metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
N1ÐC2ÐO2 groups are planar for (I), (II), and (III) (r.m.s.
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deviations = 0.010, 0.005, 0.005 A, respectively). The r.m.s.
Communications
distances of C1 and C3 from this plane in (I), (II), and (III)
are, respectively, 0.062 and 0.030, 0.114 and 0.023, and
ISSN 0108-2701
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0.112 and 0.038 A. Thus, each N1 atom is essentially planar.
The O atoms assume a syn con®guration yielding O1ÐCuÐ
O2 and supplementary angles of ꢁ84 and ꢁ96ꢂ (Table 1),
respectively, thus making a nearly square-planar geometry
about the Cu atom.
Three complexes of bis(N-methyl-
benzohydroxamato-O,O0)copper(II)
Russell G. Baughman,* Daniel J. Brink, Jill M. Butler and
Pamela R. New²
Division of Science, Truman State University, Kirksville, MO 63501-4221, USA
Correspondence e-mail: baughman@truman.edu
Received 31 August 1999
Accepted 18 January 2000
The ®rst single-crystal studies of three bis-transoid Cu±hydrox-
amate salts, bis(3-methoxy-4,N-dimethylbenzohydroxamato-
O,O0)copper(II), [Cu(C10H12NO3)2], bis(4-chloro-N-methyl-
While most of the selected distances and angles noted in
Table 1 are comparable, some signi®cant (>4ꢁ) ones are
noteworthy. In (III), the CuÐO1 distance is longer than in
complexes (I) or (II), while the CuÐO2 distance is con-
comitantly shorter than its counterparts. Similarly, in (I), the
O1ÐN1ÐC1 angle is smaller than for (II) or (III); C1ÐN1Ð
C2 is larger.
For the most part, the CuÐO1 distances in the three title
complexes are shorter than in a few other ®ve-membered,
though not hydroxamate, rings. Singly bonded CuÐO
benzohydroxamato-O,O0)copper(II),
[Cu(C8H7ClNO2)2],
bis(N-methyl-3,5-dinitrobenzohydroxamato-O,O0)copper(II)±
chloroform (1/2), [Cu(C8H6N3O6)2]Á2CHCl3, are presented.
The Cu atom in each of the title compounds sits at a center of
inversion and displays a nearly square-planar geometry with
the hydroxamate-O atoms connected to it in a syn con®gura-
tion. The N atoms are in a transoid con®guration. Each ®ve-
membered Cu±hydroxamate ring is planar, thus providing
evidence that a planar N atom is present in each ring. The
phenyl groups are twisted with respect to the hydroxamate
group by ꢁ40±54ꢂ. The angular strain of the sp2 carbonyl
oxygen is signi®cant (ꢁ10ꢂ from ideal).
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distances of 1.902 (2) and 1.892 (2) A (with cupferron;
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Elerman et al., 1995); 2.011 (2) and 2.013 (2) A (with 2-amino-
2-thiazoline-4-carboxylic acid; Stocker et al., 1999); 1.936 (3)
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and 1.959 (3), and 1.935 (5) and 1.967 (4) A (with picolin-
amide hydrazone:alanine and picolinamide hydrazone:glycine,
respectively; Thompson et al., 1998) have been reported.
Stemmler et al. (1999) reported an average oxime OÐCu
distance for the ®ve metallocrown complexes in their study as
Comment
Copper complexes containing derivatives of the N-methyl-
benzohydroxamate ligand have been prepared for the study of
the organic ligand as an ꢀ nucleophile [see, for example, Carey
& Sundberg (1990) for a discussion on the ꢀ effect]. Unlike the
only other previous single crystallographic studies involving
Cu hydroxamates [a dimer by Barclay & Raymond (1986) and
metallocrown compounds by Stemmler et al. (1999)], we are
interested in how the presence of a transition metal will affect
the role of the ꢀ nucleophile in substitution reactions. Crystal
structure determinations were performed to determine the
bonding mode of the organic ligands to the copper center, as
well as to serve as a starting point for future molecular
modeling studies.
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1.934 (6) A, a difference of ꢁ6ꢁ greater than this work. The
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average carbonyl OÐCu distance of 1.947 (6) A is just slightly
(>3ꢁ) longer than those in this report. In each of their struc-
tures, the oxime-O atoms have a third coordination to a
lanthanide facilitating a bridging of Cu atoms to the Ln atom.
The hydroxamate-N atoms are also coordinated to a Cu atom
aiding in the formation of the metallocrown complexes. They
also reported an average value for the O1ÐCuÐO2 angle
(present notation) of 85.8 (2)ꢂ, a difference of >7ꢁ from this
work. Barclay & Raymond (1986) reported a single dimeric
complex in which the N atoms are cisoid, all of which is
different from that reported in this work. Their distances for
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oxime OÐCu [1.885 (4) A] and carbonyl OÐCu [1.915 (4) A]
are both <2ꢁ of the present work. Additionally, their average
O1ÐCuÐO2 angle of 84.2 (2)ꢂ is <1ꢁ from this work. The
stronger similarity of Barclay & Raymond's (1986) complex to
the three structures reported here is likely due to the
hydroxamate groups being less constrained in all four
complexes than in the work of Stemmler et al. (1999).
All three of the title compounds have a Cu atom at a center
of inversion so the hydroxamate-N atoms are in the transoid
con®guration, thus making this the ®rst report of bistransoid
Cu±hydroxamate structures. The ®ve-membered CuÐO1Ð
² Current address: Department of Chemistry, University of Central Okla-
homa, Edmond, OK 73034-5209, USA.
ꢀ
528 # 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved
Acta Cryst. (2000). C56, 528±531
Baughman, Russell G.
