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In an aqueous alkaline reaction medium, [ ReO,] -undergoes reductive nitrosylation b y N H,OH-HCI producing [Re( NO) (OH),] -, isolated as APh,(A = P or As) salts or as a neutral complex [Re( NO) (OH),( L-L)] [L-L = 1,lO-phenanthroline (phen) or 2,2'-bipyridine (bipy)]. The complexes show v ( N 0 ) vibrations at ca. 1 680 cm-l and their e.s.r. spectra suggest that, besides the hydroxo complex (C,,), the L-L derivatives also possess axially symmetric structures. These complexes contain the Re(N0)3+ [or {Re(NO)}5] group and show spin-only magnetic moments and almost identical e.s.r: profiles in the polycrystalline condition, both at 298 and 77 K, showing (gaJ sz 2.0.A well defined sextet due to metal hyperfine structure is observed of which the t w o outermost peaks are further split t o a triplet arising from 14N (of NO) superhyperfine interaction. However, in frozen acetonitrile or dimethylformamide (dmf) the hyperfine structures collapse. These complexes of Re(N0)3+ disproportionate when boiled with H X (X = CI or Br but not I, which forms only [Rel,I3-species), producing [Re(NO)X,]-or [Re(NO)X,(phen)] [i.e. Re(NO),+], [Re(NO),X,]-[i.e. Re( suggested for the mononitrosyl halogeno complex anions from i.r. and electronic absorption spectra, these d o not distinguish between axial-equatorial (C,) or equatorial-equatorial ( C2") dispositions of the t w o nitrosyl ligands in the dinitrosyl complexes. The seven-co-ordinate complexes [Re( NO)X,(phen)] undergo thermal and electrochemical (irreversible) reduction corresponding to two one-electron steps. The six-co-ordinate Re( shows a similar electrochemical reduction process but the five-co-ordinate [Re( NO) (OH),] -is electro-inactive. The cyclic voltammogram of the Re( NO): + species, [Re( NO),CI,] -, reveals a reversible, Re( N0),3+-Re( NO): + couple at a formal potential of -0.04 V vs. a saturated calomel electrode { -0.42 V vs. [Fe(q-C,H,),]-[Fe(q-C,H,),] '}. and [Re,XJ4-(Re:' ). While a square-pyramidal structure (C,,) can be species, [Re( NO) CI,] -, The reductive nitrosylation of tetraoxometallates, viz. [MO,]"-(M = Cr or Mo, n = 2; M = V, n = 3; or M = Os, n = 0) and subsequent isolation of pure metal nitrosyl derivative^'-^ has so far been shown to occur only when another reducing agent, for instance, CN-, NCS-, N3-, or C204,is used in the reaction medium along with NH,OH, a reductant as well as a source of NO. It has been observed that ReO,-as a substrate also responds6 to the conventional 'twin-reagents' for the above reaction, producing Re(NO), + [i.e. { Re(N0))6 t] or Re(N0),2 + [i.e. {Re(N0),}7], a combination of reagents6* being necessary for the latter. However, NH,OH alone has never been shown to act simultaneously as a combined multiple-electron reductant and nitrosylating agent on tetraoxometallates of other higher valent metal ions as substrates, in order to furnish clear cut metal nitrosyl derivatives. Herein we report, for the first time, that alkaline NH,OH reacts with [ReO,] -to afford hitherto unknown rhenium nitrosyl complexes { [Re(NO)(OH),] ...

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The IR and ESR spectra indicate that the complex (IV) have C4v symmetry and that the neutral complex (VI) also possesses axially symmetric structures containing the nitrogen atoms of the ligand in equatorial‐equatorial position.