates propagation of the structure via its central amido N. Magnetic studies confirmed the high-spin electron configuration of the iron(II) centres in all three compounds and revealed the existence of weak ferromagnetic interactions in dinuclear compound 2 ( J = 1.01 cm−1)

Structural and magnetic diversity in alkali-metal manganate chemistry: evaluating donor and alkali-metal effects in co-complexation processes

By exploring co-complexation reactions between the manganese alkyl Mn(CH2SiMe3)2 and the heavier alkalimetal alkyls M(CH2SiMe3) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4-dioxane, and 1,4-diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali-metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X-ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA) 2MMn(CH2SiMe3)3] (M=Na, 3; M=K, 4) to dimers [{KMn- (CH2SiMe3)3·C6H6}2] (2) and [{NaMn(CH2SiMe3)3}2(dioxane)7] (5); and to more complex supramolecular networks [{NaMn(CH2SiMe3)3}1] (1) and [{Na2Mn2(CH2SiMe3)6- (DABCO)2}1] (7)). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4-dioxane, as 1 produces coordination adduct 5, while 2 forms heteroleptic [{(dioxane)6K2Mn2(CH2SiMe3)4(O(CH2)2- OCH=CH2)2}1] (6) containing two alkoxide-vinyl anions resulting from a-metalation and ring opening of dioxane. Compounds 6 and 7, containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways

Design and preparation of functional coordination compounds based on poly-β-diketone and polypyrazolyl ligands

[eng] Combining the judiciously designed bis−β-diketone and polypyrazolyl scaffolds with the crystal field effects on the 3d metal ions, this manuscript exposes different methods of selective preparation of new heterometallic coordination compounds and the subtle modulation of their magnetic properties. Apart from their conventional magneto-structural relevance, special interest has been dedicated to develop the systems which exhibit strong ferromagnetic coupling and slow relaxation of the magnetization, even when incorporating exclusively isotropic metal ions. Moreover, synthetic strategy based on controlled transfer of the ligand asymmetry to its coordination compounds provided several entities which fulfil the necessary requirements to be exploited as the molecular prototypes of universal logic gates in quantum information processing. Chapter II presented new synthetic strategy of rational preparation of oxo-hydroxido coupled pair of homometallic and heterometallic dimers based on bis−β-diketone ligand H4L1. Two fused phenol-β-diketone coordination pockets provided enough flexibility for selective manipulation of ligand conformation and coordination modes. Particularly, by imposing pair- impair metal-ligand ratio, with large excess of 3d metal ions, controlled assembly of coupled pairs of dimers or monomers was achieved. Moreover, it was shown that only one ligand molecule in the backbone of the structure was enough to impose desired site selectivity which was successfully exploited to generate all possible heterometallic pairs of late 3d metals. Structural analysis of those coordination entities proved that bonding details correlated with the nature of metal ions can be used as a fingerprinting evidence for correct positional assignment of heterometallic topologies. Magnetic studies proved meaningful insight in strength of antiferromagnetic interactions between identical of diverse spin carries, providing some meaningful knowledge to be exploited. Additionally, it was clearly show that [NiCu] dimers from all possible combinations provide best isolated ground state doublet and thus should be exploited as potential qubit candidates. Gathered knowledge from this section inspired the evolution of Chapter III, where novel library of structurally related asymmetric and multidentate bis−β-diketone ligand was designed and exploited in construction of molecular prototypes of multiqubit quantum logic gates. Direct transfer of imposed asymmetry of the ligands to their coordination compounds enabled successful preparation of three new compounds which fulfil the basic requirement of asymmetry and ground state doublet to be considered as molecular prototypes of C-NOT quantum gates of which one represents very first example of a coordination compound which features the triple asymmetry between the component qubits. As one of the highlights of this research line, it was shown how rational ligand design can be exploited to tune the interaction between individual qubits, while control of reaction stoichiometry can provide means of changing their topology. Also, initial steps are undertaken in expanding the coordination chemistry of more complex bis−β-diketone ligand to vanadium(IV) based qubits. Chapter IV expanded the ligand library to pyrazole derivatives of bis−β-diketone ligands and exposed extensive coordination chemistry of phenolic pyrazole ligand H4L4. Initial idea behind its implementation was to selectively chelate different 3d metals into linear arrays based on their preference towards (-N,N) or (-O,N) coordination environment of the ligand. Homometallic series of obtained compounds indicated that only vanadyl cation (VO2+) and Mn3+ ion discriminate two different ligating donor sets and reside exclusively in the (-O,N) coordination pocket, leaving central -N4 chelating metal-free, inspired their further use as metalloligands. Great structural rigidity and excessive negative charge of vanadyl metalloligand enhanced its nucleophilic nature, providing means for bitopic structural expansion in selective formation of derived heterobimetallic and heterotrimetallic clusters. Additionally, orthogonality in expansion of metalloligand structure ensured double orthogonality between magnetic orbitals of vanadyl and heavier 3d ions resulting with purely ferromagnetically coupled clusters which even exhibit slow relaxation of magnetization when constructed from isotropic metal ions. Overall, work presented in this thesis exposed different ways of constructing heterometallic compounds providing good initial playground for many novel directions of research within molecular magnetism.[cat] En aquest manuscrit es descriuen nous mètodes de preparació de compostos de coordinació hetrometàl·lics amb propietats magnètiques predeterminades, gràcies a una combinació adequada entre l’us de lligands poli-β-dicetona i polipirazolil i els efectes de camp de lligand de metalls 3d. Per un cantó s’ha estudiat les correlacions magnetoestructurals que es deriven, però sobre tot, destaquen les propietats de fort acoblament ferromagnètic i de relaxació lenta de la magnetització amb metalls isotròpics que se n’han derivat. A més, una estratègia de síntesi basada en la transferència de l’asimetria dissenyada en els lligands als corresponents compostos de coordinació ha permès generar prototips de portes lògiques quàntiques de dos qubits, basades en l’espín electrònic, per la computació quàntica. El Capítol II mostra un estratègia de síntesi per obtenir dímers homo- i heterometàl·lics amb ponts oxo-hidroxi i el lligand bis−β-dicetona H4L1. Dos unitats bis−β-dicetona fusionades no impedeixen una fructífera flexibilitat en conformació i modes de coordinació en aquest lligand. Especialment, ha estat possible controlar la nuclearitat dels compostos i la formació de dimers d’aquestes molècules jugant amb la estequiometria de les reaccions. El sistema de lligands ha permès obtenir diversos compostos de coordinació heterometàl·lics 3d d’elevada selectivitat. Estudis cristal·logràfics confirmen que l’anàlisi del paràmetres estructurals es poden utilitzar de manera fiable com a diagnòstic de la composició específica dels diferents compostos. Estudis magnètics demostren l’acoblament antiferromagnètic entre metalls idèntics o diferents. El cas dels sistemes amb parells [NiCu] és de gran rellevància per la seva explotació com a candidats a qubits. El Capítol III s’inspira en les observacions descrites en el capítol anterior. En aquest, una nova sèrie de lligands asimètrics amb unitats bis−β-dicetona ha estat dissenyada, preparada i utilitzada per obtenir nous prototips moleculars de portes lògiques de més d’un qubit. L’asimetria d’aquestes espècies imposada pels lligands permet que aquelles es puguin presentar com models satisfactoris de portes lògiques de tipus C-NOT. Un dels exemples representa el primer cas de compst de coordinació amb triple asimetria entre els qubits constituents. Un altra aspecte remarcable és la capacitat de dissenyar la intensitat de la interacció magnètica entre els qubits continguts en aquestes molècules. Igualment, el control de la estequiometria permet decidir el nombre de qubits presents en la molècula, entre dos i tres, com a resultat d’un canvi dràstic de topologia molecular. Es mostren els primers intents d’estendre aquesta química als qubits de vanadi(IV). El Capítol IV descriu la utilització dels lligads pirazol que deriven de les corresponents bis−β- dicetones, i especialment, l’àmplia química de coordinació del lligand pirazol/fenol H4L4. La seva utilització ha buscat implementar la selectivitat propiciada per la preferència respecte a entorns de coordinació basats en unitats (-N,N) o (-O,N). La idea envers aquesta implementació és la d’encapsular diferents metalls 3d en arrengements metàl·lics basats en les preferències dels entorns de coordinació del lligand. La sèrie de compostos homometàl·lics obtinguda demostra que només els cations vanadil (VO2+) i Mn3+ poden discriminar els dos entorns de coordinació, podent ser emprats així com metalolligands per la formació de derivats heterobi- i heterotrimetàl·lics. A més, l’ortogonalitat derivada del sistema assegura acoblaments ferromagnètics promovent relaxació lenta inclús amb metalls isotròpics. En resum, el treball presentat en aquesta tesi exposa diferents vies de construir compostos heterometàl·lics, aportant una bona estratègia per construir noves línies de recerca dins del camp del magnetisme molecular

Design and preparation of functional coordination compounds based on poly-β-diketone and polypyrazolyl ligands

Combining the judiciously designed bis−β-diketone and polypyrazolyl scaffolds with the crystal field effects on the 3d metal ions, this manuscript exposes different methods of selective preparation of new heterometallic coordination compounds and the subtle modulation of their magnetic properties. Apart from their conventional magneto-structural relevance, special interest has been dedicated to develop the systems which exhibit strong ferromagnetic coupling and slow relaxation of the magnetization, even when incorporating exclusively isotropic metal ions. Moreover, synthetic strategy based on controlled transfer of the ligand asymmetry to its coordination compounds provided several entities which fulfil the necessary requirements to be exploited as the molecular prototypes of universal logic gates in quantum information processing. Chapter II presented new synthetic strategy of rational preparation of oxo-hydroxido coupled pair of homometallic and heterometallic dimers based on bis−β-diketone ligand H4L1. Two fused phenol-β-diketone coordination pockets provided enough flexibility for selective manipulation of ligand conformation and coordination modes. Particularly, by imposing pair- impair metal-ligand ratio, with large excess of 3d metal ions, controlled assembly of coupled pairs of dimers or monomers was achieved. Moreover, it was shown that only one ligand molecule in the backbone of the structure was enough to impose desired site selectivity which was successfully exploited to generate all possible heterometallic pairs of late 3d metals. Structural analysis of those coordination entities proved that bonding details correlated with the nature of metal ions can be used as a fingerprinting evidence for correct positional assignment of heterometallic topologies. Magnetic studies proved meaningful insight in strength of antiferromagnetic interactions between identical of diverse spin carries, providing some meaningful knowledge to be exploited. Additionally, it was clearly show that [NiCu] dimers from all possible combinations provide best isolated ground state doublet and thus should be exploited as potential qubit candidates. Gathered knowledge from this section inspired the evolution of Chapter III, where novel library of structurally related asymmetric and multidentate bis−β-diketone ligand was designed and exploited in construction of molecular prototypes of multiqubit quantum logic gates. Direct transfer of imposed asymmetry of the ligands to their coordination compounds enabled successful preparation of three new compounds which fulfil the basic requirement of asymmetry and ground state doublet to be considered as molecular prototypes of C-NOT quantum gates of which one represents very first example of a coordination compound which features the triple asymmetry between the component qubits. As one of the highlights of this research line, it was shown how rational ligand design can be exploited to tune the interaction between individual qubits, while control of reaction stoichiometry can provide means of changing their topology. Also, initial steps are undertaken in expanding the coordination chemistry of more complex bis−β-diketone ligand to vanadium(IV) based qubits. Chapter IV expanded the ligand library to pyrazole derivatives of bis−β-diketone ligands and exposed extensive coordination chemistry of phenolic pyrazole ligand H4L4. Initial idea behind its implementation was to selectively chelate different 3d metals into linear arrays based on their preference towards (-N,N) or (-O,N) coordination environment of the ligand. Homometallic series of obtained compounds indicated that only vanadyl cation (VO2+) and Mn3+ ion discriminate two different ligating donor sets and reside exclusively in the (-O,N) coordination pocket, leaving central -N4 chelating metal-free, inspired their further use as metalloligands. Great structural rigidity and excessive negative charge of vanadyl metalloligand enhanced its nucleophilic nature, providing means for bitopic structural expansion in selective formation of derived heterobimetallic and heterotrimetallic clusters. Additionally, orthogonality in expansion of metalloligand structure ensured double orthogonality between magnetic orbitals of vanadyl and heavier 3d ions resulting with purely ferromagnetically coupled clusters which even exhibit slow relaxation of magnetization when constructed from isotropic metal ions. Overall, work presented in this thesis exposed different ways of constructing heterometallic compounds providing good initial playground for many novel directions of research within molecular magnetism.En aquest manuscrit es descriuen nous mètodes de preparació de compostos de coordinació hetrometàl·lics amb propietats magnètiques predeterminades, gràcies a una combinació adequada entre l’us de lligands poli-β-dicetona i polipirazolil i els efectes de camp de lligand de metalls 3d. Per un cantó s’ha estudiat les correlacions magnetoestructurals que es deriven, però sobre tot, destaquen les propietats de fort acoblament ferromagnètic i de relaxació lenta de la magnetització amb metalls isotròpics que se n’han derivat. A més, una estratègia de síntesi basada en la transferència de l’asimetria dissenyada en els lligands als corresponents compostos de coordinació ha permès generar prototips de portes lògiques quàntiques de dos qubits, basades en l’espín electrònic, per la computació quàntica. El Capítol II mostra un estratègia de síntesi per obtenir dímers homo- i heterometàl·lics amb ponts oxo-hidroxi i el lligand bis−β-dicetona H4L1. Dos unitats bis−β-dicetona fusionades no impedeixen una fructífera flexibilitat en conformació i modes de coordinació en aquest lligand. Especialment, ha estat possible controlar la nuclearitat dels compostos i la formació de dimers d’aquestes molècules jugant amb la estequiometria de les reaccions. El sistema de lligands ha permès obtenir diversos compostos de coordinació heterometàl·lics 3d d’elevada selectivitat. Estudis cristal·logràfics confirmen que l’anàlisi del paràmetres estructurals es poden utilitzar de manera fiable com a diagnòstic de la composició específica dels diferents compostos. Estudis magnètics demostren l’acoblament antiferromagnètic entre metalls idèntics o diferents. El cas dels sistemes amb parells [NiCu] és de gran rellevància per la seva explotació com a candidats a qubits. El Capítol III s’inspira en les observacions descrites en el capítol anterior. En aquest, una nova sèrie de lligands asimètrics amb unitats bis−β-dicetona ha estat dissenyada, preparada i utilitzada per obtenir nous prototips moleculars de portes lògiques de més d’un qubit. L’asimetria d’aquestes espècies imposada pels lligands permet que aquelles es puguin presentar com models satisfactoris de portes lògiques de tipus C-NOT. Un dels exemples representa el primer cas de compst de coordinació amb triple asimetria entre els qubits constituents. Un altra aspecte remarcable és la capacitat de dissenyar la intensitat de la interacció magnètica entre els qubits continguts en aquestes molècules. Igualment, el control de la estequiometria permet decidir el nombre de qubits presents en la molècula, entre dos i tres, com a resultat d’un canvi dràstic de topologia molecular. Es mostren els primers intents d’estendre aquesta química als qubits de vanadi(IV). El Capítol IV descriu la utilització dels lligads pirazol que deriven de les corresponents bis−β- dicetones, i especialment, l’àmplia química de coordinació del lligand pirazol/fenol H4L4. La seva utilització ha buscat implementar la selectivitat propiciada per la preferència respecte a entorns de coordinació basats en unitats (-N,N) o (-O,N). La idea envers aquesta implementació és la d’encapsular diferents metalls 3d en arrengements metàl·lics basats en les preferències dels entorns de coordinació del lligand. La sèrie de compostos homometàl·lics obtinguda demostra que només els cations vanadil (VO2+) i Mn3+ poden discriminar els dos entorns de coordinació, podent ser emprats així com metalolligands per la formació de derivats heterobi- i heterotrimetàl·lics. A més, l’ortogonalitat derivada del sistema assegura acoblaments ferromagnètics promovent relaxació lenta inclús amb metalls isotròpics. En resum, el treball presentat en aquesta tesi exposa diferents vies de construir compostos heterometàl·lics, aportant una bona estratègia per construir noves línies de recerca dins del camp del magnetisme molecular

A bis-vanadyl coordination complex as a 2-qubit quantum gate

A new bis-hydroxyphenylpyrazolyl ligand, H4L, allows isolating and structurally characterizing vanadyl and titanyl dinuclear complexes (Bu4N)2[(MO)2(HL)2] (M = V, Ti). The weak dipolar coupling and relatively short quantum coherence of the divanadyl anions are optimal for a 2-qubit molecular architecture proposed to implement electron-mediated nuclear quantum simulations

Novel Topologies in Vanadium-bis-β-Diketone Chemistry: A [V4] and a [V6] Metallacyclophane

Exploring the chemistry of vanadyl ions (VO2+) with bis-β-diketone ligands, in pyridine reactions of vanadyl sulfate with 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-benzene (H4L1) and 1,3-bis-(3-oxo-3-(2-hydroxyphenyl)-propionyl)-pyridine (H4L2), two novel clusters, [(VIVO)4(H2L1)4(py)4] (1) and [(VVO)4(VIVO)2 (O)4(L2)2(py)6] (2) were prepared and characterized. Due to the conformational flexibility of the ligands, both entities exhibit very peculiar metal topologies and composition, differing significantly from structural patterns established in the related chemistry of divalent 3d metals. Structural analysis also unveils the existence of the most complex metallamacrocycles from this family to date. Studies of the magnetic properties via bulk magnetization measurements and EPR spectroscopy confirmed the existence of uncoupled long-distant S = 1/2 metal centers and the spin ground states S = 2 and S = 1 of the clusters

Self-assembly of a trigonal bipyramidal architecture with stabilisation of iron in three spin states.

From PubMed via Jisc Publications RouterPublication status: aheadofprintSelf-assembly and characterisation of a supramolecular trigonal bipyramidal iron cage containing an [Fe (μ -F) (Fe ) ] star motif at its core is reported. The complex can be formed in a one step reaction using an heterotopic ligand that supports site-specific incorporation of iron in three distinct electronic configurations: low-spin Fe , high-spin Fe and high-spin Fe , with iron(II) tetrafluoroborate as the source of the bridging fluorides. Formation of a μ -F bridged mixed-valence Fe -Fe star is unprecedented. The peripheral high-spin Fe centres of the mixed-valence tetranuclear star incorporated in the iron cage are highly anisotropic and engage in F-mediated antiferromagnetic exchange with the central Fe ion

Structural and magnetic diversity in alkali-metal manganate chemistry: evaluating donor and alkali-metal effects in co-complexation processes

By exploring co-complexation reactions between the manganese alkyl Mn(CH2SiMe3)2 and the heavier alkalimetal alkyls M(CH2SiMe3) (M=Na, K) in a benzene/hexane solvent mixture and in some cases adding Lewis donors (bidentate TMEDA, 1,4-dioxane, and 1,4-diazabicyclo[2,2,2] octane (DABCO)) has produced a new family of alkali-metal tris(alkyl) manganates. The influences that the alkali metal and the donor solvent impose on the structures and magnetic properties of these ates have been assessed by a combination of X-ray, SQUID magnetization measurements, and EPR spectroscopy. These studies uncover a diverse structural chemistry ranging from discrete monomers [(TMEDA) 2MMn(CH2SiMe3)3] (M=Na, 3; M=K, 4) to dimers [{KMn- (CH2SiMe3)3·C6H6}2] (2) and [{NaMn(CH2SiMe3)3}2(dioxane)7] (5); and to more complex supramolecular networks [{NaMn(CH2SiMe3)3}1] (1) and [{Na2Mn2(CH2SiMe3)6- (DABCO)2}1] (7)). Interestingly, the identity of the alkali metal exerts a significant effect in the reactions of 1 and 2 with 1,4-dioxane, as 1 produces coordination adduct 5, while 2 forms heteroleptic [{(dioxane)6K2Mn2(CH2SiMe3)4(O(CH2)2- OCH=CH2)2}1] (6) containing two alkoxide-vinyl anions resulting from a-metalation and ring opening of dioxane. Compounds 6 and 7, containing two spin carriers, exhibit antiferromagnetic coupling of their S=5/2 moments with varying intensity depending on the nature of the exchange pathways

Accessing sodium ferrate complexes containing neutral and anionic N-heterocyclic carbene ligands: structural, synthetic, and magnetic insights

This study reports the synthesis and single-crystal X-ray crystallographic, NMR spectroscopic, and magnetic characterization of a series of sodium ferrates using bis(amide) Fe(HMDS)2 as a precursor (HMDS = 1,1,1,3,3,3- hexamethyldisilazide). Reaction with sodium reagents NaHMDS and NaCH2SiMe3 in hexane afforded donor-solvent-free sodium ferrates [{NaFe(HMDS)3}∞] (1) and [{NaFe(HMDS)2(CH2SiMe3)}∞] (2), respectively, which exhibit contacted ion pair structures, giving rise to new polymeric chain arrangements made up of a combination of inter- and intramolecular Na··· Me(HMDS) electrostatic interactions. Addition of the unsaturated NHC IPr (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2- ylidene) to 1 and 2 caused deaggregation of their polymeric structures to form discrete NHC-stabilized solvent-separated ion pairs [Na(IPr)2]+[Fe(HMDS)3]− (3) and [(THF)3·NaIPr]+[Fe(HMDS)2CH2SiMe3]− (4), where in both cases, the NHC ligand coordinates preferentially to Na. In contrast, when IPr is sequentially reacted with the single-metal reagents NaCH2SiMe3 and Fe(HMDS)2, the novel heteroleptic ferrate (THF)3Na[:C{[N(2,6-iPr2C6H3)]2CHCFe(HMDS)2}] (5) is obtained. This contains an anionic NHC ligand acting as an unsymmetrical bridge between the two metals, coordinating through its abnormal C4 position to Fe and its normal C2 position to Na. The formation of 5 can be described as an indirect ferration process where IPr is first metalated at the C4 position by the polar sodium alkyl reagent, which in turn undergoes transmetalation to the more electronegative Fe(HMDS)2 fragment. Treatment of 5 with 1 molar equiv of methyl triflate (MeOTf) led to the isolation and structural elucidation of the neutral abnormal NHC (aNHC) tricoordinate iron complex [CH3C{[N(2,6-iPr2C6H3)]2CHCFe- (HMDS)2}] (6) with the subsequent elimination of NaOTf, disclosing the selectivity of complex 5 to react with this electrophile via its C2 position, leaving its Fe−C4 and Fe−N bonds intact. The magnetic susceptibility properties of compounds 1−6 have been examined. This study revealed a drastic change of magnetic susceptibility in replacing a pure σ donor from an idealized trigonal coordination environment by an NHC π donating character