Cobalt, zinc, and nickel complexes of a diatopic heteroscorpionate ligand: Building blocks for coordination polymers

Article abstract of DOI:10.1021/ic701718b

New binuclear complexes of Co(II), Zn(II), and Ni(II) derived from a diatopic heteroscorpionate ligand, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl) methane (L4c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR, UV-vis spectroscopy, and magnetic susceptibility. These building blocks have been subsequently used for the construction of higher order metallosupramolecular architectures.

Full text of DOI:10.1021/ic701718b

Inorg. Chem. 2008, 47, 930−939
Cobalt, Zinc, and Nickel Complexes of a Diatopic Heteroscorpionate
Ligand: Building Blocks for Coordination Polymers
Guillermo A. Santillan and Carl J. Carrano*
Department of Chemistry and Biochemistry, San Diego State UniVersity,
San Diego, California 92182-1030
Received August 31, 2007
New binuclear complexes of Co(II), Zn(II), and Ni(II) derived from
a diatopic heteroscorpionate ligand,
(4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c), have been synthesized and characterized by X-ray
diffraction, ESI-MS, IR, UV vis spectroscopy, and magnetic susceptibility. These building blocks have been
subsequently used for the construction of higher order metallosupramolecular architectures.
−
Introduction
be amenable to the development of “controlled” self-
assembly.21,23 Thus, these building blocks can be used in
concert with polytypic linkers to produce different crystal
networks in a pseudo-controlled fashion. While polytopic
organic carboxylates and nitrogen heterocycles have been
widely used as bridging motifs in the development of these
metallosupramolecular complexes,24,25 the building blocks
themselves are more diverse. Previously, nitrogen-, oxygen-,
and sulfur-based multidentate scorpionate and heteroscor-
pionate ligands have been used almost exclusively as
nonbridging, facially coordinating ligands designed to enforce
mononuclearity.26,27 Recently, however, new bispyrazolyl
derivatives and other scorpionate ligands have been devel-
oped to generate metallosupramolecular complexes.28-32 In
Metallosupramolecular chemistry has shown explosive
development in recent years because of their actual and
potential applications in areas such as gas storage,1-6 host-
guest chemistry,7-10 molecular magnetism,11-13 and optical
devices.14,15 However, truly rational design of these metal-
losupramolecular structures still remains a largely elusive
goal. Of the many “rational” approaches to the design of
these structures,16-20 the building block route has proven to
* To whom correspondence should be addressed. E-mail: carrano@
sciences.sdsu.edu.
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J. R. J. Am. Chem. Soc. 2006, 128 (51), 16876-16883.
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R. E. J. Am. Chem. Soc. 2007, 129 (5), 1203-1209.
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pyrazolylborate Ligands; Imperial College Press: London, UK, 1999.
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930 Inorganic Chemistry, Vol. 47, No. 3, 2008
10.1021/ic701718b CCC: $40.75
© 2008 American Chemical Society
Published on Web 01/11/2008

Co, Zn, and Ni Complexes of Diatopic Heteroscorpionate Ligand
Scheme 1
this context diatopic heteroscorpionates emerge as particu-
larly attractive from the point of view of crystal engineering
because of their potential versatility. In previous work33 we
showed that a new heteroscorpionate (L4c) can adopt a
variety coordination mode toward Cu(II) which depends on
the coordination geometry preferences of the metal ion,
solvent polarity, the presence and nature of available anions,
and pH. In this paper we describe a number of related
dinuclear Co(II)-, Zn(II)-, and Ni(II)-based building blocks
that can be linked together to form interesting 1- and 2-D
coordination polymers. By studying their solution chemistry
via ESI-MS, we have also been able to enumerate species
present that are not amenable to solid-state structural analysis
by X-ray crystallography.
H, 5.08 (5.11); N, 21.48 (21.68). (KBr pellets) ν/cm-1: 3442, 2066,
1609, 1557, 1463, 1414, 1382, 1249, 1050, 835, 765, 714. λmax(CH3-
CN, ꢀ): 499 nm (377 M-1 cm-1); 549 nm (367 M-1 cm-1); 609
nm (389 M-1 cm-1). µeff ) 6.67 µB (solid, 295 K). ESI-MS
(methanol): m/z [Co2(HL4c)(L4c)(N3)2‚CH3OH]+ ) 881.69 amu.
(b) Co2(L4c)2(NCS)2 (2). This complex was prepared in a
manner analogous to that of complex 1 using ammonium thiocy-
anate in place of sodium azide. Yield: 62 mg (57.5%). Anal. Calcd
(Found) for [Co2(L4c)2(SCN)2‚1.5DMF], C42.5H48.5N11.5O5.5S2Co2:
C, 51.54 (51.87); H, 4.94 (5.13); N, 16.26 (16.55). IR (KBr pellets)
ν/cm-1: 3446, 2078, 1671, 1557, 1384, 1096, 837, 768, 711. λmax
(CH3CN, ꢀ): 543 nm (378 M-1 cm-1); 637 nm (298 M-1 cm-1).
µeff ) 6.64 µB (solid, 295 K). ESI-MS (acetonitrile): m/z
[Co2(L4c)2(SCN)2Na]+ ) 904 amu; [Co2(L4c)2SCN]+ ) 823 amu.
(c) Co2(L4c)2(O2CC6H4CN)2 (3). This complex was prepared
in a manner analogous to that of complex 1 using p-cyanobenzoic
acid in place of sodium azide. Yield: 96 mg (57%). Anal. Calcd
(Found) for [Co2(L4c)4(O2CC6H4CN)2]‚0.5CH3OH, C52.5H48N10O8.5-
Co2: C, 58.77 (58.46); H, 4.51 (4.73); N, 13.06 (13.28). IR (KBr
pellets) ν/cm-1: 3445, 2230, 1634, 1558, 1385, 1249, 1131, 849,
831, 778, 767, 715. λmax (CH3CN, ꢀ): 500 nm (548 M-1 cm-1);
549 nm (534 M-1 cm-1); 610 nm (549 M-1 cm-1). µeff ) 6.77 µB
(solid, 295 K). ESI-MS (methanol): m/z [Co2(HL4c)(L4c)(O2-
CC6H4CN)2‚CH3OH]+ ) 1089 amu.
(d) Co2(L4c)4 (4). A methanol solution (5 mL) of the ligand
L4c (126 mg, 0388 mmol) was added to a methanol solution (5
mL) of Co(acac)2 (50 mg, 0.194 mmol). The mixture was left to
stand at room temperature whereupon purple crystals were deposited
after a period of 12 h. The purple crystals were collected by
filtration, washed with methanol, and dried under vacuum for 1 h.
Yield: 54 mg (39%). Anal. Calcd (Found) for [Co2(L4c)4‚3H2O],
C72H84Co2N16O12: C, 58.30 (58.41); H, 5.71 (5.51); N, 15.11
(15.26). IR (KBr) ν/cm-1: 3431, 1613, 1560, 1414, 1385, 1252,
833, 767, 715. λmax (CH3CN, ꢀ): 516 nm (595 M-1 cm-1); 553
Experimental Section
Materials. All chemicals and solvents used during the syntheses
were reagent grade. Bis(3,5-dimethylpyrazolyl)ketone was prepared
according to the procedure described by The´ and Peterson.34
Caution: perchlorate salts are dangerous (especially if they are
dry) and should be handled with care! (4-Carboxyphenyl)bis(3,5-
dimethylpyrazolyl)methane (L4c) was prepared as previously
described.33
(A) Cobalt Complexes. (a) Co2(L4c)2(N3)2 (1). To a methanol
solution (5 mL) containing ligand L4c (94.1 mg, 0.29 mmol) and
sodium methoxide was added a methanol solution (5 mL) of Co-
(acac)2 (74.6 mg, 0.29 mmol) and sodium azide (18.8 mg, 0.29
mmol). The mixture was stirred for 5 min. The light blue precipitate
was collected by filtration, washed with methanol, and dried under
vacuum for 1 h. Yield: 48 mg (39%). Dark blue single crystals
suitable for X-ray analysis were prepared by slow evaporation of
a dichloromethane solution of the complex. Anal. Calcd (Found)
for [Co2(L4c)2(N3)2‚2CH3OH], C38H46N14O6Co2: C, 50.00 (49.66);
(31) Reger, D. L.; Semeniuc, R. F.; Pettinari, C.; Luna-Giles, F.; Smith,
M. D. Cryst. Growth Des. 2006, 6, 1068-1070.
(32) Ward, M. D.; McCleverty, J. A.; Jeffery, J. C. Coord. Chem. ReV.
2001, 222, 251-272.
(33) Santillan, G. A.; Carrano, C. J. Inorg. Chem. 2007, 46, 1751-1759.
(34) The, K. I.; Peterson, L. K. Can. J. Chem. 1973, 51, 422.
Inorganic Chemistry, Vol. 47, No. 3, 2008 931

Santillan and Carrano
932 Inorganic Chemistry, Vol. 47, No. 3, 2008

Co, Zn, and Ni Complexes of Diatopic Heteroscorpionate Ligand
Table 3. Selected Bond Lengths (Å) for [(L4c)4Co2] (4), [(L4c)4Zn2]
(10), and [(L4c)4Ni2] (11)
4
10
11
M(1)-O(1)
M(1)-O(2)
M(1)-O(3)
M(1)-O(4)
M(1)-N(1)
M(1)-N(3)
2.581(2)
1.967(2)
2.648(2)
2.006(2)
2.0757(19)
2.0359(19)
2.644(4)
1.957(4)
2.777(5)
2.035(6)
2.030(5)
2.079(5)
2.306(4)
2.188(4)
2.218(4)
2.215(4)
2.228(4)
2.198(4)
Table 4. Selected Bond Lengths (Å) for [(L4c)2Co2(O2CC6H4CO2)]∞
(5) and [(L4c)2Co2(O2C(C6H4)2CO2)]∞ (6)
5
6
Co(1)-O(1)
Co(1)-O(2)
Co(1)-O(3)
Co(1)-O(4)
Co(1)-N(1)
Co(1)-N(3)
2.729(7)
1.944(7)
3.132(7)
1.939(8)
2.046(9)
2.034(10)
2.521(12)
1.912(13)
3.008(11)
1.952(12)
2.054(13)
2.001(16)
Figure 1. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Co2-
(N3)2] showing complete atomic labeling.
Table 5. Selected Angles (deg): [(L4c)2Co2(N3)2] (1),
[(L4c)2Co2(O2CC6H4CN)2] (3), [(L4c)2Zn2(H2O)2](ClO4)2 (7), and [(L4c)
2Zn2(O2CC5H4N)2] (8)
1
3
7
8
O(2)-M(1)-N(1) 131.58(11)
98.6(3)
102.84(11) 124.2(2)
128.73(11) 100.5(2)
106.6(2)
O(2)-M(1)-N(3) 102.46(10) 130.1(3)
O(2)-M(1)-O(4)
N(3)-M(1)-O(4)
N(1)-M(1)-O(4)
O(2)-M(1)-O(3)
N(3)-M(1)-O(3)
N(1)-M(1)-O(3)
N(3)-M(1)-N(1)
100.50(18)
116.46(15)
120.67(16)
117.5(2)
115.4(2)
109.74(12)
110.65(11)
110.81(10)
88.19(11)
90.49(15)
90.97(10)
91.4(2)
N(5)-M(1)-O(2) 107.75(12)
N(5)-M(1)-N(1) 112.68(13)
N(5)-M(1)-N(3) 109.62(13)
N(5)-M(1)-O(1)
93.07(12)
N(3)-M(1)-O(1) 155.15(10)
O(2)-M(1)-O(1)
N(1)-M(1)-O(1)
59.51(9)
92.35(10)
Table 6. Selected Angles (deg): [(L4c)4Co2] (4), [(L4c)4Zn2] (10), and
[(L4c)4Ni2] (11)
Figure 2. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Co2(O2-
CC6H4CN)2] showing complete atomic labeling.
4
10
11
O(2)-M(1)-N(1)
O(2)-M(1)-N(3)
O(2)-M(1)-O(4)
N(3)-M(1)-O(4)
N(1)-M(1)-O(4)
N(3)-M(1)-N(1)
N(3)-M(1)-O(1)
O(2)-M(1)-O(1)
N(1)-M(1)-O(1)
N(1)-M(1)-O(3)
N(3)-M(1)-O(3)
O(1)-M(1)-O(4)
O(3)-M(1)-O(2)
O(3)-M(1)-O(4)
O(3)-M(1)-O(1)
100.53(7)
120.36(7)
104.24(9)
125.28(9)
111.45(8)
91.00(7)
119.88(17)
101.68(17)
106.6(2)
111.0(2)
123.0(2)
91.0(2)
87.55(15)
101.69(16)
122.99(15)
135.19(13)
93.57(14)
84.40(15)
115.38(15)
57.46(14)
141.67(13)
129.48(14)
88.08(14)
93.45(14)
142.70(15)
59.24(13)
85.71(14)
Table 2. Selected Bond Lengths (Å) for [(L4c)2Co2(N3)2] (1),
[(L4c)2Co2(O2CC6H4CN)2] (3), [(L4c)2Zn2(H2O)2](ClO4)2] (7), and
[(L4c)2Zn2(O2CC5H4N)2] (8)
1
3
7
8
M(1)-O(1)
M(1)-O(2)
M(1)-O(3)
M(1)-O(4)
M(1)-N(1)
M(1)-N(3)
M(1)-N(5)
2.384(2)
1.988(2)
2.498(4)
2.035(7)
2.797(6)
1.953(3)
2.033(4)
2.044(4)
2.508(3)
1.962(2)
1.982(3)
2.572(5)
1.983(4)
2.962(5)
1.929(4)
2.039(4)
2.044(5)
2.042(3)
2.070(3)
1.983(3)
2.072(2)
2.024(2)
nm (586 M-1 cm-1); 639 nm (507 M-1 cm-1). µeff ) 6.72 µB (solid,
295 K). ESI-MS (acetonitrile): m/z [Co2(L4c)3]+ ) 1087.97 amu.
(e) [Co2(L4c)2(O2CC6H4CO2)]∞ (5). This complex was prepared
in a manner analogous to that of complex 1 using terephthalic acid
neutralized with triethylamine in place of sodium azide. Yield: 42
mg (61%). Single crystals suitable for X-ray analysis were prepared
by slow evaporation of methanol solution of the complex. Anal.
Calcd (Found) for [Co2(L4c)2(O2CC6H4CO2)]‚3H2O, C44H48-
Co2N8O11: C, 53.77 (53.71); H, 4.92 (4.84); N, 11.40 (11.35). IR
(KBr pellets) ν/cm-1: 3448, 1607, 1557, 1386, 1343, 1261, 1028,
822, 770, 746, 714.
4,4′-dicarboxylic acid neutralized with triethylamine in place of
terephthalic acid. Yield: 58 mg (76%). Single-crystals suitable for
X-ray analysis were prepared by slow evaporation of methanol
solution of the complex. Anal. Calcd (Found) for [Co2(L4c)2(O2-
CC12H8CO2)], C50H46Co2N8O8: C, 59.77 (59.40); H, 4.61 (4.90);
N, 11.15 (11.31). IR (KBr pellets) ν/cm-1: 3447, 1618, 1560, 1458,
1396, 1343, 1261, 767, 715.
(B) Zinc Complexes. (a) Zn2(L4c)2(H2O)2 (7). A methanol
solution (10 mL) of ligand L4c (171 mg, 0.527 mmol) with sodium
methoxide (28.46 mg, 0.527 mmol) was added to an aqueous
solution (10 mL) of Zn(ClO4)2‚6H2O (196 mg, 0.527 mmol). The
(f) [Co2(L4c)2(O2C(C6H4)2CO2)]∞ (6). This complex was pre-
pared in a manner analogous to that of complex 5 using biphenyl
Inorganic Chemistry, Vol. 47, No. 3, 2008 933

Santillan and Carrano
Table 7. Selected Angles (deg): [(L4c)2Co2(O2CC6H4CO2)]∞ (5) and
[(L4c)2Co2(O2C(C6H4)2CO2)]∞ (6)
5
6
O(2)-Co(1)-N(1)
O(2)-Co(1)-N(3)
O(2)-Co(1)-O(4)
N(3)-Co(1)-O(4)
N(1)-Co(1)-O(4)
N(3)-Co(1)-N(1)
110.4(3)
121.8(3)
115.1(3)
101.9(4)
115.7(4)
89.7(4)
106.3(6)
124.9(6)
119.0(5)
100.8(6)
113.4(6)
88.8(6)
in place of Co(acac)2. Yield: 76 mg (63%). Anal. Calcd (Found)
for [Zn2(L4c)2(O2CC6H4CN)2]‚1.5H2O, C52H49N10O9.5Zn2: C, 56.94
(57.09); H, 4.50 (4.88); N, 12.77 (13.06). IR (KBr pellets) ν/cm-1
:
3423, 2228 1637, 1560, 1388, 1255, 1050, 833, 780, 767, 715. ESI-
MS (methanol): m/z [Zn2(HL4c)(L4c)(O2CC6H4CN)2‚CH3OH]+
)1102 amu.
(d) Zn2(L4c)4 (10). A methanol solution (5 mL) of ligand L4c
(130 mg, 0.402 mmol) with sodium methoxide (21.7 mg, 0.402)
was added to a methanol solution (5 mL) of Zn(acac)2‚H2O (106
mg, 0.402 mmol) at room temperature and stirred for 5 min. The
solution was left to stand at room temperature and white crystals
were obtained after a period of 12 h. The crystals were collected
by filtration, washed with water, and dried under vacuum for 1 h.
Yield: 67 mg (47%). Anal. Calcd (Found) for [Zn2(L4c)4]‚3.5H2O,
C72H83N16O11.5Zn2: C, 58.14 (58.16); H, 5.62 (5.88); N, 15.07
(15.24). IR (KBr pellets) ν/cm-1: 3448, 1630, 1560, 1465, 1385,
1257, 833, 767, 715. ESI-MS (acetonitrile): m/z [Zn2(L4c)4Na]+
) 1447.29; [Zn2(L4c)3]+ ) 1101 amu.
Figure 3. ORTEP diagram with 40% thermal ellipsoids of [(L4c)4Co2]
showing complete atomic labeling.
(C) Nickel Complexes. (a) Ni2(L4c)2(H2O)2 and Ni2(L4c)4 (11,
12). A methanol solution (5 mL) of ligand L4c (112 mg, 0.345
mmol) was added to an aqueous solution (5 mL) of Ni(ClO4)2‚
6H2O (126.3 mg, 0.345 mmol). The light green powder obtained
was collected by filtration, washed with methanol and water, and
dried under vacuum for 2 h. Yield: 41 mg (23%). Anal. Calcd
(Found) for [Ni2(L4c)2(H2O)2](ClO4)2‚2H2O, C36H46Cl2N8Ni2O16:
C, 41.77 (41.86); H, 4.48 (4.47); N, 11.34 (11.35). IR (KBr pellets)
ν/cm-1: 3422, 1560, 1431, 1396, 1119, 1090, 773, 716, 627. λmax
(CH3CN, ꢀ, M-1 cm-1); 698 nm (68 M-1 cm-1). µeff ) 3.2 µB (solid,
295 K). ESI-MS (acetonitrile): m/z [Ni2(L4c)2ClO4]+ ) 864 amu.
Single crystals suitable for X-ray analysis were prepared by the
careful diffusion of a methanol solution of L4c containing sodium
methoxide into an aqueous solution of Ni(ClO4)2‚6H2O. A light
green crystalline material was separated from the surrounding
Figure 4. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Co2(O2-
CC6H4CO2)]∞ showing complete atomic labeling.
mixture was stirred for 4 h at room temperature. The white powder
thus obtained was collected by filtration, washed with methanol
and water, and dried under vacuum for 2 h. Single crystals suitable
for X-ray analysis were prepared by the careful diffusion of a
methanol solution of L4c containing sodium methoxide into aqueous
solution of Zn(ClO4)2‚6H2O. Yield: 316 mg (68%). Anal. Calcd
(Found) for [Zn2(L4c)2(H2O)2](ClO4)2‚2H2O, C36H46Cl2N8O16Zn2:
C, 41.24 (40.87); H, 4.42 (4.23); N, 10.69 (10.85). IR (KBr pellets)
ν/cm-1: 3153, 1560, 1540, 1419, 1113, 1052, 858, 810, 761, 713,
624. ESI-MS (acetonitrile): m/z [Zn2(L4c)2ClO4]+ ) 878 amu.
(b) Zn2(L4c)2(O2CC5H4N)2 (8). This complex was prepared in
a manner analogous to that of complex 3 using Zn(acac)2‚H2O and
isonicotinic acid in place of Co(acac)2 and cyanobenzoic acid,
respectively. Yield: 53 mg (56.5%). Anal. Calcd (Found) for
[Zn2(L4c)4(O2CC5H4N)2]‚H2O, C48H48N10O9Zn2: C, 55.85 (56.1);
H, 4.78 (4.65); N, 13.29 (13.42). IR (KBr pellets) ν/cm-1: 3440,
1621, 1560, 1465, 1415, 1385, 1257, 1050, 854, 767, 746, 715.
(c) Zn2(L4c)2(O2CC6H4CN)2 (9). This complex was prepared
in a manner analogous to that of complex 3 using Zn(acac)2‚H2O
Figure 5. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Co2-
(O2C(C6H4)2CO2)]∞ showing complete atomic labeling.
934 Inorganic Chemistry, Vol. 47, No. 3, 2008

Co, Zn, and Ni Complexes of Diatopic Heteroscorpionate Ligand
Figure 6. ORTEP diagram with 40% thermal ellipsoids of the cationic
portion of [(L4c)2Zn2(H2O)2](ClO4)2 showing complete atomic labeling.
Figure 7. ORTEP diagram with 40% thermal ellipsoids of [(L4c)2Zn2(O2-
CC5H4N)2] showing complete atomic labeling.
powder by hand and proved to be that of Ni2(L4c)4 (11) rather
than that of the bulk Ni2(L4c)2(H2O)2 (12). ESI-MS (acetonitrile):
m/z [Ni2(L4c)3]+ ) 1087.50 amu.
Physicals Methods. Elemental analyses were performed by
Numega, San Diego, CA. All samples were dried in vacuum prior
to analysis. 1H and 13C NMR spectra were collected on Varian 200
or 500 MHz NMR spectrometers. Chemical shifts are reported in
ppm relative to an internal standard of TMS. IR spectra were
recorded as KBr disks on a ThermoNicolet Nexus 670 FT-IR
spectrometer and are reported in wavenumbers. Electronic spectra
were recorded using a Cary 50 UV-vis spectrophotometer. Room-
temperature magnetic susceptibility measurements of the metal
complexes were determined using a MSB-1 magnetic susceptibility
balance manufactured by Johnson Matthey and calibrated with
mercury(II) tetrathiocyanatocobaltate(II) (Xg ) 16.44(8) × 10-6 cm3
g-1). Diamagnetic corrections were taken from those reported by
O’Connor.35 Electrospray mass spectra (ESI-MS) were recorded
on a Finnigan LCQ ion-trap mass spectrometer equipped with an
ESI source (Finnigan MAT, San Jose, CA). Samples were dissolved
in either methanol or acetonitrile and eluted with acetonitrile with
0.1% formic acid or methanol with 0.1% formic acid. A gateway
PC with Navigator software version 1.3 (Finnigan Corp., 1995-
1997) was used for data acquisition and plotting. Isotope distribution
patterns were simulated using the program IsoPro 3.0.
Figure 8. ORTEP diagram with 40% thermal ellipsoids of [(L4c)4Zn2]
showing complete atomic labeling.
X-ray Crystallography. Crystals of complexes 1, 3-6, 8, 10,
and 11 were mounted on nylon loops with paratone oil (Hampton
Research) and placed in the cold stream (200 or 240 K) of a Bruker
X8 APEX CCD diffractometer. Compound 7 was mounted in a
capillary and data were collected at room temperature. The
structures were solved using direct methods or via the Patterson
function, completed by subsequent difference Fourier syntheses,
and refined by full-matrix least-squares procedures on F2. All non-
hydrogen atoms were refined with anisotropic displacement coef-
ficients while hydrogen atoms were treated as idealized contribu-
tions using a riding model except where noted. Hydrogen atoms
were generally neither located in difference maps nor placed in
idealized positions for isolated solvent molecules within the
structure. All software and sources of the scattering factors are
contained in the SHELXTL 5.0 program library (G. Sheldrick,
Siemens XRD, Madison, WI). The crystal data, data collection and
refinement parameters are given in Table 1.
Figure 9. ORTEP diagram with 40% thermal ellipsoids of [(L4c)4Ni2]
showing complete atomic labeling.
small/thin, i.e., 5 and 6, or because there was unresolved disorder
in the positions of the various solvent molecules. Thus, some of
the R factors were higher than is expected for small molecule
structures and/or data were collected only out to a relatively small
angle in 2θ. Despite these crystallographic shortcomings, the overall
features of chemical significance were quite clear and unambiguous.
It should be noted that many of the crystals used in this study
were relatively poorly diffracting either because they were extremely
(35) O’Connor, C. J. Prog. Inorg. Chem., 1982, 29, 203.
Inorganic Chemistry, Vol. 47, No. 3, 2008 935

Santillan and Carrano
Results and Discussion
Synthesis and Characterization. The reaction of the N2O
heteroscorpionate ligand designated L4c with Co(ClO4)2‚
6H2O produced a binuclear species of stoichiometry 2M:4L
(vide infra) different from that prepared with the analogous
Cu(II) salt.33 Because of this result, we found, after consider-
able experimentation, that reaction of cobalt(II) bisacetylac-
etonate or zinc(II) bisacetylacetonate hydrate in methanol
in the presence of the appropriate anion was a better synthetic
procedure for the preparation of the 2M:2L:2 anion dimeric
building blocks. Thus, reaction with a variety of different
monoanionic potential linkers including azide, thiocyanate,
cyanobenzoate, and isonicotinate smoothly yielded com-
plexes with a ratio of 2M:2L:2 anion. Although all of these
linkers had the potential to bridge between bimetallic units,
none was observed to do so in the solid state. Thus, only
dimers were isolated, which in all cases had the anionic end
of the linker bound to the metal(II) ion. In the absence of
any added exogenous anion, the use of Co(acac)2, Ni(ClO4)2‚
6H2O, or Zn(acac)2‚H2O as a starting material resulted in
the formation of the product with 2M:4L stoichiometry.
X-ray crystallography (vide infra) revealed that these prod-
ucts were in fact structurally related to the other dinuclear
complexes with the carboxylate end of another L4c ligand
functioning as the terminal anion to each metal(II) ion.
Figure 10. (a) 1-D coordination polymers of 5 along the crystallographic
c axis. Hydrogen atoms have been omitted for clarity. (b) 2-D network
coordination of 5 showing hydrogen-bonding interaction as seen along the
crystallographic c axis The dotted lines indicate interlayer hydrogen bonds.
(c) Packing diagram of 5 in the space-filling model, showing the alternation
of the coordination polymer chains along the crystallographic c axis.
While it was not surprising that the smaller ligands (i.e.,
azide or thiocyanate) were unable to function as bridges, due
to what would be expected to be severe steric repulsion
between the dinuclear units, it was unanticipated that none
of the larger monoanionic ligands (p-cyanobenzoate, isoni-
cotinate, p-aminobenzoate, etc.) could function in this regard.
On the other hand, similarly sized dianionic linkers such as
terephthalate did lead to complexes with the desired interac-
tions between dinuclear units which could be isolated as
linear polymers with a (2Co:2L:1Linker)∞ ratio. Thus, charge
considerations seem to be paramount in determining the
ability of exogenous ligands to bridge between the dinuclear
units. These reactions are summarized in Scheme 1.
Solid-State Structure of the Complexes. (A) Dinuclear
Cobalt and Zinc Complexes. Selected distances and angles
for the structures of these complexes are shown in Tables 2
and 5. Figures 1, 2, 6, and 7 contain the thermal ellipsoid
diagrams for [Co2(L4c)2(N3)2] (1), [Co2(L4c)2(O2CC6H4CN)2]
(3), [(L4c)2Zn2(H2O)2] (7), and [(L4c)4Zn2(O2CC5H4N)2] (8),
respectively. Single-crystal X-ray diffraction studies on the
neutral complexes 1, 3, 7, and 8 reveal that these complexes
possess a crystallographic center of inversion making only
one-half of these dimeric structures unique. In all these
complexes, depending on the perceived denticity of the
carboxylate ligands involved in the M2L2 core, the metal ions
can be viewed as being between four and five coordinate
and having structures ranging between distorted tetrahedral
and square pyramidal geometry. As seen from Table 2, the
M(1)-O(2) distances in the complexes 1, 3, 7, and 8 range
from 1.964 to 2.036 Å while the more weakly bound M(1)-
O(1) “bond” is between 2.38 and 2.57 Å. Both the difference
between M-O2 and M-O1 and the absolute values of
Figure 11. (a) 2-D network coordination of 6 showing hydrogen-bonding
interaction as seen along the crystallographic a axis. The dotted lines indicate
hydrogen bonds between uncoordinated carboxylates oxygen and water
molecules. Hydrogen atoms have been removed for clarity. (b) Packing
diagram of 6 in the space-filling model, showing the rectangular grid
produced along the crystallographic c axis.
M-O1 distances themselves are outside the limits of what
could be called bidentate carboxylate interactions. However,
in the cobalt complexes, the orientation of O1 and the Co-
O1 “bond” lengths are clearly also not commensurate with
simple unidentate binding; thus, we classify these interactions
as anisobibentate.
In the dinuclear unit the two pyrazolyl nitrogens, N(1) and
N(3), and the two carboxylate oxygen donors of the
scorpionate ligands occupy the four positions of a basal plane.
The apical position is then occupied by the N or O from the
936 Inorganic Chemistry, Vol. 47, No. 3, 2008

Co, Zn, and Ni Complexes of Diatopic Heteroscorpionate Ligand
Figure 13. Negative-ion ESI-MS of the formation of complex 4 in
dichloromethane. The upper frame shows the observed peak clusters
associated with [Co3(L4c)4(acac)2H2O(HCO2)]-, [Co2(L4c)4(HCO2)]-, and
[Co2(L4c)3(HCO2)2]-; the lower frame shows the calculated isotope
distribution patterns expected for these fragments (see Supporting Informa-
tion for proposed fragment compositions).
Figure 12. Positive-ion ESI-MS of the formation of complex 4 in
dichloromethane. The upper frame shows the peak clusters associ-
ated with [Co4(L4c)4(acac)4H3O]+, [Co4(L4c)3(acac)4CH3CN(H2O)]+, and
[Co3(L4c)3(acac)2CH3CN]+. The lower frame shows the calculated isotope
distribution pattern expected for these fragments.
monodentate carboxylate oxygen donors of the chelating L4c
ligands occupy the three positions of the basal plane, while
another monodentate carboxylate oxygen donor of L4c is
2.006 Å in 4 and 2.035 Å in 10 away from the metal in the
apical position. The M(1)-O(2) distances are 1.96 Å in 4
and 1.95 Å in 10. The average Npz-M(1)-O(2) is 110°
and both Npz-M(1)-O bond angles in the basal plane
deviate significantly from 90°. The average N(3)-M(1)-
N(1) angle is 91°. For the nickel complex 11, Figure 9
illustrates the pseudo-octahedral coordination around the
nickel ion with the two pyrazolyl nitrogen donors and one
oxygen from the carboxylate ligand L4c constituting one face
of the octahedron. The N(1)-M(1)-N(3) and average Npz-
M(1)-O(2) bond angles are 84.40° and 94.62°, respectively.
The deviation of bond angles from the 90° angle that is
expected for idealized octahedral geometry is presumably
due to the relatively small bite angle of the ligand. The
remaining bond distances and bond angles are unremarkable.
anionic “linkers”. Azide is N-bonded in 1 and water is bound
in 7, while carboxylate oxygens occupy this position in 3
and 8. Here the M(1)-O(4) bonds average 1.94 Å while the
M(1)-O(3) “interactions” average 2.88 Å, indicating a
largely unidentate axial carboxylate. The N(3)-M(1)-N(1)
angle for the complexes ranges from 88.19(11)° in 1 to 91.4-
(2)° in 8, while the N(1)-M(1)-O(2) bond angles range
from 98.6(3)° in 3 to 131.58(11)° in 1 and the N(3)-M(1)-
O(2) bond angles range from 100.5(2)° in 8 to 130.1(3)° in
3; both the Npz-M(1)-O(2) angles in the basal plane
therefore deviate significantly from 90°.
The metal ion sits out of the mean N1, N3, O1, and O2
plane for these complexes in the following order: 0.591 Å
[1], 0.598 Å [7], 0.708 Å [3], and 0.712 Å [8]. The
intramolecular metal-metal distance ranges from 8.192 Å
in 1 to 8.415 Å in 3. Since the zinc complex 7 is cationic,
there is a slightly disordered perchlorate in the lattice that
functions as a counterion and is involved in hydrogen-
bonding interactions that lead to extended structures in the
crystal (data not shown).
(B) Cobalt, Zinc, and Nickel 2M:4L Complexes. Single-
crystal X-ray diffraction on the neutral complexes [Co2-
(L4c)4] (4) and[Zn2(L4c)4] (10) indicate a pseudotetrahedral
coordination geometry around the metal while the corre-
sponding nickel complex Ni2(L4c)4 (11) displays a pseudo-
octahedral geometry. Selected distances and angles for the
structures of these complexes are shown in Table 3 and 6,
respectively. Figures 3, 8, and 9 contain the thermal ellipsoid
diagrams for Co2(L4c)4, Zn2(L4c)4, and Ni2(L4c)4, respec-
tively. The distorted tetrahedral structures of Co2(L4c)4 and
Zn2(L4c)4 show that the two pyrazolyl nitrogen donors and
(C) Polymeric Cobalt Complexes. Selected bond dis-
tances and angles for these coordination polymers are shown
in Tables 4 and 7, while Figures 4 and 5 contain the thermal
ellipsoid diagram of these complexes. The coordination
environments around the cobalt complexes [Co2(L4c)2(O2-
CC6H4CO2)]∞ (5) and [Co2(L4c)2(O2C(C6H4)2CO2)]∞ (6) are
considerably different from the pseudo-square-pyramidal
geometry seen in 1 and 3. Thus, the cobalt in these complexes
is best described as four-coordinate with distorted tetrahedral
geometry where two N pyrazole and one essentially mono-
dentate carboxylate of the chelating ligand L4c occupy the
base of the tetrahedron, while the monodentate carboxylate
of terephthalate or biphenyl 4,4′-dicarboxylate occupy the
apical position. Here, the Co-O1 and Co-O3 “interactions”
range from 2.52 to 3.13 Å, hence, our assignment of all the
carboxylates as unidentate. The dihedral angles between the
Inorganic Chemistry, Vol. 47, No. 3, 2008 937

Santillan and Carrano
Table 8. Theoretical and Experimental Positive and Negative Ion
ESI-MS Fragments from a Solution of Co(acac)2 with Ligand L4c in
Dichloromethanea
m/z
found
m/z
fragment
chemical formula calculated ((2 amu)
+
1
2
3
4
5
6
7
[Co4(L4c)4(acac)4H3O]+
C92H107Co4N16O17
1944.66
1661.34
1386.17
1087.97
1178.01
1456.36
1731.52
1942
1663
1385
1088
1178
1456
1734
[Co4(L4c)3(acac)4CH3CN(H2O)]+ C76H90Co4N13O15
+
[Co3(L4c)3(acac)2CH3CN]+
[Co2(L4c)3]+
C66H74Co3N13O10
+
+
C54H57Co2N12O6
C56H59Co2N12O10
C73H77Co2N16O10
C83H93Co3N16O15
[Co2(L4c)3(HCO2)2]-
[Co2(L4c)4(HCO2)]-
-
-
-
[Co3(L4c)4(acac)2H2O(HCO2)]-
a The eluent solvent was acetonitrile with 0.1% formic acid.
Figure 14. Positive-ion ESI-MS of the solution Zn(acac)2 with L4c in
chloroform The left panel shows the peak cluster associated with the
[Zn2(L4c)4Zn2(acac)4H2O]+ cation centered at 1969 amu while the right
corner panel shows the calculated isotope pattern expected for this fragment.
Table 9. Theoretical and Experimental Positive and Negative Ion
ESI-MS Fragments from a Solution of Zn(acac)2 with Ligand L4c in
Chloroforma
m/z
m/z
calculated
found
fragment
chemical formula
((2 amu)
[Zn4(L4c)4(acac)4H3O]+
[Zn3(L4c)4(acac)2H]+
[Zn2(L4c)3]+
[Zn2(L4c)3(HCO2)2]-
[Zn2(L4c)4HCO2]-
C92H107Zn4N16O17
1969.57
1688.93
1100.93
1190.96
1469.31
1969
1689
1102
1192
1469
+
1
2
3
4
5
+
C82H91Zn3N16O12
+
C54H57Zn2N12O6
C56H59Zn2N12O10
C73H77Zn2N16O10
-
-
a The eluent solvent was acetonitrile with 0.1% formic acid.
Table 10. 1H NMR Chemical Shifts for the Aromatic Region of the
Free Ligand, L4c, and a Solution of Zn(acac)2 + L4c in CDCl3
free ligand L4c
solution [Zn(acac)2 + L4c]
5.912 (s, 2H, PzH)
5.82 (s, 2H, PzH) A
6.13 (s, 2H, PzH) B
6.20 (d, 2H, ArH) C
6.82 (d, 2H, ArH) D
7.36 (s, 1H, CH) E
7.59 (s, 1H, CH) F
7.68 (d, 2H ArH) G
8.00 (d, 2H ArH) H
7.017 (d, 2H, ArH)
7.753 (s, 1H, CH)
7.946 (d, 2H, ArH)
Figure 15. 1H NMR spectrum of the aromatic region of a solution of
L4c + Zn(acac)2 in chloroform (CDCl3).
to bridge the dinuclear Co2L2 units together, no such
interaction was seen in any of the solid-state structures.
Therefore, we sought evidence for such potential interactions
in solution via electrospray ionization mass spectrometry
(ESI-MS). ESI-MS allows analysis of solution-phase species
in the gas phase without perturbation of their solution
distribution. Analysis of solutions of 1-3, 7, and 9 were all
similar and showed that the predominant species was always
the simple M2(L4c)2(anion)2 expected from the solid-state
structure. A listing of the major ion peaks along with their
formula, observed and predicted isotope patterns, and
proposed structures can be found in the Supporting Informa-
tion. We were particularly intrigued by the cobalt complex
4 and zinc complex 10 which had stoichiometry of M2(L4c)4
and whose X-ray structure revealed the axial binding of
additional L4c carboxylate anions to the basic dinuclear M2-
L4c2 unit. We were surprised that the solid-state structures
of 4 and 10 revealed two uncoordinated bispyrazole “sticky
ends”. The bispyrazole unit is a very good chelator and
therefore it was unexpected that such units should remain
uncoordinated. We consequently analyzed the ESI-MS
spectra of the complexes prepared from a mixture of metal-
(acac)2 and L4c in dichloromethane solution in both positive
and negative ion mode. The mass spectra of these complexes
in both ionization modes show several clean high mass
clusters (Figures 12-14), allowing us to identify species in
CoO2 and CoN2 planes of 80.03° in 5 and 78.85° in 6 are
less than the expected tetrahedral value, with the individual
L-Co-L bond angles also showing deviations from the
“ideal”. For example, while the O-Co-O bond angles are
115.1(3)° in 5 and 119(5)° for 6, the N-Co-N angles are
much smaller at 89.7(4)° [5] and 88.8(6)° [6], constrained
by the “bite” of the bis-chelating L4c ligand.
The packing interactions in this group of complexes
deserve some comment. Complex 5 packs in extended
columns, the uncoordinated carboxylate O atoms from the
ligand and terephthalate being involved in hydrogen bonds
with solvent methanol and water molecules. These solvent
molecules play the role of donors that exert some influence
on the overall alignment of these chains (Figure 10b). Thus,
the packing arrangement of 5 shows two different, out of
register, columns running in a parallel fashion along the c
axis.(Figure 10c). This leads to relatively tight packing
between the columns and no significant internal voids. The
crystal packing of 6 on the other hand with the longer
biphenyl linkers again displays chains arranged in a parallel
fashion along the c axis (Figure 11b). However, the chains
are now in register, leading to a two-dimensional gridlike
structure with grid dimensions ca. (12.0 × 10.8 Å) occupied
by solvent molecules.
(D) Solution Chemistry. Although complexes 1-4 con-
tain potentially diatopic “axial” ligands that could function
938 Inorganic Chemistry, Vol. 47, No. 3, 2008

Co, Zn, and Ni Complexes of Diatopic Heteroscorpionate Ligand
solution that were not amenable to solid-state structural
analysis by X-ray crystallography (Tables 8 and 9).
complexed L4c ligand along with protons assignable to
acetylacetonate, completely consistent with the ESI-MS
results and indicating formation of the tetranuclear [Zn4-
(L4c)4(acac)4] in solution. It is notable that the pure crystal-
line complexes Co2(L4c)4 and Zn2(L4c)4 are only poorly
soluble in dichloromethane or methanol but they become very
soluble in the presence of an excess of Co(acac)2 or Zn-
(acac)2. These results indicate that there is equilibrium
between the di- and tetranuclear species where the two
terminal nitrogen bis-pyrazole units coordinate to Co(acac)2
or Zn(acac)2.
In complex 4, the highest mass cluster is centered around
1942(2) amu and has an isotope pattern indicative of the
tetranuclear [Co4(L4c)4(acac)4(H3O)]+ cation. Thus, it is clear
that in solution the “sticky ends” of 4 are indeed coordinated
and capped off by Co(acac)2 units, giving an overall
tetranuclear complex. A second high mass cluster centered
about 1663(2) amu has an isotope pattern that is consistent
with a [Co4(L4c)3(acac)4(CH3CN)(H2O)]+ cation. The other
major peak envelopes are centered at 1385 and 1088 amu.
In negative ion mode there are three major peak clusters at
1735, 1456, and 1171 amu (see Figures 12, 13, Table 8, and
Supporting Information for proposed fragment composition).
We observed similar results for 10, where there are also
several clean high mass clusters in positive ion mode, the
highest mass of which is centered around 1969(2) amu and
has an isotope pattern indicative of the tetranuclear [Zn4-
(L4c)4(acac)4H3O]+ cation (Figure 14 and Table 9). The
second high mass cluster centered about 1688(2) amu has
an isotope pattern that is consistent with a [Zn3(L4c)4-
(acac)2H]+ cation. The other major peak cluster is centered
at 1102 amu. In negative ion mode there are two major peak
clusters at 1470 and 1192 amu.
In summary, we have shown that the potentially binucle-
ating heterscorpionate ligand (L4c) is capable of bridging
between metal centers and producing di-, tetra-, and poly-
nuclear species. We have been able to identify these species
both in the solid state and in solution by X-ray diffraction,
1
ESI-MS, and H NMR.
Acknowledgment. This work was supported in part by
NSF grant CHE-0313865. The NSF-MRI program grant
CHE-0320848 is also gratefully acknowledged for support
of the X-ray diffraction facilities at San Diego State
University.
Supporting Information Available: Additional crystallographic
data (CIF files) for complexes 1, 3-8, 10, and 11; observed vs
calculated isotope patterns for ESI-MS of complexes 1-4, 7, and
9-11; fragments of a solution Co(acac)2 + L4c. This material is
available free of charge via the Internet at http://pubs.acs.org.
Since a mixture of Zn(acac)2 and L4c is very soluble in
1
chloroform, we were also able to analyze the H NMR of
this solution (Figure 15 and Table 10). The 1H NMR
spectrum demonstrates that there are two distinctly different
sets of chemical shifts attributable to the two types of
IC701718B
Inorganic Chemistry, Vol. 47, No. 3, 2008 939