First-Row Transition-Metal Complexes of the 1-Methoxycyclobutenedionate(1−) Ion

Abstract

The synthesis and characterization by single-crystal X-ray crystallography of a series of monomeric first-row transition-metal complexes with the 1-methoxycyclobutenedionate(1-) ligand are described. The isomorphous compounds [M(CH(3)OC(4)O(3))(2)(H(2)O)(4)] (M = Mn, Co, Ni, Zn) are C(2) symmetric and crystallize in the monoclinic space group C2/c. The metal atom in each of these complexes is six-coordinate with two cis 1-methoxycyclobutenedionate(1-) ligands, the methoxy substituent being oriented cis with respect to the ligating oxygen atom. The remaining coordination sites are filled by four aqua ligands. Monomers are linked by O-H.O hydrogen bonds to form arrays of stepped tapes. Hydrolysis of the methoxy group on the ligand occurs during the formation of the copper complex and {[Cu(C(4)O(4))(H(2)O)(2)].0.25H(2)O}(n)() is produced. This complex crystallizes in the tetragonal space group P4/n and has a structure similar to, but differing significantly from, those of a series of 3-dimensional cage squarates which have been reported previously.

Lanthanide Complexes of 3-Diphenylamino-4-hydroxycyclobut-3-ene-1,2-dione (Diphenylaminosquarate)

“…As was observed for the transition metal complexes of both methylsquarate 7 and methoxysquarate, the pattern of bonding in the C 4 -ring in complexes 1 − 4 is the same regardless of the coordination mode. However, the individual ring dimensions vary as a function of the nature of the ring substituent, that is, the Δ(C−C) values change.…”

“…An analysis of the pattern of bonding within the diphenylaminosquarate ligands throughout the isomorphous series of complexes reveals a consistent trend wherein the longer pair of bonds within each C 4 -cycle are those not bonded to the diphenylamino group. This effect has also been observed in a series of complexes with the monosubstituted squarate ligands 3-methyl-4-hydroxycyclobut-3-ene-1,2-dione (methylsquarate) and 3-methoxy-4-hydroxycyclobut-3-ene-1,2-dione (methoxysquarate). , A pattern of delocalization, which is explicable in terms of the resonance hybrid that can be derived from the various resonance forms of the ligand, is apparent and extends between the two trans ring oxygen atoms via the carbon attached to the diphenylamino group. In the case where the coordination to the metal is via the oxygen atom cis to the diphenylamino group the Ln−O bond is significantly shorter than the corresponding bond length when the metal coordinates via an oxygen atom trans to the group.…”

<b>Synthesis, crystal structure and magnetic properties of [Cu(mal)(abpt)(H₂O)].3/2H₂O and [Cu₂(sq)(abpt) ₂].2H₂O (mal = malonate, sq = squarate, abpt =4-amino-3,5-di-2-pyridyl-4H-1,2,4 triazole)</b>

“…The displacement ellipsoid is drawn at 50% probability.The axial positions are occupied by squarato oxygen atoms. The Cu-N and Cu-O bond distances in the basal plane for Cu(1) and Cu(2) ranges from 2.042 Å to 2.495 Å which are in agreements with previously reported values for several compounds in the Cu-abpt and Cusquarato systems[23][24]. On the other hand, the longer Cu-O (squarato) distances (Cu(1)-O = 2.495 Å and Cu(2)-O = 2.495 Å are very close to those reported for other Cu(II) complexes involving O(squarato) atoms in the apical position[25][26].…”

Synthesis, crystal structure and magneto-structural correlation of two bi-bridging 1D copper(ii) chainsElectronic supplementary information (ESI) available: magnetization curve for 1 between 0 and 5 K and an EPR spectrum for 1. See http://www.rsc.org/suppdata/dt/b2/b204728b/

“…The number of tetrameric metal complexes with the four metal cations being bridged by a single squarato ligand in a µ-1,2,3,4-coordination mode is very rare. 12, 21 The most typical coordination modes are µ-1,2 (cis) and µ-1,3 (trans). The trans coordination gives a very small coupling, close to zero.…”