Syntheses and Crystal Structures of Vanadium and Iron Chloride Complexes with Diglyme

A mononuclear molecular complex fac-[VCl3(diglyme)] (1) resulted from the reaction of VCl3 and diglyme (diglyme = di(2-methoxyethyl)ether) in dichloromethane. The violet complex 1 is a sensitive substance which slowly oxidized to a new, blue mononuclear molecular complex, fac-[VOCl2(diglyme)] (2) in the presence of air. The synthesis of iron(II), iron(III) complex [FeCl(diglyme)(THF)]2[FeCl4)]2 (3) was achieved by the reaction of yellowgreen, partly oxidized FeCl2 . 4H2O, diglyme and chlorotrimethylsilane in tetrahydrofuran. The compound consists of dinuclear cations with octahedral environment of iron(II) and tetrahedral anions of iron(III). A pure iron(II) chloridediglyme complex [FeCl2(diglyme)]2 (4) was gained by the reaction of freshly prepared iron(II) chloride hydrate, diglyme and chlorotrimethylsilane in dichloromethane. Diglyme is coordinated in a meridional mode to octahedral iron(II) in dinuclear cations of 3 and in dinuclear molecules 4.


Introduction
Applying a polyether diglyme as a ligand in syntheses of alkaline earth complexes is a common approach to prevent oligomerization by bridging ligands. [1][2][3][4] Saturating a coordination sphere of a metal by the tridentate chelate ligand diglyme hinders ´metal -metal´ contacts. The formation of two five-membered puckered rings increases the stability of complexes. Minimized intermolecular solid-state interactions in monomeric complexes resulted in an enhanced volatility in comparison to oligomeric complexes, which makes mononuclear alkaline earth complexes superior metal organic chemical vapor deposition (MOCVD) precursors. A prevailingly chelate bonding of digyme to metal centers in complexes is confirmed by the structural data in the CSD (version 5.35 updated May 2014) listing only about a dozen compounds of alkali metals, aluminum and lead with bridging diglyme molecules among numerous diglyme complexes.
Suspensions of ground samples in Nujol were prepared in a dry box. IR spectra were recorded on a Perkin Elmer Spectrum 100 FT-IR spectrometer from 400 to 4000 cm -1 .
Chlorine contents were determined by potentiometric titrations of chloride ions with silver nitrate. Elemental analyses were carried out on a Perkin-Elmer 2400 Series II CHN micro analyzer at the University of Ljubljana (Department of Organic Chemistry).
Powdered samples were sealed into tubes in a dry box and room temperature magnetic susceptibility measurements were performed by a Sherwood Scientific MBS-1 balance using Hg[Co(NCS) 4 ] as a standard. Diamagnetic corrections were applied using Pascal's constants and the magnetic moments were calculated. 20

Synthesis of [ [VCl 3 (diglyme)] ], 1 Method A)
Solvent (THF, 30 mL) and diglyme (1.484 g, 11.05 mmol) were added to VCl 3 (0.810 g, 5.15 mmol) under an inert atmosphere. The suspension was stirred for three days at room temperature and then dried in vacuo. A considerable amount of unreacted VCl 3 in the resulting powder product was detected by a CHN analysis and IR spectroscopy. In order to complete the reaction of VCl 3 and diglyme additional solvent (THF, 30 mL) and diglyme (0.979 g, 7.29 mmol) were mixed with the powder product and stirred for 20 hours at 65 °C. This suspension was dried in vacuo. Although the powder product still contained unreacted VCl 3 according to results of CHN analysis, a recrystallization of the product from dichloromethane resulted in crystals of 1.

3. Synthesis of [ [VOCl 2 (diglyme)] ], 2
Air leaking to a closed system during a crystallization of 1 by a slow evaporation of dichloromethane at a reduced pressure resulted in an oxidation of 1 to crystals of the blue complex 2. Anal. Calcd. mass fractions of elements, w /%, for C 6
Petri~ek and Dem{ar: Syntheses and Crystal Structures of Vanadium ... Unreacted iron was removed by a hot filtration, a green solution was dried in vacuo and a moist green product resulted. Chlorine content (33.06%) of this product was determined by potentiometric titrations and iron content (25.98%) was calculated according to the molar ratio of iron and chlorine in FeCl 2 . Solvent (CH 2 Cl 2 , 30 mL), diglyme (1.410 g, 10.5 mmol) and (CH 3 ) 3 SiCl (13.13 g, 121 mmol) were added to the freshly prepared green iron(II) chloride hydrate (1.014 g, 4.72 mmol of Fe 2+ ). The suspension was stirred for a day at room temperature and then dried in vacuo. The procedure was repeated in the second step, because some water was present in the white product, as proven by characteristic peaks (3419 s, 1600 m cm -1 ) in IR spectrum. Solvent (CH 2 Cl 2 , 30 mL), diglyme (1.410 g, 10.5 mmol) and (CH 3 ) 3 SiCl (13.13 g, 121 mmol) were added to the white product. The suspension was stirred for a week at room temperature and then dried in vacuo, the complex 4 (0.959 g, 77.9% yield) was gained. Anal. Calcd. mass fractions of elements, w /%, for C 12

6. Crystal Structure Determination
Details of the crystal data collections and the refinement parameters of the complexes 1-4 are summarized in Table 1.
All studied compounds are hygroscopic. The crystals were mounted on a tip of a glass fiber with a small amount of silicon grease. Diffraction data were collected on a Nonius Kappa diffractometer with a CCD area detector at 150(2) K. Graphite monochromatic Mo Kα radiation (λ = 0.71073 Å) was employed for all measurements. The data were processed using the program DENZO-SMN. 21 The crystal structures were solved by direct methods implemented in SHELXS-97 22 and refined by a full-matrix least-squares procedure based on F 2 (SHELXL-97). 23 All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were included in the models at geometrically calculated positions and refined using a riding model. The calculations were performed using the WinGX program suite. 24 Absolute structures of 1 and 2 cannot be determined reliably (Flack parameter 0.51(3) and 0.53(2) respectively). 25

1. Syntheses of Vanadium Chloride Complexes with Diglyme, [ [VCl 3 (diglyme)] ], 1, and [ [VOCl 2 (diglyme)] ], 2
A choice of solvent applied in the reaction of vanadium(III) chloride and diglyme is very important. A reaction is completed in dichloromethane at room temperature, but in tetrahydrofuran even a reaction at elevated temperature (20 hours, 65 °C) resulted in a mixture of unreacted VCl 3 and complex 1. The complex 1 is a sensitive and unstable compound which is oxidized by oxygen to the V(IV) complex 2. The blue color of 2 is characteristic for almost all compounds containing a vanadyl unit.

2. Crystal Structures of 1 and 2
A distorted octahedral arrangement of ligands is observed in the mononuclear molecular complexes of 1 and 2 ( Figure 1). Three oxygen atoms of a diglyme molecule   are coordinated in a facial mode to a central vanadium(III) ion in 1 or to an oxidovanadium(IV) ion in 2. The coordination sphere is fulfilled by three or two chloride ions in 1 and 2, respectively.
The overlay of two molecules in the asymmetric unit of the complex 1 clearly shows a different puckering of coordinated diglyme ligand (Figure 2).
Interestingly, the average V-Cl bonding distances in 2 are longer than in 1 in spite of a higher oxidation state of vanadium in 2 than in 1.
V-Cl bonding distances in complexes 1 are comparable to those observed in fac-[VCl 3 (DME)(THF)] (2.298(4)-2.306(6) Å) 28   Only a few crystals of iron(II)-iron(III) complex 3 were obtained when partly oxidized FeCl 2 . 4H 2 O was used in the synthesis of iron chloride complex with diglyme. A reaction of the freshly prepared green iron(II) chloride hydrate, diglyme and (CH 3 ) 3 SiCl in excess, which should guarantee a formation of a water free complex, 32 resulted in an aqua iron chloride complex with diglyme. The complex 4 was gained only in the reaction of the aqua iron chloride complex with (CH 3 ) 3 SiCl and diglyme in dichloromethane. A one step synthesis of 4 was not successful even with a prolonged reaction time and a higher (CH 3 ) 3 SiCl content in a reaction mixture of freshly prepared moist green iron(II) chloride hydrate and diglyme in dichloromethane. A similar two step reaction was reported for a dehydration of FeCl 2 . 4H 2 O by triethyl orthoformate in propan-2-ol yielding [FeCl 2 (PrOH) 2 ] n . 33

4. Magnetic Measurements
The magnetic moment of iron complex 4 (5.48 BM) measured at room temperature suggests a high spin d 6 configuration of octahedrally coordinated Fe 2+ ions. 20
A rhombus M-Cl-M-Cl is almost the same in 4 and isostructural complexes of manganese(II), nickel(II) and cobalt(II), 13,15 while ring conformation of coordinated diglyme molecules slightly differs ( Figure 5).
The average Fe-Cl(bridging), Fe-O(diglyme) bonding distances and distances between two Fe 2+ ions linked by two μ-bridging chlorides are shorter in a cation of 3 than in a dinuclear complex 4.

Conclusions
A chelate η 3 , non-bridging coordination of diglyme as characteristic for all complexes of the first row d-block metals [13][14][15][16] was found in the four novel vanadium and iron complexes 1-4. The new complex of vanadium(III) chloride with diglyme 1 is a mononuclear compound with a facial arrangement of O-donor atoms from diglyme, which has been already reported for [MCl 3 (diglyme)] (M = Sc, Ti). 11,12 The facial coordination of diglyme molecule is retained in the vanadyl complex fac-[VOCl 2 (diglyme)], 2, achieved by an oxidation of [VCl 3 (diglyme)], 1, in the presence of air.