Coordination-Dependent Spectroscopic Signatures of Divalent Metal

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Letter

Coordination-Dependent Spectroscopic Signatures of Divalent Metal Ion Binding to Carboxylate Head Groups: H-and He-Tagged Vibrational Spectra of M ·RCO¯ (M = Mg and Ca, R = -CD, -CDCD) Complexes 2

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Joseph W. DePalma, Patrick J. Kelleher, Laís C. Tavares, and Mark A. Johnson J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b02964 • Publication Date (Web): 06 Jan 2017 Downloaded from http://pubs.acs.org on January 10, 2017

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The Journal of Physical Chemistry Letters

Coordination-Dependent Spectroscopic Signatures of Divalent Metal Ion Binding to Carboxylate Head Groups: H2-and He-Tagged Vibrational Spectra of M2+·RCO2¯ (M = Mg and Ca, R = -CD3, -CD2CD3) Complexes Joseph W. DePalma,1 Patrick J. Kelleher,1 Laís C. Tavares2 and Mark A. Johnson*1 1

Sterling Chemistry Laboratory, Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT 06520 2

Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, São Paulo, CEP 05508900, Brazil Abstract We explore the intramolecular distortions present in divalent metal ion-carboxylate ion pairs using vibrational spectroscopy of the cryogenically cooled, mass-selected species isolated in the gas phase. The spectral signatures of the C-O stretching modes are identified using the perdeutero isotopologues of the acetate and propionate anions in order to avoid congestion arising from the CH2 fundamentals. Both Ca2+ and Mg2+ are observed to bind in a symmetrical, so-called “bidentate” arrangement to the –CO2¯ group. The very strong deformations of the head groups displayed by the binary complexes dramatically relax when either neutral water molecules or counter ions are attached to the Mg2+RCO2¯ cation. These results emphasize the critical role that local coordination plays when using the RCO2¯ bands to deduce the metal ion complexation motif in condensed media.

TOC Graphic

* Email: [email protected]

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Divalent metal ion binding onto carboxylate ligands is an important structural motif in biochemistry,1-4 metal organic frameworks (MOFs),5-6 and aerosol chemistry.7-10 This interaction can

Chart 1. Schematic of three possible binding motifs between a metal ion and a carboxylate ligand: (A) bidentate, (B) monodentate and (C) bridging.

be divided into three major classifications: bidentate, when the CO2¯ interacts with the metal ion equally through both oxygen atoms (Chart 1A); monodentate, where only one oxygen atom interacts with the metal (Chart 1B); and bridging, where each oxygen atom interacts with a separate metal ion (Chart 1C). Deacon and Philips11 proposed an empirical rule correlating the splitting between the antisymmetric ( ) and symmetric ( ) stretching frequencies (∆νa-s = - ) to the local binding motif in crystalline metal acetates which has proven valid in a

limited number of simple aqueous systems.12-13 The coordination environment for which spectra were recorded in solution phase studies was often not clearly defined, and structural assignments of the binding motifs relied on solid state crystal structures of neutral species with complete coordination around the divalent metal ion from other (both charged and neutral) ligands.11 Theoretical efforts1, 13-14 to understand the microscopic origin of the correlation between binding motif and ∆νa-s have, on the other hand, focused on isolated and hydrated (with both explicit water molecules and continuum solvation) cationic M2+-RCO2¯ ion pairs which, prior to this study, have not been directly measured. Such ion pairs are considered to be the most relevant species in the context of the interfacial chemistry of sea spray aerosols, where Ca2+ and Mg2+ are postulated to be layered below carboxylate surfactants at the air-water interface.7-10 Here we determine the behavior of the cationic ion pairs through analysis of linear infrared action spectra of the isolated 20 K [M2+CD3CD2CO2¯]+ (M = Mg, Ca) contact ion pairs obtained using the


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messenger tagging IR photodissociation (IRPD) technique.14 We then explore how these binary interactions are modulated with increasing coordination of both neutral and charged ligands in the fully coordinated [Mg2+CD3CD2CO2¯]+·(H2O)4 and [Mg2+(CD3CO2¯)3]¯ clusters. We focus on the CH3CH2CO2¯ anion (OPr) in order to capture features associated with the hydrocarbon tails in surfactant spectra.8, 10, 15-16 We further concentrate on its perdeuterated isotopologue CD3CD2CO2¯ (d-OPr) because the C-H bending fundamentals are close to the C-O stretching fundamentals of the carboxylate group,8, 10 and indeed could further complicate spectral patterns by mixing with the C-O stretching modes. In fact, the CD3CD2CO2¯ ion was selected for this report precisely because it can be readily understood at the harmonic level. Figure 1A presents the H2-predissociation spectrum of d-OPr in the CO2¯ stretching region, with the positions of the and

bands reported previously for OPr using IRMPD at 293 K indicated by arrows ( (red) and (blue)).17 Positions

of all transitions presented in Fig. 1 can be

Figure 1. Vibrational predissociation spectra of (A) dOPr¯·H2, (C) d-[CaOPr]+·He and (E) d-[MgOPr]+·He with the scaled (0.976) harmonic spectra of the tagged species inverted below the corresponding experimental spectra in (B), (D) and (F). Inset are calculated structures with the calculated Rcc and OCO angles. The arrows in trace A point to the (red) and (blue) band positions from the IRMPD study of the isolated CH3CH2CO2¯ ion.17

found in Tables S1 and S2.



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Figure 1 also presents the He-predissociation spectra of the contact ion pairs d[CaOPr]+·He (Fig. 1C) and d-[MgOPr]+·He (Fig. 1E), with the corresponding calculated (CAMB3LYP/6-311++G(3df,3pd)) harmonic spectra inverted below each trace. In both cases, the widely split CO2¯ stretches observed in d-OPr (Fig. 1A) are replaced by an asymmetric doublet centered roughly below the midpoint of the isolated anion bands. These strong spectral responses are accurately captured by harmonic calculations (Fig. 1D, F). In particular, the predicted spectra recover the relative intensities of the two components comprising the doublets, where the weaker transition (red) is attributed to the symmetric stretch ( ). As such, we conclude that the energy ordering between the and bands in the binary metal-ion

complexes is in fact inverted relative to those in the isolated d-OPr anion, with values of ∆νa-s = 30 cm-1 and -34 cm-1 for Ca2+ and Mg2+, respectively. The inversion of the energy ordering of the carboxylate stretching modes was predicted in a theoretical report from Dudev and Lim1 at the harmonic level, and is experimentally confirmed here for the first time. As discussed further below, they traced this effect to strong mixing between mode and the C-C stretch involving the carboxylate carbon atom. Note that the antisymmetric stretch displays the largest response upon complexation, with a red-shift of over 200 cm-1 in both the d-[CaOPr]+ and d-[MgOPr]+ complexes. Three factors have been invoked to explain the metal-induced band shifts in previous theoretical analyses1, 18-21 of the binary systems: reduction in the OCO bond angle, strong mixing between the C-C stretching and the modes, and lowering of the force constant for the C-O stretch. The calculated structural features associated with these effects are listed in Table S3. For example, Sutton and co-workers18 have quantified the relationship between the C-O bond length and with a Badger’s rule-type correlation, and the calculated 0.03-0.035 Å C-O


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bond length increases in d-[MgOPr]+ and d-[CaOPr]+ are consistent with that trend. This bond elongation effect presumably reflects increasing electron density on the –CO2 head group, which is accommodated in an anti-bonding orbital. The situation regarding the is more complicated, however, as the calculated displacement vectors (Fig. S1) for this mode are dominated by contraction of the C1-C2 bond in both metal complexes, while the displacements of the O atoms attached to C1 are minimal. This is in sharp contrast to the situation in the isolated d-OPr ion, where the displacement of the O atoms is similar to that of the C-C stretch. The character of the motion associated with the band nominally associated with the is thus quite different in the free and metal bound carboxylates such that the ∆νa-s splitting does not reflect the coupling between the two CO oscillators. An interesting structural feature that is correlated with the C-C/C-O mode mixing evident in the composition of the normal modes is the C1-C2 bond distance, Rcc. Specifically, Rcc in dOPr is calculated to undergo a ~0.065 Å contraction upon complexation with M2+, resulting in a 53 cm-1 blue shift of the C-C stretch in d-[CaOPr]+ (and 79 cm-1 in d-[MgOPr]+) relative to the bare ion. The Rcc contraction is reminiscent of the behavior displayed by the simpler HCO2¯ ion, in which the addition of a single water molecule induces a ~104 cm-1 blue shift of the C-H stretch frequency relative to the value for the isolated ion in the gas phase (~2450 cm-1).22 This shift was correlated with the potential surface for C-H dissociation, where homolytic bond cleavage leading to CO2¯ + H· lies about 1.35 eV higher in energy than adiabatic dissociation yielding CO2 + H¯ products. The solvatochromic shift was then explained in the context of the water molecule drawing electron density toward the CO2¯ head group and raising the dissociation energy to the adiabatic dissociation pathway, thus stabilizing the C-H bond. As such, the C-H bond contraction upon solvation of the anion reflects strengthening of the anomalously weak C-



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H bond in bare anion. Metal complexation to d-OPr thus appears to similarly strengthen the bond between the carboxylate (C1) and CH2 (C2) carbon atoms to yield an Rcc value closer to that expected (~1.5 Å) for bond between atoms with sp2-sp3 hybridization.23 Finally, we remark that the ~11° contraction of the OCO bond angle plays only a minor role in the behavior of the CO2¯ stretches, as illustrated by the comparison of the calculated spectra at fixed OCO bond angles displayed in Fig. S2. The response of the RCO2¯ anion to metal ion complexation can be understood in the context of the mechanical contributions to its polarizability. The strong local fields at play in the M2+·RCO2¯ contact ion pairs contract RCC while elongating the C-O bonds, leading to very large red-shifts in the bands, while field-induced mixing between the C-C and C-O stretches

leads to a smaller perturbation of the transition nominally assigned to . Interestingly, despite the large differences in the radii of the Mg2+ and Ca2+ ions (and hence, the electric fields operative in the ion pair interactions), the overall response of the C-O stretches is quite similar for both metal complexes. Interestingly, we note that ∆νa-s recently reported for contact ion pairs between a monovalent lithium cation and phenyl-tagged carboxylate anions (∆νa-s = ~115 cm-1) lies much closer to that of the bare anion, further supporting the model of the field-dependent response of the C-O stretches.24 We now consider how solvation modifies the intrinsic spectral signatures of the binary metal ion complexes.11-12, 25-27 Figure 2 presents the vibrational spectra of the H2-tagged, d-[MgOPr]+·(H2O)n=0-4 clusters, with the transitions collected in Table S4. Fig. S3 displays the spectra of [MgOAc]+·(H2O)n=0-5 in the O-H stretching region, which supports the widely accepted conclusion the Mg2+ ion resides in a hexacoordinate environment.28-32 The new feature

highest in energy in the d-[MgOPr]+·(H2O)n=1-4 clusters, labeled as in Fig. 2B, corresponds


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to the bending motion of the water molecules, which appears as a single feature that gradually red-shifts towards its position (dashed line in Fig. 2) in an isolated water molecule.33 This behavior suggests that all water molecules in the first hydration shell of Mg2+ respond uniformly to increasing coordination around the metal center, in agreement with conclusions reached by Williams34-35 and Armentrout36-37, who confirmed the hexacoordinate geometry around the Mg2+ ion in the gas phase.

Figure 2. (B-E) H2-tagged predissociation spectra of d[MgOPr]+·(H2O)n (n = 1-4) (Trace A is the binary pair reproduced from Fig. 1E). Red and blue arrows in trace A indicate positions of the and bands in d-OPr from the current study. Inset into traces B and E are calculated structures corresponding to the monohydrate and tetrahydrate. The purple dashed line indicates the location of the water bend

( ) in the isolated water molecule (1595 cm-1).33

Turning to the C-O stretching region, the asymmetrical doublet assigned to the antisymmetric (blue) and symmetric

(red) stretches in the bare complex (Fig. 2A), first merge into a broad feature at slightly higher energy in the monohydrate before splitting apart into a clearly spaced doublet with the opposite intensity profile at n = 4. This behavior is anticipated at the harmonic level with the spectra included in Fig. S4 for the lowest energy calculated structures. These structures have been reported13,38 to be well isolated from other local minima for n ≤ 4 , which corresponds to completion of the first hydration shell. The calculated pattern indicates that (red) remains the weaker fundamental and displays a very small solvation shift, while the stronger



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transition exhibits a large incremental blue shift upon addition of each water molecule. The

two fundamentals thus cross over each other in the range n = 1 to 2 to recover the ordering in the isolated ion (arrows in Fig. 2A). This evolution can again be understood in the context of the anion polarizability discussed above in a scenario where the water molecules act to weaken the electric field at the d-OPr binding site, thus allowing the d-OPr to relax back towards its isolated geometry. This is evidenced by the calculated incremental opening of the OCO bond angle, the lengthening of the RCC and the shortening of the C-O bonds as tabulated in Table S5. The

again behaves according to the Badger’s rule correlation of Sutton and coworkers.18 This relaxation of the species in the primary hydration shell around divalent ions has been reported earlier for CuOH+·(H2O)n,39 where the very strong blue shift of the OH¯ ion stretch is reduced with sequential hydration. This indicates the strong induced dipoles on each water molecule in the first hydration shell act to oppose the net field acting at the carboxylate group as well as at the water molecules, with the net effect of relaxing all constituents in the primary hydration shell closer to their isolated structures. Generally, stepwise hydration of the binary d-[MgOPr]+ ion pair results in incremental relaxation of the both the carboxylate group and solvating water molecules. The electric field cancellation model for the behavior of the binary ion pair upon microhydration raises the question of how the system will respond when additional anionic species are present in the first coordination shell. The coordination of multiple ligands to a divalent metal ion is a fundamental motif in the rational design of many MOFs.40 Figure 3 presents the predissociation spectrum of the d-[Mg(OAc)3]¯·H2 cluster, with the spectra of the d[MgOAc]+·He and d-OAc·H2 species included for comparison. Assignments are based on harmonic calculations (Fig. 3D) from the minimum energy structure shown in the inset.


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The d-[Mg(OAc)3]¯ structure features a symmetrical arrangement in which each d-OAc ligand binds to the Mg2+ in a bidentate fashion such that the Mg2+ ion is hexacoordinated. This arrangement is consistent with X-ray crystal structures of numerous Mg2+ salts.30, 41 The fundamentals derived from the stretches in the d-

[Mg(OAc)3]¯ spectrum appear as an asymmetric doublet (split by 30 cm-1) arising from the degenerate, out-of ) and non-degenerate inphase (, phase (, ) antisymmetric stretches

on each anion. The in-phase feature highest in energy now appears very close to the fundamental in the

isolated d-OAc anion, confirming that ionic coordination dramatically suppresses the intrinsic distortions in the isolated ion pair. The calculated

Figure 3. Vibrational predissociation spectra of (A) dOAc·H2, (B) d-[MgOAc]+·He, (C) d-[Mg(OAc)3]¯·H2 and (D) the calculated (scaled by 0.976) harmonic spectrum of d-[Mg(OAc)3]¯·H2. Inset into trace (D) is the calculated structure for d-[Mg(OAc)3]¯ with the OCO angles and C1 O lengths indicated. The bands associated with are colored blue while those derived from are red. The features labeled (‡) in (B) and (C) appear to arise from the acetate scaffold but are not assigned here.

structure indicates the key structural feature underlying this relaxation in the d-[Mg(OAc)3]¯ cluster is contraction of the C1-O bonds from 1.280 to 1.256 Å . Finally, we remark that the ~150 cm-1 ∆νa-s value for the bidentate d-[Mg(OAc)3]¯ species lies in the range assigned to a “bridging” structure from the trends noted by Deacon and Phillips.11 This highlights the importance of taking into consideration the entire coordination



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environment when attempting to determine the binding motif through the location of the C-O stretching bands. Interestingly, the band has red-shifted from its position in the binary pair by only 20 cm-1 in the d-[Mg(OAc)3]¯ cluster. It is thus clear the is relatively insensitive to the coordination environment, while large changes in directly report on the local

interactions at play in the metal ion complexes. We note that there is an additional feature (‡) at 1463 cm-1 that does not appear to be dependent on the metal. This feature is also observed in the He-tagged spectra of d-[CaOAc]+ and d-[MgOAc]+ (shown in Fig. S5) in approximately the same location. This band is not anticipated by calculations at either the harmonic or VPT2 level. Summarizing, Mg2+ and Ca2+ ions are observed to bind to the carboxylate head group in a bidentate fashion, leading to very strong intramolecular distortions of the molecular anions in the binary complexes as evidenced by very large shifts in the C-O stretching features. These distortions are similar for both metals despite their different radii. The intramolecular distortion present in the ion pair is quickly suppressed, however, when either water molecules or additional RCO2¯ groups are introduced which saturate the Mg2+ ion with hexacoordinate ligation. These observations emphasize the critical role that local coordination plays in determining the binding motif between the metal and the carboxylate head group through the behavior of the C-O stretching fundamentals. This information is especially important in the interpretation of surface-specific vibrational spectroscopies to infer how alkaline earth cations to bind to surfactants.8,10,15,16,42,43


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Acknowledgments M.A.J. thanks the National Science Foundation through the Centers for Chemical Innovation Program under grant CHE-1305427 (Center for Aerosol Impacts on Climate and the Environment, CAICE) for support of this work. L.C.T acknowledges the Santander International Mobility Program (486/2015) for travel expenses.

Supplemental Information available: Experimental and computational details, tabulated structural parameters and vibrational transitions, supplemental theoretical and experimental spectra and Cartesian coordinates of all ions and clusters are provided. A brief discussion on the influence of carboxylate chain length is included accompanying Figure S5.



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References (1) Dudev, T.; Lim, C. The Effect of Metal Binding on the Characteristic Infrared Band Intensities of Ligands of Biological Interest. J. Mol. Struct. 2012, 1009, 83-88. (2) Lewandowski, W.; Kalinowska, M.; Lewandowska, H. The Influence of Metals on the Electronic System of Biologically Important Ligands: Spectroscopic Study of Benzoates, Salicylates, Nicotinates and Isoorotates. Review. J. Inorg. Biochem. 2005, 99, 1407-1423. (3) Grabarek, Z. Insights Into Modulation of Calcium Signaling by Magnesium in Calmodulin, Troponin C and Related EF-Hand Proteins. Biochim. Biophys. Acta - Mol. Cell. Res. 2011, 1813, 913-921. (4) Cates, M. S.; Teodoro, M. L.; Phillips, G. N. Molecular Mechanisms of Calcium and Magnesium Binding to Parvalbumin. Biophys. J. 2002, 82, 1133-1146. (5) Sumida, K.; Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T. H.; Long, J. R. Carbon Dioxide Capture in Metal-Organic Frameworks. Chem. Rev. 2012, 112, 724-781. (6) Howarth, A. J.; Liu, Y.; Li, P.; Li, Z.; Wang, T. C.; Hupp, J. T.; Farha, O. K. Chemical, Thermal and Mechanical Stabilities of Metal-Organic Frameworks. Nat. Rev. Mat. 2016, 1, 1-15. (7) Guasco, T. L.; Cuadra-Rodriguez, L. A.; Pedler, B. E.; Ault, A. P.; Collins, D. B.; Zhao, D. F.; Kim, M. J.; Ruppel, M. J.; Wilson, S. C.; Pomeroy, R. S.; et al. Transition Metal Associations with Primary Biological Particles in Sea Spray Aerosol Generated in a Wave Channel. Environ. Sci. Technol. 2014, 48, 1324-1333. (8) Tang, C. Y.; Huang, Z. S.; Allen, H. C. Interfacial Water Structure and Effects of Mg2+ 2+ and Ca Binding to the COOH Headgroup of a Palmitic Acid Monolayer Studied by Sum Frequency Spectroscopy. J. Phys. Chem. B 2011, 115, 34-40. (9) Ault, A. P.; Guasco, T. L.; Ryder, O. S.; Baltrusaitis, J.; Cuadra-Rodriguez, L. A.; Collins, D. B.; Ruppel, M. J.; Bertram, T. H.; Prather, K. A.; Grassian, V. H. Inside Versus Outside: Ion Redistribution in Nitric Acid Reacted Sea Spray Aerosol Particles as Determined by Single Particle Analysis. J. Am. Chem. Soc. 2013, 135, 14528-14531. (10) Tang, C. Y.; Huang, Z.; Allen, H. C. Binding of Mg2+ and Ca2+ to Palmitic Acid and Deprotonation of the COOH Headgroup Studied by Vibrational Sum Frequency Generation Spectroscopy. J. Phys. Chem. B 2010, 114, 17068-17076. (11) Deacon, G. B.; Phillips, R. J. Relationships Between the Carbon-Oxygen Stretching Frequencies of Carboxylate Complexes and the Type of Carboxylate Coordination. Coord. Chem. Rev. 1980, 33, 227-250. (12) Tackett, J. E. FT-IR Characterization of Metal Acetates in Aqueous Solution. Appl. Spectrosc. 1989, 43, 483-489. (13) Nara, M.; Torii, H.; Tasumi, M. Correlation Between the Vibrational Frequencies of the Carboxylate Group and the Types of Its Coordination to a Metal Ion: An ab initio Molecular Orbital Study. J. Phys. Chem. 1996, 100, 19812-19817. (14) Wolk, A. B.; Leavitt, C. M.; Garand, E.; Johnson, M. A. Cryogenic Ion Chemistry and Spectroscopy. Acc. Chem. Res. 2014, 47, 202-210. (15) Adams, E. M.; Allen, H. C. Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry. Atmosphere 2013, 4, 315-336. (16) Robertson, E. J.; Beaman, D. K.; Richmond, G. L. Designated Drivers: The Differing Roles of Divalent Metal Ions in Surfactant Adsorption at the Oil-Water Interface. Langmuir. 2013, 29, 15511-15520. 12 ACS Paragon Plus Environment

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(17) Steill, J. D.; Oomens, J. Action Spectroscopy of Gas-Phase Carboxylate Anions by Multiple Photon IR Electron Detachment/Attachment. J. Phys. Chem. A 2009, 113, 4941-4946. (18) Sutton, C. C. R.; da Silva, G.; Franks, G. V. Modeling the IR Spectra of Aqueous Metal Carboxylate Complexes: Correlation between Bonding Geometry and Stretching Mode Wavenumber Shifts. Chem. Eur. J. 2015, 21, 6801-6805. (19) Tafipolsky, M.; Schmid, R. A Consistent Force Field for the Carboxylate Group. J. Chem. Theory Comput. 2009, 5, 2822-2834. (20) Dudev, T.; Lim, C. Effect of Carboxylate-Binding Mode on Metal Binding/Selectivity and Function in Proteins. Acc. Chem. Res. 2007, 40, 85-93. (21) Mehandzhiyski, A. Y.; Riccardi, E.; van Erp, T. S.; Koch, H.; Astrand, P. O.; Trinh, T. T.; Grimes, B. A. Density Functional Theory Study on the Interactions of Metal Ions With Long Chain Deprotonated Carboxylic Acids. J. Phys. Chem. A 2015, 119, 10195-10203. (22) Gerardi, H. K.; DeBlase, A. F.; Su, X.; Jordan, K. D.; McCoy, A. B.; Johnson, M. A. Unraveling the Anomalous Solvatochromic Response of the Formate Ion Vibrational Spectrum: An Infrared, Ar-Tagging Study of the HCO2¯, DCO2¯, and HCO2¯·H2O Ions. J. Phys. Chem. Lett. 2011, 2, 2437-2441. (23) Loudon, M. Organic Chemistry; Roberts and Company: Greenwood Village, CO; 2009. (24) Habka, S.; Brenner, V.; Mons, M.; Gloaguen, E. J. Phys. Chem. Lett. 2016, 7, 11921197. (25) Purdie, N.; Barlow, A. J. Ultrasonic Absorption by Aqueous Magnesium and Calcium Acetate Solutions. J. Chem. Soc., Faraday Trans. 2 1972, 68, 33-40. (26) Mizuguchi, M.; Nara, M.; Kawano, K.; Nitta, K. FT-IR Study of the Ca2+-Binding to Bovine Alpha-Lactalbumin - Relationships Between the Type of Coordination and Characteristics of the Bands Due to the Asp COO- Groups in the Ca2+-Binding Site. FEBS Lett. 1997, 417, 153-156. (27) Edwards, D. A.; Hayward, R. N. Transition Metal Acetates. Can. J. Chem. 1968, 46, 3443-3349. (28) Neilson, G. W.; Enderby, J. E. The Coordination of Metal Aquaions. Adv. Inorg. Chem. 1989, 34, 195-218. (29) Skipper, N. T.; Neilson, G. W. X-Ray and Neutron-Diffraction Studies on Concentrated Aqueous Solutions of Sodium Nitrate and Silver Nitrate. J. Phys.: Condens. Matter 1989, 1, 4141-4154. (30) Batsanov, A. S. Magnesium Sulfate Hexahydrate at 120 K. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2000, 56, E230-E231. (31) Johnson, C. J.; Dzugan, L. C.; Wolk, A. B.; Leavitt, C. M.; Fournier, J. A.; McCoy, A. B.; Johnson, M. A. Microhydration of Contact Ion Pairs in M2+OH-(H2O)n=1-5 (M = Mg, Ca) Clusters: Spectral Manifestations of a Mobile Proton Defect in the First Hydration Shell. J. Phys. Chem. A 2014, 118, 7590-7597. (32) DePalma, J. W.; Kelleher, P. J.; Johnson, C. J.; Fournier, J. A.; Johnson, M. A. Vibrational Signatures of Solvent-Mediated Deformation of the Ternary Core Ion in SizeSelected [MgSO4Mg(H2O)n=4-11]2+ Clusters. J. Phys. Chem. A 2015, 119, 8294-8302. (33) Tennyson, J.; Bernath, P. F.; Brown, L. R.; Campargue, A.; Csaszar, A. G.; Daumont, L.; Gamache, R. R.; Hodges, J. T.; Naumenko, O. V.; Polyansky, O. L.; et al. IUPAC Critical Evaluation of the Rotational-Vibrational Spectra of Water Vapor, Part III: Energy Levels and Transition Wavenumbers for (H2O)-O16. vJ. Quant. Spectrosc. Radiat. Transfer 2013, 117, 2958. 13 ACS Paragon Plus Environment


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(34) Bush, M. F.; O'Brien, J. T.; Prell, J. S.; Wu, C. C.; Saylkally, R. J.; Williams, E. R. Hydration of Alkaline Earth Metal Dications: Effects of Metal Ion Size Determined Using Infrared Action Spectroscopy. J. Am. Chem. Soc. 2009, 131, 13270-13277. (35) Rodriguez-Cruz, S. E.; Jockusch, R. A.; Williams, E. R. Hydration Energies and Structures of Alkaline Earth Metal Ions, M2+(H2O)n, n=5-7, M = Mg, Ca, Sr, and Ba. J. Am. Chem. Soc. 1999, 121, 8898-8906. (36) Carl, D. R.; Armentrout, P. B. Threshold Collision-Induced Dissociation of Hydrated Magnesium: Experimental and Theoretical Investigation of the Binding Energies for Mg2+(H2O)x Complexes (x=2–10). ChemPhysChem. 2013, 14, 681-697. (37) Carl, D. R.; Armentrout, P. B. Experimental Investigation of the Complete Inner Shell Hydration Energies of Ca2+: Threshold Collision-Induced Dissociation of Ca2+(H2O)x Complexes (x = 2–8). J. Phys. Chem. A 2012, 116, 3802-3815. (38) Paterová, J.; Heyda, J.; Jungwirth, P.; Shaffer, C. J.; Révész, Á.; Zins, E. L.; Schröder, D. Microhydration of the Magnesium(II) Acetate Cation in the Gas Phase. J. Phys. Chem. A 2011, 115, 6813-6819. (39) Marsh, B. M.; Zhou, J.; Garand, E. Vibrational Spectroscopy of Small Hydrated CuOH+ Clusters. J. Phys. Chem. A 2014, 118, 2063-2071. (40) Zhai, Q. G.; Bu, X. H.; Zhao, X.; Mao, C. Y.; Bu, F.; Chen, X. T.; Feng, P. Y. Advancing Magnesium-Organic Porous Materials Through New Magnesium Cluster Chemistry. Cryst. Growth Des. 2016, 16, 1261-1267. (41) Baur, W. H. On Crystal Chemistry of Salt Hydrates. IV. The Refinement of the Crystal Structure of MgSO4·7H2O (Epsomite). Acta Crystallogr. 1964, 17, 1361-1369. (42) Robertson, E, J.; Carpenter, A. P.; Olson, C. M.; Richmond, G. L. Metal Ion Induced Adsorption and Ordering of Charged Macromolecules at the Aqueous/Hydrophobic Liquid Interface. J. Phys. Chem. C 2014, 118, 15260-15273. (43) Adams, E. M.; Casper, C. B.; Allen, H. C. Effect of Cation Enrichment on Dipalmitoylphosphatidylcholine (DPPC) Monolayers at the Air-Water Interface. J. Colloid Interface Sci. 2016, 478, 353-364.


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Chart 1. Schematic of three possible binding motifs between a metal ion and a carboxylate ligand: (A) bidentate, (B) monodentate and (C) bridging. 119x43mm (150 x 150 DPI)

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Figure 1. Vibrational predissociation spectra of (A) d-OPr¯·H2, (C) d-[CaOPr]+·He and (E) d-[MgOPr]+·He with the scaled (0.976) harmonic spectra of the tagged species inverted below the corresponding experimental spectra in (B), (D) and (F). Inset are calculated structures with the calculated Rcc and OCO angles. The arrows in trace A point to the vsCOO (red) and vasCOO (blue) band positions from the IRMPD study of the isolated CH3CH2CO2¯ ion.17 203x237mm (150 x 150 DPI)


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Figure 2. (B-E) H2-tagged predissociation spectra of d-[MgOPr]+·(H2O)n (n = 1-4) (Trace A is the binary pair reproduced from Fig. 1E). Red and blue arrows in trace A indicate positions of the νsCOO and νasCOO bands in d-OPr from the current study. Inset into traces B and E are calculated structures corresponding to the monohydrate and tetrahydrate. The purple dashed line indicates the location of the water bend (vbendHOH) in the isolated water molecule (1595 cm-1).33 189x203mm (150 x 150 DPI)



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Figure 3. Vibrational predissociation spectra of (A) d-OAc·H2, (B) d-[MgOAc]+·He, (C) d-[Mg(OAc)3]¯·H2 and (D) the calculated (scaled by 0.976) harmonic spectrum of d-[Mg(OAc)3]¯·H2. Inset into trace (D) is the calculated structure for d-[Mg(OAc)3]¯ with the OCO angles and C1-O lengths indicated. The bands associated with vasCOO are colored blue while those derived from vsCOO are red. The features labeled (‡) in (B) and (C) appear to arise from the acetate scaffold but are not assigned here. 197x203mm (150 x 150 DPI)


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Coordination-Dependent Spectroscopic Signatures of Divalent Metal

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