Squarate complexes

The divalent metal squarate complexes, M(squarate)(H20)2, decompose in a vacuum in two stages. First there is a reversible loss of two water molecules, followed at higher temperatures by decomposition to the metal. The nature of the anhydrous complexes is not fully understood but the metal atoms appear to be four-coordinate.174... 

Squarate Complexes of Heavier Transition Metals and Lanthanides The Squarate Ion as a Linking Group Spectroscopy of Squarate Complexes Luminescence Studies Electrochemistry... 

Complexes of Monosubstituted Squarate Derivatives A. Complexing Properties of Monosubstituted Squarate Ligands Substituents with Lone Pairs Substituents without Lone Pairs Effects of Substituent on Structure Squarate and Monosubstituted Squarate Complexes with jt Interactions... 

Characteristic IR Stretching Frequencies (cm ) for Squaric Acid AND Metal Squarate Complexes... 

The squarate ion is also assmned to have the potential for providing a pathway for electron conduction when it bridges metal atoms in polymeric complexes (61). Some workers have used partial oxidation to enhance the possibility that compounds will exhibit conductivity. For example, Toftlund (110) showed that the partially oxidized platinum salt K2[Pt(C404)2l 2H2O has the properties of a one-dimensional conductor, while Wrobleski and Brown (18) reported that some mixed-valence iron squarate complexes display semiconductivity. 

E. Squarate Complexes of Heavier Transition Metals and Lanthanides... 

Although there are several examples of lanthanide complexes with the squarate ion 42, 55, 57), only a few squarate complexes of second-and third-row transition metals have been reported. The platinum and... 

Infrared and UV/vis data have been used by several authors to identify the C=C, C=0, and M—O stretches in the complexes synthesized 15, 18-21, 37, 38, 41, 44, 50, 54, 56, 58, 59, 64-66, 69, 74, 78, 80, 82, 103). Except in the initial research on first-row transition metal complexes of squaric acid, where these data were used in proposing structures, IR and UV/vis analysis have been used as supporting evidence for the particular coordination mode of the ligand 19,21,22, 45, 52, 59, 65). Infrared spectroscopy has also been utilized in the study of mixed oxalate/squarate complexes 118), although not to the same extent as in complexes of the oxalate ion. For example, Scott et al. studied the IR properties of Co(III) oxalate complexes with the hgand in a variety of chelating/bridging situations 119). 

Pig. 25. The C2 symmetric monomeric cobalt(Il) metho squarate complex Co(CH30C403)2(H20)4] (111). 

In their pioneering work, West and Niu assumed that the squarate complexes of divalent cations Mg ", Ca, Mn, Fe, Co ", Ni ", Cu " and Zn form an isostructural series (Figure 1). They suggested a bis-chelating coordination mode for the squarate dianion in all the squarate complexes, but their proposed structure does not correspond to the actual coordination mode of squarate. 

Figure 1 Structure for divalent metal-squarate complexes (M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn)...

The structures of transition-metal squarate complexes consist of one-dimensional metal squarate chains interlinked by hydrogen bonding. These complexes could be possible precursors to low dimensional polymeric electrical conductors... 

Few of the squarate complexes syntheseized to date contain tetravalent metals coordinated in a tetrahedral geometry. The use of bis(cyclopentadienyl)titanium(IV) dichloride (Cp2TiCl2 or titanocene dichloride) as the metal containing ligand provides the opportunity for obtaining such a complex. 

Table 5 lists the infrared and Raman frequencies (when available), for some metal-squarate complexes in which all oxygens are coordinated. In these complexes, there are no bands in the infrared spectrum above 1600 cm In addition, there is a very strong, broad band between 1400 cm and 1700cm ... 

Tabl e 5. Vibrational Frequencies of Some Squarate Complexes and the Squarate Ion. 

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