Synthesis, Spectral, Cyclic Voltammetric Studies, and Single Crystal X-Ray Structure Determination of the Planar NiS 2 P 2 , NiS 2 PN, and NiS 2 PC Chromophores R. Thiruneelakandan ‡,a , K. Ramalingam* ,a , G. Bocelli b , and L. Righi b a Annamalainagar/India, Department of Chemistry, Annamalai University b Parma/Italy, IMEM-CNR, Parco Area Delle Scienze Received July 9th, 2004. Abstract. Synthesis, spectral and cyclic voltammetric characteriz- ation of [Ni(dedtc)(4-MP) 2 ](ClO 4 )(1), [Ni(dedtc)(4-MP)(NCS)](2), [Ni(dedtc)(PPh 3 )(NCS)] (3) and [Ni(dedtc)(PPh 3 )(CN)] (4) (dedtc = diethyldithiocarbamate, 4-MP = tri(4-methylphenyl)- phosphine, PPh 3 = triphenylphophine) are reported. IR spectra of complexes 1- 4 show the characteristic thioureide (C-N) bands at higher wave numbers compared to that of the parent dithiocarba- mate complex [Ni(dedtc) 2 ]. The d-d transitions are observed in the region 452-482 nm. Synthese, Spektroskopie, Cyclovoltammetrie und Einkristall-Strukturanalysen von planaren NiS 2 P 2 -, NiS 2 PN- und NiS 2 PC-Chromophoren Inhaltsübersicht. Es wird über die Synthese, die spektroskopische und cyclovoltammetrische Charakterisierung von [Ni(dedtc)- (4-MP) 2 ](ClO 4 )(1), [Ni(dedtc)(4-MP)(NCS)] (2), [Ni(dedtc)(PPh 3 )- (NCS)] (3) und [Ni(dedtc)(PPh 3 )(CN)] (4) (dedtc = diethyldithio- carbamat, 4-MP = Tri(4-methylphenyl)phosphin, PPh 3 = Tri- phenylphosphin) berichtet. Die IR-Spektren der Komplexe 1-4 zei- gen die charakteristische Thioharnstoff-(CN)-Bande bei größeren Wellenzahlen verglichen mit dem homoleptischen Dithiocarbamat- Komplex [Ni(dedtc) 2 ]. Die d-d-Übergänge werden im Bereich von Introduction Group X dithiolates containing planar MS 4 chromophores show interestingvariations in their reactions with Lewis bases [1, 2]. Soft Pd II and Pt II dithiolates preferably interact with soft phosphines to give rise to planar MS 2 P 2 chrom- ophores [3, 4]. Unlike its congeners, Ni II is a border line acceptor. Ni II complexes of dithiocarbamates are typical complexes containing planar NiS 4 chromophores. The planar dithiocarbamates prefer to react with soft Lewis bases such as phosphines and border line bases like isothio- cyanate and cyanide rather than hard nitrogenous bases ‡ Present address: Department of Chemistry, SET, Bharathidasan University, Tiruchirappalli - 620024/India * Dr. K. Ramalingam Department of Chemistry Annamalai University Annamalai nagar - 608 002/India e-mail: krauchem@yahoo.com Z. Anorg. Allg. Chem. 2005, 631, 187-193 DOI: 10.1002/zaac.200400245  2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 187 The CV studies clearly show the presence of reduced electron den- sity on the nickel ions in mixed ligand complexes 1-4 compared to the parent dithiocarbamate. Single crystal X-ray structure studies show all the complexes to containplanar NiS 2 P 2 , NiS 2 PN, and NiS 2 PC chromophores in keeping with the observed diamagnetism. In all the complexes the Ni-S distances are asymmetric. The thio- ureide C-N distance of the complexes 1-4 are less thanthe C-N distance observed in the parent [Ni(dedtc) 2 ]. Keywords: Nickel; Dithiocarbamates; Cyanide; Crystal structures 452-482 nm beobachtet. Die CV-Untersuchungen zeigen eine deut- lich reduzierte Elektronendichte der Nickelionen in den Gemischt- ligand-Komplexen 1-4 im Vergleich zu [Ni(dedtc) 2 ]. Nach den Ein- kristallstrukturanalysen enthalten alle Komplexe planare NiS 2 P 2 -, NiS 2 PN- und NiS 2 PC-Chromophore, entsprechend ihrem Diamag- netismus. In allen Komplexen sind die Ni-S-Bindungen asymme- trisch. Die Thioharnstoff-CN-Abstände sind in 1-4 kürzer als im Ausgangskomplex [Ni(dedtc) 2 ]. such as NH 3 and pyridine, due to symbiotically induced softness [5, 6]. On reaction with PR 3 , they form complexes with chromophore NiS 2 P 2 which are diamagnetic in nature [7-9]. Mixed ligand complexes of the type [Ni(dtc)(PR 3 )(X)] were obtained by reacting NiX 2 with dithiocarbamate and PR 3 [10]. Complexes of the type [Ni(dtc)(PPh 3 )Cl] and [Ni(dtc)(PPh 3 ) 2 ](ClO 4 ) (dtc = (H 5 C 2 ) 2 NCS 2 - , (H 10 C 5 )NCS 2 - (Pr i ) 2 NCS 2 - , HOH 4 C 2 - (CH 3 )NCS 2 - ) have also been reported from our laboratory [11-16]. Recently, single crystal X-ray structural study of [Ni(dnpdtc)(PPh 3 ) 2 ](ClO 4 ) (dnpdtc = di-n-propyldithiocar- bamate anion) complex has also been reported [17]. In this paper, we report the synthesis, spectral, CV studies and sin- gle crystal X-ray structure analysis of the complexes 1  4. Results and Discussion IR and electronic spectra IR spectra of the complexes 1  4 show thioureide (C-N) bands at 1538, 1532, 1537 and 1525 cm -1 , respectively. The