First transition row metal complexes with 3\4\5\6!tetrahydro!4\6!dioxo!ð0\1\3Łtriazolo! ð0\4!aŁpyrimidine

Complexes of 3\4\5\6!tetrahydro!4\6!dioxo!ð0\1\3Łtriazolo!ð0\4!aŁ pyrimidine "H1tpO1# with the divalent transition metals of the _rst transition series from Mn to Zn have been synthesized and characterized\ their general formula being M"HtpO1#1 = nH1O[ The crystal structure of the manganese compound\ ðMn"HtpO1#1"H1O#1Ł\ has been solved by single crystal X!ray di}raction\ showing that the ligand binds bidentately through the exocyclic oxygen O6 and the endocyclic nitrogen N0[ The deprotonation of the ligand takes place at the active methylene group at position 5\ as it happened in Na"HtpO1# = 1H1O\ and not at the N0H group at position 3[ Infrared data suggest that the ligand binds in a similar fashion in the Fe\ Co\ Ni and Zn compounds but not in the copper one[ This has been corroborated by powder X!ray di}raction\ which indicates that all compounds except Cu are isostructural[ Þ 0887 Elsevier Science Ltd[ All rights reserved Keywords] deprotonation ^ ligand ——————————————————————————————————————————————— Triazolopyrimidine derivatives are ligands that dis! play a great versatility in their interaction with metal ions\ not only because they can bind the metal atom through di}erent positions ð0Ł but also because their presence in~uence the behaviour of other auxiliary ligands\ either by electronic or steric reasons\ giving rise to compounds with interesting metal!to!metal interactions through these auxiliary ligands ð1Ł[ Nevertheless\ when the ligands act monodentately\ the preferred binding position appears to be the nitro! gen atom at position 2 ð2Ł "see diagram below for the numbering scheme#[ Polymeric compounds are usually obtained when N0 acts together with N2 ð3Ł whereas dimers with eight!member 0M0N0C0N0M0N0C0N0 rings are for! med when the binding mode is N2\N3 bidentate ð4Ł[ Author to whom correspondence should be addressed[ E!mail ] mpsansanÝgoliat[ugr[es 1366 Until now\ the study of the interaction of metal ions with these ligands has been mainly focused on those that are commercially available ] unsubstituted s!tri! azolo!ð0\4!aŁpyrimidine "tp#\ its derivative methylated at positions 4 and 6 "dmtp# and that with a methyl group at position 4 and an oxo group at position 6 "HmtpO#[ For the latter\ despite the presence of an oxygen atom\ N2 is still the primary binding site with only one example in which bidentate N0\O6 coor! dination is preferred ð5Ł[ Following this line of research\ we have recently reported the synthesis and characterization of a new triazolopyrimidine derivative\ 3\4\5\6!tetrahydro!4\6! dioxo!ð0\1\3Łtriazolo!ð0\4!aŁpyrimidine "H1tpO1# ð6Ł[ A diagram of this ligand\ together with the numbering scheme of the ring is shown over[ This compound has a very strongly acidic meth! ylene group at position 5\ which may confer inter! esting properties to it[ Molecular orbital calculations on its anion point to the oxygen atoms as the preferred S[ Orihuela et al[ 1367 binding sites ð6Ł\ the chelate O6\N0 possibly being the better choice[ This is experimentally demonstrated in this article\ in which the synthesis and characterization of metal complexes of the anion HtpO1 with the _rst transition divalent metals from Mn to Zn are reported[ The single crystal X!ray study of the Mn compound displays the expected N0\O6 bidentate behaviour\ this coordination mode being also strongly suggested for the other metals "Cu perhaps excepted# by the spec! troscopic studies and by the powder X!ray study[