Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Direct X-ray confirmation of the possible use of magnetochemical criteria for binuclear structural isomers of copper(II) complexes based on acylhydrazones of salicylic aldehyde-substituted derivatives Victor A. Kogan,a Vladimir V. Lukov,*a Sergei I. Levchenkov,a Mikhail Yu. Antipinb and Oleg V. Shishkinc a Department of Chemistry, Rostov State University, 344090 Rostov-on-Don, Russian Federation. Fax:+7 8632 28 5667 b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085 c Institute for Single Crystals, National Academy of Sciences of the Ukraine, 310001 Khar’kov, Ukraine. Fax:+7 057 232 0273 X-Ray structural investigations and magnetic measurements of binuclear copper(II) complexes with salicylic aldehyde acylhydrazone have demonstrated the possible use of magnetochemical criteria for the identification of structural isomers in the given class of compounds.It was shown earlier1–3 that complex formation between acylhydrazones of salicylic aldehyde-substituted derivatives and copper(II) acetate leads to two possible isomeric structures 1a or 1b whereas copper(II) perchlorate gives a binuclear analogue of the type 1b'.The difference between these structures lies in the different electronic nature of the bridging oxygen atoms. In fact the bridging atom in 1a is the a-oxyazinic atom of the hydrazide moiety while in 1b and 1b' it is the phenoxide oxygen atom of the salicylic moiety. We believe that the types of hybridization of these two oxygen atoms are quite different, so as a consequence the bond angles Cu–O–Cu in the exchange fragment are different too.The systematic magnetochemical study carried out by us revealed that the antiferromagnetic exchange interaction for the complexes 1b and 1b' is always much stronger (the exchange parameters 2J lie in the range –300–500 cm–1) than for the binuclear complexes 1a (2J lie in the range –20–130 cm–1).3,4 This can be explained by the greater degree of planarity of the exchange fragment including the phenoxide oxygen atom (types 1b, 1b').A geometrical model which explains these differences has been developed earlier,5 and the experimental data in this field were also systematized.These data point to a possible use of magnetochemical criterion in the identification of given structural isomers. The present paper is devoted to the first confirmation of the above hypothesis using X-ray diffraction data.† The type 1b' binuclear copper(II) complex (R1 = H, R2 = C12H25) has been used as an object of investigation; its magnetic properties have been compared with the properties of the type 1a complex (R1 = H, R2 = C12H25) which has been especially synthesized for the first time.It can easily be seen that in this particular case the exchange parameters 2J (calculated in terms of the HDVV model6) for the 1a type complex are much lower (in absolute value) than for 1b'. This can be explained3 by the geometrical differences between the exchange fragments.Indeed, the structure of the † Crystal data for 1b': C42H70N4O6Cu2 2+ · 2ClO4 – , monoclinic, space group P21/c, a = 17.528(5) Å, b = 18.087(7) Å, c = 7.812(2) Å, b = = 94.54(2)°, V = 2469(1) Å3, F(000) = 1108, Dc = 1.416 g cm–3, Z = 2. Data were measured using a Syntex P21/PC diffractometer (T = 193 K, graphite-monochromated MoKa radiation, l = 0.71073 Å, q/2q scan, 2qmax = 50°).The structure was solved by direct methods using the SHELXTL PLUS program package. Refinement against F2 in an anisotropic approximation (the hydrogen atoms isotropic in the riding model) by a full matrix least-squares method for 2888 reflections was carried out to R1 = 0.077 [for 1754 reflections with F > 4s(F), wR2 = 0.244, S = 1.02]. Atomic coordinates, bond lengths and bond angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ‘Notice to Authors’, Mendeleev Commun., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 1135/28. Cu O O Cu A R1 O N Cu O N R2 R1 O N Cu O N R2 1a R1 O N Cu O N R2 R1 O N Cu O N R2 R1 O N Cu O NH R2 R1 O N Cu O HN R2 · 2ClO4 2+ 1b 1b' aMean square error. bMole part of paramagnetic impurity.cThe value of meff is calculated per one copper ion in the binuclear molecule. Table 1 Magnetic properties of type 1a and 1b' binuclear complexes. T/K meff /B.M. (exp.) meff /B.M. (calc.) 1a: 2J = –118 cm–1, g = 2.02, r = 0.66%,a f = 0b 85.4 1.12 1.11 102 1.24 1.24 119 1.33 1.33 137 1.40 1.40 150 1.44 1.44 171 1.50 1.49 230 1.59 1.59 242 1.60 1.60 263 1.62 1.62 293 1.65 1.64 1b': 2J = –349 cm–1, g = 2.00, r = 1.47%,a f = 0.03b 77.4 0.38 0.38 101 0.46 0.47 136 0.66 0.66 160 0.78 0.78 190 0.93 0.93 216 1.04 1.04 232 1.10 1.10 254 1.17 1.16 271 1.22 1.21 299 1.27 1.28Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) complex (Figure 1) has confirmed this assumption; the exchange fragment A is strictly planar. The small displacement (0.06 Å) of the copper atom from the plane O(2), O(2A), O(1), N(2) to the O(1M) atom is possibly caused by the small differences in the Cu(1)–O (perchlorate-ion) [2.600(6) Å] and Cu(1)–O (methanol) [2.320(6) Å] bond lengths.As shown earlier the type 1b' complexes are ionic in organic solvents so Cu(1)–O (perchlorate) coordinative bonds are not strong and the anions are out of the coordination sphere in solution.Nevertheless in contrast to other types of complexes7 the type 1b' complexes, according to magnetochemical data, remain dimeric in solution. All these results confirm the high stability of the complex molecules due to their high symmetry. The following brief description of complex structure confirms this.In the crystal the molecule 1b' (R1 = H, R2 = C12H25) is arranged in the centre of symmetry which is situated at the intersection of the Cu(1)–Cu(1A) and O(2)–O(2A) lines. The copper atom is six-coordinate (taking into account weak coordination of the metal with ClO4 – ). The organic ligand is almost planar. The atom deviations from the mean plane are less than 0.04 Å.The bond length values in the O=C–NH– N=C–Car fragment indicate considerable delocalization of electron density. The five-membered metallocycle is planar. The atomic deviations from the mean plane are less than 0.05 Å. The six-membered metallocycle has a flattened sofa conformation. The deviation of the Cu(1) atom from the N(2), C(14), C(15), C(18), O(2) plane is 0.18 Å.The alkyl substituent has a trans-conformation with regard to all C(sp3)–C(sp3) bonds, excluding the C(2)–C(3) bond. This substituent is directed almost orthogonally to the plane of the organic ligand. The angle between their mean planes is 110.4°. The methanol molecule is turned, with respect to the Cu(1)–O(1) bond, by –30.0(7)° [the O(1)–Cu(1)–O(1M)–C(1M) torsion angle]. Unfortunately, the position of the hydroxy group hydrogen could not be determined. In the crystal complex molecules form infinite chains due to H-bonding H(1N)···O(25)' (1 – x, 0.5 + y, 1.5 - z) (O···H 2.06 Å, O···H–N 163.9°).Thus, the X-ray confirmation discussed in this paper allows one to use with great confidence the magnetic exchange parameters for binuclear copper(II) complexes based on acylhydrazones as the magnetochemical criterion of structural isomerism. References 1 V.A. Kogan and V. V. Lukov, Abstracts of the XXIXth Intl. Congress on Coord. Chem., Lausanne, Switzerland, 1992, p. 708. 2 E. V. Bogatyreva, V. A. Kogan, V. V. Lukov and V. A. Lokshin, Zh. Neorg. Khim., 1990, 35, 2010 (Russ. J. Inorg. Chem., 1990, 35, 1145). 3 V. V. Lukov, S. I. Levchenkov and V. A. Kogan, Koord. Khim., 1995, 21, 402 (Russ. J. Coord. Chem., 1995, 21, 385). 4 V. A. Kogan, V. V. Zelentsov, G. M. Larin and V. V. Lukov, Kompleksy perekhodnykh metallov s gidrazonami. Fiziko-khimicheskie svoistva i struktura (Transition metal complexes with hydrazones. Physicalchemical properties and structure), Nauka, Moscow, 1990, p. 112 (in Russian). 5 V. A. Kogan and V. V. Lukov, Koord. Khim., 1993, 19, 476 (Russ. J. Coord. Chem., 1993, 19, 545). 6 R.Carlin, Magnetochemistry, Springer–Verlag, Heidelberg, 1986. 7 S. I. Levchenkov, V. V. Lukov and V. A. Kogan, Koord. Khim., 1996, 22, 557 (Russ. J. Coord. Chem., 1996, 22, 523). C(13) C(12) C(11) C(10) C(9) C(8) C(7) C(6) C(5) C(4) C(3) C(2) C(1) C(14) C(15) C(16) C(17) C(18) C(19) C(20) N(1) N(2) O(1) O(2) C(1M) O(1M) Cu(1) Figure 1 Structure of complex 1b' (R1 = H, R2 = C12H25), ClO4 – anions are not shown. Selected bond lengths (Å) and bond angles (°): Cu(1)–N(2) 1.918(7), Cu(1)–O(2) 1.971(5), Cu(1)–O(2A) 1.974(5), Cu(1)–O(l) 2.011(5), O(2)–Cu(1A) 1.974(5), Cu(1)–O(1M) 2.320(6), Cu(1)–Cu(1A) 2.885(8); N(2)–Cu(1)–O(2) 90.5(3), N(2)–Cu(1)–O(2A) 170.2(2), O(2)–Cu(1)–O(2A) 80.5(2), N(2)–Cu(1)–O(1) 81.1(3), O(2)–Cu(1)–O(1) 171.2(2), O(2A)–Cu(1)– O(1) 107.6(2), Cu(1)–O(2)–Cu(1A) 99.5(2). Cu(1A) O(2A) Received: Moscow, 24th April 1998 Cambridge, 24th June 1998; Com. 8/03516D