Supramolecular architecture and a new mode of pyrazolate coordination (η3) in the first homoleptic lanthanide pyrazolate complexes

Article abstract of DOI:10.1002/(SICI)1521-3773(19990614)38:12<1766::AID-ANIE1766>3.0.CO;2-I

A linear supramoleculecular array of anions and cations is present in the solvent-free potassium salt of the homoleptic erbium pyrazolate complex [K{Er(η²-tBu₂pz)₄}n] (1). Treatment of 1 with [18]crown-6 in toluene/dimethoxyethane leads to formation of a charge-separated salt [Eq. (a)] in which the methyl group of a toluene molecule interacts with the potassium ion. tBu₂pz = 3,5-di-tert-butyl-pyrazolate.

Full text of DOI:10.1002/(SICI)1521-3773(19990614)38:12<1766::AID-ANIE1766>3.0.CO;2-I

COMMUNICATIONS
Supramolecular Architecture and a New Mode
of Pyrazolate Coordination (h3) in the First
Homoleptic Lanthanide Pyrazolate
Complexes**
Glen B. Deacon,* Ewan E. Delbridge, and
Craig M. Forsyth
The recent preparations of the first homoleptic pyrazolate
complexes [Ti(h2-Me2pz)4] (R2pz ˆ 3,5-disubstituted pyrazo-
late)[1a,b] and [Ta(h2-Me2pz)3(h1-Me2pz)2][1c] for relatively small
ions (ionic radii of Ti4‡ and Ta5‡: 0.74 Š)[2] are in contrast to
the invariable isolation of tris(h2-pyrazolate) derivatives of
the larger (ca. 1.0 Š)[2] lanthanide ions as [Ln(h2-R2pz)3(L)n]
complexes (L ˆ thf, dimethoxyethane (dme), or Ph3PO),[3]
rather than as homoleptic [Ln(R2pz)3] species. We now report
the first homoleptic pyrazolatolanthanide(iii) complexes 1 and
Figure 1. ORTEP plot of 1 (30% probability thermal ellipsoids; hydrogen
atoms and methyl groups omitted for clarity). Selected bond lengths [Š]
and angles [8]: Er N(11) 2.342(6), Er N(13) 2.292(6), Er N(21) 2.346(6),
Er N(23) 2.416(6), Er N(31) 2.350(6), Er N(33) 2.324(6), Er N(41)
2.361(6), Er N(43) 2.385(6), K N(21) 2.811(7), K N(23) 3.077(7),
K C(21) 3.187(7), K N(41) 2.842(6), K N(43) 3.130(6), K C(41)
3.093(8), K C(32') 3.162(7), K ´´´ C(31') 3.665(7), K ´´´ C(33') 3.577(7);
cen(1)-Er-cen(2) 98.1, cen(1)-Er-cen(3) 102.2, cen(1)-Er-cen(4) 137.2,
cen(2)-Er-cen(3) 136.7, cen(2)-Er-cen(4) 91.5, cen(3)-Er-cen(4) 98.7
(cen(x) ˆ center of the N(x1) N(x3) bond).
‡
the charge-separated 2. Additional novel features are the K /
[Er(h2-tBu2pz)4] supramolecular framework and a new
‡
pyrazolate coordination mode (h3 to K ) in 1, as well as the
‡
nature of the K /toluene interaction in 2. Pyrazolate ions
commonly bind as m-h1:h1, h1, or h2 ligands,[4] and m3-h1:h2:h1 (to
‡
K )[5] and m-h2:h2 (to Yb2‡)[6] coordination modes were
recently observed.
[K{Er(h2-tBu2pz)4}n]
[K([18]crown-6)(dme)(PhMe)][Er(h2-tBu2pz)4]
1
2
Complex 1 was prepared by reaction of anhydrous erbium
chloride with potassium 3,5-di-tert-butylpyrazolate in 1,2,4,5-
tetramethylbenzene at 2008C under vacuum [Eq. (a)] and
ErCl3 ‡ 4K(tBu2pz) !K[Er(tBu2pz)4] ‡ 3KCl
(a)
obtained in good yield by crystallization from toluene, while 2
was isolated by crystallization of 1 from dme/PhMe contain-
ing [18]crown-6. Not only are these the first homoleptic
pyrazolatolanthanide complexes, but they are also the first
mononuclear anionic lanthanide pyrazolates. The cages
[Ln3(Me2pz)6(m3-O)Na2L2] (L ˆ thf or Me2pzH) can be viewed
as polynuclear ªateº species.[7]
Figure 2. ORTEP plot of 2 (30% probability thermal ellipsoids; hydrogen
atoms and the methyl groups of the tBu substituents omitted for clarity).
Selected bond lengths [Š] and angles [8]: Er N(11) 2.332(3), Er N(13)
2.368(3), Er N(21) 2.359(3), Er N(23) 2.348(3), Er N(31) 2.332(3),
Er N(33) 2.378(3), Er N(41) 2.396(3), Er N(43) 2.336(6), K O(1)
2.885(3), K O(2) 2.868(3), K O(3) 2.863(3), K O(4) 2.841(3), K O(5)
2.782(3), K O(6) 2.900(3), K O(7) 2.823(3), K O(8) 3.075(3), K C(701)
3.423(4); cen(1)-Er-cen(2) 94.7, cen(1)-Er-cen(3) 135.8, cen(1)-Er-cen(4)
99.6, cen(2)-Er-cen(3) 100.9, cen(2)-Er-cen(4) 136.7, cen(3)-Er-cen(4) 96.7
(cen(x) ˆ center of the N(x1) N(x3) bond).
Analytical, IR, and Vis/near-IR data for 1 and 2 were
consistent with the proposed compositions. Conductivity
measurements in the low-polarity solvent CH2Cl2 suggest
greater ion separation in 2, although its conductivity is lower
than that typical for a 1:1 electrolyte in this solvent.[8] X-ray
crystallography[9] on 1 revealed a linear supramolecular array
of [Er(h2-tBu2pz)4] anions and potassium cations. The latter
are sandwiched between two of the pyrazolate ligands (h3
bonded), and the chains are linked by intermolecular
potassium ± carbon interactions (Figure 1). Discrete [Er(h2-
The erbium centers of 1 and 2 are coordinated to eight
nitrogen atoms of four h2-tBu2pz ligands, and the average
Er N distances (1: 2.35; 2: 2.36 Š) are comparable with those
of eight-coordinate [Er(h2-tBu2pz)3(thf)2][3a] and [Er(h2-
Ph2pz)3(Ph3PO)2][3c] (av 2.34 Š). The geometries around the
erbium atom, as defined by the centers of the N(x1) ± N(x3)
bonds (cen(x), x ˆ 1 ± 4) are highly distorted from tetrahedral
[cen-Er-cen 91.5 ± 136.7 (1); 94.7 ± 136.78 (2)]. Most likely,
these deviations minimize the steric repulsions between the
bulky tBu groups, since in the less crowded [Ti(h2-
tBu2pz)2Cl2][1b] the range of pseudotetrahedral angles
(100.5 ± 113.38) is markedly narrower. The similarity of the
‡
tBu2pz)4] anions and [K([18]crown-6)(dme)(PhMe)] cati-
ons are present in 2 (Figure 2).
[*] Prof. Dr. G. B. Deacon, E. E. Delbridge, Dr. C. M. Forsyth
Chemistry Department
Monash University
Clayton 3168 (Australia)
Fax: (‡613)9905-4597
[**] This work was supported by the Australian Research Council and an
Australian Postgraduate Award to E.E.D.
1766
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3812-1766 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 12

COMMUNICATIONS
geometries of the [Er(h2-tBu2pz)4] anions in 1 and 2 is
consistent with the supramolecular nature of the tBu2pz ´´´ K
´´´ tBu2pz interactions in 1.
Keywords: crown compounds ´ erbium ´ lanthanides ´ N
ligands ´ potassium
Two of the K N distances of
1 [K(1) N(21) and
K(1) N(41)] are comparable with the m-h1:h1 and h2 K N
distances of [{K(tBu2pz)(thf)}6].[5] Additionally, the adjacent
nitrogen and carbon atoms of both pyrazolate ligands [e.g.,
N(23) and C(21) for N(21)] are only about 0.3 Š further from
the potassium atom. These longer distances are similar to the
K N and K C distances (3.122(5) ± 3.255(5) Š) of a p-bound
K(h5-pyrrolyl) moiety[10] and hence are regarded as significant
interactions that give overall h3 coordination. The central
K N(21) and K N(41) bonds of the h3-pyrazolate ligands are
virtually normal (94.2, 92.58) to the ring planes, and this
implies p-donor bonding to potassium. Notably, the potassium
atom lies within the smallest of the intracentroid angles
(cen(2)-Er-cen(4) 91.58), and this also implies bonding. Since
the K ´´´ C distances of the remaining two C atoms of the
pyrazolate rings of each ligand are about 0.4 Š longer, it is
unlikely that they are significant interactions, especially in
[1] a) I. A. Guzei, G. P. A. Yap, A. H. Rheingold, H. B. Schlegel, C. H.
Winter, J. Am. Chem. Soc. 1997, 119, 3387 ± 3388; b) I. A. Guzei,
G. P. A. Yap, C. H. Winter, Inorg. Chem. 1997, 36, 1738 ± 1739; c) I. A.
Guzei, C. H. Winter, Inorg. Chem. 1997, 36, 4415 ± 4420.
[2] R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751 ± 767.
[3] For example: a) J. E. Cosgriff, G. B. Deacon, B. M. Gatehouse, H.
Hemling, H. Schumann, Aust. J. Chem. 1994, 47, 1223 ± 1235; b) J. E.
Cosgriff, G. B. Deacon, G. D. Fallon, B. M. Gatehouse, H. Schumann,
R. Weimann, Chem. Ber. 1996, 129, 953 ± 958; c) J. E. Cosgriff, G. B.
Deacon, B. M. Gatehouse, Aust. J. Chem. 1993, 46, 1881 ± 1896.
[4] a) S. Trofimenko, Chem. Rev. 1972, 72, 497 ± 509; b) S. Trofimenko,
Prog. Inorg. Chem. 1986, 34, 115 ± 210; c) A. P. Sadimenko, S. S.
Basson, Coord. Chem. Rev. 1996, 147, 247 ± 297; d) G. La Monica,
G. A. Ardizzoia, Prog. Inorg. Chem. 1997, 46, 151 ± 238; e) J. E.
Cosgriff, G. B. Deacon, Angew. Chem. 1998, 110, 298 ± 299; Angew.
Chem. Int. Ed. 1998, 37, 286 ± 287; f) D. Pfeiffer, M. J. Heeg, C. H.
Winter, Angew. Chem. 1998, 110, 2674 ± 2676; Angew. Chem. Int. Ed.
1998, 37, 2517 ± 2519; g) G. B. Deacon, E. E. Delbridge, B. W. Skelton,
A. H. White, Eur. J. Inorg. Chem. 1998, 543 ± 545.
Â
[5] C. Yelamos, M. J. Heeg, C. H. Winter, Inorg. Chem. 1998, 37, 3892 ±
‡
view of the position of K (see above), although they are
3894.
within the range found for potassium(h6-arene) bonding
(K C max. 3.72(1) Š; av 3.37 Š).[11, 12] The sevenfold coordi-
nation of the potassium atom in 1 is completed by a
potassium ± carbon (C32') contact (3.162(7) Š) to a neighbor-
[6] G. B. Deacon, E. E. Delbridge, B. W. Skelton, A. H. White, Angew.
Chem. 1998, 110, 2372 ± 2373; Angew. Chem. Int. Ed. 1998, 37, 2251 ±
2252.
[7] H. Schumann, P. R. Lee, J. Loebel, Angew. Chem. 1989, 101, 1073 ±
1074; Angew. Chem. Int. Ed. Engl. 1989, 28, 1033 ± 1035.
[8] a) W. J. Geary, Coord. Chem. Rev. 1971, 7, 81 ± 122; b) G. B. Deacon, T.
Feng, P. C. Junk, B. W. Skelton, A. H. White, J. Chem. Soc. Dalton
Trans. 1997, 1181 ± 1186.
ing [Er(h2-tBu2pz)4] anion (see ref. [13] for
Ag C(Me2pz) interaction). The next nearest carbon atoms
(see legend to Figure 1) are significantly more distant (by
0.4 Š or more) and are considered nonbonding.
The potassium cation in 2 is located in the cavity of an
[18]crown-6 molecule, and a chelating dme ligand is bound on
one side of the K([18]crown-6) moiety. A toluene molecule,
orientated with the methyl group toward the potassium ion,
occupies the vacant face opposite to dme. Formation of this
supramolecular K([18]crown-6)/toluene ªlock and keyº inter-
action (K C(Me) 3.423(7) Š) is remarkable given the excess
of the potential donor dme in the crystallization solution.
a similar
[9] Crystal data for 1: pink crystal, 0.25 Â 0.15 Â 0.15 mm, monoclinic,
space group P21/c, a ˆ 20.7775(10), b ˆ 12.3035(6), c ˆ 18.8274(6) Š,
b ˆ 90.527(1)8, Vˆ 4812.8(17) Š3, 1calcd ˆ 1.275 gcm 3, 2qmax ˆ 56.58,
N ˆ 11516 (Rint ˆ 0.072), No ˆ 7754, R ˆ 0.063, Rw ˆ 0.132 (all data:
R ˆ 0.112, Rw ˆ 0.147). Crystal data for 2: pink crystal, 0.25  0.13 Â
0.13 mm, monoclinic, space group P21/c, a ˆ 13.6803(2), b ˆ
21.6001(2), c ˆ 25.4376(4) Š, b ˆ 99.445(1)8, Vˆ 7414.8(3) Š3,
3
1calcd ˆ 1.227 gcm
,
2qmax ˆ 60.18, N ˆ 20450 (Rint ˆ 0.055), No ˆ
14904, R ˆ 0.051, Rw ˆ 0.108 (all data: R ˆ 0.088, Rw ˆ 0.129). A total
of N unique reflections (No with (I) > 2s(I) observed) were collected
(Enraf-Nonius CCD, monochromatic MoKa radiation, l ˆ 0.71073 Š,
Tꢀ 123 K) and used in least-squares refinement (anisotropic U for
non-hydrogen atoms, H atoms constrained (x, y, z, Uiso)) after
structure solution and expansion by Patterson and Fourier techniques.
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Center as supplementary publication no.
CCDC-112942 (1) and -112941 (2). Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
Experimental Section
1: Potassium 3,5-di-tert-butylpyrazolate (1.20 g, 5.5 mmol) was prepared
from KH and tBu2pzH in PhMe and heated with ErCl3 (0.38 g, 1.4 mmol) in
1,2,4,5-tetramethylbenzene (1.00 g) at 2008C/10 3 Torr in an evacuated
sealed Carius tube for 24 h. Extraction of the pink residue with light
petroleum (to remove C6H2Me4) followed by PhMe and subsequent
concentration yielded large pink crystals of 1 (2.58 g, 77%). IR (Nujol): nÄ ˆ
1568m, 1310w, 1285w, 1250m, 1226m, 1205m, 1129w, 1016m, 993s, 798vs,
782s, 728vs, 628w cm 1; Vis/near IR (PhMe): lmax (e) ˆ 379 (60), 490 (9),
[10] G. Solari, C. Floriani, A. Chiesi-Villa, C. Rizzoli, Organometallics
1997, 16, 508 ± 510.
[11] D. L. Clark, J. C. Gordon, J. C. Huffman, R. L. Vincent-Hollis, J. G.
Watkin, B. D. Zwick, Inorg. Chem. 1994, 33, 5903 ± 5911.
[12] C. Schade, P. von R. Schleyer, Adv. Organomet. Chem. 1987, 27, 169 ±
278.
522 (20), 595 (5), 654 (5), 980 nm (8); Lm (CH2Cl2) ˆ 0.22 Scm2 mol
1
(2.60 Â 10 3 m); elemental analysis calcd for C44H76N8ErK: C 57.23, H
8.30, N 12.13, Er 18.11; found: C 56.30, H 8.93, N 11.86, Er 18.35.
2: Compound 1 (0.10 g, 0.11 mmol) and [18]crown-6 (0.50 g, 1.9 mmol)
were dissolved in PhMe (20 mL) and dme (5 mL). Cooling of the solution
afforded a few pink acicular crystals of 2. IR (Nujol): nÄ ˆ 1606w, 1515m,
1486m, 1411m, 1319s, 1303m, 1285m, 1251m, 1225m, 1206m, 1191m,
1114brs, 1019m, 997s, 986m, 960s, 851s, 840s, 781s, 776s, 727vs, 694vs,
628w cm 1; Lm (CH2Cl2) ˆ 9.7 Scm2 mol 1 (1.31  10 3m); elemental anal-
ysis calcd for C67H118N8O8ErK: C 58.74, H 8.68, N 8.18; found: C 58.08, H
7.88, N 8.35.
Â
[13] L. R. Falvello, J. Fornies, A. Martín, R. Navarro, V. Sicilia, P.
Villarroya, Chem. Commun. 1998, 2429 ± 2430.
Received: December 30, 1998
Revised version: February 15, 1999 [Z12855IE]
German version: Angew. Chem. 1999, 111, 1880 ± 1882
Angew. Chem. Int. Ed. 1999, 38, No. 12
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3812-1767 $ 17.50+.50/0
1767