Steric Quenching of Mn(III) Thermal Spin Crossover: Dilution of Spin Centers in Immobilized Solutions

Structural and magnetic properties of a new spin crossover complex [Mn(4,6-diOMe-sal2323)]+ in lattices with ClO4−, (1), NO3−, (2), BF4−, (3), CF3SO3−, (4), and Cl− (5) counterions are reported. Comparison with the magnetostructural properties of the C6, C12, C18 and C22 alkylated analogues of the ClO4− salt of [Mn(4,6-diOMe-sal2323)]+ demonstrates that alkylation effectively switches off the thermal spin crossover pathway and the amphiphilic complexes are all high spin. The spin crossover quenching in the amphiphiles is further probed by magnetic, structural and Raman spectroscopic studies of the PF6− salts of the C6, C12 and C18 complexes of a related complex [Mn(3-OMe-sal2323)]+ which confirm a preference for the high spin state in all cases. Structural analysis is used to rationalize the choice of the spin quintet form in the seven amphiphilic complexes and to highlight the non-accessibility of the smaller spin triplet form of the ion more generally in dilute environments. We suggest that lattice pressure is a requirement to stabilize the spin triplet form of Mn3+ as the low spin form is not known to exist in solution.

In parallel with classical crystal engineering studies, a significant body of work has emerged on the properties of amphiphilic SCO complexes both in the solid state and in soft media. Amphiphilicity can be conferred relatively easily by addition of long-chain alkyl groups to a polydentate ligand and has been widely reported in Fe(II) SCO systems [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] and to a lesser extent in Fe(III) [54][55][56][57][58][59][60][61][62][63] and Co(II) [64]. Preparation of amphiphilic SCO complexes has been largely motivated by interest in surface properties, particularly in the preparation of spin-switchable Langmuir-Blodgett (LB) films for transfer as monolayers to a variety of substrates. However, the versatility of amphiphilic complexes means that their properties have also been investigated in media other than LB films. These include studies into solution properties of micelles and inverse micelles [54][55][56][57][58][59][60][64][65][66][67][68], investigation into the efficacy of using amphiphiles in formation of templated SCO nanowires [61] or thermally ordered metallomesogens [63]. Iron SCO systems, whether they are +II or +III, have responded well to derivatization as amphiphiles and SCO is usually observed to persist, and in some cases to become more abrupt, on moving from the parent compound to the amphiphilic derivative. Studies on amphiphilic Mn(III) complexes are rare with only one report to date on the effect on the SCO profile of adding alkyl chains [64]. Here we report a new cationic Mn(III) SCO complex [Mn(4,6-diOMe-sal 2 323)] + and relate the thermal SCO observed in lattices with four different counterions to the structural properties at 100 K. Attempts to prepare SCO alkylated derivatives of [Mn(4,6-diOMe-sal 2 323)] + with C 6 , C 12 , C 18 and C 22 chains yielded only high spin (HS) complexes in contrast to the thermal SCO observed in the non-alkylated analogues. The challenges in retaining the SCO functionality in Mn(III) amphiphiles were underscored by investigation of the C 6 , C 12 and C 18 alkylated complexes of a related complex [Mn(3-OMe-sal 2 323)] + which was also shown to persist in the HS state across a wide temperature range.

Magnetic Characterisation of Complexes (1)-(12)
The magnetic susceptibility of the bulk samples of compounds 1-4 were measured using a SQUID magnetometer and the data was collected between 300 K and 10 K with a cooling rate of 10 K/min and a scan interval of 5 K. All four complexes were measured using an applied dc field of 5000 Øe. Hysteretic behavior was not observed in the thermal response for any of the compounds. A bulk sample of complex (5) could not be cleanly obtained so the magnetic properties are not reported here.
Complexes 1-4 exhibit incomplete spin crossover behavior, all showing low spin behavior with χT ≈ 1.00 cm 3 mol −1 K between 25 K and 150 K at which point gradual spin crossover starts to occur. By 300 K, none of the complexes had reached a fully high spin state where a value of χT ≈ 3.00 cm 3 mol −1 K would be expected, instead values ranging between 1.98-2.22 cm 3 mol −1 K are observed ( Figure 2). Whilst the spin crossover transitions are incomplete, it is clear that [Mn(4,6-diOMe-sal 2 323)] + undergoes thermal spin crossover in four different crystalline lattices.
In our previous work with iron(III) complexes with similar ligands we observed that the addition of a long alkyl-chain could modulate the SCO behavior whilst often retaining the spin transition [55,63]. In this work, upon replacing a hydrogen atom on the back-bone 323 amine with a long alkyl chain, 6-12, the spin crossover behavior is fully quenched, and instead the complexes remain high spin across the entire temperature range (Figure 3).

Structural Characterisation of Non-Alkylated SCO Complexes (1)-(5)
Single crystal structural data was obtained for complexes 1-5 recorded at a temperature of 100 K. All five complexes contain a single complete molecule of [Mn(4,6-diOMe-sal 2 323)] + and the respective anion in the asymmetric unit, shown here for complex 1 (Figure 4a). The hexadentate Schiff base ligand chelates the metal center resulting in octahedral geometry with two cis-amine, two cis-imine and two trans-phenolate donors. This [Mn(R-sal 2 323)] + coordination motif is widely known in the spin crossover literature with many related examples previously published. Despite the different space groups (Tables S1-S4), the [Mn(4,6-diOMe-sal 2 323)] + cation exhibits the same local geometry in all five lattices, which is exemplified by the overlay of the [Mn(4,6-diOMe-sal 2 323)] + cation in the lattices with the relatively small Cl − (5) and more sterically demanding ClO 4 − (1) anions ( Figure 4b).
cooling rate of 10 K/min and a scan interval of 5 K. All four complexes were measured using an applied dc field of 5000 Øe. Hysteretic behavior was not observed in the thermal response for any of the compounds. A bulk sample of complex (5) could not be cleanly obtained so the magnetic properties are not reported here. Complexes 1-4 exhibit incomplete spin crossover behavior, all showing low spin behavior with χT ≈ 1.00 cm 3 mol −1 K between 25 K and 150 K at which point gradual spin crossover starts to occur. By 300 K, none of the complexes had reached a fully high spin state where a value of χT ≈ 3.00 cm 3 mol −1 K would be expected, instead values ranging between 1.98-2.22 cm 3 mol −1 K are observed ( Figure 2). Whilst the spin crossover transitions are incomplete, it is clear that [Mn(4,6-diOMe-sal2323)] + undergoes thermal spin crossover in four different crystalline lattices. In our previous work with iron(III) complexes with similar ligands we observed that the addition of a long alkyl-chain could modulate the SCO behavior whilst often retaining the spin transition [55,63]. In this work, upon replacing a hydrogen atom on the back-bone 323 amine with a long alkyl chain, 6-12, the spin crossover behavior is fully quenched, and instead the complexes remain high spin across the entire temperature range ( Figure  3).

Structural Characterisation of Non-Alkylated SCO Complexes (1)-(5)
Single crystal structural data was obtained for complexes 1-5 recorded at a tempera ture of 100 K. All five complexes contain a single complete molecule of [Mn(4,6-diOMe sal2323)] + and the respective anion in the asymmetric unit, shown here for complex 1 (Fig  ure 4a). The hexadentate Schiff base ligand chelates the metal center resulting in octahe dral geometry with two cis-amine, two cis-imine and two trans-phenolate donors. Thi [Mn(R-sal2323)] + coordination motif is widely known in the spin crossover literature with many related examples previously published. Despite the different space groups (Table [Mn(R-sal2323)] + coordination motif is widely known in the spin crossover literature with many related examples previously published. Despite the different space groups (Tables S1-S4), the [Mn(4,6-diOMe-sal2323)] + cation exhibits the same local geometry in all five lattices, which is exemplified by the overlay of the [Mn(4,6-diOMe-sal2323)] + cation in the lattices with the relatively small Cl -(5) and more sterically demanding ClO4 − (1) anions (Figure 4b).
(a) (b) In addition to the changes in bond lengths, six-coordinate octahedral Mn(III) compounds exhibit very little deviation from the perfect octahedral shape in the S = 1 state, whereas in the S = 2 state there is a large degree of distortion due to the Jahn-Teller effect. The degree of distortion can be quantified by two distortion parameters, ∑ and Θ. ∑ defines the angular distortion of the twelve cis octahedral angles from 90 • , and Θ measures the trigonal torsion of the perfect octahedral environment towards trigonal prismatic geometry. These parameters can be quickly obtained with the opensource software OctaDist 2.6.1 [69]. In an idealized example, a perfect octahedron would have values of zero for both parameters, however, literature values for Mn(III) compounds give a reasonable basis for spin state assignment (Table 2) [8,12]. 152°] with no other major contributions to the long-range order. A similar pattern is clear across the entire series of complexes 1-5. We observe two long-range packing modes in this family of structures with complexes 1 (P21/n), 4 (P-1), and 5 (P212121) (Figure 5a,d,e) all featuring remarkably similar, herring-bone type, long-range order, whilst complexes 2 (P21/c) and 3 (P21/c) packing in an AB type layered structure (Figure 5b

Spin State
The magnetic data for compounds 1-4 suggests the complexes are in the low spin state at 100 K and given the trend it would also be expected that complex 5, where a bulk sample was unobtainable, would also be LS. This is supported by all aspects of the structural data ( Table 3). Table 3. Metal-ligand bond lengths and distortion angle parameters, ∑ (angular deviation at the origin) and Θ (trigonal torsion angle) for complexes 1-5 at 100 K.

Structural Characterisation of Alkylated SCO Complexes (6)-(12)
The amphiphilic complexes 6, 7, and 10-12 also crystallize in a range of space groups, and, as with their non-alkylated counterparts, all feature a single Mn(III) cation and the relevant anion in the asymmetric unit cell. Each complex features the same local Mn(III) geometry which also aligns with the geometry of the non-alkylated complexes, even between spin states, as shown by the overlay between complexes 1 (low spin) and 6 (high spin) ( Figure 6).
The alkylated complexes feature two equal length alkyl chains, on the 323 amine backbone attached through the amine nitrogen atoms. The amine nitrogen atoms are located at cis positions and due to the nature of the backbone are in a non-meso configuration, as such one chain is located above the equatorial plane whilst the other points below the equatorial plane. This directional aspect of the alkyl chains is preserved for all observed chain lengths, with examples for C 6 , C 12 , and C 18 chains presented here (Figures 6 and 7).
The role these perpendicular alkyl chains play in the long-range packing can be pronounced. Instead of the herringbone structure, which was largely observed before, the cations are now dispersed within the alkylated matrix ( Figures S1-S4), this is highlighted at the extreme end with the C 18 containing complex 12 in Figure 8, which shows the view down the a-axis (a) and the b-axis (b).
Magnetochemistry 2022, 7, x FOR PEER REVIEW 9 of 21 between spin states, as shown by the overlay between complexes 1 (low spin) and 6 (high spin) ( Figure 6). The alkylated complexes feature two equal length alkyl chains, on the 323 amine backbone attached through the amine nitrogen atoms. The amine nitrogen atoms are located at cis positions and due to the nature of the backbone are in a non-meso configuration, as such one chain is located above the equatorial plane whilst the other points below the equatorial plane. This directional aspect of the alkyl chains is preserved for all observed chain lengths, with examples for C6, C12, and C18 chains presented here (Figures 6 and 7).  The alkylated complexes feature two equal length alkyl chains, on the 323 amine backbone attached through the amine nitrogen atoms. The amine nitrogen atoms are located at cis positions and due to the nature of the backbone are in a non-meso configuration, as such one chain is located above the equatorial plane whilst the other points below the equatorial plane. This directional aspect of the alkyl chains is preserved for all observed chain lengths, with examples for C6, C12, and C18 chains presented here (Figures 6 and 7).  The role these perpendicular alkyl chains play in the long-range packing can be pronounced. Instead of the herringbone structure, which was largely observed before, the cations are now dispersed within the alkylated matrix ( Figures S1-S4), this is highlighted at the extreme end with the C18 containing complex 12 in Figure 8, which shows the view down the a-axis (a) and the b-axis (b). The magnetic data for complexes 6, 7, and 10-12 indicates that the complexes are high spin across the entire temperature range, including at the X-ray measurement temperature of 100 K, which is clear from the structural parameters of the complexes (Table 4). Table 4. Metal-Ligand bond lengths and distortion angle parameters, ∑ (angular deviation at the origin) and Ѳ (trigonal torsion angle) for complexes 6, 7, and 10-12 at 100 K. The magnetic data for complexes 6, 7, and 10-12 indicates that the complexes are high spin across the entire temperature range, including at the X-ray measurement temperature of 100 K, which is clear from the structural parameters of the complexes (Table 4). Table 4. Metal-Ligand bond lengths and distortion angle parameters, ∑ (angular deviation at the origin) and Θ (trigonal torsion angle) for complexes 6, 7, and 10-12 at 100 K. It is noteworthy that the quenching of the spin crossover coincides with enforced separation of the spin labile [Mn(4,6-diOMe-sal 2 323)] + centers in the solid-state structures with alkylated ligands. Whilst there are many examples of iron containing SCO complexes featuring spin transitions in solution [54,[70][71][72][73][74], we are not aware of any report on thermal spin crossover in solution for manganese(III). Indeed we could not find any reports of low spin manganese(III) in solution even beyond the spin crossover literature. One potential reason for this discrepancy is the Jahn-Teller effect, which causes large distortions to the octahedral geometry in the Mn(III) HS state. In closely packed solid state Mn(III) structures the complexes can pack in such a way that the energy required to overcome the Jahn-Teller distortion and constrain the spin-labile cations towards an octahedral geometry is gained via packing interactions between neighboring sites leading to a more energetically favorable situation. In solution minimal external pressures are placed onto the complex and the distorted HS state becomes the most favorable configuration. This is evidenced by the overwhelming majority of Mn(III) complexes found in high spin electronic configurations [75]. In the structures of the five alkylated complexes reported here the Mn-N amine distances are the longest observed to date of complexes of this type, including complexes with other first row transition metal ions. In nearly all cases in the alkylated complexes reported here the Mn-Namine distance exceeds 2.3 angstroms, which represents a difference of close to 0.2 angstroms for the equivalent bond length in the low spin forms of complexes 1-5. We suggest therefore that packing constraints are essential to stabilize the rarer spin triplet form of Mn(III) and when these are absent (in solution) or diluted (by steric effects as is the case here), the Jahn-Teller effect dominates and stabilizes the spin quintet form.

Raman Spectra of Alkylated Complexes (10)-(12)
The high spin assignment in complexes 10-12 was confirmed by Raman spectra on powdered samples which were measured at room temperature using laser excitation of 633 nm which is out of resonance with the maximum absorbance of these compounds (Figure 9). Comparison with the data from a comprehensive Raman study of the HS and LS forms of a related complex [76] with no substitution on the phenolate ring was used to interpret the Raman spectra of HS complexes 10-12. In all three structures, the Mn(III) ion is coordinated by pairs of cis imine and amine nitrogen atoms and two trans phenolate oxygen donors, Figures 6 and 7, and the Mn-N and Mn-O modes appear in the low-wavenumber region (100-1000 cm −1 ) along with the same modes mixed with ligand centered motions. The ligand-centered vibrations are concentrated at higher energies between 1000-2000 cm −1 . The Raman feature centered around 1300 cm −1 is assigned to an aromatic in-plane ring deformation mode coupled to aromatic CH and symmetric O-Mn-O deformation while that at 1340 cm −1 is due to the wagging mode of the skeletal CH 2 groups. Symmetric O-Mn-O and ring stretch vibrations are assigned to the intense Raman feature at 625 cm −1 while that at 450 cm −1 is due to a moderate intensity Mn-N stretch and aliphatic (imine) and CH rocking modes. Comparison with Raman spectra in HS and LS states, for the related unsubstituted complex confirm, as expected, that the complexes are in the high spin state. Raman modes at higher energies of 1597 cm −1 and ≈1620 cm −1 are assigned to aromatic C-C stretching modes coupled with asymmetric H-C-N stretching and aromatic ring stretch modes. A full list of Raman spectral features can be found in Table S5. In addition to the resonances attributed to the coordination sphere of the metal complex, new features between 1400 cm −1 and 1300 cm −1 , which do not appear for the unsubstituted complexes, can be attributed to chain deformation and wagging modes of the alkyl chains. spin state. Raman modes at higher energies of 1597 cm −1 and ≈1620 cm −1 are assigned to aromatic C-C stretching modes coupled with asymmetric H-C-N stretching and aromatic ring stretch modes. A full list of Raman spectral features can be found in table S5. In addition to the resonances attributed to the coordination sphere of the metal complex, new features between 1400 cm −1 and 1300 cm −1 , which do not appear for the unsubstituted complexes, can be attributed to chain deformation and wagging modes of the alkyl chains.

Conclusions
Analysis of the structural and magnetic data of twelve new Mn(III) complexes reveals the importance of packing and lattice strain in modulating the choice of spin state and accessibility of thermal spin state switching. The efficient packing of the parent compound [Mn(4,6-diOMe-sal 2 323)] + in five different crystal lattices is connected to the ability of the system to undergo thermal spin crossover with the associated volume reduction on cooling. This demonstrates that [Mn(4,6-diOMe-sal 2 323)] + is sufficiently elastic to accommodate the significant bond length changes which accompany thermal switching between the smaller spin triplet form and larger spin quintet form which has a pronounced equatorial elongation due to a pseudo Jahn-Teller effect. Alkylation of the ligand in [Mn(4,6-diOMesal 2 323)] + results in a significant increase in the inter-cation distances and quenching of the thermal spin state switching. The quenching is also observed in alkylated derivatives of the PF 6 − salt of a related complex [Mn(3-OMe-sal 2 323)] + , where the parent compound is also known to a pronounced spin crossover. We suggest here that the long alkyl chains effectively generate an immobilized solution that reduces the lattice pressure. This in turn means the Jahn-Teller distortion, which is pronounced in the high spin form due to asymmetric population of the anti-bonding orbitals, dominates in the alkylated complexes and cooling alone is not sufficient to promote spin pairing to the spin triplet state. We further suggest that the absence of sufficient local pressure may explain why the spin triplet form of Mn(III) has not been observed in solution despite several reports in the solid state. We conclude from this study that, in contrast to ferrous or ferric spin crossover systems, alkylation of Mn(III) complexes may be a less effective route to spin switchable thin films by Langmuir-Blodgett techniques and our work to find alternative routes continues.

General Experimental Details
Physical Measurements. All measurements were carried out on powdered samples of the respective polycrystalline compound. Elemental composition was measured using a Perkin Elmer Vario EL CHN analyser. A Bruker Alpha Platinum spectrometer was used to record the infrared spectra, and mass spectra were recorded on a Waters 2695 Separations Module Electrospray Spectrometer.
Raman Spectra. The Raman spectra were acquired on a sample dispersed in KBr (5% w/w) on a confocal Labrum HR spectrometer from Horiba coupled to a 633 nm laser source using a 100 X (N.A. = 0.90) Olympus objective. Spectra were background corrected using a 4-point polynomial generated using Alspec software.
Crystal Data Collection and Refinement. Appropriate single crystals of the relevant complexes were mounted on an Oxford Diffraction Supernova A diffractometer fitted with an Atlas detector; datasets were measured using monochromatic Cu-Kα radiation or Mo-Kα radiation and corrected for absorption [77]. The temperature (100 K) was controlled with an Oxford ProSystem instrument. Structures were solved by direct methods (SHELXS) and refined with full-matrix least-squared procedures based on F 2 , using SHELXL-2016 [78]. Non-hydrogen atoms were refined with independent anisotropic displacement parameters, H-atoms were placed in idealized positions. Selected crystallographic data and structure refinements are summarized in Tables S1-S4 and crystallographic data for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC-2124577-2124586.
Magnetic Measurements. The magnetic susceptibility measurements were recorded on a Quantum Design SQUID magnetometer MPMS-XL operating between 1.8 and 300 K. DC measurements were performed on polycrystalline samples inside gelatin capsules in an applied field of 5000 Øe. Diamagnetic corrections were applied to account for the gelatin capsule and the long alkyl chains on some complexes.  −1 ): 3435, 3186, 2928, 1598, 1550, 1453,  1420, 1384, 1231, 1155, 1130, 1045, 812 (20 mL). A yellow color developed, and the solution was stirred for 15 min. Solid manganese(II) chloride tetrahydrate (113.6 mg, 0.574 mmol) was added to the reaction mixture and the resulting red-colored solution was stirred at RT for 1 h before being gravity filtered. The filtrate was dried by rotary evaporator and the resulting solute was redissolved in dichloromethane. This solution was then loaded onto a pre-prepared silica column and was eluted using a gradient increase in the polarity of the mobile phase by mixing dichloromethane with acetonitrile. The resultant eluted red solution was evaporated by rotary evaporation and the solute was redissolved in ethanol:acetonitrile (1:1) (25 mL). The filtrate was kept standing to enable the complex to crystallize. Solvent evaporation resulted in the formation of small single crystals with a red color and the structure was solved although a bulk sample could not be obtained.
In a typical procedure 3-methoxysalicylaldehyde (0.609 g, 4 mmol) was added to a solution of 1,2-bis(3-aminopropylamino)ethane (0.349 g, 2 mmol) in dry acetonitrile (50 mL). After 15 min molecular sieves and anhydrous potassium carbonate (0.552 g, 4 mmol) were added. The reaction mixture was stirred for 10 min after which the appropriate 1-bromoalkane (4 mmol) and potassium iodide (0.662 g, 4 mmol) were added and the suspension was refluxed for 48 h. The reaction mixture was filtered and the solvent removed under reduced pressure. The resulting oil was dissolved in dichloromethane and washed with brine and the organic fraction was dried with anhydrous sodium sulfate to obtain the alkylated ligand as a bright yellow oil. In all cases, this was directly used for complexation to yield complexes 10-12 which were characterized by single crystal diffraction, elemental analysis and mass spectrometry.
Complex [Mn(3-OMe-sal 2 323-C 6 )]PF 6 (10). Ligand H 2 (3-OMe-sal 2 323-C 6 ) (1.222 g, 2 mmol) was dissolved in methanol (30 mL) and was kept aside in one beaker and in a separate beaker manganese(II) chloride tetrahydrate (0.396 g, 2 mmol) was dissolved in methanol (20 mL) to which ammonium hexafluorophosphate (0.326 g, 2 mmol) was added. The pink methanolic metal salt solution was then added to the yellow ligand solution giving a deep brown solution that was stirred at room temperature for 30 min. The solvent was evaporated, and the resulting brown oil was dissolved in dichloromethane (10 mL) and the desired product was purified by filtration over a bed of silica using dichloromethane to elute the product. The dichloromethane was removed under reduced pressure to yield a brown oil that was recrystallized from methanol. The solvent was evaporated slowly at room temperature and after 4 days black crystalline needles were obtained. Yield-658 mg, 41%. Elemental analysis: C 36 (30 mL) and was kept aside in one beaker and in a separate beaker manganese(II) chloride tetrahydrate (0.792 g, 4 mmol) was dissolved in methanol (20 mL) to which ammonium hexafluorophosphate (0.652 g, 4 mmol) was added. The pink methanolic metal salt solution was then added to the yellow ligand solution giving a deep brown solution that was stirred at room temperature for 30 min. The solvent was evaporated and the resulting brown oil was dissolved in dichloromethane (10 mL) and the desired product was purified by filtration over a bed of silica using dichloromethane to elute the product. The dichloromethane was removed under reduced pressure to yield a brown oil that was recrystallized from methanol. The solvent was evaporated slowly at room temperature and after 5 days black crystals were obtained. Yield-1.274 g, 33%.
Elemental analysis: C 50 (12). Ligand H 2 (3-OMe-sal 2 323-C 18 ) (3.790 g, 4 mmol) was dissolved in methanol (30 mL) and was kept aside in one beaker and in a separate beaker manganese(II) chloride tetrahydrate (0.792 g, 4 mmol) was dissolved in methanol (20 mL) to which ammonium hexafluorophosphate (0.652 g, 4 mmol) was added. The pink methanolic metal salt solution was then added to the yellow ligand solution giving a deep brown solution that was stirred at room temperature for 30 min. The solvent was evaporated, and the resulting brown oil was dissolved in dichloromethane (10 mL) and the desired product was purified by filtration over a bed of silica using dichloromethane to elute the product. The dichloromethane was removed under reduced pressure to yield a brown oil that was recrystallized from methanol. The solvent was evaporated slowly at room temperature and after 5 days black powder was obtained. Yield-911 mg, 20%. Elemental analysis: C 61  Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/magnetochemistry8010008/s1, Figure S1: C 6 -Alkylated complex 6 viewed along b-axis, Figure S2: C12-Alkylated complex 7 viewed along the b-axis, Figure S3: C 6 -Alkylated complex 10 viewed along the c-axis, Figure S4: C 12 -Alkylated complex 11 viewed along the a-axis, Table S1: Crystallographic details for compounds 1-3, Table S2: Crystallographic details for compounds 4 & 5, Table S3: Crystallographic details for compounds 6 & 7, Table S4: Crystallographic details for compounds 10-12, Table S5: Raman vibration modes of complexes (10)-(12) collected at room temperature.

Conflicts of Interest:
The authors declare no conflict of interest.