Stereochemistry of platinum coordination compounds

Discrete Platinum(II/IV)-Arsenito Clusters with Pt-As and Pt-O Bonding: [PtIV(As3O6)2]2-, [Pt4II(H2AsO3)6(HAsO3)2]2-, and [Pt2IIAs6W4O28]10

The first two discrete, fully inorganic platinum(II/IV)-arsenito clusters, [fac-PtIV(As3O6)2]2- (PtAs6) and [Pt4II(H2AsO3)6(HAsO3)2]2- (Pt4As8), as well as the platinum(II)-arsenito heteropolytungstate [Pt2IIAs6W4O28]10- (Pt2As6W4), have been synthesized in aqueous media using simple one-pot reaction conditions. In PtAs6, a PtIV ion is coordinated to two cyclic, tridentate As3O6 units via oxo-donation (PtIV-O ∼ 2.02 Å). In Pt4As8, each PtII ion is coordinated to four AsO3 ligands via two oxygens and two AsIII atoms in a square-planar fashion (PtII-AsIII 2.31 Å, PtII-O 2.07 Å), resulting in an open cage-like structure, which forms a strong tetrameric assembly in the solid state mediated by two K+ counterions. In Pt2As6W4, each PtII ion is coordinated by the As atoms of three AsO3 ligands (PtII-AsIII 2.38 Å) and an oxo group (PtII-O 2.07 Å) in addition to bridging two tungsten ions, and this polyanion was characterized in solution by 195Pt NMR.

Heterotridentate organodiphosphines in Pt(η3-P1X1P2)(Y) (X1 = B, S, or Si) and Pt(η3-P1P2Si1)(Y) derivatives-structural aspects

This review covers almost 30 Pt(II) complexes of the composition Pt(η3-P1X1P2)(Y), (X1 = BL, SL, or SiL), (Y = H, OL, NL, CL, Cl, PL, or I) and Pt(η3-P1P2Si1)(CH3). Heterotridentate ligands form six types of metallocyclic rings: P1CNB1NCP2, P1C2S1C2P2, P1C2Si1C2P2, (most common), P1CNSi1NCP2, and P1C3Si1C3P2 with common B1, S1, or Si1 atoms. In P1C2P2C3Si1 the P2 atom is common. The structural data (Pt–L, L–Pt–L) are analyzed and discussed with an attention to the distortion of a square-planar geometry about Pt(II) atoms as well as trans-influence. The sum of Pt–L(x4) bond distances growing with covalent radius of the X1 and Y atoms.

Ligand isomerism in Pt(II) complexes – structural aspects

This review has focused on ligand isomers in Pt(II) complexes. There are a variety of inner coordination spheres about the platinum(II) atom (PtN4, PtN2Cl2, PtP2Cl2, PtPNC2, PtPNCl2, PtP2CBr, PtP2CS), build up by mono- and bidentate ligands. The bidentate ligands create a variety of metallocyclic rings. The L–Pt–L bite angle (mean values) open in the sequence: 73.1° (PNP) < 78.7° (NC2C) < 80.4° (NC2N) < 86.4° (PC2P) < 86.7° (PNNP) < 93.0° (CC3S). There are three types of isomers: ligand, mixed – (ligand + distortion), and mixed – (ligand + cis-trans), isomers, which are rarity.

Organodiphosphines in Pt{η2-P(X)nP}Cl2 (n = 9–15, 17, 18) derivatives – Structural aspects

This review covers over 20 monomeric platinum complexes of Pt{η2-P(X)nP}Cl2 (n = 9–15, 17, 19) type. The chelating P,P-donor ligands create wide varieties of the metallocyclic rings: 12-membered (PC9P, PC3NCNC3P), 13-membered (PC3NC2NC3P), 14-membered (PC11P, PO(SiO)5P, PC2OC2OC2OC2P), 15-membered (PC12P), 16-membered (PCOC9OCP), 17-membered (P(C2O)4C2P), 18-membered (PC2OC9OC2P, PC4NC2NC2NC4P), 20-membered (P(C2O)5C2P), and 21-membered (POC2NC10NC2OP). For these complexes the most common is a predominantly cis-arranged with 17 examples and only four examples with trans-configuration. The total mean values of Pt–L bond distances in the complexes with cis- versus trans-configuration are: 2.252 Å (P trans to Cl), 2.355 Å (Cl trans to P) vs 2.288 Å (P trans to P), and 2.304 Å (Cl trans to Cl). There are examples which exist in cis- and trans-isomeric forms and distortion isomers. A brief survey on the structural data of almost 180 examples of Pt{η2-P(X)nP}Cl2 (n = 1–8) type complexes is added and discussed.

Stereoisomers of Pt(PL)2Cl2 derivatives – structural aspects

The coordination complexes of Pt(PL)2Cl2type (PL = monodentate P-donor ligands) cover almost 260 examples as shown by a recent survey covering the crystallographic and structural data. About 20% of these complexes exist as isomers and are summarized in this review. Included are distortion (58.5%),cis-,trans- (37.8%) and mixed isomerism (cis-,trans- and distortion) (3.7%). Distortion isomers, differing by degree of distortion in Pt-L and L-Pt-L angles, are the most common. For these derivatives the most commoncis- arranged with 31 examples and 22 examples withtrans- arranged. The complexes withcis-configuration are more distorted than theirtrans-partners, with the comprehensive values of Pt-L bond distances: 2.246 Å (P) and 2.350 Å (Cl). Such values in the complexes withtrans-configurations are 2.323 Å (P) and 2.308 Å (Cl), respectively. These are discussed with attention to anytrans-influence.

Organophosphines in PtP4 derivatives; structural aspects

In this review, we classify and analyze the structural data of more than 80 monomeric platinum coordination complexes with an inner coordination sphere of PtP4 in which only organophosphines are involved. On the basis of the coordination mode of respective organophosphines, these complexes can be divided into six subgroups: Pt(PL)4, Pt(PL)2(PL′)2, Pt(η2-P2L)(PL)2, Pt(η2-P2L)2, Pt(η2-P2L)(η2-P2L′)2, and Pt(η4-P4L). The chelating ligands forming wide varieties of metallocycles: (P=P), (PNP), (PCP), (PC2P), (PP2P), (PC2NP), (PNCNP), (PNPNP), (POHOP), (POBOP), (PCNCP), (PC3P), (PC4P), and (PC2OC2P). The effects of both steric and electronic factors reflect on the values of P-Pt-P chelate angles. The total mean values of Pt-P elongate in the order: 2.289 Å (tetradentate)<2.306 Å (monodentate)<2.320 Å (bidentate). The same order shows the respective covalent bond weaknesses.

Structural aspects of heterooligonuclear platinum clusters – distortion isomers

This review covers 15 clusters of the compositions Pt3Re2, Pt2Os3, Pt3AgAu, Pt3Ir3, Pt2M4 (M=Ag or Pd), PtM5 [M=Ru (×2) or Os], Pt3Os4, Pt6Au2, Pt2Ru6, Pt3Ru6, Pt2Ru8, and PtAu9. Each of the cluster contains two crystallographically independent molecules that differ mostly by degree of distortion and are classical examples of distortion isomerism. Their structures are very complex. The inner coordination spheres about the metal atoms (Pt and M) are very complex as well. The clusters are rich in metal-metal bond distances with the shortest being 2.573 Å (Pt-Au), 2.615 (Pt-Pt), and 2.673 Å (Ru-Ru).

Structural aspects of heterotrinuclear Pt2M, PtM2, and PtMM′ complexes – distortion isomers

In this review, the structural parameters of 18 heterotrinuclear Pt2M (M=Hg, Zn, Cd, Au, Mn, Ag, Pd), PtM2 (M=Al, Ga, Sb, In, Mo, Fe), PtFeMn, PtHgMn, and PtFeOs types are summarized and analyzed. The Pt atoms are four-, five-, and even six-coordinated, among which the four-coordinated ones are the most common. The M atoms are found to be two- (Hg), three- (Hg), four- (Hg, Sb, In, Ag, Au), and six- (Ga, In, Al, Mo, Mn, Fe, Pd) coordinated and even sandwiched (FeC10). There is a wide variety of donor atoms (ligands) (O+NL, N+CL, NL, CO, CN, CL, Cl, SL, PL, I), which build up the respective inner coordination spheres about the metal atoms. The 17 complexes contain two crystallographically independent molecules within the same crystal, and 1 complex contains four such molecules. In each complex, the respective molecules are differing mostly by the degree of distortion in metal-metal and metal-ligand bond distances and ligand-metal-ligand bond angles, and are examples of distortion isomerism.

Structural aspects of heterotetranuclear platinum clusters-distortion isomers

This review includes 16 examples of distortion isomers of heterotetranuclear platinum clusters. The clusters are of the compositions: Pt3Sn, Pt2M2 (M=Au, Ag, W, Mo), and PtM3 (M=Os, Ru, Re). The four metal atoms are found in a distorted tetrahedral core (most common), planar-rhombohedral, spiked-triangular, and eight-membered ring skeleton. There are three pairs (Pt2W2, Pt2Au2, and Pt2Ag2) of clusters and all remainder clusters contain two crystallographically independent molecules within the same crystal. All are classical examples of distortion isomerism. Their structures are analyzed and discussed.

Stereochemistry of heterobinuclear Pt-M complexes

In this review, the structural parameters of almost 30 isomers of heterobinuclear Pt-M (M=Sn, Tl, Cu, Ag, Ti, W, Cr, Fe, Co, Ni, Mn, Pd, or Rh) complexes are summarized and analyzed. There are three types of isomers: distortion (by far the prevailing type), polymerization, and mixed isomers. On the basis of Pt-M distance, there are two groups of complexes: one in which the Pt-M bond distances are <3.0 Å (M=Sn, Tl, W, Cr, Mn, Ni, or Pd) and the other one in which the Pt-M separations are >3.0 Å (M=Cu, Ag, Ti, W, Fe, Co, or Rh). Platinum atoms exist in two oxidation states: +2 and +4. The former by far prevails with a square-planar arrangement with varying degrees of distortion. The Pt(IV) atoms are six-coordinated. The inner coordination spheres about M atoms range from two-coordinated (AgNCl) to sandwiched (FeC10). There is wide variety of donor atoms (ligands) (H, OL, NL, CL, BL, Cl, SL, PL, Br, or I) that build up the respective inner coordination spheres about central metal atoms.

Exploring the boundaries of direct detection and characterization of labile isomers - a case study of copper(ii)-dipeptide systems

The investigation of the linkage isomers of biologically essential and kinetically labile metal complexes in aqueous solutions poses a challenge, as these microspecies cannot be separately studied. Therefore, derivatives are commonly used to initially determine the stability or spectral characteristics of at least one of the isomers. Here we directly detect the isomers, describe the metal ion coordination sphere, speciation and thermodynamic parameters by a synergistic application of temperature dependent EPR and CD spectroscopic measurements in copper(ii)-dipeptide systems including His-Gly and His-Ala ligands. The ΔH = (-23 ± 4) kJ mol^-1 value of the standard enthalpy change corresponding to the peptide-type to histamine-type isomerisation equilibrium of the [CuL]⁺ complex was corroborated by several techniques. The preferential coordination of the side-chains was observed at lower temperatures, whereas, metal-binding of the backbone atoms became favourable upon increasing temperature. This study exemplifies the necessity of using temperature dependent multiple methodologies for a reliable description of similar systems for upstream applications.

Organophosphines in organoplatinum complexes: structural aspects of trans-PtP2C2 derivatives

This review summarized and analyzed the structural parameters of 174 monomeric organoplatinum complexes with an inner coordination sphere of trans-PtP2C2. These complexes crystallized in four crystal systems: hexagonal (x2), orthorhombic (x13), triclinic (x76), and monoclinic (x84). These complexes, on the basis of the coordination mode of the respective donor ligands, can be divided into the seven sub-groups: Pt(PL)2(CL)2, Pt(PL)2(η2-C2L), Pt(η2-P2L)(CL)2, Pt(PL)(η2-P,CL)(CL), Pt(η2-P,CL)2, Pt(η3-P,C,PL)(CL), and Pt(η3-C,P,CL)(PL). The chelating ligands create 4-, 5-, 6-, 16-, 17-, 18-, and 19-membered rings. The total mean values of Pt-L bond distances are 2.055 Å (C) and 2.300 Å (P). There are examples that exist in two isomeric forms and are examples of distortion isomerism. The structural parameters of trans-PtP2C2 are discussed with those of cis-PtP2C2 derivatives.

Crystallographic and structural characterization of heterometallic platinum complexes Part VI. Heterohexanuclear complexes

This review classifies and analyzes heterohexanuclear platinum clusters into seven types of metal combinations:Pt5M, Pt4M2, Pt3M3, Pt2M4, PtM5, Pt2M3M′, and Pt2M2M2′. The crystals of these clusters generally belong to six crystal classes: monoclinic, triclinic, orthorhombic, tetragonal, trigonal and cubic. Among the wide range of stereochemistry adopted by these clusters, octahedral and capped square-pyramidal are the most common. Although platinum is classified as a soft metal atom, it bonds to a variety of soft, borderline and hard metals. Nineteen different heterometal ions are involved in hexanuclear platinum clusters. The shortest Pt-M bond distance in the case of M being a non-transition element is 2.395(4) Å for germanium and for M being a transition metal ion it is 2.402(2) Å for Cobalt. The shortest Pt-Pt bond distance observed in these clusters is 2.532 Å. Several relationships between the structural parameters are identified and discussed. Some clusters exist in two isomeric forms and some show crystallographically independent molecules within the same crystal. Such isomers and independent molecules are examples of distortion isomerism.

Proton-Induced Cis−Trans Conversion of a Platinum(II) Center Coordinated by l-Cysteinatocobalt(III) Metalloligands

Treatment of LambdaL-[Co(L-cys-N,S)(en)2]+ (l-H2cys = L-cysteine) with [PtCl4]2- in water, followed by the addition of acid, gave an S-bridged CoIII2PtII trinuclear complex ([1]4+), which was reversibly converted to its deprotonated complex ([2]2+) in an aqueous solution. While [1]4+ formed only a trans isomer, [2]2+ existed as a mixture of trans and cis isomers. The selective formation of a cis isomer was achieved by treatment of [1]4+ or [2]2+ with phthalic acid in water, which afforded a unique CoIII4PtII2 hexanuclear complex ([3]4+). Complex [3]4+ was reverted back to [1]4+ by treatment with aqueous HCl, accompanied by the complete cis-to-trans conversion.