Dehydration and decomposition of divalent metal squarates

Thermal studies of some divalent metal chelates of croconic acid

“…This study verifies the stability order of the squarate complexes reported by Tangredi and coworkers [7]. The thermal decomposition temperatures for the squaric acid chelates are: nickel, 255~ cobalt, copper, 311~ and zinc, 368 ~ With the exception of the nickel squarate chelate (vide infra) the thermal stability order of the metal croconates and Squarates is the same.…”

“…The reported nickel squarate dihydrate of West and Niu was never analyzed for nickel. In the TG studies of the squarates by Tangredi and coworkers [7] it is stated, "The nickel compound is the only one here of questionable behavior, in that on long standing in a desiccator it exhibited a change in the TG curve in which roughly half of the water present came off at a lower temperature than normal. Apparently a partial rearrangement takes place with time."…”

“…Tangredi and coworkers [7] have reported the DTA plots of a series of metal squarates. They reported that the nickel squarate gave only an irregular endotherm upon decomposition.…”

“…Structurally the croconate dianion, C302-, lies between the squarate dianion, C~O 2-, and the rhodizonate dianion, C602-. Thermal studies have been performed in this laboratory by Bottei and Greene [6] on some divalent metal chelates of rhodizonic acid and by Tangredi and coworkers [7] on the thermal properties of the divalent metal chelate of squarie acid. It was therefore of interest to study the thermal properties of some croconic acid chelates and compare them where possible to those of the chelates of squaric and rhodizonic acids.…”

Synthesis and Spectrothermal Studies of Thermochromic Diamine Complexes of Cobalt(III), Nickel(II) and Copper(II) Squarate. Crystal Structure of [Co(en)3](sq)1.5 · 6H2O

“…Squaric acid, H 2 C 4 O 4 [3,4-dihydroxycyclobut-3-ene-1,2-dione, sq, Figure 1a], has been of much interest because of its cyclic structure, and possible aromaticity and coordination chemistry of the squarate ligand has been investigated in some detail [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53], which suggests that it may act as a monodentate or bridging ligand, since, the squarate anion has a very good ligating property and in some transition metal complexes, squaric acid acts as a counter ion [50][51][52][53][54][55]. Solid state thermal studies of several metal squarate and mixed ligand-metal squarate complexes have been reported, indicating a high thermal stability of the squarate moiety [10,[26][27][28]56]. Because the squarate anion is stable up to 300°C [29] and exhibits a strong hydrogen bonding network by its four oxygen atoms with hydrogen of diamines, we have described, in the present paper, the synthesis and characterization by physico-chemical methods (IR and UV-Vis.…”