Reaction of tin( IV ) phthalocyanine dichloride with decamethylmetallocenes (M = Cr II and Co II ). Strong magnetic coupling of spins in (Cp* 2 Co + )

The reaction of tin( IV ) phthalocyanine dichloride {Sn IV Cl 2 (Pc 2 − )} with decamethylmetallocenes (Cp* 2 M, M = Co, Cr) has been studied. Decamethylcobaltocene reduces Sn IV Cl 2 (Pc 2 − ) to form the (Cp* 2 Co + ) {Sn IV Cl 2 (Pc (cid:129) 3 − )} (cid:129) − ·2C 6 H 4 Cl 2 ( 1 ) complex. The negative charge of {Sn IV Cl 2 (Pc (cid:129) 3 − )} (cid:129) − is delocalized over the Pc macrocycle providing the alternation of the C – N(imine) bonds, the appearance of new bands in the NIR range and a strong blue shift of both the Soret and Q-bands in the spectrum of 1 . The magnetic moment of 1 is equal to 1.68 μ B at 300 K, indicating the contribution of one S = 1/2 spin of the Pc (cid:129) 3 − macrocycles. These macrocycles form closely packed double stacks in 1 with e ﬀ ective π – π interactions providing strong antiferromagnetic coupling of spins at a Weiss temperature of − 80 K. Decamethylchromocene initially also reduces Sn IV Cl 2 (Pc 2 − ) to form the [(Cp* 2 Cr + ){Sn VI Cl 2 (Pc (cid:129) 3 − )} (cid:129) − complex but further reaction between the ions is observed. This reaction is accompanied by the substi-tution of one Cp* ligand of Cp* 2 Cr by chloride anions originating from {Sn IV Cl 2 (Pc (cid:129) 3 − )} (cid:129) − to form the complex {(Cp*CrCl 2 )(Sn IV ( μ -Cl)(Pc 2 − ))}·C 6 H 4 Cl 2 ( 2 ) in which the (Cp*CrCl 2 ) and {Sn IV (Pc 2 − )} species are bonded through the μ -bridged Cl − anion. According to the DFT calculations, this reaction proceeds via an intermediate [(Cp* 2 CrCl)(SnClPc)] complex.


Introduction
2][3][4][5][6] They are used as sensors, and materials for optical and electronic devices. 1,24][5] Since metal phthalocyanines can contain paramagnetic metals, they are also used as active components in the design of magnetic compounds.For example, polymeric compounds with alternating (Mn III Pc) + and tetracyanoethylene (TCNE •− ) ions show ferrimagnetic ordering of spins. 6educed metal phthalocyanines can also potentially show promising conducting and magnetic properties.For example, metallic conductivity is predicted for electron doped non-transition metal phthalocyanines. 7][10][11][12][13] The reduction of iron(II) phthalocyanine by decamethylchromocene (Cp* 2 Cr) allows one to obtain a complex with π-stacks of alternating Fe I Pc (S = 1/2) and Cp* 2 Cr + (S = 3/2) ions which shows ferrimagnetic ordering of spins below 4.5 K. 14 This approach was also applied for free-base phthalocyanine (H 2 Pc).However, in this case no essential magnetic coupling was found in (Cp* 2 Cr + )(H 2 Pc          15 Here we study the interaction of strong organometallic donorsdecamethylcobaltocene (Cp* 2 Co) and decamethylchromocene (Cp* 2 Cr) 16 with tin(IV) phthalocyanine dichloride {Sn IV Cl 2 (Pc 2− )} which tend to form closely packed one-or two-dimensional structures from the radical anion macrocycles. 13,17

Synthesis
All investigations were carried out under strictly anaerobic conditions in a glove box.The addition of Cp* 2 Co to {Sn IV Cl 2 (Pc 2− )} in o-dichlorobenzene and the stirring of the solution provides complete dissolution of phthalocyanine with the formation of a deep blue solution characteristic of the reduced Pc macrocycle.Slow mixing of the obtained solution with n-hexane affords the crystals of 1 as black needles in high yield.These crystals are of small size and are suitable for X-ray diffraction analysis using synchrotron radiation.The mixing of Cp* 2 Cr and {Sn IV Cl 2 (Pc 2− )} in the same solvent is also accompanied by the formation of a deep blue solution indicating the reduction of the Pc macrocycle.However, after 4 hours of stirring at 80 °C, the color of the solution turned green which is characteristic of the dianionic Pc 2− macrocycle.A similar color change from deep blue to green is observed in the reaction of the {Sn IV Cl 2 (Pc •3− )} •− radical anions with some transition metal complexes accompanied by chloride anion abstraction and the formation of coordination complexes with neutral Sn II (Pc 2− ). 9 Obviously, further reaction between the Cp* 2 Cr + cations and the {Sn IV Cl 2 (Pc •3− )} •− radical anions occurs (Scheme 1, see also the theoretical part in the ESI †).The solution was stirred for additional 20 hours at 80 °C, preserving green color.Slow mixing with n-hexane precipitates green powder with a small amount of green plate-like crystals which were studied by X-ray diffraction on single crystals using synchrotron radiation.Thus, the composition of 1 and 2 was determined from X-ray diffraction on single crystals.The elemental analysis of green powder shows that its composition is close to that of single crystals.We also studied the optical properties of compound 2 in o-dichlorobenzene.On combining these data with X-ray diffraction data and DFT calculations, it is possible to evaluate the electronic states of the components in 2.

Crystal structures
Crystals of 1 and 2 were studied by X-ray diffraction at 100 K. Main structural blocks of these complexes except solvent individual Cp* 2 Co + cations and {Sn IV Cl 2 (Pc •3− )} •− radical anions.There is no π-π interaction between the Cp* ligand and the Pc •3− macrocycle in 1 since the Cp* 2 Cr + cations are oriented by methyl substituents towards the Pc •3− plane.At the same time, these components are oriented in such a way that relatively close distances between the positively charged Co III and negatively charged chloride anions of {Sn IV Cl 2 (Pc •3− )} •− are formed (5.6-5.8Å) (Fig. 1a).The average length of the Co-C(Cp*) bonds for Cp* 2 Co in 1 is 2.046(3) Å.This length corresponds to the formation of the Cp* 2 Co + cations which have the average Co-C(Cp*) bond length of 2.04-2.05Å, 18 whereas neutral Cp* 2 Co has longer Co-C(Cp*) bonds of 2.101(3) Å. 19 The geometry of the Pc •3− macrocycle is shown in Fig. 1a.There are two types of the C-N bonds with imine and pyrrole nitrogen atoms of Pc.Longer C-N( pyrrole) bonds with a length of 1.381(4) Å have no alternation.Shorter C-N(imine) bonds alternate in such a way that four bonds belonging to two oppositely located isoindole units are short (average length is 1.319(4) Å) and four other bonds are long (1.350(4) Å), and the difference is 0.031 Å.Such alternation is explained by the partial disruption of aromaticity of the Pc macrocycle in the formation of a less stable 19-π-electron system of Pc •3− . 20he average length of the Sn-Cl bonds is 2.485(1) Å and that of the Sn-N( pyrrole) bonds is 2.049(3) Å.These lengths are rather close to those in pristine {Sn IV Cl 2 (Pc 2− )} 0 -2.470(2) and 2.054(2) Å, respectively. 21The tin(IV) atom is positioned not exactly in the 24-atom Pc plane but is slightly displaced out of this plane by 0.034 Å.The reason for this is a slightly nonplanar saddle-like shape of Pc •3− with two phenylene groups located above the 24-atom Pc plane and two such groups located below this plane.
The crystal structure of 1 is shown in Fig. 2. It contains large channels occupied by the Cp* 2 Co + cations (Fig. 2a).The walls of these channels are formed by double stacks from the closely packed Pc •3− macrocycles (Fig. 2).There is an effective π-π interaction between Pc •3− in these double chains since the phenylene group of one macrocycle is positioned over the phenylene group of the neighboring macrocycle.The planes of these groups are nearly parallel to each other with a dihedral angle of only 2.34°, and many short van der Waals C⋯C contacts are formed between the phenylene substituents of the Pc •3− macrocycles in the 3.45-3.54Å range (Fig. 2b).Such packing is observed for the first time for the radical anion salts with {Sn IV Cl 2 (Pc •3− )} •− since previously only closely packed single stacks 17 and 2D phthalocyanine layers 13 from {Sn IV Cl 2 (Pc •3− )} •− were observed.
There are also C-N bonds with imine and pyrrole nitrogen atoms in SnClPc in 2. The length of all eight C-N( pyrrole) bonds is centered at 1.381(7) Å.In contrast to 1, the alternation of the C-N(imine) bonds is absent in 2 since oppositely located short and long bonds have the length of 1.319(6) and 1.326( 6) Å, respectively.The difference of 0.007 Å is comparable to the error for the length of these types of bonds and is essentially less than such a difference in 1 (0.031 Å).The absence of alternation justifies the formation of a dianionic Pc 2− macrocycle in 2 and that corresponds well to the green color of compound 2. Thus, we suppose that coordination units in 2 consists of the (Cp*Cr II Cl 2 ) − and {Sn IV (μ-Cl)(Pc 2− )} + ions μ-bridged through the chloride anion.Since the chloride anion is coordinated to the tin(IV) atom only from one side, it displaces towards the chloride anion by 0.98 Å (relative to the 24-atom Pc plane), and the average Sn-N(Pc) bonds are also essentially elongated up to 2.141(4) Å.As a result, the Pc macrocycle has concave conformation with the deviation of all four phenylene groups of Pc to one side relative to the 24-atom Pc plane.The {Sn IV Cl(Pc 2− )} + cation observed in 2 is a rare example of pentacoordinated tin(IV) atoms in tin(IV) phthalocyanine which has some similarities with the {Sn IV Ph(Pc 2− )} + cations also containing dianionic Pc 2− macrocycles. 28he {(Cp*CrCl 2 ){Sn IV Cl(Pc 2− )}} units in 2 form chains arranged along the c axis in which closely packed pairs of the Pc 2− macrocycles with short van der Waals C⋯C contacts can be outlined (Fig. S5 †).

Optical properties
The spectrum of 1 in the UV-visible-NIR range is shown in Fig. 3. Pristine {Sn IV Cl 2 (Pc 2− )} 0 shows Soret and split Q-bands at 381 and 670, 740 (max), and 848 nm, respectively (Fig. 3, curve a).The formation of 1 is accompanied by the appearance of new bands in the NIR range at 1010 nm and a weaker band is observed at 840 nm.Both the Soret and Q-bands are noticeably blue shifted in the spectrum of 1 appearing at 338 nm and 712, 627 (max), and 600 nm, respectively (Fig. 3, curve b).5,17 We also recorded the spectra in the o-dichlorobenzene solution of {Sn IV Cl 2 (Pc 2− )} 0 reduced by one equivalent of Cp* 2 Co (Fig. 4a) or Cp* 2 Cr (Fig. 4b) by the stirring of the solution at 80 °C for one day and filtering.The spectra show different states of complexes 1 and 2. Complex 1 has deep blue color in solution and manifests bands at 410, 588, 621, 657, 698 and 996 nm.The latter band in the NIR range and an essential blue shift of both the Soret and Q-bands are the signs of the formation of the Pc •3− macrocycles.In contrast, the spectrum of the green solution of 2 contains bands only at 452 and 716 nm without any new bands in the NIR range.This spectrum indicates the formation of the Pc 2− macrocycle in 2.

Magnetic properties
The magnetic properties of 1 were studied by SQUID and EPR techniques.The effective magnetic moment of 1 is equal to 1.68μ B at 300 K (Fig. 5a), indicating the contribution of one S = 1/2 spin of the Pc •3− macrocycles (the calculated value for the system of one noninteracting S = 1/2 spin is 1.73μ B ).The reciprocal molar magnetic susceptibility is linear in the 130-300 K range allowing one to determine the Weiss temperature to be −80 K (Fig. 5b), indicating strong antiferromagnetic coupling of spins.Deviation towards the antiferromagnetic side from the Curie-Weiss law is observed below 130 K.However, long range antiferromagnetic ordering of spins is not observed down to 1.9 K. Strong antiferromagnetic coupling of spins is probably the reason for a lower magnetic moment of 1 in comparison with the calculated value and the decreases of the magnetic moment even below 300 K (Fig. 5a).Effective π-π interactions realized between the Pc •3− macrocycles in the  closely packed double chains of 1 can explain strong antiferromagnetic coupling between the spins.
The EPR spectra of 1 were studied in the 4-295 K range.The complex shows a broad single Lorentzian line with a g-factor of 1.9958 and a linewidth (ΔH) of 16.1 mT at 295 K.The signal can be attributed to the {Sn IV Cl 2 (Pc •3− )} •− radical anions.Similar broad EPR signals were previously observed for other salts with the {Sn IV Cl 2 (Pc •3− )} •− radical anions. 13,17The signal strongly narrows and the g-factor shifts to the smaller values with the temperature decrease (spectrum at 120 K is shown Fig. S6 †).The signal splits into two lines below 30 K (Fig. 6a) which are broadened and shift strongly to the smaller and larger g-factors with the temperature decrease (Fig. 6b  and c).The broadening of lines and shift of their g-factors can be attributed to strong antiferromagnetic coupling of spins.The split signal at 9 K is shown in Fig. 6a and the parameters of the lines are g 1 = 1.9780,ΔH = 3.2 mT and g 2 = 1.9912,ΔH = 2.6 mT.The EPR spectrum of {Sn IV Cl 2 (Pc •3− )} •− generated by Cp* 2 Co was studied in o-dichlorobenzene at 77 K (Fig. S7 †), and the signals were not found at room temperature.The isolated {Sn IV Cl 2 (Pc •3− )} •− radical anions show an intense strongly asymmetric EPR signal at 77 K which can be fitted by three Lorentzian lines with g 1 = 2.0050, ΔH = 0.482 mT; g 2 = 2.0021, ΔH = 0.924 mT; and g 3 = 1.9942,ΔH = 2.704 mT.The ratio of the integral intensities of the lines is 13/20/67% for g 1 , g 2 and g 3 , respectively (Fig. S7 †).It is seen that lines are essentially narrower at 77 K in solution in comparison with the solid state.These data also show that the asymmetry of the EPR signal of 1 is intrinsic and can be realized, for example, due to the static distortion of Pc •3− at low temperatures.The behavior of the EPR signal in 1 correlates well with the behavior of salts with the radical anions of aluminium(III), gallium(III) and indium(III) phthalocyanines which show strong broadening of the EPR signal with the increasing size of the metal atom, and g-factors are noticeably lower than 2.000 and the signal shows strong asymmetry at low temperatures. 12The linewidth of the EPR signal in 1 at 295 K is comparable to that of the EPR signal from {In III Br(Pc •3− )} •− radical anions. 12The Cp* 2 Co + cations with Co III are diamagnetic and do not contribute to the EPR signal of 1.

Fig. 2
Fig. 2 (a) View along the double phthalocyanine stacks and crystallographic a axis in 1. Pairs of {Sn IV Cl 2 (Pc •3− )} •− radical anions belonging to one stack are marked as orange ellipses; (b) view on the double stacks from {Sn IV Cl 2 (Pc •3− )} •− arranged in the ab plane.Short van der Waals C⋯C contacts between the Pc •3− macrocycles are shown as green dashed lines.

Fig. 5
Fig. 5 Temperature dependencies of the effective magnetic moment (a) and reciprocal molar magnetic susceptibility (b) for polycrystalline 1 in the 1.9-300 K range.

Fig. 6
Fig. 6 (a) EPR signal from polycrystalline 1 at 9 K.The fitting of the signal by two Lorentzian lines is shown below; temperature dependencies of the g-factor (b) and the linewidth (c) of the EPR signal in 1.The signal is split into two lines below 30 K.