DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 1937–1943 1937 Technetium(V) and rhenium(V) complexes of biguanide derivatives. Crystal structures Andrea Marchi,*†a Lorenza Marvelli,a Michela Cattabriga,b Roberto Rossi,a Maria Neves,c Valerio Bertolasi d and Valeria Ferretti d a Laboratorio di Chimica Inorganica e Nucleare, Dipartimento di Chimica, Università di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy b Dipartimento di Chimica, Università di Venezia, Dorsoduro 2137, 30123 Venezia, Italy c Departamento de Química, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2685 Sacavém, Portugal d Centro di Strutturistica DiVrattometrica, Dipartimento di Chimica, Università di Ferrara, via L.Borsari 46, 44100 Ferrara, Italy Received 29th January 1999, Accepted 22nd April 1999 Biguanidine ligands HLn (HL1 = 1,1-dimethylbiguanide, HL2 = 1-phenethylbiguanide, HL3 = 1-phenylbiguanide) formed disubstituted cationic oxo- and nitrido-complexes [MO(HLn)2]31 (M = Tc or Re) and [TcN(HLn)2(H2O)]21.They are characterised by the presence of a network of N–H ? ? ? X (X = Cl or H2O) intra- and inter-molecular hydrogen bonds. The imido precursor of ReV [Re(NMe)(PPh3)2Cl3] formed monosubstituted complexes [Re(NMe)(HL1,2)(PPh3)Cl]21. In alkaline solutions deprotonation of ligands occurs and monocationic, disubstituted oxo- and imido-species [MO(Ln)2]1 (M = Tc or Re), [Re(NCH3)(L1,3)2]1 and neutral nitrido complexes [TcN(Ln)2] are obtained.Elemental analyses, FT-IR and NMR spectroscopy and conductivity measurements are consistent with the proposed formulations. Crystal structures of [TcO(L1)2]1 and [TcN(HL1)2(H2O)]21 were determined. The former shows a square pyramidal geometry in which the C–N bond distances are equivalent and indicative of p delocalisation on the chelate ring. The latter displays a pseudo-octahedral geometry with a water molecule trans to the Tc]] ] N multiple bond. The C–N bond distances inside the ligands (1.30 and 1.38 Å) are consistent with single and double bond character, and less p delocalisation through the whole ligands.Introduction Biguanide and its N-substituted derivatives are bidentate ligands which contain nitrogen donor atoms. From a chemical and structural point of view biguanide may be considered as derived from the substitution of both the oxygen atoms of biuret by imino ]] NH groups. These compounds are considered strong s- and p-donating ligands which form stable complexes with transition metal ions in high or usual oxidation states utilising the availability of vacant d orbitals of the metal which may overlap with the filled p orbitals of the ligand.1 They are highly coloured and complexes of bivalent metals such as copper, nickel, and cobalt with biguanides have long been known.2 In 1961 Ray3 reported a systematic investigation of the syntheses and properties of these and other metal complexes including the first oxorhenium( V) complex [ReO(Big)2(OH)][OH]2 (Big = biguanide).More recently, some oxorhenium(V) complexes of biguanide and 1,1-dimethylbiguanide have been formulated as [ReO- (HL)2X]X2, [ReO(L)2X] (X = Cl2 or OH2) and [Re(HL)2- (OH)2]Cl3 (HL = biguanide) on the basis of elemental analysis H2N N H NH2 H2N N H NH2 Biguanide Biuret C C C C O O NH NH † Present address: Dipartimento di Chimica, Università di Ferrara, via L. Borsari 46, 44100 Ferrara, Italy. E-mail: mgl@dns.unife.it and IR spectra.4 Up to now and to our knowledge, no technetium complex has been described.From a chemical point of view the formation of a complex has been considered similar to a protonation process.5 Moreover, EPR and UV spectral studies have been carried out to understand the chemical and pharmaceutical properties of this class of molecules.1b,6 Biguanides have attracted considerable attention for their hypoglycaemic activity 7 and, in particular, metformin (1,1-dimethylbiguanide) is an antidiabetic medication which has been used for over 30 years.This class of compounds has been also studied as antimalarial drugs 8 and more recently for therapeutic treatment of pain, anxiety, and memory disorders.9 The present paper deals with the synthesis and characterisation of rhenium(V) and technetium(V) complexes of biguanide derivatives HLn and the first structurally characterised oxo- and nitrido-complexes of technetium. H N H N H N R1 n = 2 R1 = H, R2 = C2H4-Ph HLn ligands N n = 1 R1 = R2 = Me n = 3 R1 = H, R2 = Ph N N NH C NH R2 C H 1,1-dimethylbiguanide 1-phenethylbiguanide 1-phenylbiguanide1938 J.Chem. Soc., Dalton Trans., 1999, 1937–1943 Results and discussion Syntheses Oxotechnetium(V) and oxorhenium(V) complexes. The violet complexes [TcO(HLn)2]31 1–3 were prepared by reaction of [TcOCl4]2 precursor with HLn ligands under mild conditions. The corresponding oxorhenium(V) complexes [ReO(HLn)2]31 7–9 were obtained by exchange reactions of [ReO(XPh3)2Cl3] (X = P or As) (Scheme 1).The oxorhenium(V) precursors showed a lower reactivity than [TcOCl4]2 salt which readily reacted with HLn ligands. No diVerence of reactivity was observed between the two oxorhenium(V) compounds. Complexes [MO(HLn)2]31 are violet, air stable and soluble in water, MeOH, Me2SO. Conductivity measurements in Me2SO solution seem in agreement with 3 : 1 electrolytes. The oxometal complexes [TcO(Ln)2]1 4–6 and [ReO(Ln)2]1 10–12 were synthesized in good yields following two diVerent procedures. When the reactions were carried out in the presence of base (KOH in MeOH) deprotonation of ligands occurred and the corresponding monocationic species formed.These compounds were also isolated starting from solutions of 1–3 or 7–9 by adding some drops of alkaline solution. The formation of [ReO4]2 was observed in the syntheses of 10–12 since these reactions were performed in air, at neutral or weakly alkaline pH values and under these conditions [ReO4]2 replaced Cl2 as counter ion.On the contrary, [TcO4]2 anion was never detected in the syntheses of 4–6 because technetium complexes are more diYcult to oxidise than are their rhenium analogs.10 In order to evaluate the possibility to form oxotechnetium compounds starting from pertechnetate ion, reactions in aqueous basic solution with Na2S2O4 as reducing agent were performed. Substitution of the OH2 counter ion with [BPh4] 2 gave good crystals of 4 for X-ray diVraction analysis.All of these oxo complexes [MO(Ln)2]1 are yellow and air stable in both the solid state and solution. They are soluble in MeOH, Me2SO and behave as monoelectrolytes in solution. Nitridotechnetium(V) complexes. Cationic complexes [TcN- (HLn)2(H2O)]21 13–15 were prepared starting from the precursor [TcN(PPh3)2Cl2] (Scheme 2). When the reactions were carried out with HL1,2 ligands the presence of NEt3 was required since the former were available as their HCl salts.The corresponding neutral species 16–18 were obtained in basic solution (KOH in MeOH) or alternatively after dissolution of 13–15 in MeOH and addition of alkaline solution. Cationic [TcN(HLn)2(H2O)]21 and neutral [TcN(Ln)2] compounds are yellow, air stable and soluble in CH2Cl2, MeOH, Me2SO. Conductivity measurements in Me2SO are in accord with the proposed formulations. Crystals suitable for X-ray diVraction studies of [TcN(HL1)2(H2O)]21 13 were grown from dichloromethane –ethanol.Imidorhenium(V) complexes. Monosubstituted imido com- Scheme 1 Re Ph3X Cl XPh3 Cl O Cl Tc Cl Cl Cl Cl O O Tc O O O M N N N N O M N N N N O Tc N N N N O OH – (X = P, As) OH –, S2O4 2– HLn M = Tc, 1-3 Re, 7-9 HLn M = Tc, 4-6 Re, 10-12 HN N + + HLn NH N – N N OH- H+ – 4-6 3+ plexes [Re(NMe)(HL1,2)(PPh3)Cl]21 19, 20 were synthesized starting from the easily available species [Re(NMe)(PPh3)2Cl3] (Scheme 3). Even if the ligands were used in a 1 : 2 stoichiometric ratio, attempts to obtain the corresponding disubstituted compounds failed.Monocationic disubstituted compounds 21 and 22 were recovered in the presence of base (NEt3). The complexes [Re(NMe)(HL1,2)(PPh3)Cl]21 and [Re(NMe)(L1,3)2]1 behave as 2 : 1 and 1 : 1 electrolytes, respectively in Me2SO solution. Intentionally, we decided to synthesize only some imido complexes with the aim to make a comparison of reactivity between oxo- and imido-rhenium(V) precursors.Spectroscopy In this discussion we report FT-IR wavenumbers of the ligands for an easier comparison with those of complexes. Infrared spectra of the HLn (n = 1–3) ligands exhibit an intense absorption band in the range 3100–3500 cm21 assignable to the stretching vibration of the NH groups. It is probable that interor intra-molecular hydrogen bonds overlap with NH vibrations and are responsible for this broad band. The presence of intramolecular hydrogen bonds was confirmed by structural studies of biguanides.5b,11 A set of strong bands observed in the range 1500–1700 cm21 may be attributed to C]] N stretch and NH deformation.All IR spectra of the complexes [MO(HLn)2]31 (M = Tc 1–3 or Re 7–9), [TcN(HLn)2(H2O)]21 13–15, and [Re(NMe)- (HL1,2)(PPh3)Cl]21 19, 20 display a broad intense band in the range 3100–3500 cm21 due to the stretching vibrations of the N–H groups and overlapped with stretchings of H2O or ROH (R = Me or Et) involved in hydrogen bonds.The strong bands observed in the range 1640–1700 cm21 are assigned to the n(C]] NH) of co-ordinated groups, and those at 1500–1610 cm21 attributed to n(C–N–C) (ring) and d(NH).1a,12 A new band appearing at 1320–1220 cm21 was assigned to ring vibration and supports the formation of a chelate ring.12b The infrared spectra of technetium and rhenium oxo complexes exhibit a strong M]] O (M = Tc or Re) absorption peak at 980–997 and at 990–1007 cm21, respectively.These MO stretching values are comparable with those observed for other square-pyramidal oxo complexes of Tc and Re containing s- and p-donating ligands.13 The spectra of nitrido complexes show a mediumintensity band which falls in the appropriate range for the Tc]] ] N moiety (1059–1088 cm21). Finally, a band at ca. 1095 cm21 indicates the presence of PPh3 in 19 and 20. The IR spectra of the deprotonated complexes do diVer marginally from those discussed above.For some of them, the region 3100–3500 cm21 appears better resolved, probably due to the absence of hydro- Scheme 2 Tc Ph3P Cl PPh3 Cl N Tc N N N N N H2 O Tc N N N N N 13-15 OH – 2+ HLn H + OH – 16-18 NH HLn N N HN Scheme 3 Re N N N N NMe Re Ph3P Cl PPh3 Cl NMe Cl Re N N PPh3 Cl NMe HL1,2 NEt3 HL1,3 21, 22 19, 20 2+ HN + N NJ. Chem. Soc., Dalton Trans., 1999, 1937–1943 1939 gen bonds (see Experimental section). Indeed there is an appreciable low frequency shifting of n(C]] N) (1600–1620 cm21) with respect to the values of the corresponding protonated species, as well as to HLn unco-ordinated ligands.This fact may be attributed to p-electron delocalisation on the chelate ring. Moreover, in these complexes M]] O and Tc]] ] N stretching vibrations are observed at lower wavenumbers. Finally, disappearance of the characteristic band of the PPh3 moiety in [Re(NMe)(L1,3)2]Cl 21, 22 is consistent with the formulation of the disubstituted complexes.Proton NMR spectra of the metal complexes, recorded in Me2SO-d6 solution, show a downfield shift of the NH resonances with respect to those of the unco-ordinated ligands, while aliphatic and aromatic protons do not undergo significant chemical shifts. For the technetium and rhenium oxo complexes, containing the ligands in their protonated as well as deprotonated form, the ]] NH resonances are the more signifi- cant data in the 1H NMR spectra. In particular the spectra for the oxorhenium complexes exhibit signals at higher values than those of corresponding technetium compounds.Comparing [MO(HLn)2]31 (M = Tc 1–3 or Re 7–9) with [MO(Ln)2]1 (M = Tc 4–6 or Re 10–12) complexes an analogous NH pattern may be observed in all spectra, although the signals for the latter compounds are shifted upfield with respect to the former. A similar behaviour is also observed for the corresponding nitrido derivatives. This trend may be discussed in terms of an increased shielding arising from a strong p conjugation along the chelate ring, in accord with the C–N bond distances of complexes [TcO(L1)2]1 4 and [TcN(HL1)2(H2O)]21 13 (see description of the structures) which indicate a more extensive p delocalization over the whole ligand molecule in 4 than in 13.It is interesting that complex 4 possesses a trans configuration while the corresponding compound 13 is cis. Although isomers could be expected, NMR experiments in solution and at room temperature did not reveal their presence for all oxoand nitrido-complexes.This fact cannot be attributed to steric impediments as well as electronic factors and it is hard to explain it. The presence of only one isomer could be due to a high energy barrier which does not allow inversion. The 31P and 1H NMR spectra of imido complexes 19, 20 are consistent with the formation of monosubstituted compounds such as [Re(NMe)(HL1,2)(PPh3)Cl]21. In particular, the phosphorus NMR spectra exhibit singlets at d28.95 and 26.38 for the co-ordinated PPh3 moiety of 19 and 20, respectively.The 1H NMR spectra show two singlets in the range d 10.95–8.6 attributable to (]] NH) protons. For the complexes [Re(NMe)- (L1)2]1 21 and [Re(NMe)(L2)2]1 22, the 1H spectra recorded at room temperature, as well as at 60 8C, are clearly consistent with the presence of two molecules of the ligand. In particular there is a set of four singlets (d 11.3–9.1) having equal intensity and attributed to the four ]] NH protons of the co-ordinated ligands.Another set of two singlets, twice as intense, at d 7.0– 6.4 is assigned to NH2 groups. This NMR feature could suggest the presence of a 1 :1 mixture of cis and trans isomers about the metal as well as a linear–bent isomerisation at the nitrene ligand. However, NMR spectra of the oxo- or nitrido-complexes, discussed above, did not display a cis–trans isomerization in solution at room temperature, and we believe that for 21 and 22 a non-axial disposition of the ReN–R bond is a plausible explanation.14 A series of UV absorption spectra and their pH dependence were studied in air to evaluate the basicity constants of coordinated biguanide ligand and which complexes are present in solution at diVerent pH values.In these experiments a 0.5 M solution of H3PO4 (25 cm3) was mixed in various ratios with a 1.0 M solution of NaOH and nine solutions at pH values ranging from 1.9 to 6.9 were prepared.All solutions were adjusted to ionic strength I = 0.1 M with Na2SO4. To a 1024 M aqueous solution (10 cm3) of the complex 7 an aliquot (1.0 cm3) of each solution was added and UV spectra recorded. The UV spectra collected in the pH range 1.9–3.5 show the presence of both [ReO(HL1)2]31 and [ReO(HL1)(L 1)]21 species, while at pH 3.55– 4.35 [ReO(HL1)(L1)]21 and [ReO(L1)2]1 are present. The latter was stable until pH 6.9 while at higher pH values oxidation of rhenium(V) to [ReO4]2 took place and it was complete at pH 12 after 2.5 h.From these experiments a pK1 of 3.55 and a pK2 of 4.35 have been estimated. In conclusion, we may assert that deprotonation of two molecules of ligand occurs in two well distinct steps although the two pK values are very similar. In addition, at physiological pH value the species in solution are those that contain both ligands in deprotonated form. These results may be also extended to other complexes taking into account that technetium(V) is more diYcult to oxidise than rhenium(V) 10 and the Tc]] ] N fragment is more stable than Tc]] O in alkaline solution.Crystal structures The [TcO(C4H10N5)2]1 cation of complex 4 displays a noncrystallographic C2 symmetry and a square-pyramidal geometry around Tc with two deprotonated 1,1-dimethylbiguanide molecules on the basal plane and an oxygen at the apex (Fig. 1). The Tc atom is displaced from the plane defined by N(1), N(2), N(6) and N(7) atoms toward O(1) by 0.6777(3) Å.The Tc]] O(1) bond distance of 1.645(3) Å (Table 1) indicating strong multiple bond character is in agreement with the distances found in other square-pyramidal technetium(V) oxo complexes.13a,16 The Tc–N bond distances, in the range 1.97–2.01 Å, are shorter than those observed in compound 13 due to the concomitant presence of a Tc]] O(oxo) group, which is a softer base than Tc]] ] N- (nitrido) group, and partial negative charges on the enaminic NH moieties.The C–N bonds within the two deprotonated dimethylbiguanide ligands display, in fact, almost equivalent distances, from 1.32 to 1.35 Å, indicative of a delocalisation of the double bonds and negative charges throughout the whole ligands. In the crystal packing the cation complexes are linked by hydrogen bonds between aminic hydrogens and deprotonated nitrogens while the N(1)–H and N(7)–H enaminic groups are engaged in the capture of a methanol molecule.The [TcN(C4H12N5)2(H2O)]21 cation belonging to complex 13 displays a non-crystallographic Cs symmetry and an approximately octahedral geometry with two molecules of 1,1-dimethylbiguanide on the basal plane and a water molecule at the apical position trans to the nitrido group (Fig. 2). The four basal N atoms lie approximately on a plane and the Tc atom is displaced from this plane by 0.4384(2) Å toward N(1). The Tc]] ] N triple bond distance of 1.616(2) Å is comparable with other reported distances for technetium(V) nitrido complexes.17 The long Tc–OH2 distance of 2.691(2) Å is ascribed to the strong trans influence of the nitrido ligand and is in agreement with the distances, in the range 2.48–2.95 Å, found in analogous compounds.18 These Tc–O bonds are abnormally long and can Fig. 1 An ORTEP15 view of the cation of compound 4 showing thermal ellipsoids at 30% probability.1940 J.Chem. Soc., Dalton Trans., 1999, 1937–1943 be considered as secondary bonds, intermediate between true bonds and van der Waals contacts.The presence of a water molecule in trans position is associated with a decreasing pyramidalisation of the technetium co-ordination polyhedron measured by the N]] ] Tc–N(cis) mean angle, a, which is 1028 in the present compound, and in typical square-pyramidal technetium nitrido complexes falls in the range 105–1088. The shortening of the Tc–N (sp2, enaminic) bond distances, observed in the range 2.07–2.08 Å, with respect to the Tc–N (sp3, aminic) ones of 2.15–2.22 Å,19 can be attributed to the diVerent hybridisations of the N atoms. The C–N single and double bond distances inside the ligands, of 1.30 and 1.38 Å on average respectively, display a small degree of delocalisation, the standard values of C]] N and C(sp2)–N(sp2) bond lengths being 1.27 and 1.41 Å, respectively.The crystal packing is determined by a complex network of hydrogen bonds involving all the aminic hydrogens, the chloride anions, the water molecule and the enaminic N(2)–H group.Fig. 2 An ORTEP15 view of compound 13 showing thermal ellipsoids at 30% probability. Table 1 Selected bond distances (Å) and angles (8) for complexes [TcO(L1)2]1 4 and [TcN(HL1)2(H2O)]21 13 with estimated standard deviations in parentheses [TcO(L1)2]1 4 Tc–O(1) Tc–N(1) Tc–N(2) N(1)–C(1) N(2)–C(2) N(3)–C(1) N(3)–C(2) N(4)–C(1) N(5)–C(2) O(1)–Tc–N(1) O(1)–Tc–N(2) N(1)–Tc–N(2) N(1)–Tc–N(7) N(1)–Tc–N(6) 1.645(3) 1.973(2) 2.012(3) 1.333(4) 1.336(4) 1.324(4) 1.347(3) 1.343(4) 1.331(4) 112.0(1) 108.4(1) 82.9(1) 83.4(1) 135.2(1) Tc–N(6) Tc–N(7) N(6)–C(5) N(7)–C(6) N(8)–C(5) N(8)–C(6) N(9)–C(5) N(10)–C(6) O(1)–Tc–N(7) O(1)–Tc–N(6) N(6)–Tc–N(7) N(2)–Tc–N(6) N(2)–Tc–N(7) 1.984(2) 2.006(2) 1.353(4) 1.352(4) 1.340(4) 1.345(3) 1.318(4) 1.342(4) 112.7(1) 106.4(1) 83.5(1) 84.0(1) 145.2(1) [TcN(HL1)2(H2O)]21 13 Tc–N(1) Tc–N(2) Tc–N(3) N(2)–C(1) N(3)–C(2) N(4)–C(1) N(4)–C(2) N(5)–C(1) N(6)–C(2) N(1)–Tc–N(2) N(1)–Tc–N(3) N(2)–Tc–N(7) N(2)–Tc–N(3) N(2)–Tc–N(8) N(1)–Tc–O(1) 1.616(2) 2.069(2) 2.080(2) 1.292(2) 1.299(2) 1.381(2) 1.375(2) 1.331(2) 1.344(2) 104.9(1) 100.9(1) 89.5(1) 84.2(1) 153.9(1) 177.3(1) Tc–O(1) Tc–N(7) Tc–N(8) N(7)–C(5) N(8)–C(6) N(9)–C(5) N(9)–C(6) N(10)–C(5) N(11)–C(6) N(1)–Tc–N(7) N(1)–Tc–N(8) N(3)–Tc–N(8) N(7)–Tc–N(8) N(3)–Tc–N(7) 2.691(2) 2.071(2) 2.076(2) 1.292(2) 1.303(2) 1.380(2) 1.380(2) 1.338(3) 1.341(2) 101.9(1) 101.2(1) 90.6(1) 85.4(1) 157.2(1) Conclusion The paucity of relevant IR and NMR spectral data available in the literature 1a,12a,20 makes diYcult any comparison with our results. The complexes here reported have been synthesized by facile exchange reactions between ligands and appropriate technetium and rhenium precursors.They have been fully characterised by FT-IR and NMR spectroscopy and the crystal structures of 4 and 13 determined. Conductivity measurements in Me2SO solution, of all cationic complexes, seem in agreement with literature data 21 for 1 : 1, 2 : 1 and 3 : 1 electrolytes.The charge on the complexes is neutralised by a network of N–H? ? ? Cl hydrogen bonds as demonstrated by crystal structure determinations.22 We have demonstrated that it is possible to promote deprotonation of the co-ordinated ligand and consequently to change the charge of the final complex. This aspect is of great importance in the development of 99mTC and 186/188Re radiopharmaceuticals and studies in order to understand which species are present in the biological environment could be performed.Syntheses of the corresponding 99mTcO complexes and preliminary biodistribution studies in vivo are reported elsewhere.23 Experimental Materials and methods CAUTION: Technetium-99 is a low-energy b2 emitter (E = 292 keV, t1/2 = 2.12 × 105 years). When this material is handled, normal radiation safety procedures must be used to prevent contamination. All manipulations of solids or solutions were performed in a laboratory approved for low-level radioactivity.Unless otherwise noted, all chemicals were reagent grade used without further purification. The salt [NH4][99TcO4] was obtained from the Radiochemical Centre, Amersham, UK; [AsPh4][TcOCl4],24 [TcN(PPh3)2Cl2],25 [ReO(XPh3)2Cl3] 26 (X = P or As) and [Re(NMe)(PPh3)2Cl3] 27 were prepared according to literature methods. The ligands 1,1-dimethylbiguanide (HL1), 1-phenylbiguanide (HL3) (Sigma) and 1-phenethylbiguanide (HL2) (Janssen Chimica) are commercially available products.Biguanide was synthesized according to the procedure of Karipides and Fernelius.28 Elemental analyses were performed using a Carlo Erba Instruments model EA1110 apparatus. FT-IR Spectra were recorded in the range 4000–200 cm21 on a Nicolet 510P FT-IR instrument in KBr, using a Spectra-Tech collector diVuse reflectance accessory, UV-Vis spectra on a Perkin-Elmer Lambda 5 spectrophotometer.pH Measurements were made with a Hanna HI-8417 Digital pH-meter using commercial buVer solutions (pH 4 and 7) as reference points. Proton NMR spectra of Me2SO-d6 solutions of complexes were examined on a Varian Gemini 300 spectrometer with SiMe4 as internal standard, 31P-{1H} NMR spectra on the same instrument in Me2SO-d6 solutions with a 85% H3PO4 solution as external standard. Conductivities were measured with an Amel Model 134 conductivity meter. The conductivity data were obtained at sample concentrations of ca. 1 × 1024 M in Me2SO solutions at room temperature (21 8C). Synthesis of complexes Oxotechnetium(V) complexes [TcO(HLn)2]Cl3 1–3 (n 5 1–3). To the salt [AsPh4][TcOCl4] (80 mg, 0.12 mmol) dissolved in 30 cm3 of CH2Cl2 the ligand (0.48 mmol) was added as a solution in MeOH (1 cm 3). The reaction mixture was gently warmed for 20 min and a change from pale green to violet was observed. Upon slow evaporation of solvent reddish violet crystals of the complexes were obtained.The solid was filtered oV, washed with EtOH and dried with Et2O. Yields were determined on starting technetium complex. [TcO(HL1)2]Cl3 1. Yield 90% (Found: C, 20.3; H, 4.6; N, 29.0. C8H22Cl3N10OTc requires C, 20.0; H, 4.6; N, 29.2%). IR (KBr):J. Chem. Soc., Dalton Trans., 1999, 1937–1943 1941 997 [n(Tc]] O)], 1595, 1630, 1668 [n(C–N–C), d(NH), n(C]] N)], and 3140, 3275 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 11.0 (2 H, s, C]] NH), 9.85 (2 H, s, C]] NH), 9.0 (2 H, s, CNHC), 7.7 (4 H, br s, NH2) and 3.0 [12 H, s, N(CH3)2].LM (Me2SO, 1.5 × 1024 M) 65 S cm2 mol21. [TcO(HL2)2]Cl3 2. Yield >90% (Found: C, 38.1; H, 4.7; N, 22.1. C20H30Cl3N10OTc requires C, 38.0; H, 4.8; N, 22.2%). IR (KBr): 982 [n(Tc]] O)], 1607–1690 [n(C–N–C), d(NH), n(C]] N)] and 3100–3300 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 10.9 (2 H, br s, C]] NH), 7.4–7.2 (20 H, m, C]] NH, CNHC, C6H5, NH2, PhC2H4NH), 3.7 (4 H, m, CH2) and 2.8 (4 H, m, CH2).LM (Me2SO, 1.2 × 1024 M) 80 S cm2 mol21. [TcO(HL3)2]Cl3 3. Yield 70% (Found: C, 37.4; H, 5.8; N, 19.7. C16H22Cl3N10OTc?3C2H5OH requires C, 37.0; H, 5.6; N, 19.6%). IR (KBr): 997 [n(Tc]] O)], 1489–1642 [n(C–N–C), d(NH), n(C]] N)] and 3171–3312 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 11.0 (2 H, s, C]] NH), 10.0–9.8 (4 H, 2 s, C]] NH, CNHC), 8.0–7.0 (16 H, m, C6H5, PhNH, NH2), 3.45 (6 H, q, J = 7.0, CH2) and 1.06 (9 H, t, J = 7.0 Hz, CH3). LM (Me2SO, 1.3 × 1024 M) 74 S cm2 mol21.[TcO(Ln)2]Cl 4–6 (n 5 1–3). The corresponding monocationic yellow complexes were obtained following the same procedure but in the presence of base. Some drops (3–5) of a saturated solution of KOH in MeOH were added to the violet solution. The reaction mixture became yellow, it was heated at 40 8C for 10 min and concentrated in vacuo. The residue was treated with water, filtered oV, washed with EtOH and dried with Et2O. Alternatively, these compounds can be also obtained starting from TcO(HLn)2Cl3 complexes dissolved in the minimum volume of MeOH and 1 or 2 drops of KOH solution added at room temperature.Slow evaporation of the yellow solutions gave crystals of the final products. Similar products were isolated starting from [99TcO4]2. A typical preparation is as follows: to a solution of [NH4][TcO4] in hot water (30 mg, 0.166 mmol, 2 cm3) the hydrochloride salt of HL1 (55 mg, 0.33 mmol) dissolved in 0.05 M NaOH (1 cm3) was added. Sodium dithionite (60 mg, 0.345 mmol) in 1 M NaOH (2 cm3) was added and the reaction mixture heated at 80 8C for 30 min.During this time a yellow powder of [TcO(L1)2]OH was formed. It was filtered oV, washed with water, EtOH and dried with Et2O. Crystals suitable for X-ray analysis were obtained when Na[BPh4] was added to a solution of the complex in MeOH. [TcO(L1)2]Cl 4. Yield 85% (Found: C, 23.3; H, 4.9; N, 34.2. C8H20ClON10Tc requires C, 23.6; H, 5.0; N, 34.4%). IR (KBr): 976 [n(Tc]] O)], 1435, 1501, 1557, 1608 [n(C–N–C), d(NH), n(C]] N)] and 3202, 3318, 3474 cm21 [n(NH, NH2)].NMR (Me2SO-d6): dH 10.2 (2 H, s, C]] NH), 8.6 (2 H, s, C]] NH), 6.8 (4 H, br s, NH2) and 3.2 [12 H, s, N(CH3)2]. LM (Me2SO, 1.2 × 1024 M) 22 S cm2 mol21. [TcO(L2)2]Cl 5. Yield 60% (Found: C, 43.4; H, 5.1; N, 24.9. C20H28ClON10Tc requires C, 43.0; H, 5.0; N, 25.1%). IR (KBr): 986 [n(Tc]] O)], 1449–1574 [n(C–N–C), d(NH), n(C]] N)] and 3231, 3314, 3418 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 9.0 (2 H, br s, C]] NH), 8.8 (2 H, br s, PhC2H4NH), 7.4–7.0 (16 H, m, NH2, C6H5, C]] NH), 3.65 (4 H, t , CH2) and 2.8 (4 H, t, CH2).LM (Me2SO, 1.4 × 1024 M) 26 S cm2 mol21. [TcO(L3)2]OH 6. Yield 70% (Found: C, 40.0; H, 4.4; N, 28.7. C16H21N10O2Tc requires C, 39.7; H, 4.4; N, 28.9%). FT-IR (KBr): 970 [n(Tc]] O)], 1420–1609 [n(C–N–C), d(NH), n(C]] N)] and 2900–3400 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 10.2–9.6 (4 H, br s, C]] NH, PhNH ) and 7.8–7.0 (16 H, m, C6H5, NH2, C]] NH).LM (Me2SO, 1.5 × 1024 M) 19 S cm2 mol21. Oxorhenium(V) complexes [ReO(HLn)2]Cl3 7–9 (n 5 1–3). A solution of ligand (0.36 mmol) in MeOH (1 cm3) was added to precursor [ReO(XPh3)2Cl3] (X = P or As; 0.18 mmol) dissolved in 40 cm3 of CH2Cl2. The reaction mixture was stirred and heated under reflux for 40 min. The violet solution was concentrated in vacuo and the residue treated with CH2Cl2. Violet solids formed upon addition of diethyl ether were filtered oV, washed with EtOH and dried with Et2O. Yields were determined on starting metal compounds.Recrystallisation from CH2Cl2–EtOH produced violet crystals. [ReO(HL1)2]Cl3 7. Yield 80% (Found: C, 16.7; H, 4.0; N, 24.3. C8H22Cl3N10ORe requires C, 17.0; H, 3.9; N, 24.7%). IR (KBr): 1007 [n(Re]] O)], 1597, 1630, 1678 [n(C–N–C), d(NH), n(C]] N)] and 3100–3300 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 13.0 (2 H, br s, C]] NH), 12.05 (2 H, br s, C]] NH), 11.1 (2 H, br s, CNHC), 7.7 (4 H, br s, NH2) and 3.0 [12 H, s, N(CH3)2].LM (Me2SO, 1.4 × 1024 M) 84 S cm2 mol21. [ReO(HL2)2]Cl3 8. Yield >90% (Found: C, 33.0; H, 4.1; N, 19.3. C20H30Cl3N10ORe requires C, 33.4; H, 4.2; N, 19.5%). IR (KBr): 960–990 [n(Re]] O)], 1539, 1634, 1688 [n(C–N–C), d(NH), n(C]] N)] and 3060–3300 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 12.0 (2 H, br s, C]] NH), 8.4, 8.2 (4 H, br s, C]] NH, CNHC), 7.5–7.1 (16 H, m, C6H5, PhC2H4NH, NH2), 4.0, 2.9 (8 H, m, CH2CH2). LM (Me2SO, 1.3 × 1024 M) 85 S cm2 mol21. [ReO(HL3)2]Cl3 9.Yield 70% (Found: C, 29.1; H, 4.1; N, 21.1. C16H22Cl3N10ORe requires C, 29.0; H, 3.4; N, 21.1%). IR (KBr): 993 [n(Re]] O)], 1570–1685 [n(C–N–C), d(NH), n(C]] N)] and 3100–3350 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 10.6– 10.25 (6 H, s, C]] NH, CNHC), 9.65 (2 H, br s, PhNH), 7.6, 7.3 and 7.1 (14 H, d, m, C6H5, NH2). LM (DMSO, 1.1 × 1024 M) 82 S cm2 mol21. [ReO(Ln)2]Cl 10–12 (n 5 1–3). These complexes were obtained as reported for the corresponding oxotechnetium complexes.[ReO(L1)2]Cl 10. Yield 80% (Found: C, 21.8; H, 5.0; N, 25.4. C8H20ClN10ORe?CH3OH requires C, 21.5; H, 5.1; N, 25.1%). IR (KBr): 993 [n(Re]] O)], 1437–1615 [n(CNC), d(NH), n(C]] N)] and 3204, 3319, 3462 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 11.1 (2 H, s, C]] NH), 9.8 (2 H, s, C]] NH), 7.1 (4 H, br s, NH2), 4.25 (1 H, q, J = 5.2, OH), 3.2 (3 H, d, J = 5.2 Hz, CH3) and 3.0 [12 H, s , N(CH3)2]. LM (Me2SO, 1.2 × 1024 M) 24 S cm2 mol21. [ReO(L2)2]Cl 11. Yield <50% (Found: C, 37.4; H, 4.4; N, 21.5.C20H28ClN10ORe requires C, 37.2; H, 4.4; N, 21.7%). IR (KBr): 997 [n(Re]] O)], 1450–1595 [n(C–N–C), d(NH), n(C]] N)] and 3227, 3310, 3416 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 10.2 (2 H, br s, C]] NH), 10.0 (2 H, br s, PhC2H4NH), 7.4–7.1 (16 H, m, C6H5, C]] NH, NH2), 3.45 (4 H, m, CH2) and 2.8 (4 H, m, CH2). LM (Me2SO, 1.3 × 1024 M) 29 S cm2 mol21. [ReO(L3)2][ReO4] 12. Yield 40% (Found: C, 23.9; H, 2.7; N, 17.1. C16H20N10O5Re2 requires C, 24.0; H, 2.5; N, 17.4%).IR (KBr): 910 [n(ReO4)], 966 [n(Re]] O)], 1423–1640 [n(C–N–C), d(NH), n(C]] N)] and 3285, 3420 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 10.5–10.4 (4 H, s, C]] NH), 9.8 (2 H, br s, PhNH) and 7.8–7.0 (14 H, m, C6H5, NH2). LM (Me2SO, 1.4 × 1024 M) 30 S cm2 mol21. Nitrido-complexes of technetium(V) [TcN(HLn)2(H2O)]Cl2 13–15 (n 5 1–3). The pink compound [TcN(PPh3)2Cl2] (100 mg, 0.14 mmol) in CH2Cl2 (40 cm3) was heated and stirred until all the solid dissolved.A solution of ligand (0.28 mmol, MeOH 1 cm3) was added and the reaction mixture heated under reflux. Addition of some drops of NEt3 (it was not necessary for HL3) produced a change from pink to bright yellow. After 30 min the heating was turned oV, the solution concentrated under reduced pressure and the residue taken up in CH2Cl2. The NEt3?HCl salt was filtered oV and washed with CH2Cl2 (2 × 5 cm3). To the combined organic solutions EtOH (5 cm3) was added. Slow evaporation of solvent provided yellow crystals of the desired product.It was washed with ethanol and diethyl ether and recrystallised twice from dichloromethane–ethanol. Yields are based on starting technetium complex. [TcN(HL1)2(H2O)]Cl2 13. Yield 85% (Found: C, 20.7; H, 5.2; N, 33.8. C8H24Cl2N11OTc requires C, 20.85; H, 5.25; N, 33.5%).1942 J. Chem. Soc., Dalton Trans., 1999, 1937–1943 IR (KBr): 1088 [n(Tc]] ] N)], 1497, 1632, 1668 [n(C–N–C), d(NH), n(C]] N)] and 3173–3337 cm21 [n(NH, NH2, OH)].NMR (Me2SO-d6): dH 9.65 (2 H, s, CNHC), 7.75 (4 H, br s, NH2), 7.3, 7.2 (4 H, s, C]] NH), 3.35 (2 H, s, H2O) and 3.2 [12 H, s, N(CH3)2]. LM (Me2SO, 1.4 × 1024 M) 54 S cm2 mol21. [TcN(HL2)2(H2O)]Cl2 14. Yield 90% (Found: C, 39.5; H, 5.2; N, 25.3. C20H32Cl2N11OTc requires C, 39.3; H, 5.30; N, 25.2%). IR (KBr): 1072 [n(Tc]] ] N)], 1531, 1580, 1682 [n(C–N–C), d(NH), n(C]] N)] and 3200–3400 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 10.4 (2 H, br s, CNHC), 7.6–7.0 (20 H, m, NH2, C6H5, C]] NH, PhC2H4NH), 3.6 (4 H, t, CH2), 3.35 (2 H, s, H2O) and 2.85 (4 H, t, CH2).LM (Me2SO, 1.4 × 1024 M) 64 S cm2 mol21. [TcN(HL3)2(H2O)]Cl2 15. Yield 65% (Found: C, 34.6; H, 4.25; N, 27.6. C16H24Cl2N11OTc requires C, 34.5; H, 4.35; N, 27.7%). IR (KBr): 1063 [n(Tc]] ] N)], 1516–1655 [n(C–N–C), d(NH), n(C]] N)] and 3020–3470 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 9.45 (2 H, s, CNHC), 7.4–7.0 (20 H, 2m, NH2, C6H5, C]] NH, PhNH) and 3.35 (2 H, s, H2O).LM (Me2SO, 1.2 × 1024 M): 46 S cm2 mol21. [TcN(Ln)2] 16–19 (n 5 1–3). These compounds were isolated following the procedure described for the analogous oxocomplexes. [TcN(L1)2] 16. Yield 90% (Found: C, 24.5; H, 6.6; N, 35.0. C8H20N11Tc?CH3OH?2H2O requires C, 24.7; H, 6.5; N, 35.2%). IR (KBr): 1059 [n(Tc]] ] N)], 1450–1616 [n(C–N–C), d(NH), n(C]] N)] and 3181, 3299, 3461 cm21 [n(NH, NH2, OH)]. NMR (Me2SO-d6): dH 5.95 (2 H, s, C]] NH), 5.6 (2 H, s, C]] NH), 5.45 (4 H, s, NH2), 4.25 (1 H, q, J = 5.2 Hz, OH), 3.35 (7 H, br s, CH3, H2O) and 3.0 [12 H, s, N(CH3)2].[TcN(L2)2] 17. Yield 90% (Found: C, 46.1; H, 5.5; N, 29.2. C20H28N11Tc requires C, 46.0; H, 5.4; N, 29.5%). IR (KBr): 1067 [n(Tc]] ] N)], 1450–1640 [n(C–N–C), d(NH), n(C]] N)] and 3197, 3310, 3407 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 7.3–7.1 (10 H, m, C6H5), 6.2–5.4 (10 H, m, PhC2H4NH, C]] NH, NH2), 2.8 (4 H, t, CH2) and 2.5 (4 H, t, CH2). [TcN(L3)2 ] 18. Yield 65% (Found: C, 40.9; H, 5.3; N, 29.4.C16H20N11Tc?2CH3OH: C, 40.8; H, 5.3; N, 29.1%). IR (KBr): 1072 [n(Tc]] ] N)], 1480–1640 [n(C–N–C), d(NH), n(C]] N)] and 3150–3312 cm21 [n(NH, NH2 , OH)]. NMR (Me2SO-d6): dH 7.6– 6.6 (20 H, 4m, NH2, C6H5, C]] NH, PhNH), 4.25 (2 H, q, J = 5.2, OH) and 3.2 (6 H, d, J = 5.2 Hz, CH3). Imido-complexes of ReV [Re(NMe)(HL1,2)(PPh3)Cl]Cl2 19, 20. To a solution of the precursor [Re(NCH3)(PPh3)2Cl3] (0.1g, 0.118 mmol) in CH2Cl2 (50 cm3) ligand dissolved in the minimum volume of MeOH and in a 1: 2 stoichiometric ratio was added.The reaction mixture was stirred and heated under reflux for 30 min. During this time a pink solid was formed. It was filtered oV, washed with CH2Cl2, EtOH and dried with Et2O. These complexes were recrystallised by slow evaporation of MeOH solutions. Yields are based on the starting rhenium complex. [Re(NMe)(HL1)(PPh3)Cl]Cl2 19. Yield 70% (Found: C, 38.3; H, 4.2; N, 11.9. C23H29Cl3N6PRe requires C, 38.7; H, 4.1; N, 11.8%).IR (KBr): 1094 [n(PPh3)], 1435–1680 [n(C–N–C), d(NH), n(C]] N)] and 3000, 3233, 3365 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 10.65 (1 H, s, C]] NH), 9.5 (1 H, s, C]] NH), 8.0–7.0 (18 H, m, PPh3, CNHC, NH2), 2.75 [6 H, s, N(CH3)2] and 2.5 [3 H, s, Re(NCH3)]. dP 28.95. LM (Me2SO, 1.15 × 1024 M) 77 S cm2 mol21. [Re(NMe)(HL2)(PPh3)Cl]Cl2 20. Yield >90% (Found: C, 44.4; H, 4.2; N, 10.7. C29H33Cl3N6PRe requires C, 44.1; H, 4.2; N, 10.6%). IR (KBr): 1096 [n(PPh3)], 1435, 1524, 1663 [n(C–N– C), d(NH), n(C]] N)] and 3206, 3335, 3416 cm21 [n(NH, NH2)].NMR (Me2SO-d6): dH 10.95 (1 H, br s, C]] NH), 9.8–8.6 (3 H, s, CNHC, C]] NH, PhC2H4NH), 8.0–7.0 (22 H, m, C6H5, PPh3, NH2), 2.5 [3 H, s, Re(NCH3)], 2.25, 1.8 (4 H, m, CH2CH2). dP 26.38. LM (Me2SO, 1.0 × 1024 M) 66 S cm2 mol21. [Re(NMe)(L1,3)2]Cl 21, 22. These complexes were obtained following the procedure previously described but in the presence of NEt3. When the pink solid was formed 10 drops of base were added.The mixture was heated until the solid disappeared and the solution became clear and yellow (ca. 1 h). The solution was concentrated to dryness and the residue taken up in CH2Cl2 and EtOH. Slow evaporation of solvent gave a yellow ochre powder. The complexes were recrystallised from MeOH solutions. Yields were determined based on the starting metal precursor. [Re(NMe)(L1)2]Cl 21. Yield 80% (Found: C, 21.3; H, 4.6; N, 29.9. C9H23ClN11Re requires C, 21.3; H, 4.6; N, 30.4%).IR (KBr): 1505, 1559, 1611 [n(C–N–C), d(NH), n(C]] N)], 3212, 3318, 3447 cm21 [n(NH, NH2)]. NMR (Me2SO-d6): dH 11.3, 10.25, 9.9, 9.1 (4 H, s, C]] NH), 7.0 (2 H, br s, NH2), 6.4 (2 H, br s, NH2), 3.2, 3.15 [12 H, s, N(CH3)2] and 2.5 [3 H, s, Re(NCH3)]. LM (Me2SO, 1.4 × 1024 M) 33 S cm2 mol21. [Re(NMe)(L3)2]Cl 22. Yield 80% (Found: C, 32.5; H, 4.3; N, 24.6. C17H23ClN11Re?H2O requires C, 32.9; H, 4.1; N, 24.8%). IR (KBr): 1480, 1537, 1645 [n(C–N–C), d(NH), n(C]] N)] and 3100–3400 cm21 [n(NH, NH2, OH)].NMR (Me2SO-d6): dH 10.6–9.4 (6 H, br s, PhNH, C]] NH), 7.8–7.0 (14 H, m, C6H5, NH2), 3.35 (2 H, s, H2O) and 2.5 [3 H, s, Re(NCH3)]. LM (Me2SO, 1.2 × 1024 M) 45 S cm2 mol21. Crystallography Crystal data. [TcO(C4H10N5)2]1[B(C6H5)4]2?CH3OH 4, M = 722.49, monoclinic, space group P21/c (no. 14), a = 11.589(2), b = 15.918(2), c = 18.962(4) Å, b = 96.97(1)8, U = 3472(1) Å3 (by least-squares refinement on diVractometer angles for 25 automatically centred reflections, l = 0.71069 Å), Z = 4, Dc = 1.38 g cm23, m = 4.60 cm21, F(000) = 1504, crystal dimensions 0.38 × 0.41 × 0.45 mm.[TcN(C4H11N5)2(H2O)]212Cl2 13, M = 460.16, monoclinic, space group C2/c (no. 15), a = 19.620(3), b = 7.576(1), c = 25.074(3) Å, b = 102.40(1)8, U = 3640.1(9) Å3 (by least-squares refinement on diVractometer angles for 25 automatically centred reflections, l = 0.71069 Å), Z = 8, Dc = 1.68 g cm23, m = 11.05 cm21, F(000) = 1872, crystal dimensions 0.18 × 0.40 × 0.48 mm.Data collection and processing. CAD-4 diVractometer, w–2q scan mode, graphite-monochromated Mo-K radiation, T = 295 K. Compound 4: 7561 unique reflections measured (2 < q < 28) giving 6172 with I > 3s(I ), corrected for Lorentzpolarisation and absorption (Y scan method, minimum transmission factor 0.86) eVects. Compound 13: 4367 unique reflections measured (2 < q <28) giving 3918 with I >3s(I), corrected as for 4 (minimum transmission factor 0.87).Structure analysis and refinement. Solution by Patterson and Fourier methods. For compound 4, full-matrix least-squares refinement with all non-hydrogen atom anisotropic and hydrogen isotropic, except those of methyl groups which were placed at fixed calculated positions. The Tc and O(1) atoms were disordered and refined over two positions, with occupancies 0.8 and 0.2 respectively, over and under the plane formed by N(1), N(2), N(6) and N(7) atoms. Final R = 0.042 and R9 = 0.062.Goodness of fit = 2.23. Final diVerence map peaks in the range ± 0.43 e Å23. For compound 13, full-matrix least-squares refinement on F with all non-hydrogen atoms anisotropic and hydrogens isotropic. Final R = 0.021 and R9 = 0.027. Goodness of fit = 2.34. Final diVerence map peaks in the range ±0.14 e Å23. Programs used and source of scattering factors are given in ref. 29 and the structures were drawn using ORTEP.15 CCDC reference number 186/1435. See http://www.rsc.org/suppdata/dt/1999/1937/ for crystallographic files in .cif format.J.Chem. Soc., Dalton Trans., 1999, 1937–1943 1943 Acknowledgements This work was supported by Italian MURST in the frame of the project “Pharmacological and Diagnostic Properties of Metal Complexes” (co-ordinator Professor G. Natile). We are grateful to Professor G. Annibale for obtaining and interpreting UV spectra and Dr E. Cavallari for preparing the complexes. We thank Mr M. Fratta for the elemental analyses and technical assitance, Mr P.Formaglio for recording NMR spectra. References 1 (a) C. R. Saha, J. Inorg. Nucl. 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