FULL PAPER DOI:10.1002/ejic.201201176 Unsymmetrically Substituted Mo 3 S 4 4+ Clusters Bearing Diphosphane Ligands Ivan Sorribes, [a] Rosa Llusar, [a] and Cristian Vicent* [b] Keywords: Cluster compounds / Molybdenum / Mass spectrometry / Ligand effects / Electrochemistry A unique series of unsymmetrically substituted [Mo 3 S 4 (dmpe) 3 Cl 3–x (dca) x ]PF 6 (x = 0–3) clusters that feature mixed Cl/dca terminal ligands, prepared by thermal reaction of [Mo 3 S 4 (dmpe) 3 Cl 3 ]PF 6 ([1]PF 6 ) [dmpe = 1,2-bis(dimethyl- phosphanyl)ethane] with sodium dicyanamide [Na(dca); dca = dicyanamide] is reported. The cluster/Na(dca) ratio, reac- tion time as well as the nature of the solvent dictate the rela- tive ratio of [Mo 3 S 4 (dmpe) 3 Cl 2 (dca)]PF 6 ([2]PF 6 ), [Mo 3 S 4 - (dmpe) 3 Cl(dca) 2 ]PF 6 ([3]PF 6 ) and [Mo 3 S 4 (dmpe) 3 (dca) 3 ]PF 6 ([4]PF 6 ). An electrospray ionization mass spectrometry (ESI- MS) based protocol was employed for high-throughput opti- mization of reaction conditions directed to obtain [2–4]PF 6 in optimal yield. The incorporation of dca confers significant Introduction The trinuclear Mo 3 S 4 4+ cluster core with three molybd- enum atoms that define an equilateral triangle with one capping sulfur atom and three bridging sulfur ligands is well known as one of the most common cluster structural units in group 6 metal chalcogen-rich chemistry. [1] Besides the use of Mo 3 S 4 4+ clusters as building blocks to access cubane-type heterodimetallic Mo 3 M'S 4 (M' = transition metal) clusters, [1a,2] a judicious choice of ligands in the Mo 3 S 4 4+ compounds makes them efficient cocatalysts in hy- drogen-evolution reactions, [3] nonlinear optical materials [4] or as chemoselective catalysts for the reduction of nitro- arenes. [5] In addition, these Mo 3 S 4 4+ trimetallic units are highly versatile structural-directing agents; for example, the [Mo 3 S 4 (Hnta) 3 ] 2– (nta = nitrilotriacetate) dianion has been linked to lanthanide cations to form 3D networks in the solid state or has been employed as a template during the self-condensation of the [Mo 2 O 2 S 2 (H 2 O) 4 ] 2+ dication to lead to Mo 18 (Mo 2 -based) metallamacrocycles. [6] The [Mo 3 S 4 (H 2 O) 9 ] 4+ cation is also a suitable species to form complementary hydrogen bonding with the highly symmet- [a] Departament de Química Física i Analítica, Universitat Jaume I, Av. Sos Baynat s/n, 12071 Castelló, Spain [b] Serveis Centrals d’Instrumentació Científica, Universitat Jaume I, Av. Sos Baynat s/n, 12071 Castelló, Spain Fax: +34-964-387309 E-mail: barrera@sg.uji.es Homepage: www.grupo-rllusar.uji.es Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201201176. Eur. J. Inorg. Chem. 2013, 1418–1426 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1418 polarity differences on the [2–4]PF 6 series, so that compounds [2–4]PF 6 can be efficiently isolated in analytically pure form after silica gel chromatography and represent the first exam- ples of unsymmetrically substituted Mo 3 S 4 4+ clusters that fea- ture mixed terminal ligands. The structural, spectroscopic and electrochemical consequences of the stepwise Cl/dca re- placement along the [1–4]PF 6 series are also presented. The distinctive UV/Vis and electrochemical features along the [1– 4]PF 6 series illustrate the ability to fine-tune the physico- chemical properties of Mo 3 S 4 4+ clusters upon stepwise dca incorporation more efficiently than upon complete ligand substitution. rical family of cucurbit[n]urils [7] or to be incorporated in two monovacant lacunary [SiW 11 O 39 ] 8– or [P 2 W 17 O 61 ] 10– anions, [8] or the trivacant [AsW 9 O 33 ] 9– ion. [9] A wide spec- trum of ligands can be additionally coordinated to the Mo 3 S 4 4+ cluster core, thus typically resulting in C 3v - or C 3 - symmetrized clusters as a consequence of the identical co- ordination environments around the three Mo sites. [10] In this context, preparation of unsymmetrically substi- tuted Mo 3 S 4 4+ clusters (that feature mixed terminal ligands in which the inherent C 3 symmetry of the Mo 3 S 4 4+ cluster core is reduced to C 1 ) can provide new opportunities for the fine-tuning of physicochemical properties of Mo 3 S 4 4+ clusters as well as enhance their versatility as structure-di- recting agents. This approach has been extensively used in Re 6 Q 8 (Q = S, Se) cluster chemistry in which modulation of photophysical and electrochemical characteristics of Re 6 Q 8 2+ clusters with mixed terminal ligands such as [Re 6 Q 8 F 3 (H 2 O) 3 ] – , [Re 6 Q 8 F 2 (H 2 O) 4 ] [11] or [Re 6 Q 8 (CN) 4 - (OH) 2 ] 4–[12] is well documented. This Re 6 Q 8 2+ (Q = S, Se) cluster system is particularly versatile in producing species in which the inherent octahedral symmetry of the Re 6 Q 8 2+ core is reduced on account of the presence of mixed ter- minal ligands. For example, the [Re 6 Q 8 (PEt 3 ) n (Hal) 6–n ] (4–n)– (Q = S, Se; Hal = Cl, [13] Br [14] or I [15] ) series are readily accessed by high-temperature reactions of [Re 6 Q 8 Br 6 ] 4– with triethylphosphane in which the additional substitution of halide ligands by bifunctional ligands [15,16] illustrates their utility as structure-directing agents. [17] However, isola- tion of unsymmetrically substituted Mo 3 S 4 4+ clusters in an-