study of the molecular properties of mono- and binuclear metal s...

Research ArticleStudy of the Molecular Properties ofMono- and Binuclear Metal s-Indacenyl Complexeswith Ir Rh and Re A Theoretical Approach

Ximena Zarate1 Eduardo Schott2 Emilio Bunel3 JuanM Manriacutequez2 and Ivonne Chaacutevez2

1 Instituto de Ciencias Quımicas Aplicadas Facultad de Ingenierıa Universidad Autonoma de ChileAv Pedro de Valdivia 425 Santiago Chile2Departamento de Quımica Inorganica Facultad de Quımica Pontificia Universidad Catolica de Chile Casilla 306 Santiago Chile3Argonne National Laboratory Argonne IL 60439 USA

Correspondence should be addressed to Ximena Zarate jazminacgmailcom and Ivonne Chavez ichavezuccl

Received 31 March 2017 Accepted 2 May 2017 Published 1 June 2017

Academic Editor Henryk Kozlowski

Copyright copy 2017 Ximena Zarate et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Density functional theory (DFT) calculations were performed on a new family of mono- and bimetallic complexes containing48-([10]paracyclophane)-15-dihydro-s-indacene as the bridging ligand between the two metallic centers and different ancillaryligands The s-indacene was blocked by substitution of the central benzene ring with the [10]paracyclophane to obtain the syn-conformations This would force the metallic centers to be close together It is proposed due to the calculated molecular andelectronic properties such as the reactivity indexes the delocalized nature of the s-indacenyl ligand and the electron-rich metalsthat these systems could be reactive in a catalytic reaction The results indicate that the systems with Rh and Re holding ancillaryligands such as bipy and CO show the best properties to be active in a chemical reaction In this sense by the assessed geometricaland electronic properties when comparedwith a previously reported system these complexes could be candidates for the reductionof CO2 to oxalate

1 Introduction

s-Indacene and as-indacene belong to a class of conjugatedhydrocarbons characterized by having 4119899120587 electrons (119899 =2 3) Therefore according to Huckelrsquos Rule they should beantiaromatic [1] Nevertheless they have been for decades ofsignificant interest for organic chemists as they have focusedon them upon their diverse and fascinating reactivity Dueto the synthetic challenges that these kinds of compoundspresent and the questions that have arisen over their aro-maticity and structure the potential of these systems indifferent applications such as semiconducting devices andcatalysis has been slowly explored

Even when the unsubstituted molecules are unstabletheir dianions and several substituted derivatives stabilizeboth sterically and electronically resulting in thermally stablestructures at room temperature [2]

Moreover s-indacene may connect two or more organo-metallic centers which may have different oxidation statesand allow interaction between them Binuclear metal com-plexes bearing an as-indacenyl or s-indacenyl ligand werefirst reported in the literature in 1988 [3 4] A large varietyof transition metals homobinuclear complexes have beendescribed including Fe Co Ni Ru Rh Re and Mn Alsoheterobinuclear complexes with combinations of metals suchas Rh-Ru Fe-Ru Fe-Rh Ru-Rh F-Co and Cr-Ni have beenreported [5ndash8] The most striking feature of this familyof binuclear complexes is the ability to delocalize chargeamongmetal centers upon oxidation In this sense we believethat bimetallic complexes are useful compounds that mightinduce catalytic reactions

On the other hand literature reports on the selectiveconversion of CO2 to oxalate (C2O4)

2minus point to the occur-rence of a two-metal-centers mechanism Bi- or polymetallic

HindawiJournal of ChemistryVolume 2017 Article ID 9101720 8 pageshttpsdoiorg10115520179101720

2 Journal of Chemistry

RR

(a)

- RR -

(b)

RR

MLn Lm

(c)

RR

M

-

Ln Lm

(d)

RR

M MLn LnLm Lm

(e)

Figure 1 Structures of the studied systems (a) Neutral ligand (b) dianion ligand and (c) neutral monometallic (d) monoanionmonometallic and (e) bimetallic systems R = H CH3 and CH2CH3 M = Ir Rh and Re Lm and Ln = bipy CO with m and n = 0 1 23

compounds have been studied showing a wide variationof results [9ndash12] The most important conclusion of thesereports is that for systems where the coordination of CO2is not reversible the ability to transform CO2 into othercompounds depends on the extent of the charge transfer fromthe transitionmetal to CO2 If themetal transfers an electronthe formation of C-C bonds is possible and the rigidity ofthe bimetallic system seems to play an essential role in theformation of this bond [13 14] In this sense interestinglyone of themost innovativeworks in the area of CO2 reductionreported by Angamuthu et al in 2010 consists in the synthesisof a tetranuclear complex of Cu(I) with the ligand N-(2-mercaptopropyl)-NN-bis(2-pyridylmethyl)amine whichspontaneously and selectively captures CO2 from the air[15] Cu(I) gets oxidized to Cu(II) and a bridge of oxalateis formed which links two binuclear complexes forming atetramer Adding a lithium salt to the solution allows thequantitative precipitation of lithiumoxalate Finally theCu(I)complex can be recovered by electrochemical reduction Thecrystallographic study of the Cu complex showed that the Cu-Cudistance in the complexwas 543 AThis distance is similarto the Rh-Rh distance observed in a syn binuclear com-plex synthesized by our group [(26-diethyl-48-dimethyl-s-indacenediide) Rh (COD)2] [16] of about 55 A

The largemajority of the examples of binuclear complexeswith s-indacene reported in the literature show the twometalscenters in an anticonfiguration This is due mostly to thesteric bulk imposed by the ancillary ligands In this workwe propose that it is possible to avoid the anticonfigurationby blocking one of the faces of the s-indacene introducing agroup that can effectively obstruct the access of the metalsto both faces forcing them to adopt the syn configurationThis could be easily achieved by constructing a cyclophanestructure over the plane of the rings as shown in Figure 1

Therefore in order to have the right template structurefor coupling reactions in those compounds and to favor the

reaction the right Metal-Metal (M-M) distance electronicconfiguration and lability of the ligand coordinated to themetal center (ancillary ligands) are needed Specificallybinuclear metal frameworks could play an important roleas templates for these types of reactions such as selectivereductive coupling of two molecules of CO2 to oxalate

Inspired by the work of Bouwman et al and the versatileindacene derivatives we decided to propose templates withsynthetical feasibility consisting in a family of binuclearmetal complexes

The aim of this work is to evaluate the effect of differenttransition metals (Ir Rh and Re) different ancillary ligands(bipy and CO) and -R groups (CH3 and CH2CH3) (Figure 1)over the electronic properties assessing the Frontier Molec-ular Orbitals (FMOs) location the geometrical parametershighlighting the M-M distance the global reactivity indexesthe atomic metal charges and the Fukui functions This pre-liminary study could lead experimentalist to have a hint aboutwhich metallic s-indacenyl complexes ancillary ligands andperipheral substituents might show suitable properties for avariety of chemical applications

2 Computational Details

Quantum chemical calculations were performed in orderto further investigate the electronic structure of a family ofcompounds in the ground state Density functional theory(DFT) as implemented in Gaussian 09 [17] software was usedto perform the calculations of the studied systemsThe Beckethree-parameter hybrid functional combined with Lee-Yang-Parr correlation B3LYP [18 19] was employedThe relativisticeffects of the heavy metals were incorporated using thepseudopotential LANL2DZ [20ndash22] and the Gaussian basissets 6-31G(d) were used for the nonmetallic atoms [23] Withthe aimof getting theminimapoints over the potential energysurface of the proposed compounds themolecular structures

Journal of Chemistry 3

Table 1 Selected geometrical parameters of the ground state conformers Bond lengths are given in Angstrom (A) (see Scheme 1)

(a)

Par Geo M = Ir Ln = bipy M = Rh Ln = bipy M = Re Lnm = bipy COH CH3 CH2CH3 H CH3 CH2CH3 H CH3 CH2CH3

M1-C1 222 222 221 223 222 222 225 224 224M1-C2 215 216 216 220 220 220 222 224 224M1-C3 222 221 222 223 222 222 232 231 231M1-C9 261 258 259 257 256 256 252 251 251M1-C10 262 259 260 257 256 257 253 252 252M2-C5 222 222 222 223 223 223 225 225 225M2-C6 216 216 216 220 221 221 222 224 224M2-C7 222 222 221 223 222 222 232 231 231M2-C11 260 260 261 257 256 255 252 251 251M2-C12 261 260 261 257 256 256 252 252 252M1-M2 558 553 559 545 543 541 540 543 544

(b)

Par Geo M = Ir Lnm = CO M = Rh Lnm = CO M = Re L = (CO)3H CH3 CH2CH3 H CH3 CH2CH3 H CH3 CH2CH3


RR

M1 M2

1

23

9

10

8

4

12 76

511

Ln LmLn Lm

Scheme 1

were fully optimized without symmetry constriction andthe frequency calculations were performed at the same levelof theory to confirm that all the optimized systems arestationary minima points Implicit solvation effects wereincorporated using the polarized continuum model (PCM120576 = 7426) for tetrahydrofuran [24] The local reactivityindexes and the Fukui functions computed at the ground stategeometry are also assessed and analyzed

3 Results and Discussion

The optimized ground state minima of the series of com-pounds displayed in Figure 1 ligand (s-Ic) in the neutral

and dianion states and the mononuclear and binuclearcoordination systems were obtained at the B3LYP6-31G(d)+ PCM (120576 = 7426) level of theory Selected geometricalparameters of the correspondingminima are listed in Table 1

The ligand s-Ic shows a planar structure and one planeface is blocked by substitution of the central benzene ringwith a saturated alkyl chain formed by 10 -CH2- units Thissubstitution is a proposal for experimentalist to synthesize thecompounds adopting exclusively the syn conformation aftermetallic coordination

Geometrical parameters such as C-C and C-H of the s-Ic coordinating different metals (not shown in Table 1) donot change significantly when all the studied compoundsare compared as some values show differences in the thirddecimal digit or in less proportion in the seconddecimal digitThis indicates that the different metals and ancillary ligandsdo not lead to significant changes in the structural geometryof the s-Ic

Regarding the M-M distances as observed in Table 1 thebinuclear transitionmetals frameworks show the appropriatelength between the two metal centers to act as a template forthe selective reduction of two molecules of CO2 to oxalateSpecifically the results show that the systems with Rh and


170

148

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

(c) (d) (e)

205

minus9

minus8

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1En

ergy

(eV

)

Figure 2 Compounds with Rh (c) neutral monometallic (d) monometallic monoanion and (e) bimetallic systems with L = bipy and R =CH3

Re holding ancillary ligands such as bipy and CO containing-CH3 as -R substituent present the most accurate M-Mdistance around 543 A (Table 1) This distance correspondsto the Cu-Cu distance of the complex reported by Bouwmanet al that catalyzed the transformation of CO2 to oxalate

The ancillary ligands contribute steric effects towards thedistances of the 120578 bonds between themetal and the s-Ic whileas bigger the ancillary ligand is the shorter the distancesamong the metal and the carbon atoms are (Table 1) Inthis sense it is also worth mentioning that while the -Rsubstituents in the s-Ic are changed some differences overthe M-M distances were observed however no clear trendis found

These facts lead us to conclude that the M-M distancecan be tuned by adjusting different ancillary ligands andsubstituents over the s-Ic ligand

In terms of the electronic structure as consequence ofthe formation of the s-Ic dianion species with different Rgroups the HOMO-LUMO gaps get smaller in comparisonwith the gap of the neutral species (Figures S1-S2 in Supple-mentary Material available online at httpsdoiorg10115520179101720) For the isolated ligand it is also observed thatthe FMOs structures present contribution of the s-Ic ligandexcept for the LUMO+1 of the dianionic compounds which islocalized over the alkyl chain binding across the six-edge ringof s-Ic (Figures S1-S2) The change of the R groups does notshow transcendental effect over the FMOs

In cases of the metallic complexes the localization of theFMOs does not change considerably when the comparison ismade between the monometallic and the bimetallic species(see complexes with Rh as example in Figure 2) as they areformed by contribution of the orbitals extended over the s-Icand over the transition metals

The energy levels diagrams display that the FMOs of allthe mononuclear and binuclear complexes are more stablethan the free substituted s-Ic ligand It is worth noticingthat all studied systems with ligands CO show more stableoccupied orbitals than the system with bipy

It was also observed that the different studied peripheral Rsubstituents of the s-Ic ring (-H -CH3 and -CH2CH3) showno contribution to the FMOs

In general all the complexes that have a bimetallicstructure exhibit FMOs localized mainly over the ancillaryligands and the metal centers although a slight variation ofthe FMO isosurfaces is observed specifically in the LUMOThis LUMO in cases of voluminous ancillary ligands iscomposed mainly for the ancillary ligands orbitals and thecontribution of the metals decreases (Figures S3ndashS20 in theSupplementary Material)

In these systems the mononuclear and the binuclear themetals would have a dual role The metal would be receivingelectrons therefore stabilizing the reduced fragments for theformation of the C-C bond between two CO2moleculesThisis supported by the fact that the HOMO is localized over thefragment containing the metal and the ancillary ligands (Fig-ure 2 and Figures S3ndashS20 in Supplementary Material) Thelocalization of the FMOs over these regions of the moleculessuggests their high reactivity towards any catalytic activity

To assess the atomic charges in the metals of the studiedfamily of compounds a Mulliken analysis was carried outand the values are reported in Table 2 The formation ofthe complexes involves a charge transfer from the s-Ic andancillary ligands to the metals as the atomic charges get lesspositive with respect to the oxidation state of the metals(+1 for all metals in all cases) Significant charge transfer isobserved for compounds containing Rh and CO as ancillaryligands where it is known that the back-bonding effect of theCO ligand is present In this sense it is possible to state thatin these systems the electron pair of each CO ligand donatesmore charge than it receives which is evidenced in the slightnegative charge over the metals This behavior is followed byRe compounds containing CO which show atomic chargesaround 016 au These values are significantly lower than thevalues obtained with Ir as metal center

On the other hand in cases of monometallic complexesthe charge transfer to themetals is bigger for themononuclear


Table 2 Atomic charges in au for the metal centers of the monometallic (anion and neutral) and bimetallic systems

(a)

RM = Ir Ln = bipy M = Rh Ln = bipy M = Re Lnm = bipy CO

Mono Bim Mono Bim Mono BimM1 ani M1 neu M1 M2 M1 ani M1 neu M1 M2 M1 ani M1 neu M1 M2

H 0351 0300 0297 0300 0156 0157 0152 0157 0289 0312 0315 0323CH3 0351 0299 0290 0295 0162 0159 0148 0152 0284 0308 0304 0312CH2CH3 0349 0298 0287 0295 0151 0048 0142 0147 0278 0301 0300 0309

(b)

RM = Ir Lnm = CO M = Rh Lnm = CO M = Re Lnm = CO


H 0142 0200 0221 0225 minus0202 minus0085 minus0065 minus0062 0090 0134 0165 0171CH3 0148 0198 0216 0220 minus0201 minus0089 minus0072 minus0067 0089 0132 0160 0166CH2CH3 0149 0197 0214 0219 minus0203 minus0093 minus0077 minus0071 0086 0130 0158 0164

Table 3 Estimated energies for the HOMO and LUMO chemical potential (120583) chemical hardness (120578) and electrophilicity (120596) calculated forthe optimized ground state minima of the metallic complexes

Compound HOMO LUMO HL GAP 120583 120578 120596M = Rh Ln = bipy

M1 ani minus268 minus120 148 minus194 074 255M1 neu minus397 minus182 216 minus290 108 389Bim minus361 minus190 171 minus276 085 446

M = Rh Lnm = COM1 ani minus315 minus064 252 minus189 126 142M1 neu minus513 minus144 369 minus328 184 292Bim minus518 minus177 341 minus347 170 354

M = Re Lnm = bipy COM1 ani minus276 minus143 133 minus210 066 331M1 neu minus427 minus195 232 minus311 116 417Bim minus411 minus187 224 minus299 112 399

M = Re Lnm = COM1 ani minus308 minus064 244 minus186 122 142M1 neu minus553 minus138 415 minus346 208 288Bim minus562 minus239 323 minus401 162 497

anionic systems than for the neutral mononuclear onesexcept the anionic mononuclear system containing Ir andbipy as ancillary ligands

Taking into account these results it is observed that Rhand Re bimetallic compounds might act as templates to carryout catalytic applications such as CO2 reduction reactionsThese metals when forming part of these types of systems getrich in electron charge which is in concordance with the factthat the occupied FMOs are localized over the metals Thesefacts lead us to consider these systems as better reducingagents than the compounds with Ir

In order to rationalize the chemical reactivity a set ofglobal reactivity descriptors were computed in the frameworkof the conceptual density functional theory The estimatedchemical potential (120583) chemical hardness (120578) and elec-trophilicity (120596) have been analyzed [25ndash29] This set ofvalues is reported in Table 3 Moreover the HOMO andLUMO energies and the HOMO-LUMO energy gaps arereported For this analysis we restricted the discussion to thecomplexes that are considered the best templates for catalytic

reactions as stated above that is systems with Rh and ReCO and bipy as ancillary ligands and -CH3 as peripheralsubstituent

Parr defined 120583 in (1) as the infinitesimal change of energyof the system with respect to the electron number N ata constant external potential of the nuclei (V( 119903)) that isthe potential created by the nuclei 120583 is related with itselectronegativity as minus120594 and is associated with the feasibility ofa system to exchange electron density with the environmentat the ground state [25ndash29]120578 is calculated using the second-order derivative of thechemical potential (see (2)) and can be interpreted as theresistance of a molecule to change the electron density inpresence of other species

120583 = ( 120597119864120597119873)V( 119903) = minus120594 (1)

120578 = 12 (12059721198641205971198732)V( 119903) =

12 (120597120583120597119873)V( 119903) (2)


f+ nucleophilic attack

fminus electrophilic attack

(a)



(b)



(c)



(d)

Figure 3 Condensed Fukui functions for nucleophilic (119891+) and electrophilic (119891minus) attacks for compounds with metals (M) and ancillaryligands as follows (a) Rh and bipy (b) Rh and CO (c) Re and bipy CO and (d) Re and COThe neutral monometallic anionic monometallicand bimetallic complexes are shown

In numerical applications these reactivity indexes are calcu-lated following approximations using Koopmansrsquo theory andfinite differences leading to (3) Here I and A correspond tothe ionization energy and electron affinity while 119864(120587119867) and119864(120587119871) correspond to the orbital energies of the HOMO andLUMO respectively [25ndash28]

120583 asymp minus12 (119868 + 119860) asymp12 (119864 (120587119871) + 119864 (120587119867))

120578 asymp 12 (119868 minus 119860) asymp12 (119864 (120587119871) minus 119864 (120587119867))

(3)

The 120596 index as defined in (4) measures the tendency of amolecule to receive electronic charge from a donor species

Therefore120596 is considered as a sort of ldquoelectrophilicity powerrdquo[27ndash29]

120596 = 12058322120578 (4)

When bimetallic complexes are compared (see Table 3) thevalues of 120583 of systems with Rh and bipy (ndash276 eV) andcomplex with Re and bipy and CO (ndash299 eV) are higher thanvalues presented by systems with Rh Re and CO as ancillaryligands (ndash347 eV and ndash401 eV resp) This suggests biggerreactivity of the first two named complexes towards electrondonation Hence these complexes tend to react as source ofelectrons that enhance their possible behavior as catalytictemplates for reduction reactions such as the reduction of2CO2 to C2O4

2minus


It is worthmentioning that 120583 of themonometallic neutralspecies adopts values similar to 120583 of the bimetallic complexeswhich indicates that these systems can also act as strongelectron donors Finally the anionic mononuclear speciesdisplay the highest 120583 contemplated in the range of minus186 tominus210 eV

The 120578 decreases in the order mononuclear neutral gtbimetallicgt anionicmononuclear are reasonable with respectto the impact of the global reactivitypolarization indexesThe obtained trend indicates that the last two named systemsare more reactive In case of 120596 as expected the anionicmononuclear systems show the lowest 120596 values and increasefor the neutral and bimetallic compounds

In order to clarify the dependency of the reactivity withthe molecular structure we also analyzed the condensedFukui functions [25 30 31] In Figure 3 we included thewavefunctions for nucleophilic (119891+) and electrophilic (119891minus)attacks Considering that molecules may react with sitesthat show high or low electron density to carry out areaction the 119891minus plots depict that the metallic centers areable to follow a reaction pathway to carry out a reductionas they have high density of electrons These results areconsistent with the known reactivity of ferrocene (and manyother organometallic complexes) with any reducing specieswhere the reaction involves the formation of ferroceniumTherefore the reactivity of the herein studied moleculeswill depend on the interactions occurring in the metal ofthe complex with other species Although these results arenot a definitive evidence on how the mechanism of thechemical reactions might be they are useful to understandthe chemical behavior of the family of complexes

4 Conclusions

A theoretical study of a new family of organometallic com-plexes was carried out As it is observed the results indicatethat the bimetallic systems with Rh and Re holding ancillaryligands such as bipy and CO show the best properties to beactive in a chemical reactionThis is supported by the fact thatthe most electron-rich portion of the molecule correspondsto the metallic centers and the s-Ic ligand This is shown bythe localization of the FMOs the Mulliken charges and theFukui function plots Furthermore these complexes show thehighest reactivity indexes Specifically the results display thatthe bimetallic complexes containing Rh and bipy and Re withbipy and CO would tend to be strong electron donors in achemical reaction This behavior is also observed for theirmonometallic neutral species

Finally in addition to all previously discussed results ithas been stated that an appropriate M-M distance around543 A is an important parameter for a bimetallic compoundto be able to perform the reductive coupling of twomoleculesof CO2 to oxalate All the studied complexes show an M-Mdistance around this value which would suggest that thesecomplexes might show activity in this type of reactions

This study will continue employing more ligands andmetals including the formation of oxalate and then exper-iments will be carried out

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

The authors acknowledge the financial support from thefollowing projects Fondecyt (Grants 1141138 and 1161416)CONICYT Operating Expenses (Grant no 21110092) andMilenio (RC120001 and REDES150042)

References

[1] K Hafner ldquoStruktur und aromatischer charakter nichtbenzoi-der cyclisch konjugierter systemerdquoAngewandte Chemie vol 75pp 1041ndash1044 1963

[2] K Hafner ldquoMasaichi saito simetrıardquo Pure and Applied Chem-istry vol 2 pp 950ndash969 2010

[3] E E Bunel L Valle N L Jones et al ldquoBis((pentamethylcyclo-pentadienyl)metal)pentalenes A new class of highly delocal-ized fused metallocenesrdquo Journal of the American ChemicalSociety vol 110 no 19 pp 6596ndash6598 1988

[4] J M Manriquez M D Ward W M Reiff et al ldquoStruc-tural and physical properties of delocalized mixed-valent[CpM(pentalene)M1015840Cp]n+ and [CpM(indacene)M1015840Cp]n+(M M1015840 = Fe Co Ni n = 0 1 2) complexesrdquo Journal of theAmerican Chemical Society vol 117 no 23 pp 6182ndash6192 1995

[5] E Esponda C Adams F Burgos et al ldquoNew Rh derivativesof s-indacene active in dehydrogenative silylation of styrenerdquoJournal of Organometallic Chemistry vol 691 no 13 pp 3011ndash3017 2006

[6] C Morales-Verdejo I Martınez-Dıaz C Adams et al ldquoNewmono and bimetallic iron complexes derived from partiallymethylated s-indacene Evidence of a trinuclear iron s-indacenecomplexrdquo Polyhedron vol 69 pp 15ndash24 2014

[7] C Adams C Morales-Verdejo V Morales et al ldquoHeterobinu-clear s-indacene rhodium complexes synthesis and characteri-zationrdquo European Journal of Inorganic Chemistry no 6 pp 784ndash791 2009

[8] C Morales-Verdejo I Martinez D Mac-Leod Carey et alldquoSynthesis and structure of some heterobimetallic complexeshaving a polyalkyl-s-indacenyl spacerrdquo Inorganica ChimicaActa vol 394 pp 752ndash756 2013

[9] C Song ldquoGlobal challenges and strategies for control con-version and utilization of CO2 for sustainable developmentinvolving energy catalysis adsorption and chemical process-ingrdquo Catalysis Today vol 115 no 1ndash4 pp 2ndash32 2006

[10] J Notni S Schenk H Gorls H Breitzke and E AndersldquoFormation of a unique zinc carbamate by CO2 fixationimplications for the reactivity of tetra-azamacrocycle ligatedZn(II) complexesrdquo Inorganic Chemistry vol 47 no 4 pp 1382ndash1390 2008

[11] B Verdejo J Aguilar E Garcıa-Espana et al ldquoCO2 fixation byCu2+ and Zn2+ complexes of a terpyridinophane aza receptorCrystal structures of Cu2+ complexes pH-metric spectro-scopic and electrochemical studiesrdquo Inorganic Chemistry vol45 no 9 pp 3803ndash3815 2006

[12] A Gennaro A A Isse J-M Saveant M-G Severin andE Vianello ldquoHomogeneous electron transfer catalysis of theelectrochemical reduction of carbon dioxide Do aromatic


anion radicals react in an outer-sphere mannerrdquo Journal of theAmerican Chemical Society vol 118 no 30 pp 7190ndash7196 1996

[13] T Fujihara and Y Tsuji ldquoTransition metal-catalyzed fixation ofCarbon dioxide via carbon-carbon bond formationrdquo Journal ofthe Japan Petroleum Institute vol 59 no 3 pp 84ndash92 2016

[14] E Garcıa-Espana P Gavina J Latorre C Soriano and BVerdejo ldquoCO2 fixation by copper(II) complexes of a ter-pyridinophane aza receptorrdquo Journal of the American ChemicalSociety vol 126 no 16 pp 5082-5083 2004

[15] R Angamuthu P Byers M Lutz A L Spek and E BouwmanldquoElectrocatalytic CO2 conversion to oxalate by a copper com-plexrdquo Science vol 327 no 5963 pp 313ndash315 2010

[16] G A Van Albada I Mutikainen O Roubeau U Turpeinenand J Reedijk ldquoFerromagnetic trinuclear carbonato-bridgedand tetranuclear hydroxo-bridged Cu(II) compounds with441015840-dimethyl-221015840-bipyridine as ligand X-ray structure spec-troscopy andmagnetismrdquo Inorganica Chimica Acta vol 331 no1 pp 208ndash215 2002

[17] M J Frisch G W Trucks H B Schlegel et al Gaussian 09Revision E01 Gaussian Inc Wallingford Conn USA 2009

[18] A D Becke ldquoDensity-functional thermochemistry IIIThe roleof exact exchangerdquoThe Journal of Chemical Physics vol 98 no7 pp 5648ndash5652 1993

[19] P J Stephens F J Devlin C F Chabalowski and M J FrischldquoAb Initio calculation of vibrational absorption and circulardichroism spectra using density functional force fieldsrdquo Journalof Physical Chemistry vol 98 no 45 pp 11623ndash11627 1994

[20] W R Wadt and P J Hay ldquoAb initio effective core potentials formolecular calculations Potentials for main group elements Nato Birdquo The Journal of Chemical Physics vol 82 no 1 pp 284ndash298 1985

[21] P J Hay and W R Wadt ldquoAb initio effective core potentialsfor molecular calculations Potentials for K to Au including theoutermost core orbitalerdquo The Journal of Chemical Physics vol82 no 1 pp 299ndash310 1985

[22] P J Hay and W R Wadt ldquoAb initio effective core potentials formolecular calculations Potentials for the transitionmetal atomsSc toHgrdquoThe Journal of Chemical Physics vol 82 no 1 pp 270ndash283 1985

[23] M J Frisch J A Pople and J S Binkley ldquoSelf-consistentmolecular orbital methods 25 Supplementary functions forGaussian basis setsrdquo The Journal of Chemical Physics vol 80no 7 pp 3265ndash3269 1984

[24] M Cossi N Rega G Scalmani and V Barone ldquoEnergiesstructures and electronic properties of molecules in solutionwith the C-PCM solvation modelrdquo Journal of ComputationalChemistry vol 24 no 6 pp 669ndash681 2003

[25] L R Domingo M Rıos-Gutierrez and P Perez ldquoApplicationsof the conceptual density functional theory indices to organicchemistry reactivityrdquoMolecules vol 21 no 6 article 748 2016

[26] R G Pearson ldquoThe electronic chemical potential and chemicalhardnessrdquo Journal of Molecular Structure THEOCHEM vol255 pp 261ndash270 1992

[27] R G Parr L V Szentpaly and S Liu ldquoElectrophilicity indexrdquoJournal of the American Chemical Society vol 121 no 9 pp1922ndash1924 1999

[28] X Zarate E Schott T Gomez and R Arratia-Perez ldquoThe-oretical study of sensitizer candidates for dye-sensitizedsolar cells peripheral substituted dizinc pyrazinoporphyrazine-phthalocyanine complexesrdquo The Journal of Physical ChemistryA vol 117 pp 430ndash438 2013

[29] P K Chattaraj and S Giri ldquoElectrophilicity index within aconceptual DFT frameworkrdquo Annual Reports on the Progress ofChemistrymdashSection C vol 105 pp 13ndash39 2009

[30] C E Diaz-Uribe W Vallejo W Castellar et al ldquoNovel (E)-1-(pyrrole-2-yl)-3-(aryl)-2-(propen-1-one) derivatives as efficientsinglet oxygen quenchers Kinetics and quantum chemicalcalculationsrdquo RSC Advances vol 5 no 88 pp 71565ndash715722015

[31] L Arrue T Barra M B Camarada X Zarate and ESchott ldquoElectrochemical and theoretical characterization ofthe electro-oxidation of dimethoxycurcuminrdquoChemical PhysicsLetters vol 677 pp 35ndash40 2017

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RR

(a)

- RR -

(b)

RR

MLn Lm

(c)

RR

M

-

Ln Lm

(d)

RR

M MLn LnLm Lm

(e)

Figure 1 Structures of the studied systems (a) Neutral ligand (b) dianion ligand and (c) neutral monometallic (d) monoanionmonometallic and (e) bimetallic systems R = H CH3 and CH2CH3 M = Ir Rh and Re Lm and Ln = bipy CO with m and n = 0 1 23

compounds have been studied showing a wide variationof results [9ndash12] The most important conclusion of thesereports is that for systems where the coordination of CO2is not reversible the ability to transform CO2 into othercompounds depends on the extent of the charge transfer fromthe transitionmetal to CO2 If themetal transfers an electronthe formation of C-C bonds is possible and the rigidity ofthe bimetallic system seems to play an essential role in theformation of this bond [13 14] In this sense interestinglyone of themost innovativeworks in the area of CO2 reductionreported by Angamuthu et al in 2010 consists in the synthesisof a tetranuclear complex of Cu(I) with the ligand N-(2-mercaptopropyl)-NN-bis(2-pyridylmethyl)amine whichspontaneously and selectively captures CO2 from the air[15] Cu(I) gets oxidized to Cu(II) and a bridge of oxalateis formed which links two binuclear complexes forming atetramer Adding a lithium salt to the solution allows thequantitative precipitation of lithiumoxalate Finally theCu(I)complex can be recovered by electrochemical reduction Thecrystallographic study of the Cu complex showed that the Cu-Cudistance in the complexwas 543 AThis distance is similarto the Rh-Rh distance observed in a syn binuclear com-plex synthesized by our group [(26-diethyl-48-dimethyl-s-indacenediide) Rh (COD)2] [16] of about 55 A

The largemajority of the examples of binuclear complexeswith s-indacene reported in the literature show the twometalscenters in an anticonfiguration This is due mostly to thesteric bulk imposed by the ancillary ligands In this workwe propose that it is possible to avoid the anticonfigurationby blocking one of the faces of the s-indacene introducing agroup that can effectively obstruct the access of the metalsto both faces forcing them to adopt the syn configurationThis could be easily achieved by constructing a cyclophanestructure over the plane of the rings as shown in Figure 1

Therefore in order to have the right template structurefor coupling reactions in those compounds and to favor the

reaction the right Metal-Metal (M-M) distance electronicconfiguration and lability of the ligand coordinated to themetal center (ancillary ligands) are needed Specificallybinuclear metal frameworks could play an important roleas templates for these types of reactions such as selectivereductive coupling of two molecules of CO2 to oxalate

Inspired by the work of Bouwman et al and the versatileindacene derivatives we decided to propose templates withsynthetical feasibility consisting in a family of binuclearmetal complexes

The aim of this work is to evaluate the effect of differenttransition metals (Ir Rh and Re) different ancillary ligands(bipy and CO) and -R groups (CH3 and CH2CH3) (Figure 1)over the electronic properties assessing the Frontier Molec-ular Orbitals (FMOs) location the geometrical parametershighlighting the M-M distance the global reactivity indexesthe atomic metal charges and the Fukui functions This pre-liminary study could lead experimentalist to have a hint aboutwhich metallic s-indacenyl complexes ancillary ligands andperipheral substituents might show suitable properties for avariety of chemical applications

2 Computational Details

Quantum chemical calculations were performed in orderto further investigate the electronic structure of a family ofcompounds in the ground state Density functional theory(DFT) as implemented in Gaussian 09 [17] software was usedto perform the calculations of the studied systemsThe Beckethree-parameter hybrid functional combined with Lee-Yang-Parr correlation B3LYP [18 19] was employedThe relativisticeffects of the heavy metals were incorporated using thepseudopotential LANL2DZ [20ndash22] and the Gaussian basissets 6-31G(d) were used for the nonmetallic atoms [23] Withthe aimof getting theminimapoints over the potential energysurface of the proposed compounds themolecular structures



(a)



(b)



RR

M1 M2

1

23

9

10

8

4

12 76

511

Ln LmLn Lm

Scheme 1









170

148

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

(c) (d) (e)

205

minus9

minus8

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1En

ergy

(eV

)















(a)



H 0351 0300 0297 0300 0156 0157 0152 0157 0289 0312 0315 0323CH3 0351 0299 0290 0295 0162 0159 0148 0152 0284 0308 0304 0312CH2CH3 0349 0298 0287 0295 0151 0048 0142 0147 0278 0301 0300 0309

(b)















120583 = ( 120597119864120597119873)V( 119903) = minus120594 (1)

120578 = 12 (12059721198641205971198732)V( 119903) =

12 (120597120583120597119873)V( 119903) (2)




(a)



(b)



(c)



(d)





(3)



120596 = 12058322120578 (4)


2minus





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



(a)



(b)



RR

M1 M2

1

23

9

10

8

4

12 76

511

Ln LmLn Lm

Scheme 1









170

148

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

(c) (d) (e)

205

minus9

minus8

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1En

ergy

(eV

)















(a)



H 0351 0300 0297 0300 0156 0157 0152 0157 0289 0312 0315 0323CH3 0351 0299 0290 0295 0162 0159 0148 0152 0284 0308 0304 0312CH2CH3 0349 0298 0287 0295 0151 0048 0142 0147 0278 0301 0300 0309

(b)















120583 = ( 120597119864120597119873)V( 119903) = minus120594 (1)

120578 = 12 (12059721198641205971198732)V( 119903) =

12 (120597120583120597119873)V( 119903) (2)




(a)



(b)



(c)



(d)





(3)



120596 = 12058322120578 (4)


2minus





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


170

148

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

HOMOminus1

LUMO

HOMO

LUMO+1

(c) (d) (e)

205

minus9

minus8

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1En

ergy

(eV

)















(a)



H 0351 0300 0297 0300 0156 0157 0152 0157 0289 0312 0315 0323CH3 0351 0299 0290 0295 0162 0159 0148 0152 0284 0308 0304 0312CH2CH3 0349 0298 0287 0295 0151 0048 0142 0147 0278 0301 0300 0309

(b)















120583 = ( 120597119864120597119873)V( 119903) = minus120594 (1)

120578 = 12 (12059721198641205971198732)V( 119903) =

12 (120597120583120597119873)V( 119903) (2)




(a)



(b)



(c)



(d)





(3)



120596 = 12058322120578 (4)


2minus





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



(a)



H 0351 0300 0297 0300 0156 0157 0152 0157 0289 0312 0315 0323CH3 0351 0299 0290 0295 0162 0159 0148 0152 0284 0308 0304 0312CH2CH3 0349 0298 0287 0295 0151 0048 0142 0147 0278 0301 0300 0309

(b)















120583 = ( 120597119864120597119873)V( 119903) = minus120594 (1)

120578 = 12 (12059721198641205971198732)V( 119903) =

12 (120597120583120597119873)V( 119903) (2)




(a)



(b)



(c)



(d)





(3)



120596 = 12058322120578 (4)


2minus





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




(a)



(b)



(c)



(d)





(3)



120596 = 12058322120578 (4)


2minus





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





4 Conclusions






Acknowledgments


References











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

study of the molecular properties of mono- and binuclear metal s...

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