Crystal Growth & Design
Article
2
occupancies of 85.4 and 14.6%. Because of the relatively low
contribution of the diselenide molecule to the electron density map,
numerous restraints were necessary in its refinement. These included
bond length restraints on C6B−Se2, C7B−Se3, C5B−C6B, C7B−
C8B, and Cd1B−O5B. The methylene carbons were restrained to
coplanarity with the pyridyl ring. Finally, each non-H atom in the
diselenide (except the Se atoms) was restrained to have identical
thermal parameters to its selenide counterpart.
Geometrical parameters describing the stacking interactions
between pyridine rings were determined with the CCDC Mercury
program, version 1.4.2.26 Some newer versions of Mercury lack the
ability to calculate normal projection distances between planes and
centroids (R). No hydrogen bond interactions meeting the CCDC
Mercury program, version 1.4.2 default definitions were found in
complexes 1−5.
Powder Diffraction. Powder diffraction analysis was carried out
on the instrument described above.27 Samples were ground and
prepared as mulls using Paratone N oil. Four 180 s frames were
collected, covering 8−100° 2θ. Frames were merged using the
SMART Apex II software27 and were further processed using
DIFFRAC-Plus and EVA software.28
Solution-State NMR Spectroscopy. Proton NMR spectra were
collected in 5 mm o.d. NMR tubes on a Varian Mercury 400VX NMR
or an Agilent 400-MR DD2 NMR spectrometer operating in the pulse
Fourier transform mode. Calibrated autopipets were used to prepare
nominally 1−5 mM solutions for variable temperature NMR
measurements. The sample temperature was maintained by blowing
chilled nitrogen over the NMR tube in the probe. Proton chemical
shifts were measured relative to internal solvent but are reported
relative to tetramethylsilane (TMS). Coupling constants are reported
in Hertz. Solution NMR spectra were stable over a period of days but
unstable over extended time periods.
7.62 (dt, 2Hc, JHH 1.5, 7.8), 7.21−7.14 (m, 4Hb+d), 4.06 (s, 4He, JSeH
15.3). (CD3CN): δ 8.49 (m, 2Ha), 7.67 (dt, 2Hc, JHH 1.7, 7.8), 7.24−
2
7.18 (m, 4Hb+d), 4.09 (s, 4He, JSeH 14.8).
Bis(pyridin-2-ylmethyl)selanedichlorozinc(II) (1a and 1b). Meth-
od A. ZnCl2 (37 mg, 256 μmol) was dissolved in a mixture of 2 mL of
acetonitrile and 2 mL methanol. While stirring, a solution of L (67 mg,
255 μmol) in 4 mL of CH3CN was added resulting in immediate
precipitation of a white solid. The solid complex was dissolved in 75
mL of CH3CN and 1 mL of toluene was added dropwise. A trace
amount of red precipitate was removed by vacuum filtration. X-ray
quality crystals of monoclinic 1a were harvested after slow evaporation
of ∼10 mL of the solution over the course of two months. The
remaining solution was evaporated down to ∼5 mL under a stream of
argon to recover additional 1a. Yield: 44 mg (110 μmol, 43%). Method
B: A solution of L (32 mg, 122 μmol) in 4 mL of acetonitrile was
slowly added to a solution of ZnCl2 (16 mg, 117 μmol) in 4 mL of
methanol with stirring. Colorless octahedra of tetragonal 1b suitable
for X-ray analysis were obtained in very low yield from the Celite
filtered solution following overnight storage at −20 °C. Continued
storage of the mother liquor at −20 °C provided prismatic crystals of
1a. Based on powder diffraction analysis, the isolated sample was
predominantly 1a (Figure S3, Supporting Information). Yield: 21.8 mg
(54.6 μmol, 47%). MP 239 °C (dec). Anal. Calcd for
C12H12Cl2N2SeZn: C 36.06, H 3.03, N 7.01. Found: C 35.68, H
1
2.95, N 6.95. H NMR (CD3CN, 2 mM): δ 8.90 (d, 2Ha, JHH 6.6),
8.10 (dt, 2Hc, JHH 1.7, 7.8), 7.68 (dd, 2Hd, JHH 8.0), 7.60 (dd, 2Hb, JHH
2
7.7, 5.5), 3.70 (s, 4He, JSeH 17.5).
Bis[bis(pyridin-2-ylmethyl)selanechloro(μ-chloro)cadmium(II)]
(2). A solution of L (162 mg, 0.62 mmol) in 6 mL of acetonitrile was
added to a solution of CdCl2 (58 mg, 0.32 mmol) in 6 mL of methanol
with stirring, rinsing with 2 × 0.5 mL CH3CN. The white precipitate
formed upon addition was dissolved by adding 45 mL of CH3CN in 5
mL increments with sonication. After vacuum filtration, the solution
was set aside in 5 mL aliquots for slow evaporation. Colorless X-ray
quality crystals (33 mg, 12% yield based on CdCl2) appeared within 2
days. Poor quality crystals resulted when stoichiometric amounts of
ligand were used. MP 155° (dec). Anal. Calcd for C12H12CdCl2N2Se:
Materials and Syntheses. Anhydrous DMF was obtained from
Alfa Aesar in ChemSeal bottles. Other organic solvents and reagents
were of commercial grade and either used as received or distilled from
CaH2 as indicated. Metal salts were dried under a vacuum overnight.
Elemental analyses were performed by Atlantic Microlabs, Inc. of
Norcross, GA.
1
C 32.26, H 2.71, N 6.27. Found: C 32.49, H 2.66, N 6.26. H NMR
(CD3CN, 2 mM): δ 8.85 (d, 2Ha, JHH 5.2), 7.87 (dt, 2Hc, JHH 1.6, 7.8),
7.49 (d, 2Hd, JHH 8.1), 7.42 (dd, 2Hb, JHH 7.7, 5.7), 4.20 (s, 4He, 2JSeH
12.3).
CAUTION! 2-(Chloromethyl)pyridine hydrochloride causes skin
and eye burns and is absorbed through the skin.
Bis(pyridin-2-ylmethyl)selane (L). Method I. A variation of the
method of Kreif et al. for preparation of alkyl selenides was initially
used to prepare L.29 Selenium (0.39 g, 4.9 mmol) and NaBH4 (0.37 g,
9.8 mmol) were stirred under Ar. EtOH (1.87 mL, 29.3 mmol) and
dry DMF (9 mL) were added dropwise. The initially red-brown
mixture became colorless with stirring over 90 min. (2-Chloromethyl)-
pyridine (obtained from (2-chloromethyl)pyridine hydrochloride
(2.00 g, 12.2 mmol) by neutralizing with 1.22 mL of 10 M NaOH,
extracting with ether (4 × 20 mL), drying with magnesium sulfate,
filtering, and concentrating by distillation under argon) was added
dropwise. The reaction mixture was stirred for 2−4 h. Deionized water
(5 mL) was added to quench the reaction. The solution was extracted
with ether (4 × 25 mL). Combined organics were dried with
magnesium sulfate, filtered, and concentrated in vacuo. The residue
was triturated with ether (2 × 2 mL), concentrated in vacuo, and then
purified by column chromatography on alumina using 1:3 ethyl
acetate:hexanes as the mobile phase. TLC plates were visualized with
aqueous 1% KMnO4, 2% Na2SO4. L (Rf 0.25, 0.83 g, 3.14 mmol, 64%
yield) was obtained as a pale yellow oil containing trace amounts of
L*.
Bis(pyridin-2-ylmethyl)selanedi(μ-nitrate)zinc(II) (3). Zn(NO3)2·
6H2O (56 mg, 188 μmol) was dissolved in acetonitrile (14 mL).
While stirring, a solution of L (50 mg, 190 μmol) in 6 mL of CH3CN
was added resulting in immediate precipitation of a white solid. After
stirring overnight, the precipitate was collected by centrifugation and
washed by suspension in CH3CN (43 mg, 95 μmol, 40% yield). The
supernatant was filtered through Celite and set aside for slow
evaporation. X-ray quality crystals formed in 10 days. MP 170 °C
(dec). Anal. Calcd for C12H12N4O6SeZn: C 31.85, H 2.67, N 12.38.
Found (precipitate): 31.86, H 2.52, N 12.25. 1H NMR (CD3CN,
saturated, 20 °C): δ 8.66 (d, 2Ha, JHH 5.5), 8.11 (dt, 2Hc, JHH 1.5, 7.8),
7.71 (d, 2Hd, JHH 8.1), 7.59 (dd, 2Hb, JHH 7.6, 5.4), 4.01 (s, 4He, 2JSeH
16.1).
Bis(pyridin-2-ylmethyl)selanedi(μ-nitrate)cadmium(II) (4a). A sol-
ution of L prepared by the method of Prakash (38 mg, 0.144 mmol) in
10 mL acetonitrile was added to a solution of Cd(NO3)2·4H2O (44
mg, 0.143 mmol) in 5 mL acetonitrile with stirring, rinsing with 2 × 1
mL acetonitrile. The resulting white precipitate was either collected by
centrifugation or dissolved by incremental addition of acetonitrile (4 ×
5 mL) with sonication. The clarified solution was filtered through
Celite and partitioned into roughly 10 mL fractions. Although no
Method II. The method of Prakash et al.19 provided L in high purity
following extraction and removal of solvent in vacuo. To minimize air
oxidation of the uncomplexed ligand, it was evacuated and flushed with
1
evidence for air oxidation of 4 was found by H NMR after weeks of
1
storage at room temperature in an oxygen saturated acetonitrile
solution, slow evaporation was conducted under positive pressure of
argon as a precaution against potential air oxidation. Small, colorless
crystals appeared after 4 days and were harvested after 11 days (10 mg,
14% yield). MP 160 °C (dec). Anal. Calcd for C12H12CdN4O6Se: C
28.85, H 2.42, N 11.21. Found (precipitate): C 28.76, H 2.49, N 11.07.
1H NMR (CD3CN, nominally 2 mM): 8.64 (d, 2Ha, JHH 5.3), 7.90 (dt,
argon before storage at 4 °C. H NMR (CDCl3): δ 8.53 (d, 2Ha, JHH
4.8), 7.61 (dt, 2Hc, JHH 1.9, 7.7), 7.34 (d, 2Hd, JHH 7.8), 7.12 (ddd,
2
2Hb, JHH 7.5, 5.0, 1.0), 3.92 (s, 4He, JHSe 13.7); (CD3CN) δ 8.47 (d,
2Ha, JHH 5.0), 7.66 (dt, 2Hc, JHH 1.8, 7.8), 7.34 (d, 2Hd, JHH 7.7), 7.12
2
(dd, 2Hb, JHH 7.6, 4.8), 3.91 (s, 4He, JSeH 13.0).
1,2-Bis(pyridin-2-ylmethyl)diselane (L*). The method of Bhasin et
al. was used to prepare L*.30 1H NMR (CDC13): δ 8.56 (m, 2Ha),
6500
dx.doi.org/10.1021/cg501395p | Cryst. Growth Des. 2014, 14, 6497−6507