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/

Dinuclear cobalt and manganese squarate complexes with bidentate N-donor ligand: syntheses, crystal structures, spectroscopic, thermal and voltammetric studies

“…The chelating and bis-chelating coordination modes are only possible in complexes with larger metal ions, such as alkaline and rareearth cations [18][19][20]. In all the cases reported so far, metal-squarate complexes have been found to be interesting in terms of the structural relationships between their respective solid-state architectures [21]. In our ongoing research on squaric acid, we have synthesized some mixed-ligand metal(II) complexes of squaric acid, and their structures have been reported [22][23][24][25].…”

A novel 1-D coordination Cu(II) polymer with alternating μ1,3-squarato and binucleating polypyridylamine bridges

“…In general, the dinuclear squarato-bridged Cu(II) complexes exhibit weak antiferromagnetic interaction with the singlet-triplet exchange constant, |J| values in the range 0-26 cm À1 . The failure of the squarato dianion to promote more significant magnetic coupling in these complexes was attributed to the stabilization of the ligand orbitals by the large p-delocalization associated with the squarate ring [20].Polymeric structures via bridged-squarato l-1,2-and l-1,3-coordination have also been reported but the number of these compounds is very small compared to the corresponding dinuclear species [6,8,[16][17][18][19]5,21,22]. It has been noticed that most of the squarato coordination polymers required the incorporation of another bridging ligand such as pyrazine [21], 4,4 0 -bipyridine [22], imidazole [16] or oxalate [18].…”

“…It has been pointed out that the ligand does not generally act as a bis-bidentate linker for the first raw divalent transition metal ions because of its very large bite angle relative to that observed in the oxalate dianion [15]. The geometrical and the structural nature of the coligands coordinated to the central metal ion are considered to be the major factors that determine the bonding modes in the squarato-bridged-M II complexes where the intradimer distances between the metal centers vary from ca 5 Å A 0 in the cis, l-1,2-bonding to 8 Å A 0 in the trans, l-1,3-bonding [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In general, the dinuclear squarato-bridged Cu(II) complexes exhibit weak antiferromagnetic interaction with the singlet-triplet exchange constant, |J| values in the range 0-26 cm À1 .…”

“…The coordination geometry around the Cu(II) centers is a five-coordinate with a slightly distorted square pyramidal environment which is achieved by the three N-donor atoms of each arm of the ligand L, an oxygen atom of the bridging squarato moiety and by an oxygen atom of the ClO À 4 anion. The complex shows antiferromagnetic coupling between the squarato-bridged Cu(II) ions with J = À6.3 cm À1 .Ó 2009 Elsevier B.V. All rights reserved.The squarate dianion, C 4 O 2À 4 (3,4-dihydroxycyclobut-3-ene-1,2-dionate) is a very well known ligand that is capable of binding more than one metal ion at the same time leading to a variety of coordination modes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] where four types were recognized known as l-1,3-(trans) [1,3-6], l-1,2-(cis) [1,3,7-11], l-1,2,3-and l-1,2,3,4- [2,[12][13][14]. It has been pointed out that the ligand does not generally act as a bis-bidentate linker for the first raw divalent transition metal ions because of its very large bite angle relative to that observed in the oxalate dianion [15].…”

“…The squarate dianion, C 4 O 2À 4 (3,4-dihydroxycyclobut-3-ene-1,2-dionate) is a very well known ligand that is capable of binding more than one metal ion at the same time leading to a variety of coordination modes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] where four types were recognized known as l-1,3-(trans) [1,[3][4][5][6], l-1,2-(cis) [1,3,[7][8][9][10][11], l-1,2,3-and l-1,2,3,4- [2,[12][13][14]. It has been pointed out that the ligand does not generally act as a bis-bidentate linker for the first raw divalent transition metal ions because of its very large bite angle relative to that observed in the oxalate dianion [15].…”