Spin crossover cobalt(II) complexes exhibiting temperature-and concentration-dependent optical changes in solution

This work investigated the spin states of the cobalt(II) complexes [Co(L1)2](X)2 (1·X; L1 = 4'-(4-N,N'-diphenylaminophenyl)-2,2':6',2''-terpyridine, X = PF6, BPh4) and [Co(L2)2](X)2 (2·X; L2 = 4'-(4-N,N'-dimethylaminophenyl)-2,2':6',2''-terpyridine, X = PF6, BPh4) in the solid state and in solution. In the solid state, 1·PF6 and 2·PF6, both containing smaller PF6- counter anions, showed gradual spin-crossover. In contrast, 1·BPh4 and 2·BPh4 remained in the high-spin state over the temperature range of 5-400 K due to a lower degree of molecular cooperativity. Each of the cobalt(II) complexes exhibited effects of temperature and concentration on their absorption spectra that were related to the spin states in various organic solvents. This work provides new insights into the spectroscopic properties resulting from the spin states of cobalt(II) complexes in solution.


EXPERIMENTAL SECTION
Synthesis.All reagents were commercially available and used without further purification.

Fig. S3
The selected intermolecular interactions observed in the molecular assembly of

Fig. S4
Fig. S4 (a) Crystal structure of 2•PF 6 .One diphenylamine site which of Co2 complex was located with disorder.(b) Coordination environment of the [CoN6] core and the Co-N bond length.Crystal packing of 2•PF 6 along (c) the ab plane and (d) the bc plane.Blue and pink coloured molecules are [Co(L2) 2 ] 2+ cations consisting of Co1 and Co2 metal center, respectively.
Fig. S6 (a) Crystal structure of 2•BPh 4 .H atoms are omitted for the clarity.(b) Coordination environment of the [CoN6] core and the Co-N bond length.Crystal packing of 2•BPh 4 along (c) the ab plane and (d) the bc plane.

Fig. S9
Fig. S9 Effect of temperature on the molar adsorption constant (ε) of 1•PF 6 in (a) acetonitrile, (b) DMF and (c) DMSO.The temperature was varied from 283 -343 K except for trials with DMSO, which used 293 -343 K due to the higher freezing point of this solvent.The insets show plots of T vs 1/ε.

Fig. S10
Fig. S10 Effect of temperature on the molar adsorption constant (ε) of 2•PF 6 in (a) acetonitrile, (b) DMF and (c) DMSO.The temperature was varied from 283 -343 K except for trials with DMSO, which used 293 -343 K due to the higher freezing point of this solvent.The insets show plots of T vs 1/ε.

Fig. S11
Fig. S11 Effect of temperature on the molar adsorption constant (ε) of 2•BPh 4 in (a) acetonitrile, (b) DMF and (c) DMSO.The temperature was varied from 283 -343 K except for trials with DMSO, which used 293 -343 K due to the higher freezing point of this solvent.The insets show plots of T vs 1/ε.

for 1•BPh 4 •2.5H 2 O: H
Physical measurements. 1H-NMR spectra were acquired with a Bruker AVANCE NEO 400 instrument operating at 400 MHz, using the deuterated solvent to provide the lock signal and residual solvent tetramethylsilane as the internal reference.Elemental analyses for C, H and N were carried out at the Instrumental Analysis Centre of Josai University.SC-XRD measurements were recorded on an Oxford Gemini Ultra diffractometer employing graphite monochromated Mo Kα for 2•PF 6 and NaBPh 4 for 2•BPh 4 , respectively.The precipitate was collected by filtration and washed with a small amount of MeOH to give 2•PF 6 (42.2%) and 2•BPh 4 (30.0%).Elemental analysis:Calcd.for2•PF6•2.5H 2 O: H 4.13, C 50.28, N 10.20.; Found: H 4.11, C 50.22, N 10.12.Calcd.for2•BPh 4 •1.5MeOH:H5.98, C 79.09, N 7.73., Found: H 5.85, C 78.97, N 7.72.(SQUID)magnetometer (Quantum Design MPMS-XL).Samples were put into a gelatin capsule, mounted in-side a straw, and then fixed to the end of the sample transport rod.Cooperativity was estimated from the measured χ m T versus T curves (χ m ; molar magnetic susceptibility, T; temperature) by applying the regular solution model (eq.1), where ΔH, ΔS and Γ are the enthalpy and the entropy variations and the parameter accounting for cooperativity based on SCO,