Six coordination compounds with citric acid (H4L = C6H8O7) or more preciselly with one of its anions were synthesized (two per cobalt(II), nickel(II) and copper(II)): (C(NH2)3)8[Co4L4]·8H2O 1, Na2[Co2(HL)2(H2O)4]·6H2O 2, (C(NH2)3)8[Ni4L4]·8H2O 3, Na2[Ni2(HL)2(H2O)4]·6H2O 4, [Cu2L(H2O)]n 5 and a copper compound with an undetermined formula.
Syntheses were performed with simple metal starting compounds, sodium citrate(3-) and all in water.
Compounds 1, 2, 3 and 5 were already described in the literature, which we confirmed with X-ray diffraction analysis. Compounds 1 and 2 are isostructural to 3 and 4, respectively.
The results of CHN elemental analysis for the compounds 4 and 5 are in agreement with the calculated values of proposed compound formulaes. It can therefore be concluded, that compounds 4 and 5 are pure substances. This type of data for compounds 1 and 3 does not show such agreement, therefore indicating the presence of impurities. For compounds 2 and 6 elemental analysis did not allow correlation with a formula. The CHN elemental analysis results of the compound Citrate anions bonding into all our investigated coordination compounds, as well as guanidine cations bonding into compounds 1, 3 and 6, were confirmed with infrared spectroscopy. IR spectra of isostructural pairs 1 and 3 with guanidinium cation and 2 and 4 without this cation are very similar. IR spectra of 5 amd 6 match partialy: 6 with the guanidinium pair and 5 with the other pair. The UV-Vis spectras well as the color of the six compounds differ due to different central metal cation present (Co 1/2, Ni 3/4 in Cu 5/6).
The measured effective magnetic moment of compounds 1, 2 and 4 matches well with expected values for their corresponding metal cations. For compounds 3, 5 and 6 the measurements only match partially with their expected values. The low value of effective magnetic moment for these compounds can be explained with the antiferromagnetic effect or questionable purity.
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